Fracturing flow-back fluid treatment process

Abstract

The invention relates to the technical field of sewage treatment, in particular to a fracturing flow-back fluid treatment process, according to the front-end process, a multi-time direct filtration system is adopted for pretreatment, and suspended solids and biochemically harmful substances in raw water are removed to the maximum extent through a physical method; a dual-alkali method and an ion exchange double-section hardness removal process are adopted, so that the common problem of calcium and magnesium scaling in a subsequent filtering system is solved; the crystallized salt obtained by evaporation of the MVR evaporation system is used for an ion exchange process section, so that the problem of regenerated salt is solved, and the total amount of the final crystallized salt is also reduced; the produced water of each membrane filtration system flows back to the A / O biochemical system at the front end to form internal circulation, so that the inlet water concentration of the A / O biochemical system is diluted, the problem of high salinity of the biochemical system is solved, and the problems of high COD (Chemical Oxygen Demand) in evaporated condensate water of an MVR (Mechanical Vapor Recompression) evaporation system and difficulty in degradation are also solved; the treatment method combining the A / O biochemical system and ion exchange ensures the unicity of salt in the inlet water of the MVR evaporation system.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a fracturing flowback fluid treatment process. Background Art

[0002] In the process of oil and natural gas extraction, the shale gas and tight gas extraction technologies used in China require large-scale fracturing. The large amount of return waste liquid generated after fracturing will put pressure on the environment. In the later stage of extraction, the demand for reuse of the return fluid decreases. After the return fluid is treated to meet the standards, it is discharged externally, which provides an important way for the final disposal of the return fluid.

[0003] The existing traditional flowback fluid treatment technology has the following main defects:

[0004] 1. The existing traditional technology generally uses traditional mud-water separation equipment, such as sedimentation tanks, flotation machines, etc. These traditional equipments occupy land, have high operating costs and low processing efficiency;

[0005] 2. Traditional technology generally does not use A / O biochemical method for strong oxidation, because the front-end treatment of traditional technology is not enough to ensure the stable operation of the biochemical system;

[0006] 3. Traditional technical processes generally use strong oxidation method for strong oxidation, which will produce a large amount of iron mud, increase the output of crystalline salt, and reduce the purity of crystalline salt; the strong oxidation method also requires a large amount of chemical raw materials, which causes difficulties in procurement and storage; the strong oxidation method has high operating costs and the effluent is not conducive to membrane concentration; the strong oxidation method is difficult to operate and the equipment maintenance is more frequent. Summary of the invention

[0007] In order to solve the above technical problems, the present application provides a fracturing flowback fluid treatment process, comprising the following steps:

[0008] S1. Pass the return liquid raw water into the primary direct filtration system to filter the suspended solids in the water, and then use the secondary direct filtration system and double alkali hardness removal method to remove the hardness of the water;

[0009] S2. Reduce organic pollution in water through A / O biochemical system, reduce COD in wastewater through ASSFBR biological filtration system, and further remove divalent and higher positive ions in water through softening and de-hardening ion exchange equipment;

[0010] S3, the wastewater is treated by the primary membrane concentration system to produce concentrated water, which is then separated by the secondary membrane concentration system and the DTRO membrane system. The DTRO concentrated water is then sent to the MVR evaporation system for evaporation and crystallization to obtain crystalline salt;

[0011] S4. Return the produced water filtered by the secondary membrane concentration system and the DTRO membrane system, as well as the condensed water of the MVR evaporation system to the A / O biochemical system, so that the salt content and chloride ion content in the wastewater meet the standard for normal operation of the A / O biochemical system.

[0012] Preferably, in step S2, the produced water after filtration by the primary membrane concentration system is subjected to a deep ozone oxidation treatment device to further reduce COD and TN indicators, thereby ensuring that the emission standards are met.

[0013] Preferably, the secondary membrane concentration system uses a seawater desalination membrane.

[0014] Preferably, in step S3, a portion of the obtained crystallized salt is used in the softening and hardness removal ion exchange equipment in step 2, and the rest is transported out for treatment.

[0015] Preferably, sodium carbonate and sodium hydroxide are added to the secondary direct filtration system in step S1.

[0016] Preferably, in step S2, the wastewater is filtered through an ultrafiltration system after being softened and de-hardened by an ion exchange device, and the concentrated water is passed through a primary membrane concentration system after filtration, and the filtered produced water is returned to the A / O biochemical system.

[0017] Preferably, the mother liquor obtained in the MVR evaporation system is treated with ozone and then refluxed to the softening and de-hardening ion exchange equipment for softening and regeneration.

[0018] Preferably, in step S1, the sludge obtained by filtering the primary direct filtration system and the secondary direct filtration system is passed into the sludge water withdrawal device for pressure filtration, and the produced water after the pressure filtration is returned to the primary direct filtration system.

[0019] Preferably, in step S1, PAC and PAM are added to the primary direct filtration system to remove suspended solids in the raw water and substances harmful to the biochemical system.

[0020] From the above, it can be seen that the following beneficial effects can be obtained by applying the method provided by this application:

[0021] 1. The front-end process uses multiple direct filtration systems for pretreatment, using physical methods to remove suspended matter and biochemically harmful substances in the raw water as much as possible;

[0022] 2. The double alkali method and ion exchange double-stage hardness removal process are adopted to solve the common calcium and magnesium scaling problems in the subsequent primary membrane system, secondary membrane concentration system and MVR evaporation system;

[0023] 3. The crystallized salt obtained after evaporation by the MVR evaporation system is used in the ion exchange process, which not only solves the problem of regenerated salt, but also reduces the total amount of final crystallized salt;

[0024] 4. The produced water of the secondary membrane concentration system, DTRO membrane system and MVR evaporation system flows back to the front-end A / O biochemical system to form an internal cycle, diluting the inlet water concentration of the A / O biochemical system, making full use of water resources, solving the problem of high salinity in the biochemical system, and also solving the difficulty of high COD and difficult degradation in the evaporation condensate of the MVR evaporation system;

[0025] 5. The treatment method combining A / O biochemical system and ion exchange ensures the uniformity of the salt content in the influent of the MVR evaporation system, and guarantees that the NaCl content of the crystallized salt produced by the subsequent MVR evaporation system is ≥96%;

[0026] 6. The above treatment processes are closely linked and indispensable, with the advantages of stable operation, low operating cost, low equipment maintenance frequency and easy operation, which is in line with the national policy of energy conservation and carbon reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the description of the embodiments of the present application or the prior art are briefly introduced below. Obviously, the drawings described below are only part of the embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor.

[0028] Figure 1 This is a process flow chart of fracturing flowback fluid treatment in an embodiment of the present application;

[0029] Figure 2 This is a flowchart of the fracturing flowback fluid treatment process according to an embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] In order to solve the above technical problems, this embodiment provides a fracturing flowback fluid treatment process, such as Figure 1-2 As shown, the following steps are included:

[0032] S1. The flowback liquid raw water is passed through the primary direct filtration system to filter the suspended solids in the water, and then the hardness of the water is removed by the double alkali hardness removal method through the secondary direct filtration system;

[0033] In this step, the return liquid raw water is passed into the regulating tank, and then passed into the first-level TUFBR direct filtration system from the regulating tank. The first-level TUFBR direct filtration system filters the suspended solids in the water, and then the hardness in the water is removed by the double alkali hardness removal method through the second-level TUFBR direct filtration system.

[0034] Among them, in this step S1, PAC (polyaluminium chloride) and PAM (polyacrylamide) agents are added to the primary direct filtration system to effectively reduce the concentration of suspended matter, ammonia nitrogen and COD, and remove substances in the raw water that are harmful to the subsequent biochemical system.

[0035] In the above scheme, the secondary direct filtration system uses a double alkali hardness removal method, that is, sodium carbonate and sodium hydroxide are added to the secondary direct filtration system, which can filter out more than 85% of calcium, magnesium, and iron ions and part of sulfate ions in the water.

[0036] In step S1, the sludge obtained by filtering the primary direct filtration system and the secondary direct filtration system is passed into the sludge water withdrawal device for pressure filtration, and the produced water after pressure filtration is returned to the primary direct filtration system or the regulating tank.

[0037] S2. Reduce the organic pollution in the water through the A / O biochemical system, reduce the COD in the wastewater through the ASSFBR biological filtration system, and then pass the wastewater through the softening and hardness removal ion exchange equipment to further remove the divalent and higher positive ions in the water.

[0038] In this step, TN and COD in the water can be removed by the A / O biochemical system and the ASSFBR biological filtration system, while avoiding the large amount of iron salts produced when the traditional oxidation method is used to reduce COD. The wastewater is then softened and de-hardened by the softening and de-hardening ion exchange equipment, and more than 97% of the divalent and higher metal ions such as calcium and magnesium in the water are removed for a second time, further purifying the salt components in the water. In this embodiment, the treatment method combining the A / O biochemical system and the ion exchange equipment can ensure the uniformity of the salt content of the influent of the MVR evaporation system, and ensure that the NaCl content of the crystallized salt produced by the subsequent MVR evaporation system is ≥96%.

[0039] In the above scheme, the wastewater is filtered through an ultrafiltration system after being softened and de-hardened by an ion exchange device, and the filtered water is returned to the A / O biochemical system. The ultrafiltration system further removes residual suspended matter, chroma and COD in the water.

[0040] Calcium and magnesium scaling problems often occur in primary membrane systems, secondary membrane concentration systems and MVR evaporation systems. In step S2, a double alkali method and an ion exchange double-stage hardness removal process are used to solve the common calcium and magnesium scaling problems in subsequent primary membrane systems, secondary membrane concentration systems and MVR evaporation systems.

[0041] S3, the wastewater is treated by the primary membrane concentration system to produce concentrated water, which is then separated by the secondary membrane concentration system and the DTRO membrane system. The DTRO concentrated water is then sent to the MVR evaporation system for evaporation and crystallization to obtain crystalline salt;

[0042] The wastewater produced by the ultrafiltration system is passed into the primary membrane concentration system, and concentrated water is produced after being treated by the primary membrane concentration system. This water contains a high salt content, and the primary membrane concentration system cannot separate it anymore. It needs to be separated again by a higher pressure membrane. For this reason, it needs to be separated again by a secondary membrane concentration system and a DTRO membrane system. After the DTRO concentrated water is produced, it enters the MVR evaporation system for evaporation and crystallization to obtain crystalline salt. Among them, compared with the primary membrane concentration system, the secondary membrane concentration system uses a higher pressure seawater desalination membrane.

[0043] Furthermore, in step S3, the concentrated water generated by filtration in the primary membrane concentration system is introduced into the secondary membrane concentration system, and the produced water after filtration in the primary membrane concentration system is subjected to a deep ozone oxidation treatment device to further reduce COD and TN indicators, thereby ensuring that the emission standards are met.

[0044] Furthermore, the mother liquor obtained in the MVR evaporation system is treated with ozone and then refluxed to the softening and de-hardening ion exchange equipment for softening and regeneration, thereby improving resource utilization.

[0045] In the above scheme, part of the obtained crystallized salt is used in the softening and hardness removal ion exchange equipment in step 2, and the rest is transported for treatment. Part of the crystallized salt obtained after using the MVR evaporation system is put into the softening and hardness removal ion exchange equipment, which is used for the salt required by the ion exchange process, which not only solves the problem of the demand for regenerated salt, but also reduces the total amount of the final crystallized salt.

[0046] S4, the produced water after filtering by the secondary membrane concentration system and DTRO membrane system, as well as the condensed water of the MVR evaporation system, is returned to the A / O biochemical system, diluting the salt in the inlet water of the A / O biochemical system, so that the salt content and chloride ion content in the wastewater entering the A / O biochemical system meet the normal operation standard of the A / O biochemical system, while making full use of water resources, solving the problem of high salt content in the biochemical system, and also solving the difficulty of high COD and difficult degradation in the evaporation condensed water of the MVR evaporation system. The above treatment processes are closely linked and indispensable, with the advantages of stable operation, low operating cost, low equipment maintenance frequency, and easy operation, which is in line with the national policy of energy conservation and carbon reduction.

[0047] Table 1 below shows the removal index of fracturing backflow fluid in each treatment unit.

[0048]

[0049]

[0050] Table 1

[0051] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A fracturing flowback fluid treatment process, characterized in that: The following steps are involved: S1. The flowback liquid raw water is passed through the primary direct filtration system to filter the suspended solids in the water, and then the hardness of the water is removed by the double alkali hardness removal method through the secondary direct filtration system; S2. Reduce organic pollution in water through A / O biochemical system, reduce COD in wastewater through ASSFBR biological filtration system, and further remove divalent and higher positive ions in water through softening and de-hardening ion exchange equipment; S3, the wastewater is treated by the primary membrane concentration system to produce concentrated water, which is then separated by the secondary membrane concentration system and the DTRO membrane system. The DTRO concentrated water is then sent to the MVR evaporation system for evaporation and crystallization to obtain crystalline salt; S4. Return the produced water filtered by the secondary membrane concentration system and the DTRO membrane system, as well as the condensed water of the MVR evaporation system to the A / O biochemical system, so that the salt content and chloride ion content in the wastewater meet the standard for normal operation of the A / O biochemical system.

2. The fracturing flowback fluid treatment process according to claim 1, characterized in that: In step S3, the concentrated water produced after filtration by the primary membrane concentration system is passed into the secondary membrane concentration system, and the produced water produced after filtration by the primary membrane concentration system is passed through a deep ozone oxidation treatment device to further reduce the COD and TN indicators, thereby ensuring that the emission standards are met.

3. The fracturing flowback fluid treatment process according to claim 1, characterized in that: The two-stage membrane concentration system adopts seawater desalination membrane.

4. The fracturing flowback fluid treatment process according to claim 1, characterized in that: In step S3, a portion of the obtained crystallized salt is used in the softening and hardness removal ion exchange equipment in step 2, and the rest is transported out for treatment.

5. The fracturing flowback fluid treatment process according to claim 1, characterized in that: Sodium carbonate and sodium hydroxide are added to the secondary direct filtration system in step S1.

6. The fracturing flowback fluid treatment process according to claim 1, characterized in that: In step S2, the wastewater is filtered through an ultrafiltration system after being softened and de-hardened by an ion exchange device, the concentrated water after filtration is passed into a primary membrane concentration system, and the filtered produced water is returned to the A / O biochemical system.

7. The fracturing flowback fluid treatment process according to claim 1, characterized in that: The mother liquor obtained in the MVR evaporation system is treated with ozone and then refluxed to the softening and de-hardening ion exchange equipment for softening and regeneration.

8. The fracturing flowback fluid treatment process according to claim 1, characterized in that: In step S1, the sludge obtained by filtering the primary direct filtration system, the secondary direct filtration system and the A / O biochemical system is passed into the sludge water withdrawal device for pressure filtration, and the produced water after pressure filtration is returned to the primary direct filtration system.

9. The fracturing flowback fluid treatment process according to claim 1, characterized in that: In step S1, PAC and PAM are added to the primary direct filtration system to remove suspended solids in the raw water and substances harmful to the biochemical system.

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