High-temperature-resistant membrane and reverse osmosis-based oil field sewage high-efficiency reuse boiler treatment method

Abstract

The invention is suitable for the field of oil field sewage treatment, and provides an oil field sewage high-efficiency recycling boiler treatment method based on a high-temperature-resistant membrane and reverse osmosis, which comprises the following steps: S1, pretreating and tempering; S2, carrying out oil removal, suspended matter removal, hardness removal and silicon removal treatment by adopting a high-temperature-resistant special filter membrane; s3, desalting through anti-pollution reverse osmosis; s4, the produced water enters secondary reverse osmosis and primary reverse osmosis, and concentrated water enters a whole plant sewage discharge system; s5, secondary reverse osmosis concentrated water is recycled to primary reverse osmosis inlet water, the conductivity of secondary reverse osmosis produced water is smaller than 30 microseconds per centimeter, and the system recovery rate is larger than 85%; in the invention, by reducing the dosage of the medicament, the medicament cost is saved by 40% compared with the traditional process, and the dependence on the medicament is reduced, so that the treatment cost is effectively reduced, and the economic benefit of oilfield sewage treatment is improved; by optimizing the treatment process, the output of the sludge is reduced, the sludge treatment difficulty and cost are reduced, and meanwhile, the potential harm of the sludge to the environment is also reduced.

Description

Technical Field

[0001] The present invention belongs to the field of oilfield sewage treatment, and particularly relates to a method for efficiently recycling oilfield sewage for boiler treatment based on high-temperature resistant membranes and reverse osmosis. Background Art

[0002] Oilfield sewage mainly comes from produced fluid separation water, fracturing flowback fluid, and well washing wastewater, etc. Such sewage exhibits a series of complex and intractable characteristics. Specifically, it has a high oil content (50 - 1000 mg / L), which means that the sewage contains a large amount of petroleum substances, not only hindering the subsequent treatment process but also potentially causing environmental pollution problems; a high suspended solid content (100 - 500 mg / L), and the presence of numerous suspended particles affects the clarity and stability of the water quality; a high hardness (Ca 2+ +Mg 2+ >300 mg / L), and a relatively high calcium and magnesium ion content easily leads to scaling in pipelines and equipment, seriously affecting the normal operation and service life of the equipment; a high silicon content (SiO2>160 mg / L), and the high content of silicon element increases the scaling risk and also poses higher requirements for the treatment process; as well as a high salt content (TDS>6000 mg / L), and the high salinity will corrode the treatment equipment and increase the difficulty of desalination treatment.

[0003] Traditional oilfield sewage treatment processes adopt a combination of "oil separation - air flotation - coagulation filtration - ion exchange softening"; however, in actual application, this traditional process exposes many insurmountable problems:

[0004] Reagent dependence and sludge problems: This process is highly dependent on reagents and requires a large amount of Na2CO3 / NaOH and other reagents to achieve the sewage treatment goal. The use of a large amount of reagents not only increases the treatment cost but also leads to a significant increase in sludge production. The sludge production accounts for 5% - 10% of the treatment volume. The generation of a large amount of sludge not only requires additional treatment facilities and costs but also brings problems in sludge disposal, posing a potential threat to the environment;

[0005] Low silicon removal efficiency: The traditional adsorption method has poor effects in removing dissolved silicon, and its removal rate of dissolved silicon can only reach 30% - 50%. The low silicon removal efficiency results in a large amount of silicon remaining in the treated sewage. These remaining silicons are extremely likely to form scale during the operation of the boiler, seriously affecting the heat transfer efficiency and safe operation of the boiler, and increasing the frequency and cost of boiler maintenance and cleaning;

[0006] Excessive salt residue: After ion exchange treatment, the total dissolved solids (TDS) in the sewage is still higher than 1000 mg / L, far from meeting the strict requirement of the conductivity of boiler feed water < 30 μS / cm. High salt residue will cause problems such as corrosion and scaling inside the boiler, seriously threatening the safe and stable operation of the boiler and shortening the service life of the boiler;

[0007] Low recovery rate: The comprehensive recovery rate of traditional processes is less than 60%, which means that a large amount of water resources are wasted. In the current situation of increasingly tight water resources, such a low-recovery treatment process not only does not conform to the concept of sustainable development, but also increases the dependence of oilfield production on fresh water resources, further intensifying the contradiction between water supply and demand;

[0008] Therefore, an efficient method for reusing oilfield sewage for boiler treatment based on high-temperature resistant membranes and reverse osmosis is needed to solve the above problems. Summary of the Invention

[0009] The purpose of the embodiments of the present invention is to provide an efficient method for reusing oilfield sewage for boiler treatment based on high-temperature resistant membranes and reverse osmosis to solve the problems mentioned in the above background technology.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] An efficient method for reusing oilfield sewage for boiler treatment based on high-temperature resistant membranes and reverse osmosis, including high-temperature resistant membrane cascade interception, primary anti-pollution reverse osmosis optimization, and secondary anti-pollution reverse osmosis optimization. The specific steps are as follows:

[0012] Pretreatment conditioning: First, perform pretreatment conditioning on the oilfield sewage, accurately control the sewage temperature within the appropriate range of 50 - 80 °C, and adjust the pH to 10.5 - 11.5 by adding appropriate agents. The purpose of this step is to change the existing form and chemical properties of pollutants in the sewage by adjusting the temperature and pH, making it easier for subsequent separation and removal;

[0013] High-temperature resistant membrane system: Use a PTFE special filter membrane modified by hydrophobicity (molecular weight cut-off 50 kDa). Under an operating pressure of 0.2 - 0.5 MPa, this membrane can exhibit a flux of 150 - 200 L / (m 2 ·h);

[0014] Its unique molecular interception characteristics enable it to selectively intercept Ca 2+ , Mg 2+ and SiO3 2-Plasma, the rejection rate of these ions is as high as >99%; at the same time, it also performs excellently in oil removal and suspended solid removal, with an oil removal rate of >95% and the suspended solid content (SS) in the treated sewage <1 mg / L; this efficient interception and removal ability benefits from the special material and structural design of the membrane, which can achieve the synchronous removal of various pollutants through multiple action mechanisms such as physical sieving, adsorption, and charge repulsion;

[0015] First-stage anti-pollution reverse osmosis: Polyamide composite membranes are selected for the first-stage anti-pollution reverse osmosis treatment;

[0016] Under an operating pressure of 100 MPa, this step can achieve a recovery rate of 90.1% and a desalination rate of >96.8%; Polyamide composite membranes have good chemical stability and separation performance. By allowing water molecules to pass through the membrane under pressure while intercepting solutes such as salts, the initial desalination process is achieved; at the same time, the anti-pollution treatment on the membrane surface can effectively reduce the adsorption and deposition of organic pollutants on the membrane surface, extend the service life of the membrane, and ensure the stable operation of the system;

[0017] Second-stage reverse osmosis: Anti-pollution brackish water desalination reverse osmosis membranes are used for the second-stage reverse osmosis treatment; the operating pressure is set at 1.6 MPa, the recovery rate of this step is 80%, and the desalination rate is as high as 99.5%; The second-stage reverse osmosis further performs deep desalination treatment on the water produced by the first-stage reverse osmosis. Through a more refined separation process, residual trace salts and other impurities are removed to ensure that the quality of the final produced water meets the strict requirements of boiler feed water. The anti-pollution brackish water desalination reverse osmosis membrane is optimized for the characteristics of brackish water, can operate efficiently in a high-salinity environment, and resist pollution by pollutants to ensure long-term and stable desalination effects;

[0018] Concentrate discharge: The concentrate generated by the first-stage anti-pollution reverse osmosis is returned to the whole plant sewage unit for further comprehensive treatment or discharge; by reasonably designing the reuse path of the second-stage reverse osmosis concentrate, the second-stage reverse osmosis concentrate is reused as the feed water for the first-stage reverse osmosis to achieve the recycling of water resources; This reasonable treatment and reuse method of the concentrate effectively improves the total recovery rate of the system, making the total recovery rate of the system >85%, greatly reducing water resource waste, and conforming to the concept of sustainable development.

[0019] This method innovatively utilizes a special filtration membrane to achieve the co-interception of various pollutants in a high-temperature environment. This special filtration membrane can efficiently intercept pollutants such as oil, colloid, hardness, and silicon simultaneously, breaking through the limitation in traditional treatment processes where different pollutants need to be treated separately. Through this co-pollutant removal method, not only are the treatment steps and the use of equipment reduced, but more importantly, the dosage of chemicals is decreased. In traditional processes, a large amount of chemicals often needs to be added to remove these pollutants, while the present invention realizes the synchronous removal of pollutants through the special properties of the membrane, reducing the treatment cost and the potential environmental impact of chemical use.

[0020] Moreover, a unique modification treatment is carried out on the surface of the reverse osmosis membrane. By introducing advanced materials and technologies such as zwitterionic polymers, the hydrophilicity of the membrane is enhanced. The enhanced hydrophilicity reduces the affinity of the membrane surface for organic pollutants, thereby effectively reducing the organic pollution rate by more than 50%. This anti-pollution membrane design can significantly extend the service life of the membrane, reduce the frequency of membrane cleaning and replacement, lower the operating cost, and at the same time ensure the high-efficiency and stable performance of the membrane system during long-term operation.

[0021] And through the elaborate design of the first-stage anti-pollution reverse osmosis and the second-stage reverse osmosis concentrated water recycling system, the cascade recovery optimization of water resources is achieved. The concentrated water generated by the first-stage reverse osmosis is partially recycled to the inlet of the first-stage reverse osmosis after reasonable treatment, and the second-stage reverse osmosis concentrated water is also recycled to the inlet of the first-stage reverse osmosis. Through this way of recycling concentrated water, the total recovery rate of the system is greatly improved, and the total recovery rate of the system is increased to 90%. This cascade recovery optimization strategy makes full use of water resources, reduces the amount of discharged concentrated water, reduces the environmental pressure, and at the same time improves the economic benefits and resource utilization efficiency of the entire treatment system.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] In the present invention, by reducing the dosage of chemicals, the chemical cost is saved by 40% compared with the traditional process, reducing the dependence on chemicals, thereby effectively reducing the treatment cost and improving the economic benefits of oilfield sewage treatment.

[0024] In the present invention, by optimizing the treatment process, the generation amount of sludge is reduced, the difficulty and cost of sludge treatment are lowered, and at the same time, the potential harm of sludge to the environment is reduced.

[0025] In the present invention, the water quality of the produced water after being treated by the process of the present invention can stably meet the water demand of the steam injection boiler; in terms of key indicators such as conductivity, hardness, silicon content, and oil content, they can all be strictly controlled within the boiler feed water standard range (conductivity < 30 μS / cm); the stable and up-to-standard produced water quality provides a reliable guarantee for the safe and stable operation of the boiler, reduces boiler failures and maintenance costs caused by water quality problems, and extends the service life of the boiler.

[0026] In the present invention, the "near-zero discharge" reuse of oilfield sewage is realized, greatly reducing the total amount of sewage discharge and reducing the pollution risk to the surrounding water environment; at the same time, the consumption of fresh water resources is reduced, alleviating the contradiction between water supply and demand, having significant environmental benefits, and making a positive contribution to the green development of the oilfield industry.

[0027] In order to more clearly elaborate the structural features and effects of the present invention, the present invention will be described in detail below in conjunction with the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic process flow diagram of the present invention;

[0029] Figure 2 It is a comparison table of the concentrations of oilfield sewage pollutants before and after treatment of the present invention;

[0030] Figure 3 It is a 30-day pressure decay diagram of the PTFE special membrane system, the first-stage RO membrane system, the second-stage RO membrane system, and the concentrate RO membrane system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] The following describes the specific implementation of the present invention in detail in conjunction with specific embodiments.

[0033] Example 1

[0034] As Figures 1-3 shown, a certain oilfield sewage (the pollutant indexes of which are TDS = 6000 mg / L, oil content 8.31 mg / L, hardness 340 mg / L, SiO2 = 160 mg / L, ss = 25 mg / L, water temperature 75 °C) is selected for treatment, and the specific process is as follows:

[0035] First, adjust the pH of the sewage to the specific range of 10.5 - 11.5 while maintaining the water temperature at 75°C. This step creates a favorable environment for the subsequent pollutant removal process by precisely adjusting the chemical properties and temperature conditions of the sewage.

[0036] Next, pass the sewage through PTFE special filtration.

[0037] During this process, the PTFE special filtration membrane fully exerts its unique interception and separation performance to efficiently remove various pollutants in the sewage. After treatment, the oil content significantly drops to <0.5 mg / L, the suspended solid content (SS) <0.5 mg / L, the hardness <10 mg / L, and SiO2 <10 mg / L. These data indicate that the PTFE special filtration membrane has excellent effects in removing pollutants such as oil, suspended solids, hardness, and silicon.

[0038] Subsequently, through reverse osmosis treatment, the salt content of the produced water drops to <15 mg / L, SiO2 <0.05 mg / L, and the system recovery rate reaches 85%. This result fully demonstrates the high efficiency of the process of the present invention in desalination and removing silicon elements, as well as its good performance in water resource recovery and utilization.

[0039] To accurately verify the treatment effect, a series of national standard detection methods such as GB / T7476 - 1987 Determination of Calcium in Water Quality - EDTA Titration Method, GB / T7477 - 1987 Determination of Total Calcium and Magnesium in Water Quality - EDTA Titration Method, GB / T Determination of Silicon in Industrial Circulating Cooling Water and Boiler Water, HJ637 - 2018 Determination of Petroleum and Animal and Vegetable Oils in Water Quality - Infrared Spectrophotometry Method, and GB / T11901 - 89 Determination of Suspended Solids in Water Quality - Gravimetric Method are used to comprehensively detect the treated water.

[0040] The detection results clearly show that the present invention exhibits excellent removal effects on calcium, hardness, silicon, TDS, ss, and oil in oilfield sewage, can effectively improve the water quality, making it fully meet the inlet water conditions of the steam boiler, and providing reliable water quality guarantee for the safe and stable operation of the boiler.

[0041] Example 2

[0042] As Figures 1-3 shown, in order to further verify the operation stability of the membrane system in the present invention, the following test was carried out: a 30 - day continuous operation test was conducted on the PTFE special membrane system, and the result shows that its pressure decay ≤ 5%. This indicates that the PTFE special membrane can maintain relatively stable pressure performance during long - term operation, and its filtration performance will not significantly decline due to long - term use, ensuring the continuous and efficient operation of the system.

[0043] The pressure decay of the primary RO membrane system in 30 days of operation is ≤ 3%; this indicates that the primary RO membrane has good stability during operation, can maintain stable pressure and desalination performance for a long time, ensure the stable progress of the primary reverse osmosis process, and provide stable feed water quality for the subsequent secondary reverse osmosis;

[0044] The pressure decay of the secondary RO membrane system in 30 days of operation is ≤ 5%; the secondary RO membrane also shows good stability, can maintain relatively stable performance during operation, ensure the further optimization and improvement of the water quality of the secondary reverse osmosis for the produced water, and ensure that the final produced water can meet the strict requirements of boiler feed water;

[0045] The pressure decay of the concentrate RO membrane system in 30 days of operation is ≤ 2%; this test result of the concentrate RO membrane system shows that it has excellent stability in the process of treating concentrate, can effectively treat the concentrate and maintain the stable operation of the system, and provides a strong guarantee for the water resource recovery and utilization and concentrate discharge control of the whole process.

[0046] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for efficiently recycling oilfield sewage for boiler treatment based on a high-temperature resistant membrane and reverse osmosis, characterized in that, It includes the following steps: S1. Pretreatment and conditioning: S2. Use a high-temperature resistant special filter membrane for oil removal, suspended solid removal, hardness removal, and silicon removal; S3. Desalination is carried out through anti-pollution reverse osmosis; S4. The produced water enters the second-stage reverse osmosis and the first-stage reverse osmosis, and the concentrated water enters the whole plant sewage discharge system; S5. The concentrated water of the second-stage reverse osmosis is recycled to the inlet water of the first-stage reverse osmosis, and the conductivity of the produced water of the second-stage reverse osmosis < 30 μS / cm, and the system recovery rate > 85%.

2. The high-efficiency boiler treatment method for recycling oilfield sewage based on a high-temperature resistant membrane and reverse osmosis according to claim 1, characterized in that: The high-temperature resistant special filter membrane is made of PTFE material, with a temperature resistance ≥ 80 °C and a cut-off molecular weight ≤ 50 kDa.

3. The method for efficiently recycling and treating oilfield sewage for boilers based on a high-temperature resistant membrane and reverse osmosis according to claim 2, characterized in that: The surface of the reverse osmosis membrane is treated with an anti-pollution treatment by zwitterionic polymer.

4. The method for highly efficient reuse of oilfield sewage for boiler treatment based on high-temperature resistant membrane and reverse osmosis according to claim 3, characterized in that: In the pretreatment and conditioning step, the sewage temperature is controlled at 50 - 80 °C, and the pH is adjusted to 10.5 - 11.

5.

5. The high-efficiency reuse boiler treatment method for oilfield sewage based on a high-temperature resistant membrane and reverse osmosis according to claim 4, characterized in that: When the high-temperature resistant special filter membrane is used for oil removal / suspended solid removal / hardness removal / silicon treatment, the operating pressure is 0.2 - 0.5 MPa, the flux is 150 - 200 L / (m 2 ·h), the rejection rates of Ca 2 +, Mg2+ and SiO32- are > 99%, the oil removal rate is > 95%, and the SS after treatment is < 1 mg / L.

6. The high-efficiency boiler treatment method for reusing oilfield sewage based on a high-temperature resistant membrane and reverse osmosis according to claim 5, characterized in that: The first-stage anti-pollution reverse osmosis uses a polyamide composite membrane, with an operating pressure of 100 MPa, a recovery rate of 90.1%, and a desalination rate > 96.8%.

7. The high-efficiency boiler treatment method for recycling oilfield sewage based on high-temperature resistant membrane and reverse osmosis according to claim 6, characterized in that: The second-stage reverse osmosis uses an anti-pollution brackish water desalination reverse osmosis membrane, with an operating pressure of 1.6 MPa, a recovery rate of 80%, and a desalination rate of 99.5%.

8. The method for efficiently recycling and treating oilfield sewage for boilers based on a high-temperature resistant membrane and reverse osmosis according to claim 7, wherein: After being treated by this method, the calcium content in the oilfield sewage is reduced to below 1 mg / L, the hardness is reduced to below 10 mg / L, the silicon content is reduced to below 0.05 mg / L, the TDS is reduced to below 15 mg / L, the ss is reduced to below 0.5 mg / L, and the oil content is reduced to below 0.5 mg / L.

9. The high-efficiency boiler treatment method for oilfield sewage reuse based on a high-temperature resistant membrane and reverse osmosis according to claim 8, characterized in that: The pressure attenuation of the high-temperature resistant special filter membrane system in operation for 30 days ≤ 5%, the pressure attenuation of the first-stage RO membrane system in operation for 30 days ≤ 3%, the pressure attenuation of the second-stage RO membrane system in operation for 30 days ≤ 5%, and the pressure attenuation of the concentrated water RO membrane system in operation for 30 days ≤ 2%.

10. The method for highly efficient reuse of oilfield sewage for boiler treatment based on high-temperature resistant membrane and reverse osmosis according to claim 9, wherein: This method can enable the oilfield sewage to achieve "near-zero discharge" recycling, saving 40% of the chemical agent cost and reducing the sludge by 90% compared with the traditional process.

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