High-efficiency boiler treatment method for oilfield wastewater reuse based on high-temperature resistant membranes and reverse osmosis

Abstract

This invention is applicable to the field of oilfield wastewater treatment and provides a method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis. The method includes the following steps: pretreatment conditioning: controlling the wastewater temperature at 50-80℃ and adjusting the pH to 10.5-11.5; using a high-temperature resistant special filter membrane for oil removal, suspended solids removal, hardening removal, and silica removal; two-stage anti-fouling reverse osmosis desalination; in this invention, by reducing the amount of chemicals added, the cost of chemicals is reduced by 40% compared to traditional processes, reducing dependence on chemicals and thus effectively lowering treatment costs and improving the economic benefits of oilfield wastewater treatment; by optimizing the treatment process, the amount of sludge generated is reduced, lowering the difficulty and cost of sludge treatment, and also reducing the potential environmental hazards of sludge.

Description

Technical Field

[0001] This invention belongs to the field of oilfield wastewater treatment, and particularly relates to a method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis. Background Technology

[0002] Oilfield wastewater mainly originates from produced fluid separation water, fracturing flowback fluid, and well washing wastewater. This type of wastewater exhibits a series of complex and challenging characteristics, specifically: high oil content (50-1000 mg / L), meaning it contains a large amount of petroleum-based substances, which not only hinders subsequent treatment processes but may also cause environmental pollution; high suspended solids (100-500 mg / L), the presence of numerous suspended particles affecting water clarity and stability; and high hardness (Ca). 2+ +Mg 2+ High calcium and magnesium ion content (>300mg / L) can easily lead to scaling in pipes and equipment, seriously affecting the normal operation and service life of the equipment; high silicon (SiO2>160mg / L) increases the risk of scaling and also places higher demands on the treatment process; and high salt (TDS>6000mg / L) can corrode the treatment equipment and increase the difficulty of desalination.

[0003] Traditional oilfield wastewater treatment processes employ a combination of "oil separation, air flotation, coagulation filtration, and ion exchange softening"; however, in practical applications, this traditional process has revealed numerous insurmountable problems:

[0004] Chemical dependence and sludge issues: This process is highly dependent on chemicals, requiring large amounts of Na2CO3 / NaOH and other chemicals to achieve wastewater treatment goals. The use of large amounts of chemicals not only increases treatment costs but also leads to a significant increase in sludge production, accounting for 5%-10% of the treated volume. The generation of large amounts of sludge not only requires additional treatment facilities and costs but also presents challenges in sludge disposal, posing a potential threat to the environment.

[0005] Low silicon removal efficiency: Traditional adsorption methods are ineffective in removing dissolved silicon, achieving a removal rate of only 30%-50%. This low efficiency leaves a large amount of silicon residue in the treated wastewater. This residual silicon easily forms scale during boiler operation, severely affecting the boiler's heat transfer efficiency and safe operation, and increasing the frequency and cost of boiler maintenance and cleaning.

[0006] Excessive salt residue: Even after ion exchange treatment, the total dissolved solids (TDS) in the wastewater still exceeds 1000 mg / L, far from meeting the stringent requirement of boiler feedwater conductivity <30 μS / cm. High salt residue can lead to corrosion and scaling inside the boiler, seriously threatening its safe and stable operation and shortening its service life.

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

[0008] Therefore, a high-efficiency boiler treatment method for oilfield wastewater reuse based on high-temperature resistant membranes and reverse osmosis is needed to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to provide a method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis, so as to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A high-efficiency boiler treatment method for oilfield wastewater reuse based on high-temperature resistant membranes and reverse osmosis includes high-temperature resistant membrane staged interception, first-stage anti-fouling reverse osmosis optimization, and second-stage anti-fouling reverse osmosis optimization. The specific steps are as follows:

[0012] Pretreatment and conditioning: First, the oilfield wastewater undergoes pretreatment and conditioning, precisely controlling the wastewater temperature within a suitable range of 50-80℃, and adjusting the pH to 10.5-11.5 by adding appropriate agents. The purpose of this step is to change the form and chemical properties of pollutants in the wastewater by adjusting the temperature and pH, making them easier to separate and remove in subsequent processes.

[0013] High-temperature resistant membrane: Utilizing a hydrophobically modified PTFE special filter membrane (50kDa molecular weight cutoff). Under operating pressures of 0.2-0.5MPa, this membrane exhibits a viscosity of 150-200 L / (m³). 2 •h) flux;

[0014] Its unique molecular retention properties enable it to selectively retain Ca. 2+ Mg 2 + and SiO3 2-Plasma has a rejection rate of >99% for these ions; at the same time, it also performs well in oil removal and suspended solids removal, with an oil removal rate of >95% and a suspended solids content (SS) of <1mg / L in the treated wastewater; this high efficiency in rejection and removal is due to the special material and structural design of the membrane, which can achieve the simultaneous removal of multiple pollutants through multiple mechanisms such as physical sieving, adsorption and charge repulsion.

[0015] Primary anti-fouling reverse osmosis: Polyamide composite membrane is selected for primary anti-fouling 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%. The polyamide composite membrane has good chemical stability and separation performance. By allowing water molecules to permeate through the membrane under pressure, it retains solutes such as salt, thereby achieving the initial desalination process. At the same time, the antifouling treatment on the membrane surface can effectively reduce the adsorption and deposition of organic pollutants on the membrane surface and extend the service life of the membrane.

[0017] Secondary reverse osmosis: A fouling-resistant brackish water desalination reverse osmosis membrane is used for secondary 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 secondary reverse osmosis further desalinates the primary reverse osmosis permeate through a more refined separation process, removing residual trace amounts of salt and other impurities to ensure that the final permeate water quality meets the stringent requirements for boiler feedwater. The fouling-resistant brackish water desalination reverse osmosis membrane is optimized for the characteristics of brackish water, enabling efficient operation in high-salinity environments while resisting contamination and ensuring long-term stable desalination performance.

[0018] Concentrate discharge: The concentrate produced by the first-stage anti-fouling reverse osmosis is returned to the plant's wastewater unit for further comprehensive treatment or discharge; by rationally designing the reuse path of the second-stage reverse osmosis concentrate, the second-stage reverse osmosis concentrate is reused to the first-stage reverse osmosis feed water, realizing the recycling of water resources; this rational treatment and reuse method of concentrate effectively improves the total recovery rate, which is >85%, greatly reduces the waste of water resources, and is in line with the concept of sustainable development.

[0019] This method innovatively utilizes a special filter membrane to achieve the synergistic retention of multiple pollutants under high-temperature conditions. This special filter membrane can simultaneously and efficiently retain pollutants such as oil, colloids, hardness, and silicon, breaking the limitation of traditional treatment processes where different pollutants need to be treated separately. Through this synergistic decontamination method, not only are the treatment steps and equipment used reduced, but more importantly, the amount of reagents added is reduced. In traditional processes, large amounts of reagents are often required to remove these pollutants, while this invention achieves simultaneous removal of pollutants through the special properties of the membrane, reducing treatment costs and minimizing the potential environmental impact of reagent use.

[0020] Furthermore, the reverse osmosis membrane surface has undergone unique modification treatment. By introducing advanced materials and technologies such as zwitterionic polymers, the hydrophilicity of the membrane has been enhanced. The enhanced hydrophilicity reduces the affinity of the membrane surface for organic pollutants, thereby effectively reducing the rate of organic fouling by more than 50%. This antifouling membrane design can significantly extend the service life of the membrane, reduce the frequency of membrane cleaning and replacement, reduce operating costs, and at the same time ensure the high efficiency and stability of the membrane during long-term operation.

[0021] Furthermore, through the meticulous design of a primary anti-fouling reverse osmosis and secondary reverse osmosis concentrate recycling system, a tiered water resource recovery optimization was achieved. The concentrate produced by the primary reverse osmosis system is partially reused as feed water after proper treatment, and the secondary reverse osmosis concentrate is also reused as feed water. This concentrate recycling method significantly improves the system's overall recovery rate, raising it to 90%. This tiered recovery optimization strategy makes full use of water resources, reduces the amount of concentrate discharged, lowers environmental pressure, and also 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:

[0023] This invention reduces the amount of chemicals added, saving 40% of the chemical cost compared to traditional processes, thus reducing dependence on chemicals, effectively lowering treatment costs, and improving the economic benefits of oilfield wastewater treatment.

[0024] This invention reduces the amount of sludge generated by optimizing the treatment process, thereby reducing the difficulty and cost of sludge treatment and also reducing the potential harm of sludge to the environment.

[0025] According to this invention, the produced water quality after processing can stably meet the water requirements of steam injection boilers. Key indicators such as conductivity, hardness, silicon content, and oil content can be strictly controlled within the standard range for boiler feedwater (conductivity < 30 μS / cm). The stable and compliant 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 issues, and extends the service life of the boiler.

[0026] This invention achieves near-zero discharge and reuse of oilfield wastewater, significantly reducing the total amount of wastewater discharged and lowering the risk of pollution to the surrounding water environment. At the same time, it reduces the use of fresh water resources, alleviating the contradiction between water supply and demand, and has significant environmental benefits, making a positive contribution to the green development of the oilfield industry.

[0027] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

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

[0029] Figure 2 This is a comparison table of pollutant concentrations before and after treatment of oilfield wastewater according to the present invention;

[0030] Figure 3 This is a 30-day pressure decay graph of the PTFE special membrane system, the primary RO membrane, and the secondary RO membrane of the present invention. Detailed Implementation

[0031] 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 drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0033] Example 1

[0034] like Figure 1-3 As shown, wastewater from an oilfield (with pollutant indicators of TDS=6000mg / L, oil content 8.31mg / L, hardness 340mg / L, SiO2=160mg / L, SS=25mg / L, and water temperature 75℃) was selected for treatment. The specific process is as follows:

[0035] First, the pH of the wastewater is adjusted to a 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 wastewater.

[0036] Next, the wastewater is filtered through a special PTFE filter;

[0037] In this process, the PTFE special filter membrane fully utilizes its unique interception and separation properties to efficiently remove various pollutants from wastewater. After treatment, the oil content is significantly reduced to <0.5 mg / L, suspended solids (SS) content to <0.5 mg / L, hardness to <10 mg / L, and SiO2 to <10 mg / L. These data demonstrate that the PTFE special filter membrane has excellent effects in removing pollutants such as oil, suspended solids, hardness, and silicon.

[0038] Subsequently, after reverse osmosis treatment, the salinity of the product water was reduced to <15mg / L, SiO2 <0.05mg / L, and the recovery rate reached 85%. This result fully demonstrates the high efficiency of the process of this invention in desalination and silicon removal, as well as its good performance in water resource recycling.

[0039] To accurately verify the treatment effect, a series of national standard testing methods were used to comprehensively test the treated water, including GB / T7476-1987 Determination of Calcium in Water by EDTA Titration, GB / T7477-1987 Determination of Total Calcium and Magnesium in Water by EDTA Titration, 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 by Infrared Spectrophotometry, and GB / T11901-89 Determination of Suspended Solids in Water by Gravimetric Method.

[0040] The test results clearly show that the present invention exhibits excellent removal effects on calcium, hardness, silicon, TDS, SS and oil in oilfield wastewater, effectively improving water quality and making it fully meet the water inlet conditions of steam boilers, thus providing reliable water quality assurance for the safe and stable operation of boilers.

[0041] Example 2

[0042] like Figure 1-3 As shown, in order to further verify the operational stability of the PTFE special membrane in this invention, the following test was conducted: the PTFE special membrane was subjected to a 30-day continuous operation test, and the results showed that its pressure decay was ≤5%; this indicates that the PTFE special membrane can maintain relatively stable pressure performance during long-term operation, and its filtration performance will not decrease significantly due to long-term use, thus ensuring the continuous and efficient operation of the PTFE special membrane.

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

[0044] The pressure drop of the secondary RO membrane is ≤5% after 30 days of operation; the secondary RO membrane also shows good stability, maintaining relatively stable performance during operation, ensuring further optimization and improvement of the product water quality by the secondary reverse osmosis, and ensuring that the final product water can meet the strict requirements of boiler feedwater.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis, characterized in that, Includes the following steps: S1. Pretreatment and conditioning: Control the wastewater temperature at 50-80℃ and adjust the pH to 10.5-11.5; S2. High-temperature resistant special filter membranes are used for oil removal, suspended solids removal, hardening removal, and silicon removal. The high-temperature-resistant special filter membrane is used for oil removal, suspended matter removal, hardness removal and silicon removal, the operation pressure is 0.2-0.5 MPa, the flux is 150-200 L / (m 2 ·h), the interception rate of Ca 2+ , Mg 2+ and SiO3 2- is >99%, the oil removal rate is >95%, and the SS after treatment is <1 mg / L. The high-temperature resistant special filter membrane is a hydrophobically modified PTFE high-temperature resistant special filter membrane, which has a temperature resistance of ≥80℃ and a molecular weight cutoff of ≤50kDa. S3, Two-stage anti-fouling reverse osmosis desalination: The effluent from step S2 enters the first-stage anti-fouling reverse osmosis membrane for desalination treatment; the first-stage anti-fouling reverse osmosis permeate enters the second-stage anti-fouling reverse osmosis membrane for further desalination; the first-stage anti-fouling reverse osmosis concentrate is discharged into the plant's wastewater discharge system; the second-stage anti-fouling reverse osmosis concentrate is reused in the first-stage reverse osmosis feed water; the conductivity of the second-stage reverse osmosis permeate is <30μS / cm, and the total system recovery rate is >85%.

2. The method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis according to claim 1, characterized in that: The surface of the reverse osmosis membrane is treated with zwitterionic polymers for antifouling.

3. The method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis according to claim 1, characterized in that: The first-stage anti-fouling reverse osmosis uses a polyamide composite membrane, operates at a pressure of 100 MPa, has a recovery rate of 90.1%, and a desalination rate of >96.8%.

4. The method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis according to claim 1, characterized in that: The secondary reverse osmosis uses a fouling-resistant 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%.

5. The method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis according to claim 1, characterized in that: After treatment using this method, the calcium content in oilfield wastewater was reduced to below 1 mg / L, the hardness to below 10 mg / L, the silicon content to below 0.05 mg / L, the TDS to below 15 mg / L, the SS to below 0.5 mg / L, and the oil content to below 0.5 mg / L.

6. The method for efficient reuse of oilfield wastewater in boilers based on high-temperature resistant membranes and reverse osmosis according to claim 1, characterized in that: The pressure drop of the high-temperature resistant special filter membrane is ≤5% after 30 days of operation, the pressure drop of the first-stage RO membrane is ≤3% after 30 days of operation, and the pressure drop of the second-stage RO membrane is ≤5% after 30 days of operation.

Images