A chemical cleaning method for tubular ultrafiltration membrane used in oilfield water treatment

Abstract

The application belongs to the technical field of oil and gas field development, and particularly relates to a tubular ultrafiltration membrane chemical cleaning method for oilfield water treatment, and aims to solve the membrane pollution problem of the tubular ultrafiltration membrane. The application comprises the following steps: cleaning pretreatment, alkali cleaning, membrane group emptying, acid cleaning and emptying cleaning. In the alkali cleaning and acid cleaning steps, two cleaning modes of low pressure and low speed and high pressure and high speed are respectively adopted. The application has the characteristics that the cleaning device pipeline structure is simple, and two cleaning modes share one set of pipeline.

Description

Technical Field This invention belongs to the field of oil and gas field development technology, and specifically relates to a chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment. Background Technology

[0001] Produced water is a major byproduct of oil extraction, transportation, and storage. Deep treatment of produced water to meet reinjection standards before reinjection into the formation to replenish formation pressure has become essential. Reinjection not only avoids environmental pollution but also conserves significant water resources.

[0002] Membrane technology is an important technological means to solve current resource and environmental problems. Ultrafiltration technology is a material separation technology that uses the micropores of the membrane material itself to achieve heterogeneous separation of substances. Compared with traditional filtration technology, ultrafiltration technology has advantages such as low energy consumption and high efficiency. However, membrane fouling has always been the biggest challenge facing the application of ultrafiltration membranes.

[0003] Ultrafiltration is a pressure-driven membrane separation technology. Under pressure, small-molecule solutes and solvents pass through an ultrafiltration membrane with a specific pore size, while large-molecule solutes cannot pass through and remain on one side of the membrane, thus partially purifying the large molecules. Ultrafiltration is one of the pressure-driven membrane separation technologies, aiming to separate large molecules from small molecules.

[0004] Ultrafiltration technology has various applications. For example, in the extraction, transportation, and storage of oil, produced water is a major byproduct of oil extraction. Current technologies mostly employ tubular ultrafiltration membranes for deep treatment of produced water, which is then reinjected into the formation after meeting reinjection standards to replenish formation pressure. Produced water reinjection not only avoids environmental pollution but also conserves significant water resources.

[0005] However, membrane fouling of tubular ultrafiltration membranes remains the biggest challenge in ultrafiltration membrane applications. As the ultrafiltration membrane flux continuously declines, the pressure difference across the membrane and the pressure drop across the membrane gradually increase, leading to production disruptions. This is especially true in the later stages of membrane operation, where the composition of membrane contaminants becomes more complex, increasing the difficulty and time required for cleaning. Therefore, how to quickly and efficiently restore the operating efficiency of tubular ultrafiltration membranes is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, namely the membrane fouling problem of tubular ultrafiltration membranes, this invention provides a chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment.

[0007] The technical solution of the present invention includes:

[0008] A method for chemical cleaning of a tubular ultrafiltration membrane for oilfield water treatment, characterized by comprising the following steps:

[0009] Step S1, cleaning pretreatment, using clean water from the product water tank to clean the membrane tube to be cleaned through a backwash pump;

[0010] Step S2, alkaline washing: Add alkaline cleaning solution to the cleaning tank, perform alkaline cleaning on the membrane tube to be cleaned, and then drain the alkaline cleaning solution.

[0011] Step S3: Empty the membrane module. After cleaning in step S2, empty the alkaline solution and add clean water to the cleaning tank. Circulate the cleaning using a circulation pump. Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes. Stop the circulation pump when the pH value of the test water sample reaches 7. Circulate the cleaning using the cleaning pump and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7.

[0012] Step S4, pickling: Add acidic cleaning solution to the cleaning tank, perform acidic cleaning on the membrane tube to be cleaned, and then drain the acidic cleaning solution.

[0013] Step S5: Empty and clean the membrane tube by adding clean water to the cleaning tank.

[0014] As an optional technical solution, in step S2, the alkaline cleaning solution is a 1% sodium hydroxide + sodium hypochlorite solution, wherein the mass percentage of sodium hydroxide in sodium hydroxide + sodium hypochlorite is 99.4% to 99.6%.

[0015] As an alternative technical solution, in step S2, clean water is first added to the cleaning tank, and the membrane tube to be cleaned is then cleaned at low pressure and low speed using a cleaning pump. The pressure is 0.1 MPa and the flow rate is 55 m / s. 3 The process involves gradually adding alkaline solutes, sodium hydroxide and sodium hypochlorite solution, to the cleaning tank until the pH reaches 12-14. Then, the process is switched to high-pressure, high-speed cleaning of the membrane tubing using a circulating pump at a pressure of 0.3 MPa and a flow rate of 266 m / h. 3 / h.

[0016] As an optional technical solution, in step S2, the low-pressure, low-speed cleaning time is 30 minutes, and the high-pressure, high-speed cleaning time is 60 minutes.

[0017] As an optional technical solution, in step S2, during the process of adding alkaline solutes sodium hydroxide and sodium hypochlorite, a test water sample is taken from the sampling port of the membrane tube to be cleaned every 3 minutes and its pH value is detected, and the temperature of the cleaning solution is controlled to be less than or equal to 40°C throughout the alkaline cleaning process.

[0018] As an optional technical solution, in step S4, the acidic cleaning solution is a 30% hydrochloric acid + citric acid + sodium dodecylbenzenesulfonate solution, wherein the hydrochloric acid has a mass percentage of 8% to 10% and the sodium dodecylbenzenesulfonate has a mass percentage of 0.1% to 0.15%.

[0019] As an alternative technical solution, in step S4, clean water in the cleaning tank is used to perform low-pressure, low-speed cleaning of the membrane tube to be cleaned via a cleaning pump. The pressure is 0.1 MPa and the flow rate is 55 m / s. 3 / h, and gradually add the acidic solutes hydrochloric acid + citric acid + sodium dodecylbenzenesulfonate to the cleaning tank until the solution reaches a pH of 2-3; then switch to high-pressure, high-speed cleaning of the membrane tube to be cleaned via a circulating pump, with a pressure of 0.3 MPa and a flow rate of 266 m / s. 3 / h.

[0020] As an optional technical solution, in step S4, the low-pressure, low-speed cleaning lasts for 30 minutes, and the high-pressure, high-speed cleaning lasts for 60 minutes.

[0021] As an optional technical solution, in step S4, during the process of adding alkaline solutes sodium hydroxide and sodium hypochlorite, a test water sample is taken from the sampling port of the membrane tube to be cleaned every 3 minutes and its pH value is detected, and the temperature of the cleaning solution is controlled to be less than or equal to 40°C throughout the alkaline cleaning process.

[0022] A tubular ultrafiltration membrane chemical cleaning device includes a membrane tube to be cleaned and a product water tank. A backwashing pump is provided between the product water tank and the membrane tube to be cleaned and connected by a pipeline. The device is characterized by further including a cleaning tank. One path of the cleaning tank is connected to the pipeline of the membrane tube to be cleaned via a cleaning pump, and another path is connected to the pipeline of the membrane tube to be cleaned via a circulation pump. The membrane tube to be cleaned is also connected to the pipeline of the cleaning tank via a reflux valve. The cleaning tank is provided with a chemical dosing port and a temperature transmitter, and the membrane tube to be cleaned is provided with a sampling port.

[0023] The beneficial effects of this invention are:

[0024] (1) The chemical cleaning method for tubular ultrafiltration membranes for oilfield water treatment of the present invention adopts a combination of alkaline cleaning followed by acid cleaning. On the one hand, it overcomes the shortcomings of traditional single-sided alkaline cleaning or acid cleaning. On the other hand, this specific combination of alkaline and acid cleaning has a more significant cleaning effect compared with the acid cleaning method followed by alkaline cleaning.

[0025] (2) By utilizing a cleaning tank, a cleaning pump, and a circulation pump, this invention can achieve continuous low-pressure, low-speed and high-pressure, high-speed chemical cleaning. By utilizing different cleaning flow rates and pressures, a more efficient cleaning effect can be achieved.

[0026] (3) The role of adding sodium hypochlorite to alkaline cleaning agents is twofold: First, it enhances the cleaning effect. Sodium hypochlorite is a strong oxidant that can effectively decompose and remove organic pollutants on the surface of membrane tubes, such as extracellular polymers produced by microorganisms and oil stains. These organic pollutants may be difficult to completely remove by alkaline washing alone. Sodium hypochlorite can oxidize them into smaller molecules, making them easier to clean. Second, it disinfects and sterilizes. It can kill bacteria, algae, and other microorganisms growing on the surface of membrane tubes, preventing microorganisms from scaling and multiplying on the membrane tube surface, thereby extending the service life of the membrane tubes, maintaining good membrane tube performance, and ensuring the normal functioning of filtration, separation, and other functions.

[0027] (4) The role of adding sodium dodecylbenzenesulfonate to acidic cleaning agents is as follows: First, it cleans stains. Sodium dodecylbenzenesulfonate can effectively dissolve dirt and deposits in membrane tubes, especially various types of dirt composed of organic matter. If these dirt are not removed, they can easily lead to membrane tube blockage and performance degradation. The cleaning effect of sodium dodecylbenzenesulfonate can ensure unobstructed flow of membrane tubes and improve their operating efficiency. Second, it prevents corrosion and erosion. Sodium dodecylbenzenesulfonate can regulate surface tension, thereby forming a protective film on the surface of the membrane tube. This protective film can prevent the membrane tube from being corroded and oxidized, thereby extending its service life. This is undoubtedly an important guarantee for membrane systems that need to operate for a long time. Third, it improves the pickling effect. During the pickling process, sodium dodecylbenzenesulfonate can reduce the surface tension of the acid solution, making it easier to penetrate into the tiny gaps in the membrane tube. This not only improves the pickling effect, but also ensures the uniform distribution of acid solution in the membrane tube, avoiding local over-acidity or under-acidity. Fourth, it reduces frictional resistance. Sodium dodecylbenzenesulfonate can also reduce the surface tension of liquids and increase lubricity, thereby reducing the frictional resistance of the membrane tube during pickling. This not only reduces energy consumption but also protects the membrane tube from unnecessary mechanical damage. Fifth, synergistic effects. During pickling, sodium dodecylbenzenesulfonate can also produce synergistic effects with other chemical reagents. This synergistic effect can further improve the pickling effect and ensure thorough cleaning of the membrane tube.

[0028] (5) The acidic cleaning solution of the present invention uses both alkaline cleaning agent sodium hypochlorite and acidic cleaning agent sodium dodecylbenzenesulfonate. By utilizing the different mechanisms of action of these two agents, sodium hypochlorite can effectively decompose organic pollutants accumulated on the ultrafiltration membrane and sterilize and disinfect, addressing the defects in the ultrafiltration process of oilfield water.

[0029] (6) The cleaning device of the present invention has a set of cleaning tank pipelines and the characteristic of sharing both alkaline and acidic cleaning modes, which simplifies the cleaning pipeline system, reduces costs, and has better economic efficiency. Attached Figure Description

[0030] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 This is a schematic diagram of the piping for the chemical cleaning method of the tubular ultrafiltration membrane of the present invention;

[0032] Figure 2 This is a schematic flowchart of the chemical cleaning method for the tubular ultrafiltration membrane of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1-Sampling port, 2-Dosing port, 3-Temperature transmitter. Detailed Implementation

[0035] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] This invention provides a chemical cleaning method for tubular ultrafiltration membranes.

[0038] like Figure 1 The diagram shows a pipeline schematic of the chemical cleaning method for tubular ultrafiltration membranes according to the present invention.

[0039] One pipeline of the membrane to be cleaned is connected to the backwash pump and the product water tank pipeline respectively. The backwash pump is equipped with an inlet valve and an outlet valve. The membrane to be cleaned is equipped with an outlet valve. This part of the pipeline is used for backwashing the ultrafiltration membrane module.

[0040] Another line of the membrane tube to be cleaned is connected to the cleaning tank. The cleaning tank is divided into two lines, which are connected to the cleaning pump and the circulation pump respectively. An inlet valve and an outlet valve are installed before and after the cleaning pump and the circulation pump respectively. The membrane tube to be cleaned is also connected to the cleaning tank via a check valve.

[0041] The membrane tube to be cleaned is also equipped with a sampling port 1, and the cleaning tank is equipped with a dosing port 2 and a temperature transmitter 3.

[0042] like Figure 2 The diagram shows a flow chart of the chemical cleaning method for the tubular ultrafiltration membrane of the present invention.

[0043] The process includes six steps: pre-treatment cleaning, alkaline washing, membrane module venting and cleaning, acid washing, membrane module venting and cleaning, and restoring the operation of the membrane tube to be cleaned.

[0044] Step 1: Cleaning Pretreatment

[0045] The membrane tube to be cleaned is cleaned using clean water from the product water tank via a backwash pump.

[0046] Step 2: Alkali washing process

[0047] After completing the pre-treatment cleaning, close the inlet valve, outlet valve, and outlet valve of the backwash pump; open the vent valve of the membrane tube to be cleaned to drain all liquid from the membrane tube, then close the vent valve; open the water inlet valve of the cleaning tank and add 2m³ of clean water to the tank. 3 Clean water; close the water inlet valve of the cleaning tank; open the inlet valve, outlet valve, and return valve of the cleaning pump; start the cleaning pump at 0.1 MPa, 55 m 3 Operating at a low flow rate of / h; once clean water is circulating into the clean water tank, add alkaline cleaning agent (sodium hydroxide + sodium hypochlorite, alkaline solution concentration 1%, sodium hydroxide mass percentage concentration in the alkaline cleaning agent is 99.4%~99.6%) to the cleaning tank in several batches through the dosing port, and continue the circulation cleaning. Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 12-14, then stop adding chemicals, keep the pH value of the test water stable at 12-14, and the liquid temperature of the observed temperature transmitter should not exceed 40℃ during the cleaning process. Circulate cleaning for 30 minutes, then stop the cleaning pump; close the cleaning pump inlet valve and cleaning pump outlet valve; open the circulation pump inlet valve and circulation pump outlet valve, start the circulation pump, 0.3MPa, 266m 3 High-flow-rate circulation cleaning for 60 minutes per hour.

[0048] The addition of sodium hypochlorite to alkaline cleaning agents serves two main purposes: First, it enhances the cleaning effect. Sodium hypochlorite is a strong oxidizing agent that effectively decomposes and removes organic contaminants from the membrane tube surface, such as extracellular polymers produced by microorganisms and oil stains. These organic contaminants may be difficult to completely remove by alkaline washing alone; sodium hypochlorite oxidizes them into smaller molecules, making them easier to wash away. Second, it disinfects and sterilizes. It kills bacteria, algae, and other microorganisms that thrive on the membrane tube surface, preventing microbial scaling and reproduction, thereby extending the membrane tube's lifespan, maintaining its good performance, and ensuring the normal operation of filtration and separation functions.

[0049] Step 3: Vacuum and clean the membrane module

[0050] After the alkaline washing process is completed, stop the circulating pump, open the vent valve of the cleaning tank and the vent valve of the membrane tube to be cleaned to drain all liquid from the membrane tube to be cleaned, and close the vent valve of the membrane tube to be cleaned and the vent valve of the cleaning tank; open the water inlet valve of the cleaning tank and add 2m³ of water into the cleaning tank. 3 Fill the tank with clean water and close the water inlet valve of the cleaning tank; start the circulation pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7; stop the circulation pump and close the circulation pump inlet valve and circulation pump outlet valve; open the cleaning pump inlet valve and cleaning pump outlet valve, start the cleaning pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7.

[0051] Step 4: Pickling process

[0052] After venting and cleaning the membrane module, acidic cleaning agent (hydrochloric acid + citric acid + sodium dodecylbenzenesulfonate, acidic solution concentration 30%, of which hydrochloric acid is 8%–10% by mass, sodium dodecylbenzenesulfonate is 0.1%–0.15% by mass, and the remainder is citric acid) is added in stages to the cleaning tank through the dosing port. The cleaning process is carried out at 0.1 MPa and 55 m... 3 Low-flow-rate circulating cleaning: Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 2-3. Stop adding chemicals and maintain the pH value of the test water at a stable 2-3. During the cleaning process, the liquid temperature on the temperature transmitter should not exceed 40℃. Circulate cleaning for 30 minutes, then stop the cleaning pump; close the cleaning pump inlet valve and cleaning pump outlet valve; open the circulating pump inlet valve and circulating pump outlet valve, and start the circulating pump at 0.3MPa, 266m 3 High-flow-rate circulation cleaning for 60 minutes per hour.

[0053] The purpose of adding sodium dodecylbenzene sulfonate to acidic cleaning agents is fourfold: First, it cleans stains. Sodium dodecylbenzene sulfonate effectively dissolves dirt and deposits in membrane tubes, especially various types of organic dirt. If these deposits are not removed, they can easily lead to membrane tube blockage and performance degradation. The cleaning effect of sodium dodecylbenzene sulfonate ensures unobstructed flow of the membrane tubes, improving their operating efficiency. Second, it provides corrosion and erosion protection. Sodium dodecylbenzene sulfonate can regulate surface tension, thereby forming a protective film on the surface of the membrane tubes. This protective film prevents the membrane tubes from being corroded and oxidized, thus extending their service life. This is undoubtedly an important guarantee for membrane systems that require long-term operation. Third, it improves the pickling effect. During the pickling process, sodium dodecylbenzene sulfonate can reduce the surface tension of the acid solution, making it easier to penetrate into the tiny gaps in the membrane tubes. This not only improves the pickling effect but also ensures the uniform distribution of acid solution within the membrane tubes, avoiding localized over- or under-acidity. Fourth, it reduces frictional resistance. Sodium dodecylbenzenesulfonate can also reduce the surface tension of liquids and increase lubricity, thereby reducing the frictional resistance of the membrane tube during pickling. This not only reduces energy consumption but also protects the membrane tube from unnecessary mechanical damage. Fifth, synergistic effects. During pickling, sodium dodecylbenzenesulfonate can also produce synergistic effects with other chemical reagents. This synergistic effect can further improve the pickling effect and ensure thorough cleaning of the membrane tube.

[0054] Step 5: Vacuum and clean the membrane module

[0055] After the pickling process is complete, stop the circulation pump, open the vent valve of the cleaning tank and the vent valve of the membrane tube to be cleaned to drain all the liquid from the membrane tube to be cleaned, and close the vent valve of the membrane tube to be cleaned and the vent valve of the cleaning tank; open the water inlet valve of the cleaning tank and add 2m³ of water into the cleaning tank. 3 Fill the tank with clean water and close the water inlet valve of the cleaning tank. Start the circulation pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7. Stop the circulation pump and close the circulation pump inlet valve and circulation pump outlet valve. Open the cleaning pump inlet valve and cleaning pump outlet valve, start the cleaning pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7. Stop the cleaning pump, open the circulation pump inlet valve, circulation pump outlet valve, cleaning tank vent valve, and membrane tube vent valve to drain all liquid from the membrane tube to be cleaned, and close the circulation pump inlet valve, circulation pump outlet valve, cleaning pump inlet valve, cleaning pump outlet valve, and reflux valve.

[0056] Step 6: Restore the operation of the membrane tube to be cleaned

[0057] After the membrane module is vented and cleaned, open all production control valves of the membrane tube to be cleaned, as well as the inlet valve of the backwash pump, the outlet valve of the backwash pump, and the outlet valve of the membrane tube to be cleaned. Start the backwash pump and restore the operation of the membrane tube to be cleaned.

[0058] Table 1 shows the experimental data using traditional cleaning methods;

[0059] Table 1

[0060] Table 2 records the experimental data using the cleaning method of the present invention;

[0061] Table 2

[0062] Table 3 records the experimental data for three different cleaning processes: acid washing + alkali washing, alkali washing + acid washing, and acid washing.

[0063] Table 3 Based on the experimental data, it can be seen that the cleaning method of alkaline washing (adding sodium dodecylbenzenesulfonate) + acid washing (adding sodium hypochlorite) of the present invention can significantly improve the membrane flux of tubular ultrafiltration membranes compared with conventional cleaning methods. Specific Implementation

[0065] Example: Chemical cleaning process for the tubular ultrafiltration membrane at the J95 station of the Fifth Oil Production Plant.

[0066] The water treatment system at station J95 uses a combination of microbial and tubular ultrafiltration membranes. After six years of operation, the tubular ultrafiltration membranes reach the later stages of operation, resulting in severe membrane fouling and making it impossible to guarantee normal production operations.

[0067] The cleaning process for the J95 station-type ultrafiltration membrane includes:

[0068] Step 1: Cleaning Pretreatment

[0069] The membrane tube to be cleaned is cleaned using clean water from the product water tank via a backwash pump.

[0070] Step 2: Alkali washing process

[0071] After completing the pre-treatment cleaning, close the inlet valve, outlet valve, and outlet valve of the backwash pump; open the vent valve of the membrane tube to be cleaned to drain all liquid from the membrane tube, then close the vent valve; open the water inlet valve of the cleaning tank and add 2m³ of clean water to the tank. 3 Fill the tank with clean water and close the water inlet valve; open the inlet valve, outlet valve, and reflux valve of the cleaning pump, and start the cleaning pump at 0.1 MPa, 55m. 3Operating at a low flow rate of / h; once clean water is circulating into the clean water tank, add alkaline cleaning agent (1% solution concentration, with sodium hydroxide at 99.5% mass percentage and the remainder being sodium hypochlorite) in several batches through the dosing port into the cleaning tank, and continue the circulation cleaning. Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 12-14, then stop adding chemicals. Maintain the pH value of the test water at a stable level of 12-14, and ensure that the liquid temperature on the temperature transmitter does not exceed 40℃ during the cleaning process. Circulate the cleaning pump for 30 minutes, then stop the cleaning pump; close the cleaning pump inlet valve and the cleaning pump outlet valve; open the circulation pump inlet valve and the circulation pump outlet valve, and start the circulation pump at 0.3MPa, 266m 3 High-flow-rate circulation cleaning for 60 minutes per hour.

[0072] Step 3: Vacuum and clean the membrane module

[0073] After the alkaline washing process is completed, stop the circulating pump, open the vent valve of the cleaning tank and the vent valve of the membrane tube to be cleaned to drain all liquid from the membrane tube to be cleaned, and close the vent valve of the membrane tube to be cleaned and the vent valve of the cleaning tank; open the water inlet valve of the cleaning tank and add 2m³ of water into the cleaning tank. 3 Fill the tank with clean water and close the water inlet valve of the cleaning tank; start the circulation pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7; stop the circulation pump and close the circulation pump inlet valve and circulation pump outlet valve; open the cleaning pump inlet valve and cleaning pump outlet valve, start the cleaning pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7.

[0074] Step 4: Pickling process

[0075] After venting and cleaning the membrane module, acidic cleaning agent (30% solution concentration, 10% hydrochloric acid, 0.15% sodium dodecylbenzenesulfonate, and the remainder citric acid) was added to the cleaning tank in stages through the dosing port, and the solution was subjected to 0.1 MPa and 55 m... 3 Low-flow-rate circulating cleaning: Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 2-3. Stop adding chemicals and maintain the pH value of the test water at a stable 2-3. During the cleaning process, the liquid temperature on the temperature transmitter should not exceed 40℃. Circulate cleaning for 30 minutes, then stop the cleaning pump; close the cleaning pump inlet valve and cleaning pump outlet valve; open the circulating pump inlet valve and circulating pump outlet valve, and start the circulating pump at 0.3MPa, 266m 3 High-flow-rate circulation cleaning for 60 minutes per hour.

[0076] Step 5: Vacuum and clean the membrane module

[0077] After the pickling process is complete, stop the circulation pump, open the vent valve of the cleaning tank and the vent valve of the membrane tube to be cleaned to drain all the liquid from the membrane tube to be cleaned, and close the vent valve of the membrane tube to be cleaned and the vent valve of the cleaning tank; open the water inlet valve of the cleaning tank and add 2m³ of water into the cleaning tank. 3 Fill the tank with clean water and close the water inlet valve of the cleaning tank. Start the circulation pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7. Stop the circulation pump and close the circulation pump inlet valve and circulation pump outlet valve. Open the cleaning pump inlet valve and cleaning pump outlet valve, start the cleaning pump to perform circulation cleaning, and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7. Stop the cleaning pump, open the circulation pump inlet valve, circulation pump outlet valve, cleaning tank vent valve, and membrane tube vent valve to drain all liquid from the membrane tube to be cleaned, and close the circulation pump inlet valve, circulation pump outlet valve, cleaning pump inlet valve, cleaning pump outlet valve, and reflux valve.

[0078] Step 6: Restore the operation of the membrane tube to be cleaned

[0079] After the membrane module is vented and cleaned, open all production control valves of the membrane tube to be cleaned, as well as the inlet valve of the backwash pump, the outlet valve of the backwash pump, and the outlet valve of the membrane tube to be cleaned. Start the backwash pump and restore the operation of the membrane tube to be cleaned.

[0080] The tubular ultrafiltration membrane of the J95 station water treatment system adopts the chemical cleaning process of this invention. The cleaning effect is as follows: the cleaning time of a single cleaning session or a single set of membrane tubes is reduced by 20 hours, the membrane permeate flux recovery rate is increased by 10%, and the membrane cleaning cycle is extended by 30 days. This achieves the purpose of quickly restoring the membrane permeate flux, delaying the cleaning cycle of the ultrafiltration membrane tubes, and ensuring the stable operation of the oilfield water treatment system.

[0081] In the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. These are used merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0082] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0083] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0084] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for chemical cleaning of tubular ultrafiltration membranes for oilfield water treatment, characterized in that, Includes the following steps: Step S1, cleaning pretreatment, using clean water from the product water tank to clean the membrane tube to be cleaned through a backwash pump; Step S2, alkaline washing: Add alkaline cleaning solution to the cleaning tank, perform alkaline cleaning on the membrane tube to be cleaned, and then drain the alkaline cleaning solution. Step S3: Empty the membrane module. After cleaning in step S2, empty the alkaline solution and add clean water to the cleaning tank. Circulate the cleaning using a circulation pump. Take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes. Stop the circulation pump when the pH value of the test water sample reaches 7. Circulate the cleaning using the cleaning pump and take a test water sample from the sampling port of the membrane tube to be cleaned every 3 minutes until the pH value of the test water sample reaches 7. Step S4, pickling: Add acidic cleaning solution to the cleaning tank, perform acidic cleaning on the membrane tube to be cleaned, and then drain the acidic cleaning solution. Step S5: Empty and clean the membrane tube by adding clean water to the cleaning tank.

2. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 1, characterized in that: In step S2, the alkaline cleaning solution is a 1% sodium hydroxide + sodium hypochlorite solution, wherein the mass percentage of sodium hydroxide in the sodium hydroxide + sodium hypochlorite solution is 99.4% to 99.6%.

3. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 2, characterized in that: In step S2, clean water is first added to the cleaning tank, and the membrane tube to be cleaned is then cleaned at low pressure and low speed using a cleaning pump. The pressure is 0.1 MPa and the flow rate is 55 m / s. 3 The process involves gradually adding alkaline solutes, sodium hydroxide and sodium hypochlorite solution, to the cleaning tank until the pH reaches 12-14. Then, the process is switched to high-pressure, high-speed cleaning of the membrane tubing using a circulating pump at a pressure of 0.3 MPa and a flow rate of 266 m / h. 3 / h.

4. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 3, characterized in that: In step S2, the low-pressure, low-speed cleaning lasts for 30 minutes, and the high-pressure, high-speed cleaning lasts for 60 minutes.

5. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 3, characterized in that: In step S2, during the addition of alkaline solutes sodium hydroxide and sodium hypochlorite, a test water sample is taken from the sampling port of the membrane tube to be cleaned every 3 minutes and its pH value is tested. The temperature of the cleaning solution is controlled to be less than or equal to 40°C throughout the alkaline cleaning process.

6. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 1, characterized in that: In step S4, the acidic cleaning solution is a 30% hydrochloric acid + citric acid + sodium dodecylbenzenesulfonate solution, wherein the hydrochloric acid has a mass percentage of 8% to 10% and the sodium dodecylbenzenesulfonate has a mass percentage of 0.1% to 0.15%.

7. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 6, characterized in that: In step S4, clean water from the cleaning tank is used to perform low-pressure, low-speed cleaning of the membrane tube to be cleaned via a cleaning pump. The pressure is 0.1 MPa and the flow rate is 55 m / s. 3 / h, and gradually add the acidic solutes hydrochloric acid + citric acid + sodium dodecylbenzenesulfonate to the cleaning tank until the solution reaches a pH of 2-3; then switch to high-pressure, high-speed cleaning of the membrane tube to be cleaned via a circulating pump, with a pressure of 0.3 MPa and a flow rate of 266 m / s. 3 / h.

8. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 7, characterized in that: In step S4, the low-pressure, low-speed cleaning lasts for 30 minutes, and the high-pressure, high-speed cleaning lasts for 60 minutes.

9. The chemical cleaning method for tubular ultrafiltration membranes used in oilfield water treatment as described in claim 7, characterized in that: In step S4, during the addition of alkaline solutes sodium hydroxide and sodium hypochlorite, a test water sample is taken from the sampling port of the membrane tube to be cleaned every 3 minutes and its pH value is tested. The temperature of the cleaning solution is controlled to be less than or equal to 40°C throughout the alkaline cleaning process.

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