Membrane PSA: [Weekly Topic] {April 4, 2011} What are the methods for oil-water separation! Wish everyone a happy Tomb-Sweeping Day!

This post was last edited by siena2008 on 2011-4-7 at 18:53. Oil-containing wastewater treatment technology. Abstract: It introduces the principles and characteristics of common technologies for treating oil-containing wastewater, as well as the equipment used for oil removal, and provides an overview of the methods for treating such wastewater. Keywords: oily wastewater; technologies; wastewater treatment methods. Oily wastewater is generated in large quantities and across a wide range of industries; for example, it is produced during oil extraction, petroleum refining, petrochemical processing, oil storage and transportation, oil tanker accidents, ship navigation, vehicle cleaning, machinery manufacturing, food processing, and other processes. Oil pollution, as a common form of pollution, poses a severe threat to environmental protection and ecological balance. Currently, there are many oil-water separation technologies available. Commonly used methods include gravity separation, air flotation, coarsening, filtration, adsorption, ultrasonic treatment, and other techniques. Moreover, new oil removal technologies are still being developed continuously. This article introduces the principles and methods of oil removers. 1 Gravity separation method: The gravity separation method is a typical primary treatment technique that takes advantage of the density difference between oil and water as well as their immiscibility to separate oil droplets, suspended particles from water, whether in a stationary or flowing state. Oil droplets dispersed in water rise slowly upward due to buoyancy and separate into layers; the rising speed of these oil droplets depends on the size of the droplets, the density difference between oil and water, the flow conditions, and the viscosity of the fluid. Their relationship can be described by laws such as Stokes’ and Newton’s laws. 1. 1 Transverse-flow oil remover: The transverse-flow oil-containing wastewater oil removal device was developed on the basis of the inclined-plate oil remover; it consists of a coagulation zone and a separation zone for the oil-containing wastewater. The oily wastewater first passes through a cross-plate type coalescer, where small, dispersed oil droplets combine to form larger ones, and small solid particles aggregate into larger particles. The thus enlarged oil droplets and solid particles are then separated from the water via a transverse flow separation plate section with unique channels. While separating oil from water and solid substances, gas (natural gas) can also be separated. 1. 2 Wave-plate coalescing oil-water separator: The principle behind oil removal using wave-plates relies on the density difference between oil and water, which causes oil droplets to float to the peaks of the plates and thus be separated. The key lies in applying the Hazen-Williams shallow tank settling principle to create wave-plates with varying spacing and flow patterns; as a result, the cross-sectional area through which water flows changes, and the water flow alternates between expanded and contracted states, generating pulsating (sinusoidal) flow. This increases the probability of collisions between oil droplets, helps larger droplets form from smaller ones, and accelerates the upward movement of the oil droplets, thereby achieving oil-water separation. 1. 3 Aggregated oil-water separators: The Austrian company Fere was the first in the world to develop the CPS integrated corrugated plate gravity-accelerated aggregated oil-water separator. This corrugated sheet is a patented product of Feirei Company. Made from polypropylene and containing various additives, it features oil affinity without being sticky to oil, as well as resistance to aging. The corrugated plates are stacked one on top of another, with a spacing of generally 6 mm (a spacing of 12 mm can be used when the concentration of suspended particles in the water is high). 1. 4 High-efficiency elevated-angle free water separators: These combine horizontal and vertical free water separators and feature an elevated-angle design. This design overcomes the drawbacks of vertical containers, where the oil-water interface covers a small area, as well as those of horizontal containers, where the distance between the oil-water interface and the water outlet is short, resulting in insufficient separation time. The incoming liquid inlet is located at the upstream end of the tubular container; oil droplets in the water can coalesce and rise to the top oil outlet, while the water sinks to the bottom water outlet for discharge. The elevation angle of this device is less than 12°; it is 18.3 m long, and is available in two sizes with diameters of 1,372 mm and 914 mm. 2 Filtration method: The filtration method involves passing wastewater through a device with pores or through a filter layer made of certain granular media; the retention, screening, and inertial collision effects of these elements are used to remove harmful substances such as suspended solids and oils from the wastewater. There are 3 common filtration methods: layer filtration, diaphragm filtration, and fiber media filtration. Membrane filtration, also known as membrane separation, uses microporous membranes to retain oil droplets and surfactants, and is primarily used to remove emulsified oils and certain dissolved oils. Filter membranes include ultrafiltration membranes, reverse osmosis membranes, and hybrid filter membranes, among others. Membrane materials are divided into organic membranes and inorganic membranes. Common organic membranes include cellulose acetate membranes, polysulfone membranes, polypropylene membranes, etc., while common inorganic membranes include ceramic membranes, aluminum oxide, cobalt oxide, titanium oxide, etc. The emulsified oil remains in a stable state; it is difficult to separate it using physical or chemical methods. With the rapid development of membrane science, the use of membrane processes for treating emulsified oil wastewater has gradually been accepted and applied in industry. 3 Centrifugal separation method: The centrifugal separation method involves rotating a container containing oily wastewater at high speed to create a centrifugal force field. Due to the different densities of solid particles, oil droplets, and wastewater, they experience varying levels of centrifugal force, which enables the removal of solid particles and oil droplets from the wastewater. The commonly used device is a hydrocyclone separator. The application of cyclone separators in liquid-solid separation began in the 1840s; they are now quite mature, but research in the field of oil/water separation started much later. Although the basic principles of liquid-solid separation and liquid-liquid separation are the same, the geometric structures of the equipment used for these processes differ significantly. The oil-removing cyclone separator originated in the UK. Starting from the late 1960s, the Multiphase Flow and Mechanical Separation Laboratory led by Professor Martin Thew at the University of Southampton in the UK began research on swirl separators for oil removal from water, and invented a double-cone, dual-inlet liquid-liquid swirl separator. Satisfactory results were achieved during the testing process. Subsequently, Young GAB and others designed a single-cone cyclone separator that possesses the same separation performance as the biconic cyclone but has a processing capacity twice as high. Through geometric optimization, Conoco developed the K-type cyclone separator, which exhibits a more significant improvement in the separation performance of oil droplets with diameters less than 10 μm. Due to the many unique advantages of cyclone separators, cyclone de-oiling technology has become an irreplaceable standard equipment for treating oily wastewater in developed countries—especially on offshore oil drilling platforms. 4 Flotation method: The flotation method, also known as air flotation, is a water treatment technology that is being extensively studied and increasingly adopted both domestically and internationally. This method involves introducing air or other gases into water to generate fine bubbles. As a result, tiny suspended oil droplets and solid particles in the water adhere to these bubbles and rise to the water surface together with them, forming scum (an oil-containing foam layer). An appropriate oil skimmer is then used to remove the oil. This method is primarily used to treat dispersed oil, emulsified oil, and fine suspended solids with particle sizes of 10–60 μm that remain in the water after treatment in oil separators; the oil content in the effluent can be reduced to 20–30 mg/L. Depending on the method used to generate bubbles, air flotation is divided into pressure dissolved air flotation, air sparging flotation, electrolytic flotation, etc., among which pressure dissolved air flotation is the most widely used. 5 Bio-oxidation method: The bio-oxidation method is a technique that uses the biochemical actions of microorganisms to purify wastewater. Oils are hydrocarbon organic compounds that can be broken down into carbon dioxide and water through biological processes such as the metabolism of microorganisms. The organic matter in oily wastewater exists mainly in dissolved and emulsified forms, with a high BOD5 value, which facilitates biological oxidation. For wastewater with an oil concentration of 30–50 mg/L or less, and which also contains other biodegradable harmful substances, biochemical treatment is commonly used; it is primarily aimed at removing dissolved oil from the wastewater. Common biochemical treatment methods for oily wastewater include the activated sludge process, biological filtration, and biological rotating disk process. The activated sludge process offers good treatment results and is mainly used for treating wastewater with high requirements and stable water quality. Compared with the activated sludge process, in the biofilm process, biofilms adhere to the surface of filler carriers, allowing microorganisms with slow reproduction rates to survive as well, thereby forming a stable ecosystem. However, since it is difficult to control the amount of microorganisms attached to the surface of the carrier, there is limited flexibility in operation, and the volume load is also restricted. 6 Chemical method: The chemical method, also known as the chemical treatment method, is a technique in which chemicals are added to convert the pollutants present in wastewater into harmless substances through chemical reactions, thereby purifying the wastewater. Common chemical methods include neutralization, precipitation, coagulation, oxidation-reduction, etc. Coagulation is mainly used for oily wastewater. The coagulation method involves adding a certain proportion of flocculant to oil-containing wastewater. After hydrolyzing in water, it forms positively charged colloidal particles that undergo electroneutralization with negatively charged emulsified oil. As a result, oil particles aggregate and their size increases; meanwhile, flocs are generated to adsorb tiny oil droplets. Finally, oil-water separation is achieved through sedimentation or flotation. Common coagulants include inorganic coagulants such as polyaluminum chloride (PAC), ferric chloride, aluminum sulfate, and ferrous sulfate, as well as organic polymer coagulants such as acrylamide and polyacrylamide (PAM). Different coagulants require different dosages, and there are also varying suitable pH ranges for them. This method is suitable for oil droplets in an emulsified state and other fine suspended particles that cannot be separated by gravity settling. 7 Adsorption method: The adsorption method utilizes oleophilic materials to adsorb dissolved oils and other soluble organic substances in wastewater. The most commonly used oil absorption material is activated carbon, which can adsorb dispersed oil, emulsified oil, and dissolved oil in wastewater. Due to the limited adsorption capacity of activated carbon (typically 30–80 mg/g for oils), its high cost, and the difficulties associated with its regeneration, it is generally used only as the final stage in the multi-stage treatment of oily wastewater, enabling the oil concentration in the effluent to be reduced to 0.1–0.2 mg/L. In 1976, the Changling Refinery in Hunan utilized activated carbon adsorption for advanced treatment in its wastewater treatment process. Some useful results have also been achieved domestically and internationally in the development of new adsorbents. Studies have found that flake graphite can adsorb heavy oil released from oil tanker leaks and can be easily separated from water. Adsorption resins are a new type of organic adsorbent that have been developed in recent years. They possess excellent adsorption properties and are easy to regenerate; as a result, they are gradually replacing activated carbon. An increasing number of industry professionals are researching the synthesis and application of high-efficiency oil-absorbing resins. Studies have shown that the use of polypropylene oil-absorbing materials to adsorb, separate, and recover oil substances from oil industry wastewater allows for the selection of appropriate purification methods based on factors such as the initial condition of the wastewater, the desired final outcome, and the flow rate of the water. In addition, coal ash, modified bentonite, sulfonated coal, crushed coke, organic fibers, oil-absorbing felt, ceramsite, quartz sand, wood chips, straw, and the like can also be used as oil-absorbing materials. After becoming saturated with oil, the oil-absorbing material can, depending on the specific circumstances, be regenerated for reuse or used directly as fuel. 8 Coarsening method: The coarsening method takes advantage of the significant difference in the affinity between oil and water for such coalescing materials; oil particles are captured by the material and remain on its surface and in its pores, forming an oil film. When this oil film reaches a certain thickness, it detaches under the action of hydraulic forces and buoyancy, and then combines to form larger oil particles. According to Stokes’ law, the rising speed of oil particles in water is proportional to the square of their diameter. After coalescence, oil droplets with larger diameters can be easily separated from water. In the coarsely granulated wastewater, the oil content and properties of the oily sludge remain unchanged; it is simply easier to remove the oil using gravity separation. 8.1 Newly developed high-efficiency oil removers. Cyclonic oil removal, coalescence-based oil removal, and inclined plate oil removal technologies are currently regarded as highly efficient oil removal techniques. The high-efficiency oil remover is a combined device that integrates multiple aforementioned high-efficiency oil removal technologies. Its overall structure is designed to be horizontal, consisting of a cyclone (vortex section), a coarsening section, and an inclined-plate oil removal section. It not only improves oil removal efficiency but also is easy to operate and requires less space. Based on the characteristics of the produced water from the Jianghan Oilfield, two-stage coarsening and two-stage inclined plate oil removal are employed; when the inlet ρ(oil) is ≤1,000 mg/L, the outlet value meets the requirement of the subsequent treatment equipment (filters), namely ρ(oil) ≤30 mg/L. 8. 2 EPS oil-water separation technology: The EPS oil-water separator is a highly efficient and advanced device for separating oil from water. It integrates modern advanced plate-based oil removal and coagulation technologies, combining functions such as pretreatment of wastewater, oil-water separation, secondary sedimentation, and oil recovery. It features low installation and operation costs, excellent oil-water separation performance, and easy operation and maintenance. It serves as an upgraded alternative to vertical oil removal tanks and inclined plate oil removal devices such as those specified by the American Petroleum Institute (API), corrugated plate inclined plate oil removal devices (CPI), and parallel inclined plate oil removal devices (PPI). The EPS oil-water separator has currently been put into practical use in countries such as South Korea, the United States, Poland, India, Thailand, and China, with generally good wastewater treatment results. 9 Sound wave, microwave, and ultrasonic dehydration technologies: Sound waves can accelerate the coalescence of water droplets, thereby improving the efficiency of crude oil dehydration; ultrasonic waves can reduce energy consumption and the amount of demulsifiers required; while microwaves not only decrease the stability of emulsions but also heat them, further promoting the coalescence of water droplets. These technologies hold great potential for addressing the problem of deep dehydration in old oil fields in eastern China, where the complex properties of crude oil result from various extraction methods. Microwaves refer to electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz. Microwave water treatment technology is a novel approach to water treatment that utilizes the strong catalytic effect, penetration capability, selective energy supply, and microbial killing properties of microwave fields on the physicochemical reactions in single-phase and multiphase flows. Ultrasonic waves are high-frequency mechanical waves, with frequencies generally ranging from 2 ×104 to 5 ×108 Hz; they feature concentrated energy and strong penetration power. Ultrasonic waves can induce coagulation effects, cavitation, or cavitation effects in water. When ultrasound passes through a solution containing sewage, it causes tiny oil droplets to vibrate together with the water. However, since particles of different sizes have different relative vibration speeds, the oil droplets will collide with each other and stick together, increasing the volume of the oil droplets. Subsequently, as the particles have grown larger and can no longer vibrate with the sound waves, they move in a random manner. Finally, the small oil droplets in the water coalesce and rise to the surface, achieving good oil-water separation. When using ultrasound to treat emulsified oil wastewater, it is necessary to conduct experiments first to determine the optimal sound frequency; otherwise, an ultrasonic crushing effect may occur, affecting the treatment efficiency. To date, scholars at home and abroad have used ultrasound technology to degrade dozens of pollutants in water. However, the systems studied are mostly single-component simulation systems, while actual wastewater often contains multiple pollutants; therefore, the applicability of ultrasound technology in actual wastewater treatment still requires further investigation. Furthermore, most current research on using ultrasound technology to degrade pollutants in water is still at the laboratory stage. Due to insufficient research on aspects such as the degradation mechanism of acoustic chemical reactions, reaction kinetics, and the design of reactors for scale-up, it is currently difficult to implement this technology on an industrial scale. 10 Ultrasound/electrochemistry combined technology: By utilizing the cavitation effect of ultrasound, it is possible to prevent the formation of a coating on the electrodes during electrochemical reactions, thereby avoiding a decline in electrode activity. The ultrasonic cavitation effect also facilitates the generation of ·OH radicals in the electrocatalytic process, accelerating the decomposition of pollutants in wastewater. Additionally, ultrasound helps to disperse organic substances thoroughly in aqueous solutions, thus significantly enhancing the processing capacity of the reactor. Mizera et al. found that when electrolytic oxidation was used to treat phenol-containing wastewater, the decomposition rate was only 50% in the absence of ultrasound; however, when ultrasound with a frequency of 25 kHz and an intensity of 104 W/m2 was used, the decomposition rate of phenol increased to 80%. Liu Jing et al. utilized an ultrasonic/electrochemical combined technique for treating printing and dyeing wastewater. Their results showed that under the synergistic effect of ultrasound and an electric field, the decolorization rate of the wastewater was **higher than that achieved when ultrasound was used alone.

This post was last edited by siena2008 on 2011-4-7 at 18:53. The new oil-water separation filter material uses a PTFE polymer solution produced in the United States, to which oil-loving additives are added; after mixing, this mixture is evenly sintered on a stainless steel mesh, resulting in a filter surface that is water-repelling and oil-loving yet does not stick to oil (with a surface tension of 18.5 mN/m). When oil comes into contact with the filtering material, it aggregates the tiny oil droplets into larger ones, which then rise to the surface of the liquid as the water flows, forming an oil layer. The media area and external dimensions of the filter can be designed and installed according to actual usage conditions. Generally, it is capable of processing 500 to 1000 tons per hour of products containing 90% floating oil. 1. Discussion on oil-water separation: Both oil and water are liquids; therefore, the process of separating a mixture of these two liquids is referred to as liquid-liquid separation technology. When the two are mixed, a true solution is formed. Due to the difference in density between oil and water, oil appears to float on top of the water. However, as a result of oxidation, organic acids containing carboxyl groups (–COOH) are generated in the oil-water mixture; these acids have an affinity for the hydroxyl groups (–OH) in water, forming spherical structures. This phenomenon is commonly referred to as oil-in-water or water-in-oil, resulting in a stable emulsion. When the diameter of water particles in oil is ≤0.4–0.7 μm, it appears transparent; this is also known as a true solution. However, it is quite difficult to separate the dissolved water from a true solution. In the past, methods such as static sedimentation, vacuum treatment, centrifugal processing, and heating distillation were commonly used; none of these, however, could meet the operational requirements. The main reason is the hindering effect of the surface tension of the oil; even when heated to 100–115°C, the water-in-oil mixture does not vaporize, making it difficult to separate the water from the tiny oil-water particles. Recent studies have shown that the demulsification process can be used to break apart water-in-oil particles; the water contained in particles with a size of ≤0.4–0.7 μm is separated and aggregated into larger particles, after which oil-water separation of 5 μm particles can be carried out. II. Latest methods for oil-water separation: Our company’s research personnel have worked together with several experts in China who have long been engaged in research on oil-water separation technologies and polymer materials to develop new techniques for this purpose. After numerous tests and validations, and by drawing on the advanced technical design concepts of American companies such as Douglas, Wayne, Hydrolux, as well as the Austrian company Frey, while also taking into account the performance-to-price ratio of domestic raw materials. It has been processed into a product for market use, and has achieved good performance. The new oil-water separation filter media developed by our company use PTFE polymer solutions produced in the United States, to which oil-loving additives are added. After mixing, this mixture is evenly sintered on a stainless steel mesh, resulting in a filter media surface that is water-repelling and oil-loving, yet does not stick to oil (with a surface tension of 18.5 mN/m). When oil comes into contact with the filtering material, it aggregates the tiny oil droplets into larger ones, which then rise to the surface of the liquid as the water flows, forming an oil layer. The media area and external dimensions of the filter can be designed and installed according to actual usage requirements. Generally, it is capable of processing 500 to 1,000 tons per hour of material containing 90% floating oil. The entire setup can be adjusted based on the amount of material to be processed, by adding or removing filters, and the equipment can be moved to any location for use. Another type of filter material uses a PTFE polymer solution produced in Japan, with the same processing technique. The surface tension of water on the filter material can be such that, when water droplets fall freely from a height of 20 to 50 mm onto the surface of the filter material, no water seeps through to the back side of the filter material. The pore size of the mesh plate can be adjusted based on the viscosity of the oil. Under normal conditions, the diesel after separation can reach 8–10 ppm/kg, while transformer oil can reach 2–5 ppm/kg. These two types of filter media are used for oil-water separation and floating oil collection, featuring simple operation, high filtration efficiency, and a long service life. This effect is particularly evident when dealing with large volumes of mixed liquids, allowing operating costs to be reduced by 40–60%. III. Main application areas of oil-water separation technology 1. Filtration, demulsification, and oil-water separation of waste diesel in shipyards, with a water content of 5–8 ppm/kg ； 2. Transformer oil filtration, demulsification, oil-water separation; water content: 2–5 ppm/kg ； 3. Turbine oil filtration, oil-water separation, decolorization, demulsification, and fine filtration for power plants; water content: 2–5 ppm/kg ； 4. Handling of marine crude oil spills: collection, filtration, oil-water separation ； 5. Oil filtration, cleaning, and oil-water separation at the oil field site ； 6. Oil collection, oil-water separation, and heating-based separation on offshore drilling platforms, with water content < 100 ppm/kg ； 7. Collection, filtration, and oil-water separation of floating oil in the stratified oil sedimentation tank of steel mills ； 8. Large amounts of oily wastewater from refineries are collected, filtered, and separated into oil and water.

After emulsification, membrane filtration is sufficient

This post was last edited by siena2008 on 2011-4-7 18:54: Cyclone separation； Membrane filtration ； Demisters, and so on.

This post was last edited by siena2008 on 2011-4-7 at 18:54. Let me tell you the methods I have used: (1) Air flotation, (2) Centrifugation, (3) Extraction + distillation, (4) Membrane filtration (oil-water separation membranes, ultrafiltration)

;P Hehe, what method does the original poster suggest for separating oil from water? It’s simple: install a three-stage separator for oil, water, and gas. As for the principle, it involves demulsification at the source (that is, adding chemical agents to carry out demulsification there); experience has shown that this method yields very good dehydration results. ) Crude oil enters the separator, where gas is first separated, followed by the filtration of solid particles. Oil and water are separated using differences in sedimentation rates; specifically, a water chamber and an oil chamber are provided within the tank, with their bottoms connected to maintain balance. The oil is then extracted and sent to the filtration tank. Wastewater enters the water treatment plant. Of course, there are many other separation methods; I think this one is okay. The effect is also good. It’s the most reasonable thing I’ve ever seen anyway.