WO2008147785A1

WO2008147785A1 - Tangential flow filtration to remove contaminants from oil

Info

Publication number: WO2008147785A1
Application number: PCT/US2008/064283
Authority: WO
Inventors: Barry R. Breslau; Khalid Farooq; Stanton R. Smith; Shawn P. Tansey
Original assignee: Pall Corporation
Priority date: 2007-05-23
Filing date: 2008-05-21
Publication date: 2008-12-04

Abstract

Systems and methods of treating processed oil may comprise directing a processed oil feed stream including contaminants at a temperature no higher than 80° C along a porous medium having a removal rating from 0.02 to 2 microns. The processed oil feed stream may have a viscosity that is not chemically altered. The systems and methods may further comprise separating a permeate that passes through the porous medium and has a lower concentration of contaminants from a retentate that does not pass through the porous medium and has a higher concentration of contaminants.

Description

TANGENTIAL FLOW FILTRATION TO REMOVE CONTAMINANTS FROM OIL

This application claims priority based on United States Provisional Application No. 60/939,646, which was filed on May 23, 2007, and is incorporated by reference.

FIELD OF THE INVENTION

[0001] The present invention relates to methods and systems for treating oil. More particularly, the present invention relates to methods and systems for removing contaminants from processed oil used in various industrial systems.

[0002] Processed oil may include various contaminants that may compromise the performance of the industrial system in which it is used. These contaminants may include hard contaminants such as, for example, dirt, debris, and metal wear particles, as well as soft contaminants such as, for example, oil degradation by-products. [0003] The theories of developing hard and soft contaminants described below are believed to be the mechanisms through which hard and soft contaminants are produced in oil. However, other factors or phenomena not described can also give rise to hard and soft contaminants or contribute to their development in some way. Without wishing to be bound to any particular theory, the following mechanisms are described as one of many possible mechanisms that may give rise to hard and soft contaminants.

[0004] Hard contaminants may be generated in any of a variety of different ways. One of many possible mechanisms for generating hard contaminants in the oil may include the friction or wear of internal industrial system components, e.g., metal components, such as bearings, gears, etc. Another possible mechanism for generating hard contaminants in oil may include contamination of the oil from the external environment. Hard contaminants may include any of a variety of different materials. For example, hard contaminants may include solid, particulate contaminants that are insoluble in the oil phase. Some examples of hard contaminants may include dirt, debris, and metals, particularly corrosion metals and metal wear particles.

[0005] Soft contaminants may be generated in any of a variety of different ways. One of many possible ways to generate soft contaminants in the oil includes degradation of the oil. Degradation may be initiated in any of a variety of different ways. Possible ways that oil may be degraded may include, for example, exposure of the oil to any of a variety of different factors including, e.g., at least one of air, water, mechanical stresses, and high temperatures. Degradation may involve any of a variety of different processes including, e.g., the chemical alteration of the hydrocarbon molecule that makes up the oil, and may be carried out by a variety of different mechanisms. A few of the possible mechanisms of degradation may include, for example, oxidation and thermal degradation of the hydrocarbon chain. One possible mechanism of oxidation degradation may include a chemical reaction between the hydrocarbon and air, e.g., surrounding air or air trapped with the oil. Oxidation may replace the hydrogen atoms with oxygen atoms along the hydrocarbon's carbon chain, and may occur through any of a variety of different chemical reactions. Oxidation may be catalyzed in any of a variety of different ways, and may include the presence of at least one of water, heat, and metal components such as iron and copper. Thermal degradation may involve any of a variety of different mechanisms. One possible mechanism of thermal degradation may include chemical reactions such as chain and/or step polymerization of the hydrocarbon molecule. Thermal degradation may be initiated in any of a variety of different ways. One possible mode of initiating thermal degradation may include the application of high temperatures caused by any of a variety of different sources. Possible sources of high temperature may include, for example, adiabatic compression, localized hot spots, chemical reactions involving various foreign contaminants, friction between system components, or spark discharges, particularly electrostatic spark discharges, from, e.g., mechanical filters. [0006] Degradation of the oil molecule, e.g., through oxidation, nitration, hydrolysis, or thermal degradation, may produce any of a variety of products. One example of a product that may be produced from degradation of the oil may include free radicals. Free radicals may be charged species with unpaired electrons, and may be therefore highly reactive and likely to participate in chemical reactions. These reactions may occur by reacting any of a variety of different molecules having any of a variety of different functional groups, e.g., alcohol, amine, carboxylic acid, or any other carboxyl derivative functional groups, and may include oxidation. Any of a variety of different catalysts may accelerate these chemical reactions. One example of a possible catalyst includes heat. The free radicals may chemically react to form any of a variety of different types of compounds. One possible example of compounds that may be formed include polar compounds. Polar compounds may be highly soluble in other polar compounds but may be virtually insoluble in nonpolar compounds such as oil. Because oil may be nonpolar, the newly formed, polar compounds may be unstable in the oil, may be repelled from the oil, may aggregate with themselves or other contaminants, and/or may eventually settle out of the oil onto the surfaces of industrial system components in the form of varnish.

[0007] Soft contaminants may include any of a variety of different compounds produced from any of a variety of different mechanisms, chemical reactions, alterations, or degradations. For example, soft contaminants may include any of a variety of different oil degradation by-products, such as, for example, at least one of oil oxidation by-products, oil combustion by-products, and oil thermal degradation by-products. One possible example of a soft contaminant may include polar compounds that may result from the degradation of hydrocarbons by any of several different mechanisms, e.g., thermal degradation and oxidation, that may be insoluble in a nonpolar substance such as oil and which may lead to the development of varnish on the surfaces of industrial system components. Alternatively or additionally, soft contaminants may include any soft, high molecular weight, polymeric material, for example, oxidized polymeric components. Soft contaminants may, alternatively or additionally, include any agglomerated, semi-solid, resinous material. Soft contaminants may, alternatively or additionally, include those contaminants that may not be soluble in the oil phase at a temperature of about 80° C or below, about 65° C or below, about 45° C or below, and/or about 35° C or below. Soft contaminants may, alternatively or additionally, include any contaminants that may give rise to the development of varnish and/or sludge on the surfaces of industrial system components, including, e.g., sulfates, phosphates, and acryloid polymers.

[0008] Soft contaminants may lead to the development of varnish on the internal surfaces of an industrial system. Varnish may collect on any industrial system surface that contacts the oil. For example, varnish may collect on the surfaces of heat exchangers, hot surfaces, metallic surfaces, conduits, engines, strainers, filters, cooling systems, valve spools, reservoir walls, sleeves, gears, bearing surfaces, pumps, and small clearance zones, e.g., valves, drains, and plugs. Varnish may deposit in the form of a thin, insoluble film in a wide variety of colors and consistencies. For example, varnish may appear as a black, tar- like lacquer or an opaque, petroleum-jelly like deposit.

[0009] Hard contaminants and varnish may cause a number of problems when present on the internal surfaces of industrial systems. For example, hard contaminants and varnish may clog any industrial system component, e.g., engines, valves, strainers, conduits, and filters. Hard contaminants and varnish may insulate industrial system components and compromise the effectiveness of heat exchangers and cooling systems. Moreover, hard contaminants and varnish may increase friction between any industrial system components, e.g., valve spools, sleeves, bearing surfaces, gears, etc., causing components such as valves to stick, increasing wear of components, as well as increasing the amount of energy consumed. Additionally, varnish may also provide a sticky surface on industrial system surfaces to which hard contaminants may adhere, creating an abrasive surface that may accelerate the wear of industrial system components. Varnish may also build up on bearing surfaces and cause an oil provision system to change from full-film, hydrodynamic to boundary, increasing metal- to-metal contact and the possibility industrial system failure. Varnish may also reduce clearance zones, increasing the wear rates of any industrial system components, e.g., pumps, bearings, and gears. Moreover, varnish may also increase the viscosity of the oil. Varnish may also have an acidic nature and corrode industrial system components. Hard contaminants and varnish may also make it necessary to clean the system more frequently to remove varnish and hard contaminants, increasing the amount of maintenance required to run the system. Hard contaminants and varnish may present costly problems that affect a wide variety of industries, for example, mechanical industries, engine industries, internal combustion engine industries, turbine industries, electrical industries, electrical transformer industries, dielectric system industries, hydraulic system industries and lubrication system industries. In accordance with the invention, substantial amounts of hard and soft contaminants may be removed from processed oil to provide a processed oil that has reduced hard and soft contaminants and which deposits less or no varnish on industrial system components.

BRIEF SUMMARY OF THE INVENTION

[0010] According to one aspect of the invention, methods of treating processed oil may comprise directing a processed oil feed stream including contaminants at a temperature no higher than 80° C along a porous medium having a removal rating from 0.02 micron to 2 microns. The processed oil feed stream may have a viscosity that is not chemically altered. The methods may further comprise separating a permeate that passes though the porous medium and has a lower concentration of contaminants from a retentate that does not pass through the porous medium and has a higher concentration of contaminants. [0011] According to another aspect of the invention, methods of treating processed oil may comprise filtering a processed oil feed stream having a viscosity and containing contaminants by tangential flow filtration at a temperature no higher than 80° C using a porous medium having a removal rating from 0.02 micron to 2 microns, including forming a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream. The viscosity of the processed oil feed stream may not be chemically altered.

[0012] According to another aspect of the invention, systems for treating processed oil may comprise a source of contaminated processed oil having a viscosity that has not been chemically altered and a tangential flow filtration separator including a porous medium having a removal rating from 0.02 micron to 2 microns. The separator may separate the contaminated processed oil by tangential flow filtration at a temperature no higher than 80° C. The separator may further comprise an inlet coupled to the source, a permeate outlet for directing a permeate out of the separator, the permeate having passed through the porous medium and including a lower concentration of contaminants. The separator may further comprise a retentate outlet for directing a retentate out of the separator, the retentate having not passed through the porous medium and including a higher concentration of contaminants. [0013] According to another aspect of the invention, systems for treating processed oil may comprise a source of contaminated processed oil having a viscosity that has not been chemically altered and a tangential flow filtration separator including an inlet coupled to the source and providing a processed oil feed stream, a permeate outlet, a retentate outlet, and a porous medium having a removal rating from 0.02 micron to 2 microns. The source, the inlet, the permeate outlet, the retentate outlet and the porous medium may be arranged to separate contaminated processed oil by tangential flow filtration at a temperature no higher than 80° C, including directing a permeate out of the permeate outlet, the permeate having a lower concentration of contaminants than the processed oil feed stream and directing a retentate out of the retentate outlet, the retentate having a higher concentration of contaminants than the processed oil feed stream.

[0014] Methods and systems embodying one or more aspects of the invention have many advantages. For example, at least a portion of the contaminants that compromise the performance of industrial systems may be effectively removed from the processed oil. More particularly, at least a portion of the hard contaminants may be very effectively removed from the oil, decreasing or eliminating friction and wear on the industrial system components. Moreover, at least a portion of the soft contaminants may be very effectively removed from the oil, decreasing or eliminating the amount of varnish that may form on the surfaces of industrial system components. Furthermore, tangential flow filtration may remove more contaminants, particularly more soft contaminants, than dead-end filtration, which may allow contaminants, particularly soft contaminants, to pass through the dead-end medium. [0015] As at least a portion of the soft contaminants that give rise to varnish may be effectively removed from the processed oil, the problems caused by hard contaminants and varnish may also decrease accordingly. For example, there may be less or no hard contaminants or varnish present to clog any industrial system components, e.g., engines, valves, conduits, strainers, conduits, or filters. Additionally, the methods and systems of the invention may reduce or eliminate varnish that may insulate and compromise the effectiveness of heat exchangers and cooling systems. Moreover, eliminating or reducing varnish and hard contaminants may reduce the friction between any industrial system components, e.g., valve spools, sleeves, bearing surfaces, gears, etc., preventing industrial system components such as valves from sticking and lowering the amount of energy consumed. Additionally, the methods and systems of the invention may reduce or eliminate the amount of varnish present to adhere hard contaminants that would create an abrasive surface that would accelerate the wear of industrial system components. Reducing or eliminating varnish may also prevent the varnish from building up on bearing surfaces, thereby maintaining a full-film, hydrodynamic system and preventing the development of a boundary system with increased metal-to-metal contact. Moreover, reducing or eliminating varnish may prevent the reduction of clearance zones and prevent the increase of wear rates of any industrial system components, e.g., pumps, bearings, and gears. Accordingly, the amount of maintenance required to run the industrial system may be decreased. For example, the industrial system may require less frequent cleaning. Moreover, the reduction of varnish may preserve the viscosity of the oil as well as protect the industrial system components from varnish-induced corrosion.

[0016] Additionally, the methods and systems of the present invention may operate at a temperature that prevents a substantial portion of the soft contaminants that give rise to varnish from becoming soluble in the oil phase and passing through the porous medium as permeate, entering the filtered oil and leading to the development of varnish upon cooling of the oil. Moreover, methods and systems of the present invention may make it unnecessary to chemically alter the viscosity of the contaminated oil to be effectively filtered. [0017] The methods and systems of the present invention provide the additional advantage of having the option of providing filtered oil to the industrial system as the oil is being circulated in the industrial system or providing the filtered oil to be separately collected or stored.

[0018] Tangential flow filtration according to the methods and systems of the present invention may generate a shear force that lifts contaminants off the medium, which may advantageously reduce fouling and clogging of the porous medium. Moreover, tangential flow filtration according to the invention may permit the rejection of contaminants that would pass through a medium as permeate in dead-end filtration.

[0019] According to yet another aspect of the invention, methods of filtering processed oil with a porous medium and cleaning the medium may comprise filtering a processed oil feed stream having contaminants by directing the processed oil feed stream along a porous medium at a first temperature to separate the processed oil feed stream into a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream. The methods may further comprise cleaning the medium by directing processed oil along the medium at a second temperature, wherein the second temperature is higher than the first temperature. [0020] According to another aspect of the invention, methods of filtering processed oil with a porous medium and cleaning the medium may comprise filtering a processed oil feed stream having contaminants by directing the processed oil feed stream along a porous medium to separate the processed oil feed stream into a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream. The methods may further comprise cleaning the medium by directing the permeate along the medium.

[0021] The methods of filtering processed oil with a porous medium and cleaning the medium according to the invention may provide the advantage of simply and effectively removing foulants from the medium, including at least a portion of the gel layer. Cleaning the porous medium by raising the temperature of the filtration feed stream to a temperature that is higher than the temperature at which filtration is carried out may simply and effectively remove foulants from the medium, advantageously without requiring any external components such as, e.g., pipes, pumps, tanks, additional cleaning fluids, or additional oil. Cleaning the medium by directing the permeate along the medium may advantageously remove foulants without requiring an increase in temperature of the permeate that cleans the medium. Cleaning the medium according to the methods of the invention may advantageously maintain and/or restore the filtration efficiency of the porous medium. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022] Figure 1 is a schematic view of one embodiment of an oil treatment system in batch processing mode.

[0023] Figure 2 is a schematic view of an industrial system including an oil provision system that may be functionally, though not structurally, coupled with an embodiment of an oil treatment system in batch processing mode.

[0024] Figure 3 is a schematic view of another embodiment of an oil treatment system in continuous processing mode.

[0025] Figure 4 is a partial schematic view of another embodiment including a second tangential flow filtration separator.

[0026] Figure 5 is a graph showing the relationship between the rejection coefficient of the porous medium for soft contaminants and the temperature at which filtration is carried out.

DETAILED DESCRIPTION OF THE INVENTION

[0027] One of many examples of an oil treatment system 14 according to the invention is shown in Figure 1. Oil treatment systems of the invention may remove contaminants from processed oil used in any of a variety of different types of industrial systems including, for example, electrical or mechanical arrangements. Electrical devices, for example, may include any of a variety of electrical or electromechanical devices or machines that transfer or utilize electrical energy. Although electrical arrangements may include many different devices, some exemplary electrical arrangements may include, for example, dielectric systems or electrical transformers. Mechanical arrangements may include any of a variety of mechanical devices that include moving and fixed components. Although mechanical arrangements may include many different devices, some exemplary mechanical devices may include, for example, engines, turbines, internal combustion engines, injection molding machines, industrial and mobile hydraulic equipment. For example, as shown in Figure 1, industrial system 13 may include electrical or mechanical device 1.

[0028] Industrial systems 13 may be supplied with processed oil for any of a variety of reasons. For example, processed oil may provide thermal or electrical insulation, may lubricate moving components, reducing friction or wear, or may apply a hydraulic force. To provide this oil, industrial systems 13 may include an oil provision system 12. "Processed oil" includes any oil that has been processed and/or refined for a particular application such as those applications found in, for example, mechanical industries, engine industries, internal combustion engine industries, turbine industries, electrical industries, electrical transformer industries, dielectric system industries, hydraulic system industries and lubrication system industries. "Processed oil" does not include heavy or crude oil.

[0029] Oil provision systems may be configured in any of a variety of different ways. Oil provision systems may comprise a reservoir in which to contain the oil. Further, the oil provided by the oil provision system in any industrial system may be stationary or circulating. For example, an electrical transformer may include an oil provision system including a reservoir of stationary dielectric oil in which to insulate the electrical components. Alternatively, electrical transformers may include circulating oil provision systems. As another example, any industrial system may include a stationary or a circulating oil provision system such as a lubrication system or a hydraulic system. For example, as shown in Figure 1, oil provision system 12 may circulate oil through industrial system 13 including device 1 via main reservoir 3 and pump 2.

[0030] As oil provision systems operate to provide oil to the overall industrial system, the oil may accumulate either or both of hard and soft contaminants. Oil treatment methods and systems according to the invention may remove hard contaminants, soft contaminants, or both hard and soft contaminants from the oil.

[0031] The oil treatment system may be coupled to an oil provision system in any of a variety of different ways. For example, the oil treatment system may be coupled to the oil provision system structurally, e.g., by fluid communication. Fluid communication may include any structure connected to transfer fluid, e.g., conduits, feed streams, or pipes. In the embodiment illustrated in Figure 1, for example, oil treatment system 14 may be in fluid communication with main reservoir 3 of the oil provision system 12, for example, in a kidney- loop fashion via working container 8 and valve 9. Flow of the contaminated oil from the main reservoir 3 to the oil treatment system may be controlled by valve 9. [0032] The oil treatment system 14 may comprise source of contaminated processed oil 16, tangential flow filtration separator 4 which includes, for example, porous medium 17, separator inlet 18, permeate outlet 6, and retentate outlet 7 in fluid communication with one another. The source of contaminated oil 16 and the tangential flow filtration separator 4 may be arranged to effectively separate contaminates from oil by tangential flow filtration. [0033] The oil treatment system 14 may be arranged in a variety of different ways. For example, the oil treatment system 14 may be arranged to filter processed oil in a batch process, i.e., including, e.g., a working container 8. A source of contaminated oil 16 may be structurally coupled to deliver oil from the source 16 to the tangential flow filtration separator 4. For example, in the embodiment illustrated in Figure 1, the tangential flow filtration separator inlet 18 may be in fluid communication with source 16 via feed conduit 5 and a pump (not shown).

[0034] Source of contaminated oil 16 may be configured in any of a variety of different ways. For example, source 16 may include any container capable of containing and delivering contaminated oil to the tangential flow filtration separator 4. In some embodiments, a source of contaminated oil may include a conduit such as, e.g., a pipe or a feed stream, either alone or in combination with a container such as, e.g., a tank or a storage vessel. In the embodiment illustrated in Figure 1, the source of contaminated oil 16 may include working container 8 in fluid communication with the tangential flow filtration separator inlet 18 via feed conduit 5.

[0035] In the methods and systems of the invention, the viscosity of the oil feed stream may not be chemically altered. The viscosity of the oil can be chemically altered in any of a variety of different ways. For example, the viscosity of the contaminated oil may be chemically altered by dissolving in the contaminated oil a super-critical substance in the super-critical state that has a viscosity very much less than that of the contaminated oil to obtain a single phase oil whose viscosity is reduced in comparison with the initial viscosity of the contaminated oil. A technique for chemically altering the viscosity of oil is disclosed, for example, in United States Patent No. 6,331,253. However, chemically altering the viscosity of the oil may potentially contaminate the oil. Tangential flow filtration of contaminated processed oil according to the invention makes it unnecessary to chemically alter the viscosity of the oil feed stream in order to effectively remove contaminants, particularly soft contaminants, from the oil as well as maintain a less contaminated feed stream. [0036] The tangential flow filtration separator 4 may be configured in any of a variety of different ways. The tangential flow filtration separator 4 may include at least one porous medium 17, at least one separator inlet 18, at least one permeate outlet 6, and at least one retentate outlet 7. The tangential flow filtration separator may have completely or substantially open feed channels, for example, as disclosed in World Intellectual Property Organization Publication Number WO 05/094963, which is incorporated herein by reference for any and all purposes. The tangential flow filtration separator may also advantageously have a short path length along a permeate channel, for example, as disclosed in World Intellectual Property Organization Publication Number WO 00/47307, which is incorporated herein by reference for any and all purposes. Such channel arrangements may substantially enhance shear rates and reduce blockage and fouling of the channels and the porous medium. [0037] The tangential flow filtration separator may separate components in the contaminated processed oil by directing the contaminated processed oil along a porous medium. For example, the oil feed stream may flow along the porous medium. The permeate may pass through the porous medium and may include a lower concentration of contaminants. Soluble oil, including dissolved components and components in solution, may pass through the medium as permeate. At least a portion of, preferably substantially all of, the components that may be insoluble in the processed oil, such as hard and soft contaminants, may not pass through the medium, and may pass into the tangential flow filtration retentate. For some embodiments, the fluid flow may be associated with a Reynolds number of about 4,000 or less. Preferably, the flow may be laminar, e.g., the Reynolds number may be about 2,100 or less.

[0038] The porous medium may be porous, e.g., permeable, semipermeable or permselective, and may be microporous, ultraporous or nanoporous. A broad range of tangential flow filtration media having various rejection characteristics may be selected. The rejection characteristics of the porous medium may be sufficient to allow oil and components soluble in the oil, including dissolved molecular and ionic components in solution, to pass through the medium as permeate and to reject at least a portion of those components that may be insoluble in the oil, such as hard and soft contaminants, into the tangential flow filtration retentate. Preferably, the porous medium may have rejection characteristics that allow oil additives to pass through as permeate. The rejection characteristics of the porous medium may be sufficient to produce a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream. For example, the porous medium may have a removal rating from approximately 0.02 micron to approximately 2 microns, preferably from approximately 0.05 micron to approximately 0.45 micron.

[0039] The porous medium may be fashioned from any material suitable for a porous medium, including, for example, ceramic material, polymeric material, or metallic material. Polymeric materials may include any of a variety of different polymers. The polymeric material may include, for example, any polymer that is suitable for filtering oil. Suitable polymers may include, but are not limited to, polysulfone, polyethersulfone, polytetrafluoroethylene, polypropylene, polyethylene, and polyacrylonitrile. Preferred polymers may include hydrophobic polymers. A preferred polymeric material may be polyvinylidene fluoride (PVDF). A particularly preferred porous medium may be PVDF hollow fiber membranes such as, for example, the Microza® PVDF hollow fiber membranes, available from Asahi Kasei Corporation, Osaka, Japan. Metal materials may include any of a variety of different porous metals with or without ceramic coatings. A preferred metal medium may include a porous stainless steel membrane, available under the trade name of Accusep® from Pall Corporation, East Hills, New York, USA. The ceramic coatings and the ceramic medium may also be made of any of a variety of different ceramic media. Some exemplary ceramics may include zirconia, titania, and alumina. Preferred ceramic media may include, for example, Membralox® and Schumasiv™ ceramic membranes, available from Pall Corporation, East Hills, New York, USA. The porous medium may take any form suitable for tangential flow filtration, including for example, membrane(s), membrane cushion(s), tubular membrane(s), monolith membrane(s), disk membrane stack(s), hollow fiber(s), or spiral, pleated, or flat sheet(s).

[0040] The tangential flow filtration may generate a shear force that lifts contaminants off the medium in any of a variety of different ways. Many different factors and phenomena not described herein may contribute to the operation of a shear force. However, not wishing to be bound to a particular theory, one example of a possible mechanism that may provide a shear force is described in United States Patent No. 6,478,969, which is incorporated herein by reference for any and all purposes.

[0041] Methods and systems of the invention may be operated at a temperature that does not make a substantial portion of the soft contaminants soluble in the oil phase. Increased temperatures may render a substantial portion of the soft contaminants in the oil feed stream soluble in the oil. When soluble, the soft contaminants may pass through the porous medium as permeate, contaminate the filtered oil, and settle out of the oil as varnish onto the internal surfaces of industrial systems. At lower temperatures, the porous medium may retain more soft contaminants, i.e., the rejection coefficient of the porous medium may be higher for soft contaminants at lower temperatures. To keep the soft contaminants insoluble in the oil phase and capable of being captured by the porous medium, the methods and systems of the invention may include filtering at temperatures up to approximately 80° C, preferably up to approximately 65° C, most preferably up to approximately 45° C, and even more preferably up to approximately 35° C. At temperatures up to approximately 80° C, preferably up to approximately 65° C, most preferably up to approximately 45° C, and even more preferably up to approximately 35° C, at least a substantial portion of the soft contaminants in the contaminated oil remains insoluble in the oil phase so that they may be removed from the oil by the porous medium.

[0042] Alternatively or additionally, the methods and systems of the invention may include a cooling mechanism. The cooling mechanism may include any of a variety of devices that lowers the temperature of the contaminated oil that is supplied from the industrial system, such as, e.g., a cooling line, a chiller, fan, heat sink, refrigerator, etc. The cooling mechanism may be configured in any of a variety of different ways. For example, the cooling mechanism may be coupled between the oil provision system and the oil treatment system to cool the oil supplied to the oil treatment system.

[0043] The cooling mechanism may cool the oil in any of a variety of different ways. For example, the oil supplied to the oil treatment system may be cooled to a temperature that keeps a substantial portion of the soft contaminants insoluble in the oil phase. Cooling may lower the temperature of the contaminated processed oil to be lower than the temperature of the oil in the oil provision system, e.g., the main reservoir. For example, the contaminated oil in the main reservoir may be at any temperature that is appropriate for the operation of the industrial system, for example, from approximately 100° C or less to approximately 200° C or more. The contaminated oil may then be cooled to a temperature up to approximately 80° C, preferably up to approximately 65° C, most preferably up to approximately 45° C, and even more preferably up to approximately 35° C prior to directing the contaminated oil to the tangential flow filtration separator or during tangential flow filtration. [0044] The contaminated oil may be cooled at any time and in any place during or following exit from the main reservoir 3 and during or prior to direction to the tangential flow filtration separator 4 or during tangential flow filtration. The contaminated oil may be cooled before it is directed to the tangential flow filtration separator or during tangential flow filtration. For example, oil in the feed conduit 5, working container 8, tangential flow filtration separator 4, conduit leading to the working container, and/or any other additional containers may be cooled by cooling mechanism 24. Following tangential flow filtration of the cooled contaminated oil, the permeate may be returned to the oil provision system 12, e.g., main reservoir 3, and reheated to any temperature appropriate for the operation of the industrial system, with or without a heat exchanger. [0045] The oil treatment system 14 may be arranged to direct permeate in any of a variety of different ways. The permeate may pass through the porous medium and may include a lower concentration of contaminants. For example, the permeate may simply be collected by directing the permeate out of the permeate outlet to a collection container, such as a tank or a vessel, and the main reservoir 3 may be replenished with clean oil, e.g., from a source external to the oil provision system, to maintain operation of the industrial system during treatment of the batch. Alternatively or additionally, the permeate may be returned to the oil provision system from the collection container for use in the industrial system. Preferably, the permeate may be directed out of the permeate outlet and redirected back to the oil provision system to be used in the industrial system. Accordingly, the oil in the oil provision system may be filtered as it circulates through the oil provision system. For example, as shown in Figure 1, permeate may be directed out of the tangential flow filtration separator 4 and returned to the main reservoir 3 of oil provision system 12 in a kidney- loop fashion via permeate outlet 6.

[0046] The oil treatment system 14 may be arranged to direct retentate in any of a variety of different ways. The retentate, which does not pass through the porous medium, may include a higher concentration of contaminants. For example, the retentate may be redirected back to the tangential flow filtration separator for further filtering either directly or via a working container. For example, as shown in Figure 1, the retentate may be directed out of the tangential flow filtration separator 4 and back to the tangential flow filtration separator 4 via retentate outlet 7 and working container 8. The working container 8 may redirect the retentate back to the tangential flow filtration separator 4 via feed conduit 5 and inlet 18. Alternatively or additionally, the retentate may be further processed in any of a number of different ways. For example, the retentate may be directed to a depth filter for additional filtration, e.g., to capture soft contaminants, hard contaminants, and/or resinous material. [0047] Alternatively, the retentate may simply be disposed of in any of a variety of different ways. As shown in Figure 1, for example, the retentate may be drained as waste from the working container 8 via drain 10. Alternatively, the retentate may be drained from the tangential flow filtration separator 4. The retentate may be drained to a waste container, e.g., a waste tank. In many embodiments, the retentate may be drained from the working container when the concentration of contaminants in the oil held in the working container becomes too high to yield effective filtration. [0048] Figure 2 depicts another embodiment of the methods and systems of the present invention. Like the first embodiment, the oil treatment system may filter processed oil by tangential flow filtration as part of a batch process. Unlike the first embodiment, however, the oil treatment system 14 may be functionally coupled to the oil provision system 12 without being structurally coupled to the oil provision system. Like the first embodiment, the oil provision system 12 may circulate oil through the industrial system 13 via pump 2 and main reservoir 3, as shown in Figure 2, and the oil may collect contaminants. The contaminated oil may be collected for filtration by draining the contaminated oil from main reservoir 3 by drain 15 and, if necessary, the main reservoir 3 may be refilled with clean oil. Alternatively, the oil provision system may include a main reservoir of stationary oil in, for example, an electrical transformer. Contaminated stationary oil may likewise be drained from the reservoir and refilled with clean oil.

[0049] According to the second embodiment, the contaminated oil drained from the main reservoir may be housed in any type of suitable transport container and transported to an oil treatment system 14 that is structurally separate from the oil provision system 12, as depicted in Figure 2. The contaminated oil may be emptied from the transport container into a tangential flow filtration separator 4 directly or, as shown in Figure 2, via a working container 8. The oil treatment system 14 may filter the contaminated oil by tangential flow filtration to remove contaminants in any of the ways described for the first embodiment. The permeate, e.g., filtered processed oil with reduced hard and/or soft contaminants, may be collected and returned to the main reservoir 3 of the oil provision system 12. For example, the permeate may be directed to a tank where it is stored until it is returned to the oil provision system, e.g., the main reservoir. The retentate may be further directed in any of the ways described in the first embodiment.

[0050] Figure 3 shows an additional embodiment of the methods and systems of the present invention. Like the first embodiment, and unlike the second embodiment, the oil treatment system 14 may be structurally coupled to the oil provision system 12 by e.g., fluid communication. Unlike the first embodiment, the oil treatment system may filter the processed oil as part of a continuous process, i.e., without a working container. Like the first two embodiments, the oil provision system may circulate the oil through the industrial system 13 via pump 2 and main reservoir 3. Alternatively, the oil provision system 12 may include a main reservoir of stationary oil in, for example, an electrical transformer. [0051] As depicted in Figure 3, tangential flow filtration separator 4 may be in fluid communication with main reservoir 3 either directly or via feed conduit 5 without a working container. The tangential flow filtration separator 4 may separate the contaminated oil in any of the ways described for the first embodiment.

[0052] The permeate may be directed out of the tangential flow filtration separator in any of a variety of different ways, e.g., in any of the ways described in the first two embodiments. For example, it may be separately collected, as in the second embodiment, and the main reservoir 3 may be replenished with clean oil. Alternatively, as depicted in Figure 3, the permeate may be redirected back the main reservoir 3 and reused in the industrial system 13. [0053] The retentate may be directed out of the tangential flow filtration separator in any of a variety of different ways, e.g., in any of the ways described for the first two embodiments. For example, it may be redirected back to the tangential flow filtration separator 4 for further filtration. Alternatively, as shown in Figure 3, the retentate may be drained from the tangential flow filtration separator via retentate outlet 7. The retentate may be disposed of, for example, by collection into a waste tank 11.

[0054] For example, in any of the first three embodiments, the retentate may be directed to a second tangential flow filtration separator. A second tangential flow filtration separator may additionally filter the retentate from the first tangential flow filtration separator by tangential flow filtration and further concentrate the retentate. For example, as shown in Figure 4, the retentate produced by the first tangential flow filtration separator 4 may be directed to second tangential flow filtration separator 19 via first tangential flow filtration separator retentate outlet 7 and second tangential flow filtration separator inlet 22. Second tangential flow filtration separator 19 may include second porous medium 20, which may have any of the same characteristics as those described for the medium of the first tangential flow filtration separator 4. The second tangential flow filtration separator 19 may further separate the retentate produced by the first tangential flow filtration separator 4 by tangential flow filtration as described above for the first tangential flow filtration separator 4. Furthermore, the permeate and retentate produced by the second tangential flow filtration separator 19 may be directed out of the second tangential flow filtration separator permeate outlet 21 and retentate outlet 23, respectively, and to any destination, in any of a variety of different ways, including those described for the direction of the permeate and retentate produced by the first tangential flow filtration separator.

[0055] Methods for treating processed oil may also include filtering the oil by tangential flow filtration with a porous medium and cleaning the porous medium. The methods including cleaning the porous medium may include filtering the processed oil by tangential flow filtration in any of a variety of different ways, including, but not limited to, filtering the processed oil in accordance with any of the embodiments described above. The methods including cleaning the porous medium are described below with reference to the above embodiments by way of example only.

[0056] The methods may include filtering a processed oil feed stream by tangential flow filtration to remove contaminants. For example, the processed oil feed stream may be directed along a porous medium to separate the processed oil feed stream into a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream. The permeate may pass through the porous medium and the retentate may not pass through the porous medium. The tangential flow filtration may remove contaminants, including those contaminants believed to give rise to varnish, from the processed oil feed stream.

[0057] The processed oil feed stream may be filtered by tangential flow filtration at any temperature, e.g., a first temperature. The temperature of filtration, e.g., a first temperature, may be any temperature at which filtration of the processed oil effectively removes contaminants, including those contaminants believed to give rise to varnish. For example, the processed oil feed stream having contaminants may be filtered by directing the feed stream along a porous medium at a temperature, e.g., a first temperature, of approximately 80° C, preferably up to approximately 65° C, most preferably up to approximately 45° C, and even more preferably up to approximately 35° C. Filtering the processed oil feed stream may also include cooling the processed oil feed stream from an operating temperature, e.g., from an operating temperature of the industrial system, prior to or during tangential flow filtration, for example, as described in any of the embodiments described above.

[0058] Tangential flow filtration of processed oil may cause foulants to accumulate on the porous medium. Foulants may include any of a variety of components that may accumulate on the feed side of the medium and compromise the filtration efficiency of the porous medium including, for example, a gel layer, varnish, and/or soft contaminants that are believed to give rise to varnish. Foulants may accumulate on the porous medium in any of a variety of different ways. One of many possible ways to foul a porous medium may include, for example, the development of a gel layer by, e.g., gel polarization.

[0059] The methods may also include cleaning the porous medium in any of a variety of different ways. In some embodiments, the methods may include cleaning the porous medium by directing processed oil along the porous medium at a second temperature that is higher than the temperature at which filtration was carried out. The processed oil may be directed along the porous medium at any second temperature that removes foulants from the medium. The processed oil may be filtered at a temperature that is lower than the temperature at which the medium is cleaned. Conversely, the medium may be cleaned at a temperature that is higher than the temperature at which the processed oil is filtered. For example, the medium may be cleaned by directing the processed oil along the medium at a temperature that is from approximately 20° C to approximately 50° C higher than the first temperature or from approximately 30° C to approximately 40° C higher than the first temperature. For example, the medium may be cleaned by directing processed oil along the medium at a temperature of at least approximately 60° C, at least approximately 70° C, at least approximately 85° C, or at least approximately 90° C.

[0060] The methods may include cleaning the porous medium with processed oil from any of a variety of different sources. For example, the processed oil that cleans the medium at the second, higher temperature may include the processed oil feed stream that is directed to the porous medium from an oil provision system, e.g., in a manner described for any of the embodiments described above, for filtration. For example, the processed oil that cleans the medium may be the processed oil that is being filtered by directing the processed oil feed stream from an oil provision system to a tangential flow filtration separator in a continuous or a batch process, e.g., as in any of the embodiments described above. [0061] Alternatively, the processed oil that is directed along the medium at the second, higher temperature to clean the medium may include processed oil from a container that is external to the oil provision system. The container may contain clean or contaminated processed oil from any source. The processed oil may be directed to the tangential flow filtration medium from the container to clean the medium in any of a variety of different ways. For example, as shown in Figure 3, the processed oil may be directed from container 25 to the porous medium 17 via, e.g., pump 2, valve 9, pipes, and/or conduits, and directed along the medium at the second temperature to clean the medium in any of the ways described above.

[0062] Alternatively, the processed oil that is directed along the medium to clean the medium may include the permeate. For example, as shown in Figure 1, cleaning the porous medium may include redirecting the permeate to the medium via permeate recirculation loop 26. As shown in Figure 1, recirculation loop 26 may include, for example, permeate reservoir 27, pump 2, valve 9, pipes, and/or conduits. Alternatively, the permeate may be transferred to a container external to the oil provision system and redirected to the medium from the external container 25 via, e.g., pump 2, valve 9, pipes, and/or conduits, to clean the medium, as shown in Figure 3. The medium may be cleaned by directing the permeate along the porous medium at any temperature. For example, the medium may be cleaned by directing the permeate along the porous medium at approximately the same temperature at which filtration is carried out, e.g., at a temperature of approximately 80° C, preferably up to approximately 65° C, most preferably up to approximately 45° C, and even more preferably up to approximately 35° C. Alternatively, the temperature of the permeate that is directed along the medium to clean the medium may be raised to a temperature that is higher than the temperature at which filtration is carried out, for example, as described above. [0063] For any of the above embodiments, the processed oil may be directed along a porous medium to clean the medium in any of a variety of different ways. For example, the processed oil may be directed along a feed side of the porous medium, e.g., from the feed inlet to the retentate outlet, or from the retentate outlet to the feed inlet. The permeate side of the medium may be turned off during the cleaning of the medium. [0064] For any of the above embodiments, the temperature of the processed oil that cleans the medium may be raised in any of a variety of different ways. For example, the temperature of the processed oil that cleans the medium may be raised using any heating mechanism such as, e.g., a heater, a pump, or by simply shutting off a cooling mechanism. Preferably, the method includes shutting off the cooling mechanism so that the temperature of the processed oil feed stream rises as the oil treatment system continues to circulate the retentate stream along the feed side of the medium at the second temperature to clean the medium. Cleaning the medium by simply raising the temperature of the filtration feed stream may have the advantage of cleaning the medium in situ without requiring any additional external tanks, piping, pumps, additional cleaning fluid or additional oil. [0065] For any of the above embodiments, the methods may include cleaning the medium at any time that cleaning is desireable. For example, the medium may be cleaned anytime the filtration efficiency of the medium is compromised by the accumulation of foulants. For example, the medium may be cleaned when filtration of the processed oil is complete, between filtration of batches, anytime in between batches, or anytime before, during, or after filtration.

[0066] Cleaning the medium may include, for example, removing foulants, including a gel layer, varnish, and/or soft contaminants that give rise to varnish, from the medium. Foulants may be removed if at least a portion of the foulants is removed from the medium so as to improve or restore filtration efficiency of the porous medium. Preferably, most or substantially all of the foulants are removed from the porous medium. Removing the foulants may include removing at least a portion, most, or substantially all of a gel layer from the porous medium.

[0067] Without wishing to be bound to a particular theory, directing processed oil along the medium at a temperature higher than the filtration temperature may clean the porous medium by causing at least a portion of the foulants, including varnish, a gel layer, and soft contaminants believed to give rise to varnish to become soluble in the processed oil and be removed from the medium. The foulants may, for example, pass through the medium or, alternatively, may be lifted off the medium and carried away in the retentate stream. [0068] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.

EXAMPLE 1

[0069] This example demonstrates that tangential flow filtration of a contaminated processed oil feed stream produces a permeate having less contaminants, including contaminants believed to lead to the development of varnish, than the processed oil feed stream.

[0070] Lubrication oil (American Petroleum Institute Group II base stock oil) is used in a 6,000-gallon capacity, 600 GPM flow rate lubrication oil system of a combined cycle GE 7FA gas turbine. A 5-gallon sample of oil is obtained. The viscosity of the oil sample is not chemically altered.

[0071] The sample is filtered by tangential flow filtration. The sample is directed along a single module of Microza® PVDF hollow fiber membrane (0.2 micron removal rating, 2.6 mm inner diameter, 3.9 mm outer diameter, 347 mm nominal length, 0.08 m² membrane area) at 32° C. The permeate passes through the membrane and the retentate does not pass through the membrane. Samples of the feed oil and the permeate oil are reserved for testing. [0072] The samples are analyzed by the Quantitative Spectrophotometric Analysis (QS A^SM test, available from Analyst, Inc., Louisville, Kentucky, USA). The QSA^SM test assigns a quantitative value on a scale of 1 to 100 (Varnish Potential Rating (VPR^SM) value) to the samples based on the amount of soft contaminants collected on the analysis membrane. An aliquot (50 mL) of the feed oil is mixed with petroleum ether and drawn down through an analysis membrane. The gravimetric value of the insoluble material collected on the analysis membrane is measured by petroleum ether insoluble/toluene soluble gravimetric test. The discoloration of the membrane due to the presence of the insoluble material is measured by a colorimeter. The discoloration of the membrane and the gravimetric value of the insoluble material present on the membrane are used to assign a VPR^SM value to each sample. Higher VPR^SM values reflect a higher potential for the development of varnish. These steps are repeated with an aliquot (50 mL) of the permeate oil. The results of the QSA^SM test are given in Table 1.

TABLE 1

[0073] The permeate oil VPR^SM value of 13 is significantly lower than the feed oil VPR^SM value of 74. Additionally, the permeate gravimetric value of 220 mg/L is significantly lower than the feed oil gravimetric value of 314 mg/L. These results indicate that the permeate oil contains lower levels of the contaminants believed to produce varnish. These results indicate that tangential flow filtration of the oil removes contaminants, including contaminants believed to contribute to the development of varnish, from contaminated oil.

EXAMPLE 2

[0074] This example demonstrates that tangential flow filtration of a contaminated oil feed stream produces a permeate having less contaminants, including contaminants believed to lead to the development of varnish, than the oil feed stream. The oil feed and oil permeate samples are analyzed by an ExxonMobile ultracentrifuge analysis proprietary test. [0075] Lubrication oil is used in a gas turbine, a sample is filtered by tangential flow filtration, and samples of the feed and permeate oil are reserved for testing as described in Example 1. An aliquot of the feed oil is placed in a tube and ultracentrifuged at approximately 17,500 revolutions per minute (RPM). The fluid insoluble material is separated from the fluid at the bottom of the tube and is rated on a visual scale from 1 to 8. A higher visual scale rating indicates a higher potential for the development of varnish. These steps are repeated with an aliquot of the permeate oil. The results of the ultracentrifuge analysis are given in Table 2.

TABLE 2

[0076] The permeate oil has an ultracentrifuge rating only one third that of the feed oil, which indicates that the permeate oil has a lower potential for the development of varnish than the feed oil. These results indicate that tangential flow filtration removes contaminants, including contaminants that are believed to lead to the development of varnish, from contaminated oil.

EXAMPLE 3

[0077] This example demonstrates that tangential flow filtration of a contaminated oil feed stream produces a permeate having less fluid insoluble material, including material believed to lead to the development of varnish, than the oil feed stream. Oil feed and oil permeate samples are analyzed by an analysis membrane drawn-down test.

[0078] Lubrication oil is used in a gas turbine, a sample is filtered by tangential flow filtration, and samples of the feed and permeate oil are reserved for testing as described in

Example 1.

[0079] A 50 mL aliquot of the feed oil is mixed with 50 mL of pre-filtered petroleum ether in a clean glass bottle. The sample is drawn down through a nylon analysis membrane

(0.2 microns) and the amount of fluid insoluble material on the membrane is visually evaluated. These steps are repeated with a 50 mL aliquot of the permeate oil.

[0080] A visual comparison of the membranes reveals a lower amount of fluid insoluble material and discoloration on the permeate oil membrane than on the feed oil membrane.

These results indicate that tangential flow filtration of oil removes fluid insoluble material, including material believed to lead to the development of varnish, from contaminated oil. EXAMPLE 4

[0081] This example demonstrates that tangential flow filtration of a contaminated processed oil feed stream provides lubrication oil having less contaminants, including contaminants believed to lead to the development of varnish, than unfiltered processed oil. [0082] Lubrication oil (American Petroleum Institute Group II base stock oil) is used in a 600 GPM flow rate lubrication oil system of a combined cycle GE MS7001B gas turbine. The lubrication system main reservoir volume is 2,500 gallons. The viscosity of the oil sample is not chemically altered. The lubrication oil is filtered in a batch process using a working tank, as shown in Figure 1. The permeate is directed out of the tangential flow filtration separator and redirected back to the main reservoir of the lubrication system so that the oil in the oil provision system is filtered as it circulates through the lubrication system. [0083] The lubrication oil is filtered by tangential flow filtration. The lubrication oil is directed along a single module of Microza® PVDF hollow fiber membrane (0.2 micron removal rating, 2.6 mm inner diameter, 4.1 mm outer diameter, 1129 mm nominal length, 2.2 m² membrane area) at 42° C. The permeate passes through the membrane and the retentate does not pass through the membrane.

[0084] Samples of oil are obtained from the lubrication system main reservoir prior to filtration and when 1,773 gallons of permeate are generated. The samples are analyzed by the QS A^SM test to determine the VPR^SM value of each sample, as described for Example 1. The results of the QSA^SM test are given in Table 3.

TABLE 3

[0085] The VPR^SM value of 58 obtained when 1,773 gallons of permeate are generated is significantly lower than the VPR^SM value of 96 obtained prior to filtration. These results indicate that lubrication oil filtered by tangential flow filtration in a batch process in which the permeate is redirected back to the lubrication system provides oil that contains lower levels of the contaminants believed to produce varnish. These results indicate that tangential flow filtration of the oil removes contaminants, including contaminants believed to contribute to the development of varnish, from contaminated oil.

EXAMPLE 5

[0086] This example demonstrates that the rejection coefficient of the porous medium for soft contaminants increases as the temperature at which filtration is carried out decreases.

[0087] Lubrication oil is used in a gas turbine and filtered by tangential flow filtration in a batch process as described in Example 4, but with a heat exchanger so that the temperature at which filtration is carried out decreases throughout the duration of the filtration. The permeate is redirected back to the main reservoir of the lubrication system as described in

Example 4. Samples of oil are obtained from the feed side of the membrane and from the permeate side of the membrane at various temperatures and reserved for testing. The samples are analyzed by the QSA^SM test to determine the VPR^SM value of each sample, as described for Example 1. The VPR^SM values are used to determine the rejection coefficient of the medium for soft contaminants at each temperature according to Formula (1):

[0088] σ = (1 - Cp/c), where

[0089] σ = rejection coefficient;

[0090] C_p = VPR^SM value on the permeate side of the membrane; and

[0091] c = VPR^SM value on the feed side of the membrane.

[0092] The value of the rejection coefficient falls between 0.000 < σ < 1.000, with 0.000 being the rejection coefficient of a porous medium that does not retain any soft contaminants

(C_p = c), and 1.000 being the rejection coefficient of a porous medium that retains all soft contaminants (c_p = 0.000).

[0093] The results of the QSA^SM tests and the rejection coefficients measured at each temperature are given in Table 4 and illustrated in Figure 5. TABLE 4

[0094] As can be seen in Table 4 and Figure 5, higher rejection coefficients of the porous medium for soft contaminants may be obtained at lower filtration temperatures. These results indicate that the porous medium retains more soft contaminants at lower temperatures than at higher temperatures. These results indicate that tangential flow filtration of the oil at lower temperatures removes soft contaminants from contaminated oil more effectively than tangential flow filtration of the oil at higher temperatures.

EXAMPLE 6

[0095] This example demonstrates that cleaning the medium by directing processed oil along the medium at a temperature that is higher than the temperature at which filtration of the processed oil feed stream is carried out removes foulants, including a gel layer, from the porous medium.

[0096] Lubrication oil (American Petroleum Institute Group II base stock oil) is used in a 600 GPM flow rate lubrication oil system of a combined cycle GE 7FA gas turbine. The lubrication oil is cooled to 45° C with a cooling line. The cooled lubrication oil is filtered by tangential flow filtration by directing the feed stream along a porous hollow fiber membrane. The permeate passes through the membrane and the retentate does not pass through the membrane. The permeate includes a lower concentration of contaminants than the feed stream and the retentate includes a higher concentration of contaminants than the feed stream. The membrane accumulates foulants, including a gel layer.

[0097] The membrane is cleaned by increasing the temperature of the feed stream. The temperature of the feed stream is increased by closing the cooling line. The feed stream is directed from the feed inlet to the retentate outlet along the feed side of the medium at a temperature of 60° C. At least a portion of the foulants, including the gel layer, are removed from the membrane.

[0098] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0099] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[00100] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

CLAIMS:

1. A method of treating processed oil, comprising: directing a processed oil feed stream including contaminants at a temperature no higher than 80° C along a porous medium having a removal rating from 0.02 micron to 2 microns, wherein the processed oil feed stream has a viscosity that is not chemically altered; and separating a permeate that passes though the porous medium and has a lower concentration of contaminants from a retentate that does not pass through the porous medium and has a higher concentration of contaminants.

2. A method of treating processed oil, comprising: filtering a processed oil feed stream having a viscosity and containing contaminants by tangential flow filtration at a temperature no higher than 80° C using a porous medium having a removal rating from 0.02 micron to 2 microns, including forming a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream, wherein the viscosity of the processed oil feed stream is not chemically altered, and wherein filtering the processed oil includes producing a permeate containing a lower amount of contaminants capable of giving rise to varnish than that found in the feed stream.

3. A method of filtering processed oil with a porous medium and cleaning the medium comprising filtering a processed oil feed stream having contaminants by directing the processed oil feed stream along a porous medium at a first temperature to separate the processed oil feed stream into a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream, and cleaning the medium by directing processed oil along the medium at a second temperature, wherein the second temperature is higher than the first temperature.

4. A method of filtering processed oil with a porous medium and cleaning the medium comprising filtering a processed oil feed stream having contaminants by directing the processed oil feed stream along a porous medium to separate the processed oil feed stream into a permeate having a lower concentration of contaminants than the feed stream and a retentate having a higher concentration of contaminants than the feed stream, and cleaning the medium by directing the permeate along the medium.

5. The method according to any one of claims 3-4, wherein filtering the processed oil feed stream at the first temperature includes filtering the processed oil feed stream at a temperature no higher than 80° C.

6. The method according to any one of claims 3-5, wherein cleaning the medium at the second temperature includes directing processed oil along the medium at a temperature that is 20° C to 50° C higher than the first temperature.

7. The method according to any one of claims 3-6, wherein cleaning the medium at the second temperature includes directing processed oil along the medium at a temperature that is 30° C to 40° C higher than the first temperature.

8. The method according to any one of claims 3-7, wherein cleaning the medium includes removing a gel layer from the medium.

9. The method according to any one of claims 3-8, wherein cleaning the medium includes removing foulants from the medium.

10. The method according to any one of claims 3-9, wherein cleaning the medium includes directing the processed oil feed stream along the medium at the second temperature.

11. The method according to any one of claims 3-10, wherein filtering the processed oil feed stream includes directing the processed oil feed stream to the medium from an oil provision system, and wherein cleaning the medium includes directing processed oil to the medium from a container external to the oil provision system.

12. The method according to any one of claims 3-11, wherein cleaning the medium includes directing the permeate along the medium at the second temperature.

13. The method according to any one of claims 3-12, wherein filtering the processed oil feed stream includes passing the permeate through the porous medium, wherein the porous medium has a removal rating from 0.02 micron to 2 microns.

14. The method according to any one of claims 3-13, wherein filtering the processed oil feed stream includes not chemically altering the viscosity of the processed oil feed stream.

15. The method according to any one of the preceding claims, wherein filtering the processed oil includes passing the processed oil along a porous medium including at least one material selected from the group consisting of ceramic material, polymeric material, and metallic material.

16. The method according to any one of the preceding claims, wherein filtering the processed oil includes passing the processed oil along a porous medium at a temperature no higher than 65° C.

17. The method according to any one of the preceding claims, wherein filtering the processed oil includes passing the processed oil along a porous medium having a removal rating from 0.05 micron to 0.45 micron.

18. The method according to any one of the preceding claims, wherein filtering the processed oil includes passing the processed oil along a porous medium including at least one form selected from the group consisting of a membrane, a membrane cushion, a disk membrane stack, a tubular membrane, a monolith membrane, a hollow fiber, a spiral sheet, a pleated sheet, and a flat sheet.

19. The method according to any one of the preceding claims, wherein filtering the processed oil includes passing the processed oil along a porous medium including polyvinylidene fluoride.

20. The method according to any one of the preceding claims, wherein filtering the processed oil includes producing a permeate containing a lower amount of contaminants capable of giving rise to varnish than that found in the feed stream.

21. The method according to any one of the preceding claims, wherein filtering the processed oil includes producing a permeate containing a lower amount of oxidized polymeric components.

22. The method according to any one of the preceding claims, further comprising redirecting the permeate to the industrial system, wherein the permeate is capable of depositing less varnish on industrial system components than the feed stream.

23. The method according to any one of the preceding claims, further comprising separating the retentate by tangential flow filtration.

24. The method according to any one of the preceding claims, further comprising cooling the contaminated processed oil prior to or during tangential flow filtration.

25. A system for treating processed oil, comprising: a source of contaminated processed oil having a viscosity that has not been chemically altered; a tangential flow filtration separator including a porous medium having a removal rating from 0.02 micron to 2 microns, wherein the separator separates the contaminated processed oil by tangential flow filtration at a temperature no higher than 80° C, the separator including an inlet coupled to the source; a permeate outlet for directing a permeate having a lower concentration of contaminants out of the separator; and a retentate outlet for directing a retentate having a higher concentration of contaminants out of the separator.

26. A system for treating processed oil, comprising: a source of contaminated processed oil having a viscosity that has not been chemically altered; a tangential flow filtration separator including an inlet coupled to the source and providing a processed oil feed stream; a permeate outlet; a retentate outlet; and a porous medium having a removal rating from 0.02 micron to 2 microns, wherein the source and the tangential flow filtration separator are arranged to separate contaminated processed oil by tangential flow filtration at a temperature no higher than 80° C, including being arranged to direct a permeate out of the permeate outlet, the permeate having a lower concentration of contaminants than the processed oil feed stream, direct a retentate out of the retentate outlet, the retentate having a higher concentration of contaminants than the processed oil feed stream.

27. The system according to any one of the preceding claims, wherein the porous medium includes at least one material selected from the group consisting of ceramic material, polymeric material, and metallic material.

28. The system according to any one of the preceding claims, wherein the temperature is no higher than 65° C.

29. The system according to any one of the preceding claims, wherein the porous medium has a removal rating from 0.05 micron to 0.45 micron.

30. The system according to any one of the preceding claims, wherein the porous medium includes at least one form selected from the group consisting of a membrane, a membrane cushion, a disk membrane stack, a hollow fiber, a spiral sheet, a pleated sheet, a tubular membrane, a monolith membrane, and a flat sheet.

31. The system according to any one of the preceding claims, wherein the porous medium includes polyvinylidene fluoride.

32. The system according to any one of the preceding claims, further comprising a second tangential flow filtration separator.

33. The system according to any one of the preceding claims, further comprising a cooling mechanism.