US3324026A

US3324026A - Electric filter

Info

Publication number: US3324026A
Application number: US336905A
Authority: US
Inventors: Logan C Waterman; Albert D Franse
Original assignee: Petrolite Corp
Current assignee: Baker Petrolite LLC
Priority date: 1964-01-10
Filing date: 1964-01-10
Publication date: 1967-06-06
Anticipated expiration: 1984-06-06

Description

J 6, 9 1.. c. WATERMAN ETAL 3,324,026

ELECTRIC FILTER Filed Jan. 10, 1964 2 l6 /5 Z6 Z2 Z4 25 22a 26a 2 Sheets-Sheet 1 INVENTORS.

54 53 a5 LOGAN CZ MTERMAM ALBERT D. Ham/5E 15y THE/E A7'702A/575 HARE/5, MECH, RUSSELL 8: K57? June 6, 1967 L. c. WATERMAN ETAL 3,

ELECTRIC FILTER Filed Jan. 10, 1964 2 Sheets-Sheet 2 HARR/S, K/EcH, RUSSELL & KERN United States Patent I 3,324,026 ELECTRIC FILTER Logan C. Waterman and Albert D. Franse, Houston, Tex., assignors to Petrolite Corporation, Wilmington, Del., a corporation of Delaware Filed Jan. 10, 1964, Ser. No. 336,905 13 Claims. (Cl. 204-302) Our invention relates to the removal of dispersed contaminants from high-resistivity oils thatare substantially free of dispersed water or that are free of significant amounts of dispersed water by which we have reference to dispersed water contents so low that they cannot be measured by centrifugal methods. More particularly the invention relates to an electric filter and method for removing contaminating dispersed particles, usual-ly solid particles, from such an oil.

Contaminants in oils give rise to severe problems and various attempts have been made to remove them by electrical, chemical or mechanical means. Contaminants in lubricating oils induce wear on the surfaces to be lubricated. Contaminants in fuels tend to clog and erode burner orifices of critical size. In jet fuels contaminants are particularly troublesome and are thought to have been the cause of many crashes of jet aircraft. Contaminants in hydraulic oils tend to clog and/ or erode valve orifices and pumps or impede the free operation of valve elements or other elements actuated by the oil.

Such contaminants may enter such oils from different sources or may be present as the result of production techniques. Commonly the contaminants are considered as including siliceous material, e.g. road dust or atmospheric dust; metallic materials, e.g. particles of metal picked up from storage or transfer equipment; metallic compounds, such as rust (iron oxide), etc.; or nonmetallic materials, e.g. particles of carbon, filaments of animal or vegetable origin, etc.

The size of such contaminating particles in such oils may vary from less than one micron up to 100 microns or more. Conventional filters are capable of removing most of the particles in the larger portion of this range but are either incapable of removing particles less than about 5 microns or become quickly clogged therewith or build up pressure drops which become impracticably high. It is presently possible by various known techniques to count the number of contaminating particles in such an oil within the range up to 2,000,000 particles/100 ml. of oil, considering particles of a size greater than 1 micron. While there are no fixed standards as to permissible contamination, which of course will depend upon ultimate use, it is generally desirable that the filtered or purified oil contain less than 2,000 particles/ 100 ml. of oil and for more highly purified oils less than about 1,000 particles/100 ml. or even less than 500 particles/100 ml. For example, it is not uncommon to find jet fuels containing far in excess of 2,000,000 particles/100' ml. and to meet requirements in which purified oil from the filter shall contain less than .7 mg. per liter of oil.

The present invention is capable of removing substantially all of the contaminating particles greater than 5 microns in size, usually to a value of 99.9% or more, and is capable of removing particles less than 5 microns in size to a much greater degree than any known mechanical filter. It is an object of the invention to provide an electric filter and method capable of such results, but which can also be used where less exacting results are acceptable. A further object is to provide an electric filter characterized by low pressure drop,'high throughput and an extraordinary ability to remove extremely small particles, e.g. less than 5 microns in size.

It has previously been proposed, e.g. in the patent to 3,324,026 Patented June 6, 1967 Hamlin 2,573,967, to remove dirt particles from cleaning solvent by flowing the solvent through screen electrodes with the inter-electrode space filled with a loosely packed mass of fibrous material such as glass wool, rock wool or synthetic plastic fibers. In the laboratory-type equipment of this patent the flow is parallel to the lines of force and the container is formed of insulating material. This type of filter and interelectrode packing is not capable of producing the results of the present invention. It has also been elsewhere suggested that a mass of open-pore polyurethane foam should fill the interelectrode space but this alone has not solved the problem.

It is an object of the present invention to provide an improved electrode configuration excellently suited to the purification of contaminated oils when the interelectrode treating spaces are filled with suitable porous material. In this respect it is an object of the present invention to flow the oil in directions parallel to the electrodes and transverse to the lines of force of the field.

The present invention is based also on the discovery that new coactions and unexpected results are obtainable if the interelectrode treating spaces are narrow and are filled in substantially all sections thereof with a multielement mass of porous material of high electrical resistivity bridging the electrodes. In the preferred practice of the invention each interelectrode treating space in each section thereof contains a multi-element mass comprising at least two thin sheets or layers of such porous material in face-to-face con-tact, the sheets extending in each section of the interelectrode treating space as layers parallel to the electrodes and being compressed therebetween with only suificient pressure to provide good electrical contact between the electrodes and the outermost surfaces of the stacked sheets or layers. It is an object of this invention to provide such a multi-layer filling for each interelectrode treating space. In other instances the multi-element mass of porous material may be made of chunks of such porous material in random arrangement in contact with each other, the mass bridging the electrodes and being composed of chunks that are individually porous. It is an object of the invention to employ such a multi-element mass in which the elements are chunks of porous material.

The preferred type of porous material, whether used in layers or chunks, is filamentary polyurethane foam. In making this material polyurethane is foamed by conventional methods and leached or otherwise processed to produce passages throughout the mass. The result is a filamentary network, best described as a three-dimensional network of filaments that are unitary at their junctions. Many of the filaments appear as filamentary arcs or circles joined unitarily at points of tangency to other filaments. Such filamentary polyurethane foam is commercially available in different porosities. Use of such filamentary polyurethane foam in layers or chunks and with flow parallel to the electrode surfaces and transverse to the lines of force of the field represents the preferred practice of the invention. It should be understood however that other porous materials can be substituted if used in sheet or chunk form and if less exacting results are acceptable. The same is true of an orientation of filamentary polyurethane foam or other porous materials arranged in layers or chunks with flow transverse to the layers and electrodes although the results with such arrangement will ordinarily be distinctly inferior to the preferred practice of the invention.

It is a further object of the invention to provide a dualflow electric filter in which the contaminated oil advances in opposite directions in axially aligned sections of a container.

A further object of the invention is to subject the incoming contaminated oil to an intense electric discharge, produced by relatively sharp electrode points, before the 3 oil enters the first interelectrode space. Another object is to subject the incoming contaminated oil to one or more magnetic fields before entry into the interelectrode spaces to remove at least a part of any particles of magnetic material from the oil. Further objects and advantages of the invention lie in the particular arrangements of stacked, superimposed or concentric electrodes forming a part of the invention; also in the arrangement of electrodes in a replaceable pack which will permit precise spacing of the electrodes and easy replacement in an existing container.

Another object of the invention is to provide electrical equipment in which contaminated oils flow to-and-fro with respect to the central axis of the container during advancement therealong and in which seals are provided to prevent any of the oil bypassing the interelectrode spaces.

In the electric filter of the invention the contaminants are electrically attracted to and deposited on the filaments of the interelectrode packing material. It is of importance that these contaminants remain in such deposited condition throughout the time that oil is flowing through the filter for purification. It has been discovered that this requires maintenance of substantially uniform electrical conditions and that various deviations therefrom will cause the filter to unload a part of the collected contaminants to augment the content thereof in the effluent oil rather than to diminish same. For example, unloading will take place upon power failure or a substantial undervoltage applied to the electrodes. Likewise unloading tends to occur with overcurent, arcing or instantaneous overload conditions or in the presence of high voltage transients. It is an object of the invention to divert, bypass, stop or modify the flow of oil through the electric filter upon occurrence of any such adverse condition.

In this connection the invention preferably includes an efliuent or outlet valve and a bypass valve in a bypass line interconnecting the efliuent and influent lines of the electric filter. It is an object of the invention to divert the effluent of the electric filter, as by closing the effiuent valve and opening the bypass valve to recycle the fluid, upon power failure or substantial undervoltage applied to the electrodes or when overcurrent, arcing or instantaneous overload or any high voltage transient occurs.

In the preferred embodiment of the invention we provide an undervoltage relay producing a signal when the voltage applied to the electrodes drops below a predetermined value; also an overcurrent relay producing a signal when the current to the electrodes exceeds a predetermined value. It is an object of the invention to close the efiiuent valve and open the bypass valve upon receipt of either of such signals to prevent fiow of possibly contaminated oil to the outlet line. A further object is to provide means for periodically testing the electrode current after an overcurrent condition has ocurred to determine when the overcurrent condition (which normally is only temporary in nature) has cleared up, with normal flow through the system being restored after normal operating current has been achieved. A particular object of the invention is to provide for recycling of fluid through the filter during an overcurrent condition so as to maintain fluid flow therein and facilitate -reestablishment of normal electrical operating conditions and to provide a time delay mechanism for maintaining the recycle flow a period of time after establishment of normal electrical conditions to permit cleaning up of the effluent oil before coupling same to the outlet line.

Further objects and advantages of the invention will be apparent to those skilled in the art from the following description of exemplary embodiments.

Referring to the drawing:

FIG. 1 is a vertical sectional view of one embodiment of the invention;

FIG. 2 is a transverse sectional view thereof taken along the line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary view illustrating layers of porous material between electrodes;

FIG. 4 is an enlarged fragmentary view illustrating chunks of porous material between electrodes;

FIG. 5 is a longitudinal sectional view of an alternative embodiment, while FIGS. 6 and 7 are perspective views of electrode elements thereof;

FIG. 8 is a longitudinal sectional view of a further alternative construction; and

FIG. 9 is a diagram illustrating a preferred arrangement for fluid flow and for the electrical control circuitry.

The electric filter of FIGS. 1 and 2 includes a grounded tubular housing having an inner wall 16. The housing 15 is preferably cylindrical but can be of other cross-sectional shape. It is closed at its ends by removable heads 18 and 18a held in place by studs 19 and nuts 20. The interior of said tubular housing comprises opposed

end zones

22 and 22a spaced from each other along the central axis A-A of the housing, opposed treating zones 24 and 24a spaced along said axis inwardly of said end zones and bounded outwardly by the inner wall 16, and a small central zone 25 between the two treating zones.

In the illustrated embodiment the pressured contaminated oil is divided between pipes 26 and 26a respectively opening on the

end zones

22 and 22a and forming a first pipe means. The two portions of contaminated oil flow toward each other through the respective treating zones 24 and 24a in sinuous or to-and-fro paths, as will be described, to the central zone 25. The streams here meet and the composite stream discharges through a second pipe means shown as a pipe 27 opening on the central zone 25.

A central shaft 28 is mounted in cantilever fashion along the axis A-A by a bushing 30 suitably secured to the head 18 The conductor of a high-voltage cable 32 traverses the bushing 30 and is electrically connected to the shaft 28. The tubular housing 15 and the heads 18 and 18a are preferably grounded.

The shaft 28 carries a plurality of disc-like plate electrodes 35 with intervening spacers 36 comprising a spacing means for spacing the plate electrodes in each treating zone equally along the axis A--A. A large barrier 38 formed of insulating material is disposed between the treating zones 24 and 24a and may provide an inner portion disposed between the innermost spaces 36 of the two groups thereof in the respective treating zones. A nut 39 within the end zone 22a is threaded to the shaft 28 to clamp the plate electrodes 35, the barrier 38 and the spacers 36 against the bushing 30 as an assembled unit. Each plate electrode 35 is peripherally smaller than the inner wall 16 to form an annular passage 40 therebetween.

electrodes 35. Each annular electrode 42 has a centralopening 46 of substantially smaller radius "than the outer periphery of each plate electrode 35 so that the annular electrodes 42 and the plate electrodes 35 overlap to form radial spaces therebetween providing the interelectrode treating spaces containing the porous material as Will be described. The outer periphery of each annular electrode 42 is slightly smaller than the inner wall 16 and is sealed thereto by any suitable annular sealing member 48 formed of resilient material such as synthetic rubber or a resilient plastic, these sealing members being in the zone between the spacers 44 and the inner wall 16. Such scaling members prevent any peripheral bypassing of the oil and are important if best operating results are to be obtained.

The annular electrodes 42 are electrically connected to the grounded tubular housing 15 through the spacers 44 and the shafts 45. If a high-voltage source of unidirectional potential is connected between the tubular housing 15 and the conductor of the cable 32 the annular electrodes 42 will constitute two sets of grounded electrodes, respectively in the treating zones 24 and 24a, while the plate electrodes 35 will constitute two sets of live electrodes interspaced with the grounded electrodes. Electrostatic fields will be established in the radial spaces between the live and grounded electrodes so that such fields exist in the interelectrode treating spaces filled with the porous material as will now be described.

Except for the two outermost interelectrode zones 50 and 50a each section of each interelectrode treating space that is disposed outwardly of the central zone 25 is filled with a multi-element mass of porous material of high electrical resistivity bridging the electrodes of the interelectrode treating space and comprising individual elements of the porous material compressed lightly into contact with each other and with the electrode surfaces bounding such interelectrode treating space. In the embodiment of FIGS. 1 and 2 the individual elements of the multi-element mass comprise at least two thin layers or sheets 54 of the porous material in face-to-facecontact, preferably of annular configuration to occupy compositely substantialy the entire volume of such interelectrode treating space. These sheets are preferably made of filamentary polyurethane foam for best results but other porous materials in sheet form can be substituted with substantially improved results as compared with the same material in block form filling the entire interelectrode space. The electrical and physical properities and functioning of such sheets will be later described.

Means may be provided for subjecting the incoming contaminated oil to an electric blast action tending to impart to the dispersed contaminating particles an electric charge just prior to entry into the first porous-materialfilled interelectrode treating zone. As shown in FIG. 1 this is accomplished by a plurality of relatively sharp pointed pins 56 extending into each of the outermost interelectrode zones 50 and 50a from one of the electrodes bounding same in a direction toward the other such electrode. These pins are shown as mounted in a circular pattern on the outermost plate electrodes 35 with their points facing the outermost annular electrode 42 in a circular zone just beyond its central opening 46.

If the contaminated oil contains particles of magnetic material these can be partially or substantially completely removed by establishing magnetic fields in the

end zones

22 and 22a. The invention oomprehends any arrangement of permanent magnets in these end zones, exemplified in FIG. 1 as a series of oppositely poled bar magnets 58 mounted in a circular pattern by the heads 18 and 18a in positions extending toward the outermost annular electrodes 42. Magnetic fields are established between adja cent bar magnets to attract thereto such magnetic particles. The collected particles can be removed upon disassembly of the filter. The pins 56 and the magnets 58 are permissive and need not always be incorporated in the structure.

The radial intermernber spaces within the central zone 25 may be interelectrode zones if one of the plate electrodes 35 is substituted for the barrier 38. However with the barrier 38 of insulating material, as shown, the space between the innermost annular electrodes 42 of the two sets will be equipotential, as will be the radial spaces between the barrier 38 and each such electrode. Such radial spaces may be filled with the sheets 54 as previously described, such sheets then acting merely in a filter capacity, or they may be filled with porous material having better filter characteristics to act as a mechanical filter collecting some residual contaminants or blocking discharge of a mass of contaminants should the system be inadvertently or accidentally operated to unload the collected contaminants.

With the electric filter shown in FIG. 1 each portion of the incoming stream of contaminated oil enters one of the pipes 26, 26a, flows inwardly through the magnetic fields between the bar magnets 58 and outwardly in the first or end interelectrode space 50, 50a to be subjected to the blast discharges from the relatively sharp pointed pins 56. Thereafter this portion flows through the annular passage 40 around the end plate electrode 35, radially inwardly through the sheet-filled interelectrode space, forwardly through the central opening 46 of the next annular electrodes 42, then outwardly through the next sheet-filled interelectrode space, and so on. The oil thus moves inwardly and outwardly toward and away from the central axis AA during its forward advancement toward the central zone 25 where it moves outwardly to be subjected to the filtering action of any porous material therein before discharging through the pipe 27.

The filter of FIG. 1 can also be employed by reversing the flow in which event the total incoming stream will be supplied to the pipe 27 to be divided by the barrier 38 into portions flowing outwardly through the two sets of electrodes in the two treating zones 24, 24a with the same toand-fro movement relative to the axis AA. In this instance the porous material in the central zone 25 will act as an initial filter and the pointed pins 56 and the bar magnets 58 can be eliminated. The purified oil will then flow as two streams from the

opposite end zones

22, 22a and can be combined into a single stream passing along an efiluent pipe toa point of storage or use.

As the contaminated oil flows outward or inward through the sheet-filled interelectrode treating spaces it is subjected to the unidirectional electrostatic fields therein. The porous material therein exerts substantially no mechanical filtering action but forms a network of bonded filaments on which the contaminants deposit because of the action of the electric field. This can best be explained by reference to FIG. 3 which shows diagrammatically portions of three sheets 54 between

electrodes

35 and 42. The stacked sheets 54 fill the interelectrode space and exist therein in slightly compacted form so that the end faces of the outermost sheets make good electrical contact with the metal of the

electrodes

35 and 42. The sheets act as voltage dividers and appear to act to some extent as individual electrodes. In this latter respect each sheet appears to have positive and negative surfaces on opposite sides thereof. Some cantaminants, such as carbon, will deposit on the positive surface of each sheet while other contaminants, such as iron oxide, will deposit on the negative surface. Siliceous particles, e.g. road dust, may deposit within the interstices of the foam. The existence of these deposits on such positive and negative surfaces can be proved by analyzing the deposited material on opposite sides of a sheet when separated from neighboring sheets.

The incremental voltage drop or gradient measured on a line between any two electrodes is not uniform. In this respect, the positive surface of one sheet is in high-resistive contact with the negative surface of its cont-acting neighbor. The voltage drop across the narrow interfacial contact zone Z (FIG. 3) of two sheets is higher than the average voltage drop across each sheet per se even though the thickness of such interfacial contact zone is minute compared with the sheet thickness. The result is a much higher voltage gradient in the interfacial contact zone Z, as compared with the voltage gradient in the internal portions of each sheet or the nominal (aver-age) voltage gradient between the electrodes calculated by dividing the total applied voltage by the spacing of the

electrodes

35 and 42.

The use of stacked sheets or contacting layers filling the interelectrode treating space has been found to be much superior to the action when a single body of the same material fills the interelectrode space as illustrated by the following example employing electric filters having 18 pairs of the aforesaid plate and annular electrodes spaced /2 inch differing only in that each of the interelectrode treating spaces of filter A contained a single /2 inch layer of filamentary polyurethane foam while each such treating space of filter B contained four layers of the same foam material each /s inch thick. With a unidirectional applied voltage of 15 kv. and with oils equally contaminated supplied to each filter at the same rate (velocity normal to field being 81 inches/min.) and temperature, all other conditions being the same including time of residence in the intense electric fields (18.4 seconds), the number of residual particles in the oil after a single pass through filters A and B was not significantly different as to particles in the range of 25-100 but was much lower with filter B than with filter A as concerns smaller particles. In the range of l525,u. the residual particles per 100 cc. were 187 with filter B as compared to 220 with filter A. In the range of 5-15 1. the residual particles on this basis were 1,745 for filter B as compared to 13,200 for filter A. A recycle operation in which the same oil was recycled through filter B for approximately 30 min. reduced the residuals in the l5-25u range to 155 and in the 5-15 r range to 785, as compared to filter A in which such recycle reduced the residuals in the 15-25,u range to 215 and in the 5-15 range to 1,360 particles per 100 cc. These runs evidence the unexpected superiority of the multi-layer filter B on a single-pass operation particularly as concerns removal of contaminating particles of very small size.

Materials and operating conditions in the multi-layer electric filter of the invention are critical to the extent indicated in the following paragraphs if the highest percentage removal of contaminants is to be achieved. It should be understood however that the materials and operating conditions herein set forth are capable of modification if less exacting results are tolerable.

As to the porous material in sheet form, filamentary polyurethane foam is preferred but other junction-bonded filamentary networks made of glass or synthetic fibers can be employed. Sheets of other porous material of high resistivity, such as mats of randomly arranged or woven fibers of glass or synthetic fibers if employed in sheet form will produce results substantially superior to the same uusheeted material employed as a single mass filling the interelectrode zones. Synthetic fibers such as polytetarafluoroethylene (Teflon), trifiuorochloroethylene (Kel-F), polyethylene, etc. can thus be employed in matted or junction-bonded form, the fibers being spun of such materials or being shavings thereof.

The porous material should be of high resistivity but will usually have a conductivity, somewhat higher than that of the oil measured in either its purified or contaminated state. In this respect the conductivity of the porous material will usually be about 5-15 times that of the oil, often in the neighborhood of times the oil conductivity. However this relative resistivity is not always a critical factor.

The porosity of the porous material for best results will depend upon the particular material but will always be such that the material exerts substantially no mechanical filtering action on the contaminants in the absence of the electric field. With filters of the invention there will be virtually no removal of contaminants by the porous material if the electrodes are not energized. Likewise there will be virtually no removal of contaminants if the porous material is eliminated and the electrodes are energized, as compared with the same electrode system with the sheets of porous material energized at the same voltage. Filamentary polyurethane foam of various porosity is commercially available and this material in porosities ranging from about 10-30 p.p.i. (pores per inch) will be found quite satisfactory.

The degree of compaction of the layered material in the interelectrode space is not critical so long as good electrical contact is established with the bounding electrode surfaces. Compaction of the porous material will ordinarily be about 10-30%, usually 20-25% for best results when using filamentary polyurethane foam. Compaction less than 10% will usually give poor results.

The layers or sheets 54 are desirably quite thin, thicknesses of about being usually preferred. Likewise the interelectrode treating spaces are desirably narrow in width, this width ranging from approximately twice the thickness of the sheets 54 to about 10 times the thickness thereof. Widths of about /2-2" will ordinarily be used and such width will preferably be in the range of about /4-l%.

The direction of oil flow through the sheets is critical if best results are to be obtained. Oil flow in a direction longitudinally of the layers or sheets from end to end thereof is unexpectedly beneficial as compared with oil flow in a direction through the sheets perpendicular thereto and parallel to the lines of force, as by using a radial fiow through perforated electrodes.

Satisfactory purification will be obtainable at various rates of flow through the interelectrode spaces, rates of about 10-100"/min. or more can be used. With a total residence time of 20 seconds in the interelectrode spaces a purified oil containing about 2,000 particles/100 ml. can be obtained at flow rates ranging from about 60- min. A 30-second residence time will produce a purified oil containing in the neighborhood of about 1,200 partieles/ ml. within the same range of forward velocities.

Nominal or average gradients may vary over a relatively wide range but are relatively high as compared with gradients employed in electric emulsion treaters. The nominal gradient will normally exceed 20 kv./in. and best results will usually be obtained in the range of about 30-60 kv./in. or higher. This is true over a wide range of conductivities of the oil but the desirable gradients will usually be higher with oils of higher resistivity. For example an oil of a specific resistance (ohm-cm.) of 1X10 containing a large amount of contaminants was reduced to 900 particles/100 ml. at a gradient of 30 kv./in. while a similar oil of a specific resistance of 17 l0 contained 1,000 particles/100 ml. of contaminants when treated at 50 kv./in.

Avoidance of bypassing at the peripheries of the annular electrodes 42 is important for best results. For example, if the metal electrodes form a snug sliding fit with the inner wall 16 without the sealing members 48 the effluent particle count will be double or more as compared with elimination of such bypassing. It is not uncommon to be able to reduce the efiluent particle count from about 2,000 to about 1,000 per 100 ml. of oil merely by eliminating the minute bypassing which takes place between snug-fitting electrode peripheries and the inner wall 16.

Some types of contaminants are more easily removed from the oil by the filter than others. Among those commonly found in fuels or hydraulic oils iron oxide is the most difficult to remove, followed by siliceous particles such as road dust and by filamentary contaminants such as fibers of animal or vegetable origin. Under the same conditions, an oil contaminated with iron oxide alone was found to have an effluent particle count of about 1,450 particles/100 ml. When the contaminant was road dust present in the same amount the particle count was about 820/ 100 ml. and when the contaminant was a mixture composed largely of minute filamentary material the count was about 335 particles/100 ml. On the other hand a mixture of the above contaminants, similarly treated, give a particle count of about 966 parts/100 ml., evidencing that a mixture of contaminants is more readily purified than some of the contaminants alone.

The multi-layer porous-material filling for the interelectrode treating spaces has a relatively long useful life but this life will of course depend upon the degree of contamination of the oil being purified. It has been found that filamentary polyurethane foam remains excellently effective until loaded with solids to the extent of about 2% or more of the Weight of the foam. The particle content of the efiluent oil increases gradually with progressively greater loadings of the foam up to a loading of about 10% of solids but above this the residual particle count and the electrical load increase rapidly. The above is with once-through treatment. If the contaminated oil is recirculated through the treating zone a count of less than 2,000 particle-s/ 100 ml. can be obtained even with loadings up to 10% by weight of the foam.

When the porous material in the interelectrode spaces becomes loaded to such an extent that continued operation becomes unsatisfactory on a once-through or recirculation basis it is best to replace the porous material rather than to attempt to remove the collected contaminants. About 10% or more of the collected solids can be washed from the porous material by turning off the voltage and continuing the oil flow. Vibration of the porous material will remove a portion of the collected material as will reversal of the polarity applied to the electrodes.

The temperature of the contaminated oil is not critical and the electric filters of the invention remain operative over a wide temperature range. Commonly the oil will be at or near atmospheric temperature but oils of a temperature of about -100250 F. or beyond can be purified satisfactorily.

There is very little pressure drop on the oil during flow through the electric filters of the invention. This pressure drop is ordinarily substantially less than 10 psi. and commonly much less. The pressure drop is reduced even more if a double-flow filter of the type shown in FIG. 1 is employed. Also such double-flow filter makes possible the use of closer electrode spacings for the same eifectiveness of particle removal.

The invention may be incorporated in various other embodiments. FIG. for example illustrates an embodiment in which the housing or casing is formed by a flanged housing 60 to which flanged heads 61 and 62 are bolted, these heads respectively having outlet and

inlet pipes

63 and 64 attached thereto. The electrode unit is encapsulated and easily replaced by merely removing one of the heads. This electrode unit comprises a plurality of annular electrodes 65 with central openings 66, see FIG. 6, held apart by spacing members 67 stacked one above the other. Annular electrodes 65 are disposed there- 'between and centered by shoulders at one or both ends of each spacing member. Each spacing member also has an intermediate shoulder 69 on which rests the peripheral edge of a plate electrode 70 having a ring of openings 71 near the periphery, see FIG. 7, corresponding to the annular passages 40 of the embodiment of FIG. 1. Each interelectrode treating space is filled with stacked sheets 72 as previously described.

Each plate electrode 70 may carry an attached contact spring 74 at its center, each such contact spring depending through the central opening 66 of the annular electrode 65 therebelow and pressurally contacting the next lower plate electrode 70. With this arrangement the electrode assembly can be stacked progressively at the point of manufacture, the spring contacts serving to electrically connect the plate electrodes 70. Alternatively both ends of each spring contact may be welded or otherwise attached to the plate electrodes during assembly. The lowermost depending contact spring may hang free and depend into the space provided by the head 62 to create an electric blast from its lower end, acting to charge dispersed particles in the oil entering through the pipe 64. This oil advances longitudinally of the housing 60 with a to-and-fro motion as indicated by the arrows. The required high-voltage unidirectional potential may be delivered to the top plate electrode 70 by a spring contact 75 permanently fixed to a bushing 76 which conducts the high-voltage lead to the interior of the vessel.

The entire structure may be rigidified by encapsulation within a sheath 77 with the encapsulating material extending inward at the ends to hold the end annular electrodes 65 in place. Most desirably the encapsulating sheath 77 may be molded in place in the flanged housing 60 so that the housing and electrode assembly can be replaced as a unit when the porous material becomes contaminated. Alternatively the encapsulating sheath 77 and its electrode assembly can be replaced by making the sheath a sliding fit within the flanged housing 60.

FIG. 8 illustrates another embodiment in which sheets or layers of porous material 79 are stacked side-by-side in each section of each interelectrode treating space between concentric or

planar electrodes

80 and 82 corresponding generally to the

electrodes

35 and 42 of FIG. 1 or the

electrodes

70 and 65 of FIG. 5. The electrodes 80 are electrically connected and supported by a framework 83 which in turn is supported by insulators 84. These electrodes are energized by a high-voltage lead extending through a bushing 85. The electrodes 82 are electrically connected by a framework 86 grounded to the housing 87. In this embodiment the interelectrode spaces are not radial but it will be observed that the flow of contaminated oil is longitudinally of the sheets 79 of porous material, parallel to the electrodes and transverse to the lines of force of the field.

In each of the embodiments thus far described the porous material filling the interelectrode treating spaces is in sheet form. It is possible in some instances to substitute chunks of the same porous material as suggested in FIG. 4 to form the multi-element mass. The chunks 90 there shown are compressed lightly between oppositelypoled electrodes 91 and 92. It is essential that each chunk be of highly porous material, preferably one of the filamentary materials previously described. The degree of compaction is similar to that previously described, being sufficient to maintain good electrical contact with the electrode surfaces and to form zones of interfacial con tact between the chunks. Here the zones of interfacial contact will be randomly arranged and not continuous or irregularly continuous along the length of the interelectrode space. The porous material of each chunk is readily compressible, causing adjacent chunks to conform and contact over substantially their entire surfaces. As a result the oil does not flow through pores between the chunks but rather is confined to flow through the pores of the chunks themselves while being acted upon by electrostatic stress. The chunks here act as voltage dividers in somewhat the same manner as in the previously described embodiments. The size of the chunks is not critical but there is some preference for chunks of irregular shape, e.g. chunks torn or chopped from a sheet or block of material and of an average size from about /s up to about A" or more with electrode spacings within the range previously described, the larger chunks being employed with larger electrode spacings.

Referring to FIG. 9, a filter 95, which may be any of the filters previously described, has a fluid inlet 96 and a fluid outlet 97, with a high voltage line 98 entering through an insulating bushing 99. A pump 101 is positioned in the inlet line and is driven by a pump motor 102 energized from a separate power source 102a under the control of a magnetic switch shown. A valve 103 is positioned in the outlet line for controlling flow of fluid from the filter. Another valve 104 is connected in a bypass line 105 which provides for fluid flow from the filter outlet back to the filter inlet. It is preferred to have the valve 103 normally closed and moved to the open position by a valve solenoid 106. Similarly it is preferred to have the valve 104 normally open and move to the closed position by a valve solenoid 107. Then in the event of any electrical power failure to the valves, possibly contaminated oil from the filter would be diverted from the outlet line and, in the embodiment shown herein, recycled through the filter.

The high voltage supply for the filter is indicated generally at and may be conventional in design. A 110 volt 60 cycles per second power source may be connected through the power winding of a saturable core reactor 111 to the primary winding of a voltage step-up transformer 112. The secondary winding of the transformer 112 is connected to a rectifier 113 with one terminal, usually the positive terminal, of the rectifier connected to the high voltage line 98 and with the other terminal of the rectifier connected through a milliammeter 114 and a variable resistor 115 to circuit ground. A voltage

divider comprising resistors

116, 117 may be connected across the rectifier output with a kilovoltmeter 118 coupled across the resistor 117. A DC. current source 119 is connected to the control winding of the saturable core reactor 111 providing means for controlling the output of the rectifier by varying the impedance drop across the power winding of the reactor. A typical filter may operate at about 18,000 volts D.C. at 1.5 milliamperes current.

The control circuitry preferably includes an undervoltage sensing device and an overcurrent sensing device. Short duration overcurrent conditions may occur from time to time in the operation of electric filters and it is preferable to maintain the filter in operation as this normally provides the best means for terminating the overcurrent condition. However, during the existence of an overcurrent, the effluent from the filter may contain contaminants in excess of that normally in the effiuent. The control circuitry includes means for diverting filter efiluent from the outlet line during and for a period of time after the existence of overcurrent in the filter. The control circuitry also includes means for periodically checking the current after detection of an overcurrent for the purpose of restoring the filter flow pattern as early as practicable after restoration of normal current in the filter.

The overcurrent detecting device is indicated at 125 and may comprise a thyratron tube 126 and a relay K1. The control grid and cathode of the thyratron 126 are connected across the resistor 115 and the plate is connected to the positive terminal of a DC power source 127. The negative terminal of the power source is connected through the coil of the relay K1 and through a normally closed contact set 128 of a relay K3 to circuit ground. The resistor 115 is adjusted so that the voltage developed thereacross by the electrode current will fire the thyratron into conduction when the electrode circuit current exceeds a predetermined value. Conduction in the thyratron actuates the relay K1 to open the normally closed contact set 129 and close the normally open contact set 130.

The undervoltage responsive device is indicated at 133 and may comprise a relay K4 having its coil connected in parallel with the primary of the transformer 112. Relay K4 will be actuated when the voltage at the primary of the step-up transformer reaches a preset value and will drop out when the primary voltage falls below a preset value. Hence under normal operation, the relay K4 is actuated and its contact set 134 is closed, connecting power to the coil of relay K5.

The relay K5 has a contact set 135 connected in the control circuit for the pump motor 102 and another contact set 136 connected in the control circuit for the valve solenoids 106, 107. The relay K5 permits operation of the pump motor 102 and also permits actuation of the valves to direct the filter effluent to the outlet line only when both voltage and current conditions are within prescribed limits, thereby functioning as an and or combination control device. These actions are effected as follows.

With normal operating voltage applied to the system, undervoltage relay K4 is energized to close contact set 134 which in turn energizes relay K5 closing contact sets 135 and 136. Closing of contact set 135 energizes the pump motor 102 from its separate power source 102a to pump fluid through the filter. When contact set 136 is closed, power is coupled through it and the contact set 129 to the coil of a relay K6 which functions as a recycle time delay device. Under the circumstances just described, power is also coupled through contact set 129 and contact set 136 to contact set 137 of relay K6 and thence to solenoids 106 and 107 to move valve 103 to the open condition and valve 104 to the closed condition. This is the normal operating condition of the system.

If the voltage across the primary of transformer 112 falls below the predetermined value, relay K4 is de-energized, relay K5 is de-energized, relay K6 is de-energized, valve solenoids 106 and 107 are de-energized, and pump motor 102 is de-energized. When the voltage across the transformer primary increases to the predetermined value, relay K4 is energized, relay K5 is energized, relay K6 is energized, and pump motor 102 is energized. Relay K6 incorporates a time delay mechanism which delays the closing of contact set 137 a predetermined period of time after closing of contact sets and 136. Typically this may be in the order of two to four minutes. This delay permits the establishment of fluid flow through the filter and the recirculating or recycling or filtered fluid one or more times through the filter so that normal filtering operation can be established to bring the efiluent to its normally purified condition. After passage of the predetermined time, contact set 137 is closed and valves 103, 104 are actuated to direct the filter effluent to the outlet line.

The control system includes means for periodically testing the existing current in the electrode circuit after actuation of the overcurrent device to determine if the overcurrent condition has been cured. In the preferred embodiment disclosed herein, this periodic checking is accomplished by a reset and test device 140 which periodically resets the overcurrent device, permitting the overcurrent device to be again actuated if the overcurrent condition still exists. This resetting and testing operation is carried out within the time delay period of the recycle time delay relay K6 so that the bypass fluid fiow pattern is not disturbed. Then if normal current conditions exist, the bypass fluid flow path will be restored to the normal flow pattern by closing of contact set 137. If normal current conditions do not exist at the time of resetting and testing, the relay K6 will be de-energized before its time delay period has expired.

The reset and test device 140 includes a relay or switch K2 and another relay or switch K3. The coil of the relay K2 is energized from the power source through contact set 130 of relay K1 when relay K1 is actuated by an overcurrent condition. Relay K2 includes a time delay element which delays closing of the contact set a predetermined period after closing of contact set 130. Typically this delay may be about sixty seconds and should always be less than the delay in closing of contact set 137 of relay K6. Closing of contact set 150 energizes the coil of relay K3 through a DC. power source 151. Actuation of relay K3 opens contact set 128 and thereby opens the plate circuit of the thyratron 126 and de-energizes the coil of relay K1.

De-energization of relay K1 opens contact set 130 which in turn opens contact set 150 and de-energizes relay K3. A resistor 152 and capacitor 153 are connected in parallel with the coil of relay K3 to provide a short time delay in the de-energization of relay K3 before contact set 128 is closed. This short time delay permits the thyratron tube to de-ionize after removal of the plate potential.

If the overcurrent condition no longer exists, the thyratron 126 will remain extinguished and the contact set 129 will remain closed, permitting the relay K6 to complete its time delay, close contact set 137 and actuate both valves. If however the overcurrent condition still exists, closing of contact set 128 will apply potential to the plate of the thyratron and it will be triggered into conduction by the high grid potential developed across the resistor 115. Conduction of the thyratron will open contact set 129 and de-energize relay K6 before the time delay period thereof expires, thus maintaining the bypass fluid flow pattern established on initial detection of the overcurrent condition. Conduction in the thyratron will 13 result in closing of contact set 130 and the initiation of another reset and test cycle as previously described. The reset and test cycle will continue periodically until the overcurrent condition has terminated.

Manual override switches may be interposed in the system to change the automatic operation described above and permit manual control. Thus manual closing of an override switch 160 in the control circuit of the motor 102 will permit starting the pump 101 at any time. Manual closing of an override switch 161 in the control circuits of the valves 104 and 106 will shift the system from bypass to on-stream operation. Manual override switches can be provided at other or alternative positions to permit manual control of the system.

The control circuitry of FIG. 9 and the control of actions thereby eflected are useful with various electric filters or treaters irrespective of the material bridging the electrodes and the arrangement thereof in multiple layers. Such a control insures that the effluent delivered to other equipment will be above set specifications.

Various changes and modifications can be made in the above-exemplified apparatus and methods without departing from the spirit of the invention as defined in the appended claims.

We claim:

1. An electric filter for removing suspended contaminants from high-resistivity oils free of significant amounts of dispersed water, said electric filter including in combination:

a pair of spaced parallel electrodes providing an interelectrode treating space therebetween;

a multi-element mass of porous material of high electrical resistivity filling all sections of the interelectrode treating space and bridging said electrodes, 'said rnulti-element mass comprising deformable individual elements of said porous material compressed together in each section of said interelectrode treating space sufliciently to block significant fluid flow between the elements, whereby fluid flow takes place substantially exclusively through the pores of said elements;

means for electrically insulating said electrodes from each other and for establishing a high-gradient unidirectional electric field in said interelectrode treating space; and

means for flowing the contaminated oil through the pores of said elements.

2. An electric filter as defined in claim 1 including a housing surrounding said electrodes providing an entrance zone for the contaminated oil opening on one end of said interelectrode treating space, a plurality of relatively sharp pointed pins in said entrance zone electrically connected to one of said electrodes, and a member of opposite polarity toward which said pointed pins face but spaced therefrom to establish electric blasts from said pins toward said member, said electric blasts acting on said contaminated oil before its passage through said pores of said elements.

3. An electric filter as defined in claim 1 including a housing surrounding said electrode-s providing an entrance zone for the contaminated oil opening on one end of said interelectrode treating space, and means for establishing magnetic fields in said entrance zone acting on said contaminated oil before its passage through said pores of said elements.

4. An electric filter as defined in claim 1 in which said interelectrode treating space is of a length much greater than its width, and including a housing surrounding said electrodes providing entrance and exit zones respectively communicating with opposite ends of said interelectrode treating space, said flow means including an influent pipe means delivering the contaminated oil to said entrance zone and an eflluent pipe means conducting the purified oil from said exit zone, said oil flowing lengthwise of said interelectrode treating space transverse to 14 the lines of force of said field and through the pores of said elements. 1

5. An electric filter as defined in claim 1 in which said individual elements of the multi-element mass in each section of the interelectrode treating space comp-rise at least two thin sheets of said porous material disposed side by side in face-to-face contact extending parallel to the electrodes bounding said interelectrode treating space and compressed lightly together therebetween.

6. An electric filter as defined in claim 5 in which said thin sheets are formed of filamentary polyurethane foam.

7. An electric filter as defined in claim 6 in which said flow means includes means for flowing the contaminated oil in a direction parallel to said electrodes and longitudinally of said sheets of filamentary polyurethane foam.

8. An electric filter as defined in claim 1 in which said porous material is an easily deformable material, and in which said individual elements of said multi-element mass are chunks of such deformable porous material in random arrangement and in contact with each other filling said interelectrode treating space, said chunks being compressed together to deform the contacting chunks sufficiently to substantially close any spaces therebetween and thus compel said oil to flow through the pores of such deformed chunks, such compression being sufficient to force the chunks at the boundaries of said mass into electrical contact with the elect-rode surfaces bounding such interelectrode treating space.

9. An electric filter as defined in claim 8 in which said chunks of deformable porous material are chunks of filamentary polyurethane foam.

10. An electric filter for removing suspended contaminants from high-resistivity oils free of significant amounts of dispersed water, said electric filter including in combination:

sets of closely spaced electrodes providing interelectrode treating spaces each of a width of about V2-2 and of a length several times such width;

a plurality of thin sheets of porous material of high resistivity extending lengthwise of each interelectrode treating space in each section thereof lightly compacted together therein between the electrode surfaces thereof with the outermost surfaces of the outermost sheets in electrical contact with said electrode surfaces, each of said sheets being of a thickness of about /s%", each sheet having a porosity of about 10-30 pores per inch, the degree of compaction of the porous material being about l0-30%;

means for insulating said electrode sets from each other and for establishing high-gradient unidirectional electric fields in said interelectrode treating spaces; and

means for flowing the contaminated oil lengthwise of said interelectrode treating spaces and said sheets of porous material therein to flow transverse to the lines of force of said electric fields.

11. An electric filter for removing suspended contaminants from high-resistivity oils free of significant amounts of dispersed water, said electric filter including in combination:

a grounded tubular housing having an inner wall;

a plurality of annular electrodes within and spaced along said housing in parallel relation, said annular electrodes having peripheries adjacent said inner wall, each annular electrode having a central opening;

sealing means including sealing members at the peripheries of said annular electrodes sealing same in fluid-tight relation with said inner wall;

means for electrically connecting said annular electrodes together and to said housing, said annular electrodes forming a grounded set of electrodes;

a plurality of plate electrodes respectively between said annular electrodes having peripheries larger than said central openings thereof but smaller than said inner wall to form annular passages between such inner wall and such peripheries;

means for electrically connecting said plate electrodes together and insulating same from said housing, said plate electrodes forming an energized set of electrodes, there being an annular interelectrode treating space between each pair of opposed electrodes of said sets having inner and outer ends respectively communicating with the central opening and the annular passage of the electrodes bounding such interelectrode treating space;

a source of unidirectional potential connected between said electrode sets to establish electric fields in said interelectrode treating spaces;

a mass of porous material of high electrical resistivity filling each of said interelectrode treating spaces and in contact with the plate and annular electrodes bounding same; and

means for flowing said high-resistivity oil successively through said interelectrode treating spaces and thus through the masses of porous material therein, such oil moving toward and away from said central axis in its successive flow through said interelectrode treating spaces, said central openings and said annular passages.

12. An electric filter as defined in claim 11 in which said housing provides an entrance zone communicating with a first of said interelectrode treating spaces, said means for flowing said high-resistivity oil successively through said interelectrode treating spaces including a pipe delivering such oil to said entrance zone, there being a plurality of relatively sharp pointed pins in said entrance zone electrically connected to one of said electrodes, and a member of opposite polarity toward which said pointed pins face but spaced therefrom to establish electric blasts from said pins toward said member, said electric blasts acting on said oil before its passage through said first interelectrode treating space.

13. An electric filter for removing suspended contaminants from high-resistivity oils, said electric filter including in combination:

a tubular housing having a central axis, opposed end zones spaced along said axis, an inner wall extending between said end zones, opposed treating zones spaced along said axis inwardly of said end zones and bounded outwardly by said inner wall, and a central zone between said treating zones;

a first pipe means comprising two pipes respectively communicating with said end zones;

a second pipe means communicating with said central zone;

means for flowing portions of said contaminated oil in opposite directions respectively through said treating zones, said last-named means including means for delivering said contaminated oil to one of said pipe means to advance toward the other of said pipe means and means for withdrawing purified oil from the latter;

means for diverting each of said oppositely-flowing oil portions to flow successively toward and away from said central axis during flow through the respective treating zones, said diverging means including a plurality of parallel electrically-connected annular electrodes spaced from each other along said axis forming a grounded set of electrodes, each annular electrode having a central opening, a plurality of plate electrodes respectively between said parallel annular electrodes and having outer peripheries spaced from said inner wall, and means extending from plate electrode to plate electrode through said central openings of said annular electrodes electrically connecting said plate electrodes together to form an energized set of electrodes electrically insulated from said grounded set of electrodes, there being annular interelectrode terating spaces between said annular electrodes and said plate electrodes;

masses of porous material filling said interelectrode treating spaces; and

means for establishing a unidirectional potential difference between said sets of electrodes to establish electrostatic fields in said interelectrode treating spaces. 1

References Cited UNITED STATES PATENTS 531,183 12/1894 Harris 204--302 661,189 11/1900 Olsen et al. 2l0336 1,293,114 4/1919 Kendrick 210496 2,534,907 12/1950 Ham et al 204-188 2,573,967 11/1951 Hamlin 204-302 3,190,827 6/1965 Kok et al. 204-186 3,252,885 5/1966 Griswold 204302 JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

T. TUFARIELLO, Assistant Examiner.

Claims

1. AN ELECTRICE FILTER FOR REMOVING SUSPENDED CONTAMINANTS FROM HIGH-RESISTIVITY OILS FREE OF SIGNIFICANT AMOUNTS OF DISPERSED WATER, SAID ELECTRIC FILTER INCLUDING IN COMBINATION: A PAIR OF SPACED PARALLEL ELECTRODES PROVIDING AN INTERELECTRODE TREATING SPACE THEREBETWEEN; A MULTI-ELEMENT MASS OR POROUS MATERIAL OF HIGH ELECTRICAL RESISTIVITY FILLING ALL SECTION OF THE INTERELECTRODE TREATING SPACE AND BRIDGING SAID ELECTRODES, SAID MULTI-ELEMENT MASS COMPRISING DEFORMABLE INDIVIDUAL ELEMENTS OF SAID POROUS MATERIAL COMPRESSED TOGETHER IN EACH SECTION OF SAID INTERLECTRODE TREATING SPACE SUFFICIENTLY TO BLOCK SIGNIFICANT FLUID FLOW BETWEEN THE ELEMENTS, WHEREBY FLUID FLOW TAKES PLACE SUBSTANTIALLY EXCLUSIVELY THROUGH THE PORES OF SAID ELEMENTS; MEANS FOR ELECTICALLY INSULATING SAID ELECTRODES FROM EACH OTHER AND FOR ESTABLISHING A HIGH-GRADIENT UNIDIRECTIONAL ELECTRIC FIELD IN SAID INTERELECTRODE TREATING SPACE; AND MEANS FOR FLOWING THE CONTAMINATED OIL THROUGH THE PORES OF SAID ELEMENTS.