ELECTROSTATIC ADSORPTIVE FLUID FILTERING APPARATUS

Abstract: An electrostatic adsorptive fluid filtering apparatus wherein an adsorbent provided in a flow path of fluid to be treated has adsorption capacity as well as adsorption power substantially improved as as a result of enhancement of a potential inherently carried by the adsorbent on its adsorptive hole surface by impressing a DC voltage onto a charging elec­ trode provided with the adsorbent or by placing the adsorbent in an electric field.

Description: BACKGROUND OF THE INVENTION The present invention relates to a fluid filtering apparatus adapted for removal of various noxious gases such as chlorine gas and ammonium gas or noxious ions present in the air; ions, moisture or molecular impurities present in non-aqueous liquids such as lubricating oil, machining oil, cleaning oil and organic solvents; and oily contents, ions or molecular impurities present in aqueous liquids such as potable water, waste water, lubricating liquid, working water and cleaning liquid, and more particularly to such fluid filtering apparatus utilizing adsorbent. In the conventional adsorptive fluid filtering apparatuses utilizing adsorbent, the fluid to be treated passes through the apparatus merely in contact with the adsorbent or passes first through an electric field so that any impurities contained therein are charged and then passes in contact with the adsorbent. Such adsorptive filtering apparatuses of prior art have been unsatisfactory in their adsorption capacities and also because of the limited saturated adsorption levels of used adsorbents, since these well known apparatuses exclusively rely upon a relatively low inherent adsorption potential of the adsorbent on its effective hole surface as an adsorption power. Additionally, after saturated, the adsorbent can not be reused and must be thrown away. This disadvantageously increases the operation cost and requires a large-sized waste disposal equipment. Regeneration of the adsorbent material has been proposed in the specification of European Patent Application No. 0032317 in which a liquid to be cleared is fed through an adsorbent material which is positioned between two electrodes. A potential is applied across the electrodes to create an electric field in the adsorbent material. This electrical field assists in the filtering action. By reversing the polarity of the potential applied to the electrodes and by passing a clearing liquid through the adsorbent material filtered residue can be discharged from the material and the adsorbent is thus regenerated for re-use. A disadvantage of the device described in EP 0032317 is that a single filter stage only is applied to the liquid being treated. There is no ability for differing sizes of particles to be filtered out or for any pre-filtering to take place. Consequently, it is possible swiftly to block the adsorbent material with larger particles leading to the need for repeated cleaning of the adsorbent material which causes unnecessary interruptions to the filtering process. It is an object of the present invention to provide a filter which is capable of regeneration and which, employing a principle to create an electric field in the area of an adsorbent material, provides an ability for large particles to be separated from smaller particles in successive parts of the filter. A further object of the present invention is to provide an electrostatic adsorptive fluid filtering apparatus adapted to improve an adsorption power as well as an adsorption capacity of the adsorbent by enhancing an inherent adsorption potential of the adsorbent on its adsorptive hole surface so as to increase a Coulomb's force developed between said adsorptive hole surface and matters to be adsorbed thereonto, for example, impurities. Another object of the present invention is to provide an electrostatic adsorptive fluid filtering apparatus adapted to improve the adsorption power as well as the adsorption capacity of the adsorbent as a result of enhancement of said inherent adsorption potential of the adsorbent on its adsorptive hole surface by impressing an electric voltage onto a charging electrode provided with an adsorbent or onto the adsorbent itself. Still another object of the present invention is to provide an electrostatic adsorptive fluid filtering apparatus adapted to improve the adsorption power as well as the adsorption capacity of the adsorbent as a result of enhancement of said inherent adsorption potential of the adsorbent onto its adsorptive hole surface by exposing the adsorbent to an electric field. The invention relates for an electrostatic adsorptive fluid filtering apparatus of the kind having a charging electrode provided with an adsorbent having a fluid flow path therethrough, and a concentric outer electrode, the charging electrode having, in use, a voltage applied to it to generate an electric field in the flow path of the fluid so as to enhance a surface potential on adsorptive holes of the adsorbent placed in the flow path, in which the outer electrode is of cylindrical form and has a fluid inlet and a drain; all the above features are known from EP-A-032 317; the charging electrode being of cylindrical form and being mounted concentrically within and spaced from the outer electrode to form a hollow interior area, said charging electrode comprising a pair of concentrically arranged spaced cylindrical conductors made of a porous or reticulated material, the space between the cylinder being filled with the adsorbent; a perforate tubular electrode mounted axially in the apparatus and being spaced from the surrounding charging electrode and having an outlet for the discharge of filtered fluid, and means whereby power from an electrical source can be applied to the electrodes, and in that in use fluid to be filtered is fed through the fluid inlet to be subjected to the electric field whereby in the said hollow interim area a Van de Waal force is created which causes larger particles of impurities to cohere and deposit for discharge through the drain, smaller particles being adsorbed on the hole surface of the adsorbent and any remaining particles being polarized, in the area between the central electrode and the charging electrode, by being subjected to a Coulomb force and caused to re-enter the adsorbent and to remain there. Reference will now be made to the accompanying drawings in which: Figs. 1 through 3 illustrate a filter indicating the principles of operation of a filter using an electric field. Fig. 1 is a perspective view partially broken to show an interior of filter apparatus, Fig. 2 is a vertical section of the apparatus combined with a diagram illustrating a system of wiring and piping associated with the apparatus itself, and Fig. 3 is a radial cross-section of the apparatus itself; Figs. 4 through 6 illustrate a first embodiment of the present invention, of which Fig. 4 is a perspective view partially broken to shown an interior of the apparatus, Fig. 5 is a vertical section of the apparatus itself, and Fig. 6 is a radial cross-section of the apparatus itself; Figs. 7 and 8 illustrate a second embodiment, of which Fig. 7 is a vertical section of the apparatus itself and Fig. 8 is a radial cross-section; Figs. 9 and 10 illustrate a third embodiment, of which Fig. 9 is a vertical section of the apparatus itself and Fig. 10 is a radial cross-section of the apparatus itself; The present invention will now be described in more detail hereafter with respect to the principles illustrated in Figs. 1 through 3, the first embodiment illustrated by Figs. 4 through 6, the second embodiment illustrated by Figs. 7 and 8, and the third embodiment illustrated by Figs. 9 and 10. Referring to Figs. 1 through 3, reference numeral 1 designates an outer cylindrical electrode having defined therein a slow rate treatment chamber 2 and having at vertically opposite ends an inlet 3 communicating with said slow rate treatment chamber 2 and an electrode bearing opening 4. Reference numeral 5 designates a charging electrode centrally provided within said outer cylindrical electrode 1 and having a passage axially extending therethrough. The charging electrode 5 has its peripheral wall, which is provided adjacent its upper end, with a plurality of through-holes 5a and surrounded by an adsorbent layer 6. The peripheral wall has at its opposite i.e. lower end, an outlet 7. The adsorbent layer 6 is, in turn, surrounded by a porous or reticulated electric conductor 8 which is electrically connected to said charging electrode 5. It should be noted that the adsorbent constituting said adsorbent layer 6 is slected so that the surface potential on the adsorptive hole thereof has a polarity opposite to that of the surface charge carried by impurities or like to be removed. Usually, carbonaceous adsorbents are used for gases, adsorbent containing as main ingredients activated clay, zeolite, activated alumina or a mixture thereof are used for non-aqueous liquids, and adsorbents containing therein as main ingredients activated carbon, zeolite or a mixture thereof for aqueous liquids. Reference numberal 9 designates an insulator carried on the electrode bearing opening 4 of the outer cylindrical electrode 1 to electrically insulate the outer cylindrical electrode 1 from the charging electrode 5 covered with the adsorbent layer 6 within the slow rate treatment chamber 2 of the outer cylindrical electrode 1. Reference numeral 10 designates DC source means having positive and negative termals. Source lines wired from these terminals are connected via a change-over switch 11 to the outer cylindrical electrode 1 and to the charging electrode 5, respectively, said change-over switch 11 being operable to change-over the polarity of voltage impressed across the outer cylindrical electrode 1 and the charging electrode 5. In this form of apparatus a pipe line starting from a reservoir T₁ for fluid to be treated extends through a pump P₁ and a valve V₁, then is branched into two lines, the one communicating with the inlet 3 of the apparatus itself and the other communicating via a valve V₂ with a reservoir T₂ for impurities. Another pipe line starting from the outlet 7 is also branched into two lines, the one communicating via a pump P₂ with a reservoir T₃ for flushing purposes and the other communicating via a valve V₃ with a reservoir T₄ for treated fluid. Now, the manner in which this apparatus operates will be described. In adsorption treatment, the fluid to be treated is supplied by the pump P₁ from the reservoir T₁ for fluid to be treated into the slow rate treatment chamber 2 of the apparatus and, after passage through the adsorbent layer 6, discharged through the charging electrode 5 into the reservoir T₄ for treated fluid while the conductor 8 surrounding the charging electrode 5 and, therefore, the adsorbent layer 6 is applied with a voltage of a polarity opposite to that of the surface charges of impurities to be removed. Upon saturation of the adsorbent layer 6, the change-over switch 11 is operated, the valve V₁ of inlet side is closed and the valve V₂ in the branched line is opened so as to form a passage leading to the reservoir T₂ for impurities, and thereafter, the pump P₂ for counter flushing is driven to wash the absorbed impurites away. Such operation may be manually or automatically repeated in a continuous manner to treat the fluid containing impurities under the effect of electrostatic adsorption and electrostatic removal. As has been mentioned above, one of the opposing electrodes is provided with the adsorbent layer which is surrounded by the conductor electrically connected to this electrode and which is comprised of the material selected for the matters to be adsorbed thereonto. The fluid to be treated is guided to pass between these electrodes across which a DC voltage is impressed, and thereby the impurities or like are adsorbed onto the adsorbent layer having its adsorption capacity improved. More specifically, the adsorbent layer carried by the one electrode has its adsorption surface potential enhanced under the effect of said DC voltage impressed onto the charging electrode and the conductor surrounding the latter. The impurities or like contained in the fluid guided to pass between said electrodes are exposed to an electric field and thereby polarized or charged to increase a quantity of electricity. In consequence, the Coulomb's force acting between the adsorptive hole surface and the matters to be adsorbed thereonto rapidly increases, so that said matters to be adsorbed are attracted onto said adsorptive hole surface. During this process, the impurities of relatively large sizes and relatively high specific gravities contained in the same fluid have their zeta potentials (due to induced electricity and/or ion bonding) erased as these impurities pass by the surface of the charging electrode. As a result, these impurities cohere together into coarse particles under effect of van der Waals' force and settle. The remaining impurities which do not settle are attracted by the intensive Coulomb's force as has mentioned above into the adsorptive hole, filling this, and adsorbed onto the adsorbent. Thus, the surface potential of the adsorbent at its adsorptive hole is enhanced to increase the Coulomb's force acting between the latter and the impurities, enabling the impurities to fill the adsorptive hole. Thus, it will be recognized that it is possible to utilize the adsorbent substantially more effectively than when the charging electrode is applied with no DC voltage. This results in increase of the adsorbed quantity and prolongation of the useful life of the adsorbent. When the adsorbent is saturated, the change-over switch 11 may be operated so as to change-over the polarity of the DC source 10 connected to the outer cylindrical electrode, on one side, and to the charging electrode 5, on the other side, and thereby to generate the Coulomb's force of the reverse polarity with respect to the Coulomb's force acting during the adsorption process as mentioned above. The voltage supplied from the DC source means 10 may be a DC voltage or a DC/AC superposed voltage. Preferably, a DC voltage of 1,000 to 3,000 V/cm is used for gases, a DC voltage of 10 to 200 V/cm for non-aqueous liquids, a DC voltage or DC/AC superposed voltage of 1 to 20 V/cm for aqueous liquids, respectively. It should be noted here, however, that the selection of the DC voltage or superposed voltage to be impressed and the selection of a voltage value depend on the electric resistance specific to the particular fluid and it is desired to select these factors experimentally. Therefore, both the type and the value of impressed voltage are not limited to those as set forth above. Additionally, the flow velocity of fluid depends on the viscosity thereof. Although the adsorbent layer 6 is surrounded by the conductor 8 electrically connected to the charging electrode 5 in the apparatus as illustrated, when an electrically conductive adsorbent such as activated carbon or activated alumina is employed, the presence of the conductor is sometimes unnecessary since the surface of the adsorbent can be maintained at a potential equal to that of the charging electrode through the adsorbent layer directly in contact with the charging electrode. A first embodiment of the invention will now be described by referring to Figs. 4 through 6, in which the outer cylindrical electrode 21 is in the form of a cylinder closed at opposite ends and provided with a fluid inlet 22 and a drain 23. The charging electrode 24 is disposed concentrically into the outer cylindrical electrode 21 and comprises two concentrically arranged cylindrical conductors 24a, 24b made of porous or reticulated material between which an adsorbent 24c is filled. The type of this adsorbent 24c depends on those of fluid and matters to be adsorbed thereonto. Upper and lower insulator plates 25, 26 serve to insulate and support the charging electrode 24 with respect to the outer cylindrical electrode 21. A central electrode 27 comprises a pipe-having a plurality of through-holes 27a and extends into the hollow interior of the charging electrode 24 along the axis of the outer cylindrical electrode 21 and through a top surface 21a of the outer cylindrical electrode 21 and the upper insulator plate 25. The electric source means 28 is connected at its one end to the charging electrode 24 through an insulating bushing 29 and at the other end both to the outer cylindrical electrode 21 and the central electrode 27. Now the manner in which this embodiment operates will be considered. Voltage is impressed onto the fluid flowing between the outer cylindrical electrode 21 and the charging electrode 24 as the fluid is supplied under a pressure in the direction of arrow X through the fluid inlet 22 into the outer cylindrical electrode 21. The type and value of this voltage are identical to those in the case of the apparatus of Figures 1 through 3. In consequence, the impurities of relatively large particle sizes and relatively high specific gravities contained in the fluid thus flowing under a pressure between the outer cylindrical electrode 21 and the charging electrode 24 are attracted under the effect of Coulomb's force to the charging electrode 24, then electrophoretically collected around the charging electrode 24 where the zeta potential of these impurities disappears. Thus, these impurities cohere together into coarse particles, then settle down and are discharged through the drain 23. Such settlement of the impurities having relatively large particle sizes prevents the adsorptive hole of the adsorbent 24 from being clogged with the impurities. The remaining impurities are polarized or ionized under the effect of the impressed voltage, then attracted by the charging electrode 24 and brought into contact with the adsorbent 24c so as to be attracted by the Coulomb's force towards, or adsorbed onto, the potential-enhanced adsorptive hole surface of the adsorbent 24c. In the second embodiment, voltage is impressed also across the charging electrode 24 and the central electrode 27, so any impurities possibly remaining in the fluid which has once passed by the adsorbent 24c will be again polarized or ionized in the region between the charging electrode 24 and the central electrode 27 and adsorbed onto the adsorptive hole surface. Therefore, the apparatus according to the first embodiment can provide an adsorption capacity higher than provided by the apparatus of Figures 1 through 3. The fluid thus filtered is discharged through an opening formed in the upper end of the central electrode 27 as indicated by an arrow Y. As in the apparatus of Figs. 1 to 3, the change-over switch provided on the output side of the electric source means 28 is operated to reverse the polarity of the voltage impressed between the outer cylindrical electrode 21 and the charging electrode 24 and thereby to dislodge the matters from the adsorbent 24c so that the adsorbent 24 may be repeatedly reused. Furthermore, the matters which have been adsorbed onto the adsorbent 24c can be collected in thickened condition. The second embodiment illustrated by Figs. 7 and 8 is a modification of the above-mentioned first embodiment and similar to the first embodiment except that the outlet Y for the filtered fluid is provided at the lower end of the central electrode and the latter is surrounded by a filter. As seen, the outer cylindrical electrode 41 is in the form of a cylindrical container provided with the fluid inlet 42 and the drain 43, and has an upper opening 41a closed with a closure 41b. The charging electrode 44 is, as is the case of the charging electrode 24 in the first embodiment, disposed concentrically within the outer cylindrical electrode 41, and comprises two concentrically disposed cylindrical conductors 44a, 44b made of porous or recticulated material and an adsorbent 44c filling a space defined by these two conductors. Upper and lower insulator plates 45, 46 serve as insulated support of the charging electrode with respect to the outer cylindrical electrode 41. The central electrode 47 comprises a pipe having a plurality of through-holes 47a, and extends into the hollow interior of the charging electrode 44 along an axis of the outer cylindrical electrode 41 and through the upper insulator plate 45, the lower insulator plate 46, and a bottom wall 41c of the outer cylindrical electrode 41. The filter 48 is made of an electric conductor, arranged to surround the central electrode 47 and supported by the upper and lower insulator plates 45, 46 within the outer cylindrical electrode 41. The electric source means 49 is, as is the case of the electric source means in the above-mentioned second embodiment, connected at one end to the charging electrode 44 through the insulating bushing 50 and at the other end both to the outer cylindrical electrode 41 and the central electrode 47. The type and the value of the voltage supplied from this electric source means 49 are as in the previously mentioned first embodiment. In the apparatus according to the second embodiment of the arrangement as has been described above, the impurities of relatively large particle sizes contained in the fluid introduced under a pressure through the fluid inlet 42 as indicated by the arrow X settle down, as in the above-mentioned first and second embodiments, as the fluid passes between the outer cylindrical electrode 41 and the charging electrode 44, and the remaining impurities are adsorbed onto the potential-enhanced adsorptive hole surface of the adsorbent 44c under the effect of a Coulomb's force generated by said enhanced potential. Thus, a desired filtering effect is achieved to a certain degree. Further fine filtering is achieved by the filter 48 interposed between the charging electrode 44 and the central electrode 47. More specifically, any colloidal particles possibly remaining in the fluid after the latter has passed by the adsorbent 44c are attracted by a greater zeta potential developed on the surface of the filter 48 due to the voltage impressed across the charging electrode 44 and the central electrode 47 and thereby adsorbed onto said surface. In this way, such colloidal particles are effectively removed from the fluid. Reference numeral 52 indicates how the filter 48 is polarized to cause the zeta potential. A cake formation occurs on the surface of the filter 48 due to adsorption of the colloidal particles thereonto and such case serves for a cake-filteration. As a result, a fine filtering effect is maintained even when the fineness of the filter 48 itself has been deteriorated, and the filter 48 is always free from being clogged by colloidal particles penetrating into the interior of the filter 48. Thus, the useful life of the filter 48 is prolonged to 5 to 10 times with respect to the case in which the filter 48 is used without any impressed voltage. The fluid thus finely filtered by the filter 48 is discharged through the opening at the lower end of the central electrode 47 as indicated by arrow Y. Now an electric field is generated in the passage of the fluid which has passed by the adsorbent 44c, thus enhancing adsorption capacity, and the filter 48 is placed in this electric field so that said fluid may be further filtered at a fineness or precision substantially higher than that inherent to this filter 48, providing a more effective electrostatic adsorptive fluid filtering apparatus. The third embodiment illustrated by Figs. 9 and 10 is distinguished from the first embodiment illustrated by Figs. 4 through 6 only in that there is provided a dielectric substance between the outer cylindrical electrode 21 and the charging electrode 24. Accordingly, all other parts or components are similar to those in said second embodiment and designated by the same reference numerals. These parts will be not described here in detail. Referring to Figs. 9 and 10, a fibrous dielectric substance as made of glass wool is employed to comprise said dielectric substance 30 between the outer cylindrical electrode 21 and the charging electrode 24. The dielectric substance 30 is polarized upon impression of a voltage and this creates a situation equivalent to a plurality of electrodes being interposed between the outer cylindrical electrode 21 and the charging electrode 24. As a consequence, zeta potentials carried by impurities rapidly disappear and thus the impurities of relatively large particle sizes will reliably settle down, so that a probability at which the adsorptive holes of the adsorbent 24c might be clogged with impurities may be reliably reduced. Interposition of the dielectric substance between the outer cylindrical electrode and the charging electrode as in this embodiment may be effectively employed also in the second embodiment. The electrostatic adsorptive fluid filtering apparatus according to the present invention as has been described with reference to the respective embodiments permits gaseous, non-aqueous or aqueous fluid to be filtered with a high efficiency. Such electrostatic adsorptive fluid filtering apparatus may be utilized, when the fluid is gas, for air cleaning, or removal of noxious gases or ions; when the fluid is non-aqueous liquid, for regeneration or purification of oils such as lubricating oil and machining oil, organic solvents, raw oil or like; and when the fluid is aqueous liquid, for waste water disposal, production of potable water, production of purified water or like. Practical examples or recovery of adsorbed matters by changing over the polarity of the electric source means include recovery of heavy metals contained in oil or solvent and similar recovery from waste water or sea water or like. An experimental apparatus has been trially manufactured in accordance with the present invention particularly as has been described above as the second embodiment and this electrostatic adsorptive fluid filtering apparatus has provided filtration results as set forth below: It will be obvious from the filtration results as set forth above that the electrostatic adsorptive fluid filtering apparatus according to the present inventionpermits gaseous, non-aqueous or acqueous fluid to be filtered with an extremely high efficiency. Particularly, the data as set forth in the above-mentioned (b) clearly suggests that the efficiency with which the filtration can be achieved is substantially improved by the voltage impression across the outer cylindrical electrode and the charging electrode, as compared to the case in which such voltage impression is not effected. It is also proved by the data as set forth in (b) that said efficiency has been improved by enhancing the surface potential on the adsorptive hole of the adsorbent.

Claims: An electrostatic adsorptive fluid filtering apparatus of the kind having a charging electrode provided with an adsorbent having a fluid flow path therethrough, and a concentric outer electrode, the charging electrode having, in use, a voltage applied to it to generate an electric field in the flow path of the fluid so as to enhance a surface potential on adsorptive holes of the adsorbent placed in the flow path, in which the outer electrode (21) is of cylindrical form and has a fluid inlet (22) and a drain (23); characterised in that the charging electrode (24) is of cylindrical form and is mounted concentrically within and spaced from the outer electrode (21) to form a hollow interior area, said charging electrode (24) comprising a pair of concentrically arranged spaced cylindrical conductors (24a,24b) made of a porous or reticulated material, the space between the cylinder being filled with the adsorbent (24c); a perforate tubular electrode (27) mounted axially in the apparatus and being spaced from the surrounding charging electrode (24) and having an outlet for the discharge of filtered fluid, and means whereby power from an electrical source (28) can be applied to the electrodes (21, 27; 24a,24b), and in that in use fluid to be filtered is fed through the fluid inlet (22) to be subjected to the electric field whereby in the said hollow interim area a Van de Waal force is created which causes larger particles of impurities to cohere and deposit for discharge through the drain (23), smaller particles being adsorbed on the hole surface of the adsorbent (24c) and any remaining particles being polarized, in the area between the central electrode (27) and the charging electrode (24), by being subjected to a Coulomb force and caused to re-enter the adsorbent (24c) and to remain there. An electrostatic adsorptive fluid filtering apparatus according to claim 1, characterized in that there is provided a filter (48) around the central electrode (27). An electrostatic adsorptive fluid filtering apparatus according to claim 1 or claim 2 characterized in that a dielectric substance (30) is interposed in the area between the outer cylindrical electrode (21) and the charging electrode (24). An electrostatic adsorptive fluid filtering apparatus according to any preceding claim, characterized in that a polarity of voltage impressed across the charging electrode (24) and the outer cylindrical electrode (21) is changed over by a change-over switch (70) and thereby matter previously adsorbed onto the adsorbent (24c) are discharged.

Inventors: INOUE, NOBORU
Applicants: INOUE, NOBORU
Application year: 1986
Main classification: B03C5
IPC codes: B03C5, B01D35, B01D15, B01D17, B01D53