Patent Publication Number: US-5290457-A

Title: Filter element with regenerable bulk material filling and method for making same

Description:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT. 
     Research and development of the present invention and application have not been Federally-sponsored, and no rights are given under any Federal program. 
    
    
     The present application is a continuation-in-part of our co-pending application U.S. Ser. No. 07/632,394 filed Dec. 20, 1990, which is now U.S. Pat. No. 5,169,528, entitled FILTER ELEMENT, and having common ownership with the present application. 
    
    
     CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119, of West German Application No. P 39 43 249.1 filed Dec. 29, 1989, by Seitz-Filter-Werke Theo &amp; Geo GmbH &amp; Co KG, and entitled &#34;Geschlossenes Filterelement&#34;. 
     BACKGROUND OF THE INVENTION FIELD OF THE INVENTION 
     This invention relates to a closed filter element for filtering flowable, in particular fluid, media, such as pharmaceutical or chemical preparations, drinks, etc., of which the inner space comprises at least one hollow-cylindrical chamber which is delimited by peripheral walls, through which the medium to be filtered can flow over the entire axial length thereof, and by sealing closure components at the end face, and contains a filter member which can accommodate flow in an essentially radial manner. 
     DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR §§1.97-1.99 
     Filter elements of this type, also known as filter cartridges, are described in DE-OS 38 17 793, for example. In the case of filter cartridges of this type, there is formed between a central tube and a support casing tube, which are both provided in a grid-like manner with apertures, a hollow-cylindrical chamber which is closed at both front ends with end caps and in which a wound or folded filter member, which is formed from filter layers or filter membranes, is mounted. The filtration operations which can be performed with these known filter cartridges are consequently restricted to filtration with filter layers or filtration with filter membranes. In particular, the possibilities for flushing back and regeneration with filter elements of this type are considerably limited. 
     There is known from DE-OS 38 02 816 a cartridge-like filter element in the case of which the outer peripheral wall is formed as a porous support layer for a filter cake. This filter cake is formed by the deposition of filter material, for example pebble-like bulk material and/or fibre mixtures and adsorbents, such as activated carbon, silicic acid and the like. 
     When the filter cake has been used to the point of clogging, it is removed, or washed away by flushing back, and replaced by new filter material, which is to be newly deposited, it being alternately possible, however, for the deposit-filter material of the removed filter cake to be regenerated outside the filter housing in a complicated manner, and re-used if desired. A new or substitute filter cake must, however, be loaded into the filter element each time before the filtration process is continued. 
     There is disclosed in DE-OS 32 04 022 a filter cartridge in the case of which a hollow-cylindrical chamber is formed between an outer peripheral wall and an inner peripheral wall and is divided into two hollow-cylindrical partial chambers by an impermeable intermediate wall extending only over a part of the axial length of the chamber. In this connection the outer peripheral wall and the inner peripheral wall are formed on a part of the axial length thereof, lying opposite the intermediate wall such that they are porous and also leaktight. The chamber is filled with a granulated material of filter agents and adsorption agents. As a result of the construction of the peripheral walls and the arrangement of the impermeable intermediate wall, a flow path is determined within this granulated material in an essentially axial manner through the one partial chamber and, aligned in the opposite direction, axially through the second partial chamber. A filter cartridge of this type is designed for the adsorptive purification of fluids at low flow velocities and does not provide any possibility for performing clarification and particle filtration operations. 
     SUMMARY OF THE INVENTION 
     In contrast thereto, the invention has for an object the provision of a closed filter element having means by which unique filtration operations of the deposition filtration type can be performed, characterized by the filtering material in part migrating and being deposited to form a filter cake which can be washed out while still remaining in the closed system with an improved degree of efficiency, as by flushing or washing back as well as by being chemically regenerated, and, after such washing out and regeneration processes, such cake is directly available to be used again without any appreciable loss of material. 
     In accordance with the invention, this object is achieved in that the filter member disposed in the interior of the hollow-cylindrical chamber is formed by a bulk-material filling of regenerable, filtration-active substances characterized by a particulate and/or fibrous structure, and by forming the peripheral walls of the chamber so as to have a level of porosity which is capable of retaining the filtration-active substances of the filter member while still ensuring that the medium to be filtered can pass through, the filtration-active substances being selected to act as auxiliary filter agents which can form a deep bed filter and are capable of migrating and being deposited, and at least one peripheral wall of the filter element being formed in the manner of a porous, wet-resistant support layer. 
     The bulk-material filling of regenerable filtration-active substances accommodated in the hollow-cylindrical chamber is formed very quickly into a high-performance, asymmetrical deep bed filter on the porous peripheral wall, on the discharge side of the chamber by the action of the medium being filtered as it flows radially through the chamber and the bulk-material filling. If the deep bed filter formed in this way becomes completely filled or clogged with filtered out substances, in particular also turbidities during the course of the filtration process, then by flushing back in the direction opposite to that of filtration, the bulk-material filling (filtration-active substances) which was retained in this connection in the chamber, can be washed out rapidly and effectively, for example, using hot water and/or hot water and a mixture of the fluid being filtered, thus providing improved results. If necessary, the filtration-active substances can also be regenerated from time to time by means of through-flowing steam and/or chemical agents such as solvents, wherein it is also particularly advantageous for this purpose that the filtration-active substances to be regenerated are retained in the hollow-cylindrical chamber. Both after each washing-out process and also after the regeneration process the filtration-active substances retained in the interior of the hollow-cylindrical chamber are immediately available again in the form of a deep bed filter. Regeneration can be carried out through the use of steam and/or other chemical substances, in order to achieve the original state, i.e. that existing prior to filtration having occurred. Steam and/or chemical regeneration is employed when the effect of washing with hot water and/or the fluid being filtered does not result in sufficient decrease in filtering back-pressure after a washing operation has been completed and filtering is resumed. This indicates that the filter is still clogged. The regeneration process is intended to remove turbidities as well as slimy matter, with the help of steam and/or solvents, not only by mechanical agitation or turbulent action, but also by chemical action or reaction, i.e. dissolving some of the filter particles and/or diminishing the size of some of the filter particles. 
     Although the filtration-active substances could essentially have the same structure such that the structural geometry thereof is symmetrical with respect to the direction of filtration, within the scope of the invention, however, the filtration-active substances are preferably disposed inside the hollow-cylindrical chamber with a structural geometry which is asymmetrical with respect to the direction of filtration. This can be achieved in a particularly simple and preferred manner in that the bulk-material filling forming the deep bed filter consists of a mixture of filtration-active substances of differing thicknesses and/or charges and/or fibre lengths and/or particle sizes and/or particle geometries, i.e. random asymmetrical geometries. As a result thereof, when a radially outward flow filter element is subjected to forward flow, in a corresponding manner there results a heterogeneous radial distribution of the porosity, or a radial density gradient, within the chamber. The fine particles and fibres are rinsed and moved radially outward in the direction of the flow, i.e. towards for example, the outer, discharge side, and together form a dense yet porous outer layer, whilst the coarser and longer particles of fibres are not rinsed to such an extent, and form a correspondingly more porous inner layer. There thus results a deep bed filter, of which the pore diameters decrease as the thickness increases toward the outside and one which is thus able to separate coarse particles fractionally and counteract an early blockage. 
     Examples of materials useable as filtration-active substances include but are not limited to: cellulose acetate fibres, perlite, diatomite, PA-staple fibre, PP-pulp fibres, PE-staple fibres, PE-pulp fibres, and cellulose fibres. 
     The filter element of the invention can be employed for the filtration of beverages such as beer, wine, fruit juices and the like; various chemical substances requiring high purity; and pharmaceutical products (e.g. cough mixtures, etc.). 
     The material composition of the bulk material filling forming the deep bed filter can be adapted to special filtration operations in each case. Thus regenerable adsorption agents can be added to the bulk-material filling of the hollow-cylindrical chamber, forming the deep bed filter. Substances bringing about the stabilization of the medium to be filtered during filtration, such as polyvinylpolypyrrolidone, for example, can also be added, with the filtration-active substances, to the bulk-material filling of the hollow-cylindrical chamber, forming the deep bed filter. The latter addition is particularly suitable for stabilizing beer during filtration. 
     Other useable regenerable adsorption agents that have been found to be satisfactory include, but are not limited to: active carbon, zeolite, TiO 2 , Al 2  O 3 , SiO 2  with irreversibly bound cationic and anionic groups (e.g. polyamid-amine-acrylate, carboxyl-base, resin particles, microcrystalline cellulose or cellulose with functional groups, cationic starch). 
     In accordance with the invention, two or more hollow-cylindrical chambers with a filling of filtration-active substances can also be mounted in an essentially coaxial arrangement within a common housing and separated from one another by porous intermediate walls, the latter being connected at the axial ends thereof in a sealed manner to closure elements common to all chambers. The development of coaxial chambers separated from one another offers the possibility of providing the various hollow-cylindrical chambers with fillings of filtration-active substances which are different from one another. As a result thereof, variations of the filtration operations to be performed can be carried out over considerably broader ranges. 
     In a particularly advantageous embodiment of the invention the hollow-cylindrical chamber or chambers are disposed inside a filter element support frame which is in the form of a filter cartridge and comprises a perforated core tube, a perforated peripheral tube and closure caps which hold these two tubes together and are secured on at least one of these tubes, the outer porous peripheral wall of the chamber or the outermost hollow-cylindrical chamber being supported on the inner side of the peripheral wall tube, and the inner porous peripheral wall of the chamber or the innermost hollow-cylindrical chamber being supported on the outer side of the core tube and all the porous peripheral walls being connected to the closure caps at both axial ends in a sealed manner. 
     In this connection the perforated core tube is formed in such a way that at both ends it comprises two sections which are impervious to fluids. The object of these sections is to prevent a short circuit between the non-filtered and the filtered fluid material if hollow spaces form in the chamber as a result of the filter materials being compressed. 
     The porous peripheral walls may be in the form of support layers known for deposition filtering, in particular the pebble-like bulk material deposition filtration process (DE-PS 32 04 120). Within the scope of the invention, however, porous peripheral walls formed from a semi-permeable filter layer, a filter membrane, non-woven filter material and/or a combination thereof may be provided on the hollow-cylindrical chamber or chambers. In order to achieve the possibility of using the filter element according to the invention in a manner which is as universal as possible, it can be attempted for this purpose to form the filter element in such a way that flow can be either forward from the exterior inward or from the interior outward. In order to enable the filter element to adapt to flow either inwardly or outwardly it is advantageous if the two porous peripheral walls of each hollow-cylindrical chamber have an essentially identical structure and identical pore diameters. 
     The invention thus provides a filter cake deposited in a hollow chamber between porous supporting layers, and such filter cake material being held captivated therein. The flow or movement of the filtering material within the hollow chamber can be easily reversed, without requiring a complete removal of this material from the hollow chamber. This is in contrast with the disclosure of DE-OS 38 02 816, where it was necessary to physically remove the filter material itself from the chamber in order to wash it, or alternately, to regenerate it. 
     Other features and advantages will hereinafter appear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described in further detail in the following with reference to the drawings, wherein: 
     FIG. 1 shows a filter element according to the invention in the form of a (single component) filter cartridge, equipped with only one hollow-cylindrical chamber, partially in axial section. 
     FIG. 2 shows the filter element according to FIG. 1 in section along the line A-B in FIG. 1, the medium to be filtered being assumed to flow in the direction from the outside radially to the inside. 
     FIG. 3 shows a dual component filter element according to the invention, provided with two coaxial chambers, in a type of illustration corresponding to FIG. 2, the medium to be filtered being assumed to flow from the outside radially to the inside. 
     FIG. 4 shows a section A-B through a filter element according to FIG. 1 with the assumption that the medium to be filtered is flowing from the inside radially to the outside. 
     FIG. 5 shows an illustration corresponding to FIG. 4, of a dual element according to the invention with the assumption that the medium to be filtered is flowing from the inside radially to the outside. 
     FIG. 6 is a fragmentary longitudinal section of the filter element of the invention, showing the filtration-active substances from a disassociated filter cake, as they would appear during reverse flow, during &#34;in situ&#34; washing out, or &#34;in situ&#34; regeneration of the filter element, and 
     FIG. 7 is a view similar to FIG. 6, but illustrating the filtration-active substances during actual filtration and following initial contact by the fluid being filtered, wherein there has been formed on the core tube 12, a filter cake, and there exists a space 22 above the cake, resulting from a compaction of the filtration-active substances, and migration of the components of the filtration-active substances which has resulted from the fluid flow. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The examples illustrated are filter elements in the form of filter cartridge, in particular deep bed filter cartridges 10. These deep bed filter cartridges 10 comprise a filter element support frame 11 which comprises a perforated core tube 12, a perforated support casing 13, a completely closed or impervious upper end wall or closure cap 14, bearing a guide element, and a lower impervious end wall or closure cap 15 which has a central opening to which an adapter 16 is connected. In the examples illustrated the hollow space formed between the core tube 12, the support casing 13 and the two closure caps 14 and 15 constitutes one hollow-cylindrical chamber 17 (FIG. 2 and 4) or two hollow-cylindrical chambers 17a, 17b disposed coaxially with respect to one another (FIG. 3 and 5). Each of these chambers 17, 17a, 17b is delimited at the inner periphery thereof and the outer periphery thereof by a peripheral wall 18, 19, 20 which extends over the entire axial length of the chamber 17, 17a, 17b in each case. These peripheral walls 18, 19, 20 comprise respectively outer, inner and intermediate porous, tubular wall members of the filter element, and are connected to the closure caps 14 and 15 on the inner side thereof in a manner such that they are sealed against flowable media, such that the hollow-cylindrical chambers 17, 17a, 17b are sealed on all side and can be flowed through in an essentially radial manner through the porous peripheral walls 18, 19, 20. In the examples given in FIG. 2 and 4, the outer peripheral wall 18 of the chamber 17 abuts against the inner side of the support casing 13 and the inner peripheral wall 19 abuts against the outer side of the core tube 12, facing the hollow-cylindrical inner space. In a corresponding manner, in the examples in FIGS. 3 and 5, the outer peripheral wall 18 of the outer chamber 17a abuts against the inner side of the support casing 13 and the inner peripheral wall 19 of the inner chamber 17b abuts against the outer side of the core tube 12, whilst a separating wall is disposed as a peripheral wall 20 common to both chambers 17a and 17b between the two latter chambers. The peripheral wall 20 may likewise be supported by a support casing. 
     The peripheral walls 18, 19, 20 may be formed in the manner of chemically, thermally and mechanically resistant support layers, which contain 20 to 50 weight percent (in relation to the dry fibre structure) of polyolefin fibres with a fibre length of 0.8 to 1.2 mm., preferably polyethylene fibres or polypropylene fibres. Porous, wet-resistant support layers of this type are known from DE-PS 32 04 120, for example, for the deposition of gravel or pebble-like bulk material filter cakes. Other structural possibilities can also be considered, however, for the porous peripheral walls 18, 19, 20, for example in the form of filter layers, filter membranes, and/or a combination thereof, of which the pore diameter is adapted to the filtration operation to be performed in each case, in such a way that they retain a fraction of particles which are coarse to a greater or lesser extent, whilst fine particles are retained in the deep bed filter 21 disposed in the chamber 17 or in the deep bed filters 21a and 21b disposed in the chambers 17a and 17b, respectively. 
     The deep bed filter cartridges 10 may be formed in order that they accommodate flow in only one direction for the filtration process, optionally from the outside to the inside (FIGS. 2 and 3), or from the inside to the outside (FIGS. 4 and 5). In such a case the pore diameters of the peripheral walls can be arranged in such a way that they are selected so as to decrease in size from the input side to the output side. If it is desired to construct a deep bed filter cartridge in order that it can accommodate flow from either the outside or the inside, depending on the case, then the peripheral walls 18, 19, 20 can have essentially the same porosity. 
     In the examples illustrated the deep bed filters 21, 21a, 21b mounted in the chambers 17, 17a, 17b are formed by regenerable, filtration-active substances which have both a particulate and a fibrous structure. These filtration-active substances can be deposited or collected on the porous peripheral walls, on the discharge side in each case, of the chambers 17, 17a, 17b in the manner of filter cakes by means of the medium to be filtered flowing radially through the chambers 17 or 17a and 17b respectively. Since the bulk material-like mixtures of filtration-active substances comprise finer and coarser particles as well as fibre particles of larger and smaller lengths in the examples illustrated, i.e. in all, components having different densities, charges, fibre lengths, sizes and geometries, the fine particles and fibres are rinsed by the medium or fluid to be filtered, flowing through the chambers in the flow direction, i.e. towards the discharge side, and form a structurally dense yet porous layer on the wall on the discharge side, whilst the coarser particles or longer fibres are not rinsed to such an extent and form a correspondingly more porous layer. There thus results a deep bed filter 21, 21a, 21b of which the pore diameters decrease as the thickness increases and is thus able to deposit impurities fractionally and counteract an early blockage. For flow towards the deep bed filter cartridge 10 from the outside to the inside, FIGS. 2 and 3 show the manner in which the coarser particles and longer fibres of the mixture of filtration-active substances remain in the outer area of the deep bed filter 21, 21a, 21b in each case, whilst, in the inner area of the deep bed filter 21, 21a, 21b, the intermediate spaces between the coarser particles are filled by the fine particles and short fibres. 
     For a deep bed filter cartridge 10, which in the filtration process is essentially flowed through from the outside to the inside, FIG. 3 further shows that the inner hollow-cylindrical chamber 17b contains a filter member 21b which is totally formed of particles which are finer and fibres which are shorted than the deep bed filter 21a in the outer chamber 17a. In both deep bed filters 21a and 21b during the filtration process, however, the above-mentioned deposition of the fine particles and short fibres occurs in the radially inner area of the deep bed filter 21a or 21b respectively. Conversely, FIGS. 4 and 5 show deep bed filter cartridges 10 towards which the medium to be filtered is to flow from the interior. In such a case, the fine particles and short fibres are in each case deposited on the inner side of the outermost peripheral wall 18 or 20 of the chamber 17 or 17a, 17b respectively. In the example shown in FIG. 5 the filtration process employs flow generally from the interior to the exterior; the deep bed filter 21b disposed in the inner chamber 17b comprises coarser particles and longer fibres than the deep bed filter 21a disposed in the outer chamber 17a. 
     For flushing back, flow in the deep bed filter cartridge 10 is reversed, i.e. the flow direction is opposite to that for the filtration process. The mixture of filtration-active substances is treated inside the respective chamber with the rinsing or regeneration medium. The particles or impurities washed out during the flushing back process, or other particles absorbed by the deep bed filter during the filtration process, are rinsed and discharged through the peripheral chamber wall 18, 19, 20 on the discharge side in each case during the flushing back process. The regeneration of the filtration-active substances forming the respective deep bed filter 21, 21a, 21b in each case occurs in a corresponding manner. 
     In FIG. 6 there is illustrated a fragmentary longitudinal section of the filter element of the invention, with like reference numerals having been assigned to components similar to those of FIG. 1. In particular, there is shown the support tube 12, a perforated support casing 13, and closure caps 14 and 15, the latter having an adapter 16 connected thereto. The deep bed filter bulk filling material 21 is shown as it would appear during reverse flushing of the filtration-active substances, as by washing with hot water and/or a mixture of hot water and the fluid being filtered, flowing in the direction of the large arrows, i.e. opposite the direction of flow of the fluid during normal filtering operation. This figure also depicts the step of regeneration of the filtration-active substances, as by forcing steam and/or a chemical substance, such as a solvent, through the filtration-active substances, also in the direction of the large arrows. 
     The filtration-active material, when initially introduced into the chamber or hollow space between the core tube 12 and support casing 13, is dry, and loosely packed and bulky in composition, being relatively voluminous because of air beads (not shown) which adhere to the fibres and/or particles. These air beads maintain a relatively large air spacing between the particles/fibres when the latter are in this loose, uncompacted dry condition or state, and dissolve in the fluid to be filtered. The air beads are flushed away by the fluid when filtering commences. 
     In contrast, FIG. 7 shows the fibres and/or particles of FIG. 6 having migrated under the action of fluid flow during filtering, in a radially inward direction, with the larger or more massive particles/fibres being retained near the upstream side (outside) wall 18 of the filter, and the smaller or denser particles/fibres having migrated toward the inner wall 19 of the chamber. The compaction which occurred upon the particles/fibres being wetted by the fluid is shown in this figure, leaving a space 22 in the chamber. Also, following migration, by virtue of the flow of the fluid being filtered there exists a radial density gradient, with the more porous material lying outside of the less porous material. The drawing clearly shows the &#34;cake&#34; which has been formed on the wall 19. The material having the larger pores or spaces is indicated diagrammatically in FIG. 7 by the circles to the right of the figure, near the casing 13, with material of medium density being represented by the smaller circles, and the high density material being indicated by the dots adjacent the tube 12. This disposition of the filtration-active substances is a result of the compaction thereof in the direction of flow. There is thus established a heterogeneousasymmetrical structure to the filter cake, following the establishment of the initial fluid flow, and a free space 22 created as a consequence of compaction of the material resulting from such flow. The cake is characterized by a solid, channeling-resistant matrix that forms out of the fibre/particle filtration-active material. During the washing or regeneration, the cake is disassociated, and heterogeneously loosened and cleaned, as in FIG. 6. 
     Stated in somewhat different terms, the porous cake formed in FIG. 7 has a non-uniform filtration density along the direction of flow of the filtrate, caused by flow-induced migration of the dissimilar particles and/or fibres of the filtration-active substances with relation to particle/fibre length and size. Such filter cake has structural integrity as long as the flow of the filtrate is in one direction. The cake disassociates in response to washing, i.e. a reverse flow of the filtrate or a mixture of the filtrate and hot water, or by regeneration, using steam and/or chemicals, such reverse flow releasing trapped particles which can be thereby flushed out of the filter cartridge while the disassociated cake is still contained in the chamber. The material of the cake is thus capable of being repeatedly washed, and/or regenerated, by such reverse flow, without the need to remove from the chamber, the material of which the cake is constituted. 
     The following substances can be taken into consideration as filtration-active substances in the deep bed filters 21, 21a, 21b, for example, including: cellulose acetate fibres, perlite, diatomite, gravel or pebble-like bulk material, synthetic or natural fibres, freshly precipitated silicic acid, PA-staple fibre, PP-pulp fibres, PE-staple fibres, PE-fibres, PE-pulp fibres, cellulose fibres, and other substances. In addition, the deep bed filters may be mixed with adsorption agents, for example carbon, activated carbon, zeolite, TiO 2 , Al 2  O 3 , SiO 2  with irreversibly bound cationic and anionic groups (e.g. polyamid-amine-acrylate, carboxyl-base, resin particles, microcrystalline cellulose or cellulose with functional groups, cationic starch). 
     Finally, substances which are necessary or advantageous for special filtration operations, for example substances causing stabilization of the medium to be filtered, such as polyvinylpolypyrrolidone, can be added to the deep bed filters 21, 21a, 21b. If substances of this type are used during the filtration process, they can be mixed with the medium to be filtered which is absorbed in the interior of the chamber 17 or chambers 17a, 17b respectively of the deep bed filter 21 or 21a and 21b respectively. 
     Variations and modifications are possible without departing from the spirit of the invention. 
     Each and every one of the appended claims defines an aspect of the invention which is separate and distinct from all others, and accordingly it is intended that each claim be treated in this manner when examined in the light of the prior art devices in any determination of novelty or validity.