CA1186638A

CA1186638A - Filter and related apparatus

Info

Publication number: CA1186638A
Application number: CA000421871A
Authority: CA
Inventors: Rodney I. Frost; Max R. Montierth
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1982-02-22
Filing date: 1983-02-17
Publication date: 1985-05-07
Also published as: EP0089127A1; DE3370286D1; EP0089127B1; US4419108A; JPS5976516A

Abstract

ABSTRACT

Filtering capacity of a honeycomb filter having a plurality of cells formed by a matrix of thin, porous intersect-ing walls and used for removing solid particulates mixed in fluids is improved by providing a porous outer wall around the thin walls through which the fluid is also filtered.
particulate barrier is provided between the outer wall and a conduit carrying the contaminated fluid to and filtered fluid from the filter which allows the fluid to flow along and through a substantial portion of the porous outer surface of the filter while preventing contaminated fluid from bypassing the filter.
The carrier is preferably formed near an inlet or an outlet end face of the filter and those cells which are located around the periphery of the end faces are preferably open at that same end face and closed at the remaining end face to assure fluid flow across the porous outer wall.

Description

I
Frsst-Mon~ierth 15 6 IMPROVED FILTER END RELATED APPARATUS

BACKGROUND OF THE INVENTION
. . _ -The inverltion relates to apparatus for filtering solid particulate matter from fluids and, it particular, to improved . filters formed from thin, porous walled honeycomb structures and means for mounting the jilters for advantageous operation.
The removal of so' id particulate Metro from fluids (gases or liquids) in which they are mixed is typically accom-polished by means of filters made from solid materials formed into articles or masses and having a plurality ox pores extend-in through them (which may be interconnected) owe a small cross-sectional size such that the solid materials are both permeable - to the fluids and capable of restraining most or all of the solid particulate matter carried by the fluid from passing through the article or mass. Such pores constitute what is towered "open porosity" or "accessible porosity" . The minimum crosscut oval size of some or all of the pcires can be larger Han the size of some or all of the particulate q to be filtered, jut only to the extent that a' 1 or significant desired amounts of sufficiently large partlculates become trapped on the inlet o surfaces and/or within the pore during the transit t of the fluid through the article or mass.
A pending Canadian application Serial No. 380,875, filed June 30, 1981, assigned to the assignee of this application, describes honeycomb filters preferably formed from extruded and sistered ~'~.`' 631~3 ceramic materials which may be used or removing carbonaceous particulate from diesel engine exhaust gases and for other nigh temperature rlllid filtering applications. The filters are of honeycomb structure Mach comprising a matrix of thin, porous 5 interconnected ~tJalls which doffer inlet and satellite end faces on opposing outer surfaces of the filter and a plurality of hollow passages or cells which extend through the f titer body between the inlet and outlet end laces., The thin, porous cell walls may Norm the outer surface of the filter body between the end 10 faces but more typically" a somewhat thicker, smooth continuous surface or skin is provided surrounding the cells or strength, uniform outer dimensioning, etc. One end of each of the cells is bloclced to form inlet and outlet cells, the inlet group of cells being blocked near the outlet: end face and the inlet 15 group of cells being blocked near the outlet end face The opposing end of each of the cells remains open at the opposing end face The inlet and outlet cells are alternated so as to adjoin one another and share in common the thin porous walls which define each of the cells. A contaminated fluid introduced 20 under pressure kiwi the inlet end face passes into the f if ton body through the inlet cells and it forced through the thin, porous wall r which trap the solid particulate present in the fluid, and into ad joining outlet cells through which the now cleansed fluid exits the idler body. Particles are dew 25 posited on the thin wall surfaces of the inlet cell or are trapped in the pores within these walls.

The described honeycomb filters are typically post-toned for use in a housing or can which is installed across or a a component of conduits transporting contaminated fluid to and filtered fluid from the filter. A seal is fished along 5 the outer longitudinal surface owe the filter and an inner surface of the surrounding conduit structure to channel contami noted fluid to the inlet face and filtered fluid from the outlet face and to prevent the contaminated fluid from bypassing the , filter body. Means used to form the sea may also support and 10 fix thy position. of the filter with respect to the conduit.
Typically, means are provided at either end of the filter body or along the longitudinal outer Ursa extending between its inlet and outlet end faces both to hold the body in position within the supporting conduit structure and to provide the 15 aforesaid seal. For example, a seal may be formed about the dispel engine exhaust spas filter in the manner described in the aforementioned Canadian application Serial No. 380,875 by providing flange-like mounting members or other comparable mounting members protruding from the inner surfaces of the surrounding I`

9~3 conduit structure which are compressed against the outer edges of the filters opposing inlet and outlet end faces. Seals are sometimes also wormed by packing a suitably impermeable material into a gap foxed between the longitudinal outer surface of the filter and the support structure, either at the ends of the inter or along a substantial portion ox the outer longitudinal surface of the filter, between the filter and the conduit structure so as to provide both the required support and a seal in a single manufacturing step. In each case, the seal thus formed prevents the flow of the fluid along any appreciable length of the outer surface of the filter extending between its inlet and outlet faces. An additional problem is created by the first described sealing method in that pressing flanges, O-rings or the like against the end faces tends to cover and bloc the cells located at the port-phony of the end faces reducing the effective volume of the filter body and, in a filter used with a hot fluid, to create : radially oriented thermal gradients giving rise to possibly detrimental thermal stresses within the filter.

OBJECT AND SUMMARY OF TOE INVENTION
It is an object of the invention to maximize the lit-- toning surface area ox a solid particulate filter of honeycomb structure by using all or substantially all of its longitudinal-: 25 lye extending outer surface as a filtration surface.
It is another object of the invention to optimize the operation ox a filter of honeycomb structure by providing I

means which prevents particles in the fluid from flowing past the filter but which does not block any appreciable number of cells of the filter near the periphery of it end faces.
It is yet antiwar object or the in~en~lon to mini-mite the creation of axially oriented thermal gradients in solid particulate filter of honeycomb construction which it used to filter hot fluids.
According to the invention, these and other objects are accomplished by providing a solid particulate filter of honeycomb structure hiving a matrix of inure porous intersecting thin walls defining an inlet end face and an outlet end face of the jilter and a multiplicity of hollow passages or cells extending longitudinally through the filter between the two end faces, and a porous outer wall extending between the two end feces and around the matrix of thin walls ~ormincJ a Lange tudinal outer surface of the jilter. The thin walls and outer wall each contain interconnected internal open porosity of a volume and size sufficient to enable the fluid to flow completely across the thin walls and outer wall while restraining at least a significant portion of the particulate from Wang : completely across the thin walls or outer wall. The multiplicity of culls are divided into an inlet group each cell of which is closed near the outlet end face and open at the inlet end face and an outlet group each cell of which is closed near the inlet end race and oxen at the outlet end face The filter it positioned within conduit moans which channel contaminated fluid to and filtered fluid away from the filter. Sealing means, preferably a particulate barrier is provided between the long tudinally extending outer wall of the filter and an inn r surf face conduit means encircling the filter. This barrier prevents particulars in the contaminated fluid from flailing unrestricted S lye past the filter end mixing with the filtered fluid being carried azalea from the filter by the conduit means According to one important aspect of the invention, the barrier is sufficiently narrow where it contacts the filter to allow fluid Jo flow along and through a substantial pyre of the exterior surface of the outer wall According to one important aspect of the invention, the barrier contacts the filter along its outer longitude-net surface in the vicinity of one of its two end faces to maximize outer wall filtration surface area.
lo according to another important feature of the invent . lion, all or substantially all of the cells around the periphery of the end races are blocked at their ends opposite the one end face where the sealing moans are located. This arrangement -I maximizes fluid flow through the outer surface and the port-furl located cells and minimizing the generation of radially oriented thermal greediness within the filter where a hot fluid is being filtered.
According to another important aspect of the invention, the barrier is essentially impervious to the fluid thereby main twining a pressure drop across the filter fostering fluid flow there through.
According to yet another important feature of thy in-mention, moans may alto be provided bitterly the conduit means and the filter for restricting the movement of the filter in reloan to the conduit mean. These additional mean do rot impede the flow of fluid along the outer longitudirlal surface 5 of the inter According to yet another faker of the invention, the particulate barrier may Allah be fabricated so as to restrict or minimize the movement of the f titer with respect to the con-d us t means ,.
l o A preferred use of the filter is to remove particulate from diesel engine exhaust gases. In such an application, the filter is located within an exhaust gas conduit interposed across the exhaust gas path leading from the engine, The invention also includes the improved method ox Jo 15 filtering particulate from a fluid passed through a honeycomb filter by additionally filtering the fluid through a substantial portion of the outer wall of the filter body.

The various above identified an other aspects of the invention will be better understood by reference to the accompanying drawings in which it 1 is a longitudinal view of a conduit partially broken away to reveal a contained filter with its longitudinally extending outer wall partially broken away TV reveal cells 25 along the peripheral edge of the if ton;
Fig. 2 is a cross-sectional view of the apparatus of it Fig. 1 along the lines 2-2 depicting the inlet end face of the filter body;
Fig 3 is a longitudinally sectioned view of the lit-ton body of Figs. 1 and 2 along the lines 3-3 d plating fluid S flow through the filter body and its outer wall;
Fig. 4 is a diagrammatic view, similar to that of Fig it of an alternate embodiment of the present invention depicting a longitudinally sectioned length of contained filter with partially broken awry outer wall;
Fig. 5 is a cross-sectional view of the apparatus of Fig. 4 along the lines 5-; depicting the inlet end face of this filter body embodiment;
Fig. 6 its a diagrammatic view, similar to those of Figs 1 and 4, showing yet a third filter apparatus embodiment according to the present invention;
Figs 7 and 8 are diagrammatic views of other types of conduits with which the invention may be used; and Figs. and 10 are diagrammatic views of yet other embodiments of the invention having particulate barriers formed by mutually contacting surfaces of a filter and conduit.

DETAILED Inscription OF TIE INt7ENT::ON
Figs. 1 through 3 depict a first exemplary preferred embodiment of the invention comprising housing or can 20, a filter 30 of honeycomb structure and sealing means in the form of a particulate barrier 40 byway the conduit 20 and filter 30~ The can 20 may be of unitary construction but desirably it it s~tioned to allow easy access to the filter 30. the can 20 comprises two parts, 21 and 22, ore by substantially identical filter holding sections 23 and 23 ' and conical sea-lions 24 and 25 respectively joining a fluid inlet connector 26 and a flute outlet connector 27 to the filter holding portion 3 and 23' and Managua flanges pa . The ends 26' and 27' or the fluid connectors 26 and 27 have been sectioned for compactness in Fig. 1 but would connect with upstream conduit carrying contaminated fluid to and downstream conduit carrying filtered fluid from the can I The flanges 28 may be mechanic gaily fastened together (ego by bolts and nuts not shown) to keep the conduit means 20 properly assembled for use but to alto allow it to be unfastened for replacement of the filter : 30 or fixedly joined by welding rivets or the like for disposal of the can 20 and filter 30 after use. The filter 30 is of honeycomb structure having a matrix of thin porous inter sooting walls 31 defining an upstream "inlet" end face 32 and a downstream outlet" end face 33 and a plurality of hollow passages or cells 34 extending substantially longitudinally therewith filter 30 between the end faces 32 and 33. A
porous outer wall or skin 35 extends longitudinally between the end faces 32 and 33 and around the matrix of thin walls 31. Besides providing a smooth outer surface to the filter 30, the skin 35 may be formed thicker than the thin wall 31 for strength. The exterior surface aye of the skin 35 forms the longitudinal outer surface of the filter 30. According to the invention, the thin walls 31 and skin 35 each have 63~3 interconnected open porosity of a size and volume sufficient to allow the fluid to flow completely across the thin walls between adjoining cells and across the slain 35 between the interior and exterior of the filter I (en vice versa) and, S preferably, completely through the thin walls 31 and skin 35 in their longer domination and to prevent at least a significant portion of the solid particulate in the fluid from passing either completely across or completely through the thin walls 31 or skin 35 in any direction The portion of particulate desired to be trapped will vary with the filtering application and may even be less Han so%. Filter efficiency Jay by own-trolled by a proper selection of open porosity and wall thick-news. The skin 35 has been partially broken away near each of the end faces 32 and 33 to reveal some of the cells 34 along the periphery of the end faces 32 and 33. Plugs 36 or other suitable means are provided for blocking covering, sealing or otherwise closing the peripherally located cells 34 near the inlet end face 32~ Fig. 2 depicts the upstream facing inlet end face 32 and indicates by shading the plugs 36 formed in the cells at the periphery of that end face as well us in other selected cells 34 at that end face. Each of the cells 34 is preferably sealed at only one of its two ends; the pattern of plugged cells at the end face 33 is therefore the reverse of the plugging pattern at end foe 32 depicted in 25 Fig I This is better seen in Fig. 3 which shows the filter body 30 longitudinally sectioned along the line 3-3 ox Fig and the plugs 36 formed in one end of each of a column of culls 34 Those cells 34 closed i e . plugged ) at the outlet end face 33 and open at the inlet end face 32 are referred to as " inlet' cells. Those cells 34 open it the outlet end face 33 and cloyed at the inlet end face 32 are outlet culls.
Roaring now to Fits . 1 and 3, a corltamin~ted f lurid, represented by the arrow 37 it introduced through the inlet pipe 26 and is passed through the filter 300 Filtered fluid, represented by the arrow 38 r is transported away frill thy filter Cody 30 and can 20 by the fluid outlet pipe 27, The outer diameter of the filter I is less than the inner diameter ox the filter holding sections 23 and 23' of the can 20 forming a gap 39 between the inner surfaces aye and aye' of those sections and the exterior surfaces aye of the skin 35~ The contaminated fluid is introduced to the inlet end face I and a portion of the fluid represented by the arrow 37b enters thy filter 30 through those interior cells 34 which are not plugged at the end face 32 (i.e. the "inlet cells). A portion of contaminated fluid indicated by the arrows aye also flows passed the end face 32 and along the gap 39 between the skin 35 and filter holding sections I and 23' of the con 20. Sealing mean on provided between the can 20 and filter 30 near it outlet end face 33 prevents the passage of the contaminated fluid passe the filter body 30 and its mixture with the filtered fluid 38 being collected in the conical section 22 fox removal through the outlet pipe 27. The sealing means 40 extend con-tenuously around and between the nor Sirius aye and 23 a ' 118~;63B

of the isle holding section 23 and 23 ' and the exterior surface aye of the filler skin 35. The barrier 40 is essentially impermeable to the solid particulate in the contaminated fluid to be removed by the jilter 30 but may, it desired, be 5 permeable to the fluid The contaminated fluid aye in the gap 39 enters to skin 35 and flows across its i~hickrless through its interconnected open porosity into the peripherally located outlet cells passing through those cells, a indicated by the arrows 38b, and from the filter 30. A portion of the fluid in the skin 35 may also exit the filter 30 through the skin 35 a-t the outlet end face 33, as is indicated by the arrows 38c or pass through the sealing means 40 if fluid permeable. Fluid 37b in the inlet cells passes through and across the porous, thin walls 31 exiting the filter through adjoining and/or : 15 neighboring outlet cells, as is partially represented by the arrows Brie or exits the filter on through the portions of the porous thin walls 31 extending between the plugs 36 at the outset end face 33, as is also represented by the arrows 38c.
The filtered fluid 38 (i.e. aye and 38c) passing out of the 20 filter body 30 through the end face 33 is collected by the conical conduit section 22 and channeled into the outlet pipe 27 for removal.
Preferably, the Swahili means 40 contact the skin 35 of the filter 30 near one of the end faces I or 33. Where the I cells 34 near the periphery or edgy of the end faces 32 or 33 are all or su~stantial7y all closed near one end face as is preferred t the sealing means 40 are preferably located near the I -i63~3 remaining end face. In Yoga he cells 34 located at the periphery of the end faces are sealed near the inlet end face 32 and the sealing means 49 has been locked near the outlet end face 33 of the filter OWE
Figs. 4 and 5 depict in a more simplified diagrammatic view, an alternate configuration of the embodiment of the invent lion depict Ed in Figs 1 3 preferred Jo maximize fluid flow through the peripherally toga Ed cells and whereby reduce possible thermal gradients in the thin walls. Again, a can 20, a filter aye and sealing means 40 between an inner surface aye of the can and the exterior surface aye of the filter skin US
have been provided. The sealing means I aye now located in the vicinity of the inlet end face 32 of the filter body aye.
The skin 35 of the filter aye has again been partially broken away to reveal some of the cells 34 along the periphery of the end face 32 and 33 which have now been blocked with plugs 36 or other suitable means at the opposite, outlet end face 33.
Fig. 5 depicts the inlet end face 32 of the filter aye of Fig.
4 and reveals the inlet cells opera at the depicted inlet end 20 race 32 and closed at the outlet end face 33~ locked around the periphery of the end face I and interspersed with out t cells closed with plugs 36 or other suitable means at the inlet end face 32 and olden at thy outlet end face 33. As is I disclosed in the U.S. Patent No. 4,417,908, more collective inlet cell than outlet cell thin wall surface area has been : provided to improve the capacity and operating life owe the - 13 ;

US I

~8~;63~3 filter by providing more inlet Han ou~lek cell 34~ Contain axed fluid flow and filtered fluid flow are again indicated by arrow 37 and 38, respectively. Contaminated fluid 37 is brought to the upstream, inlet end face 32 of the filter aye and passes into the filter aye through the inlet cells (i.e.
those cells open at the inlet end face 32~ A portion of the contaminated fluid (37b) passes into thy non-peripherally located inlet cells and flow across their thin porous wills 31 into adjoining outlet cells and through the longer dimension of lo the walls 31 into adjoining or nearby outlet cells exiting the filter body through the outlet cells (as is represented by the lined arrows 38b3 or thin walls 31 at the outlet end face 33 (as indicated by arrows 38c). A portion of the con-laminated fluid 37c enters the peripherally located inlet cells, passes across the porous skin 35 into the gap 39 between the exterior surface aye or the skin 35 and the inner surface aye ox the can 20. This filtered fluid, represented by the lined arrows aye, travels through the gap 39 and pat the outlet end face 33. Some of the contaminated fluid 37c and Z0 37b in the peripherally and non-peripherally located cells passes through the skin 35 and thin walls 31 along their longer dimensions and out thy no face 33, as is represented by the lined axr~ws 38c. The filterer fluid 38 (i.e. aye, 3~b and 38c) is collected by the downstream portion of the can 20 and conducted away from the filter aye.
The scaling means 40 may be sufficiently strong and rigid to center and immobilize the filter body 30 or aye within the can 20. However, additional means such as the pylons 41 indicated in Fig. 1 may be provided between the outer wall 35 of the filter 30 and the inner surface of the filter holding sections 23 and 23' to laterally or laterally and longitudinally fix the filter 30 in the can 20. As can be better seen in Fig 2, the pylons 41 occupy a very small portion of the annular gap 39 between the filter body 30 (or aye) and filter holding sections 23 and 23^ and do not substantially interfere with the flow of the contaminated fluid aye (Figs. 1-3 and 6) or filtered fluid aye (Figs. 4 5) along the exterior surface aye of the skin 35. Alternatively or additionally, longitudinal movement of the filter 30 (or aye) within the can 20 may be further limited by the provision of other suitable support means such as tabs 42 (depicted in phantom in Fig. 1) which pro true from the inner surface of the can 20 and contact the end face(s) 32 and/or 33, again without covering any significant number of cells.
Fig. 6 depicts in a simplified diagrammatic view, yet another configuration of the invention. In this embodiment, sealing means 40 are located near the outlet end face 33 of a filter 30b and all cells 34, including those located around the peripheral edge of the end faces 32 and 33, are also sealed near the outlet end face 33. This embodiment is concerned with maxim mixing Jo 63~3 ho capacity of a filter of given geometry and both the inner and outer sides aye and 35b of the skin 35 and the two opposing exposed surfaces of each thin wall 31 are used as a filtration surface. Fluid entering the skin 35 traveler along its Lyon through it interconnected open porosity Jo the outlet end face 33 and/or into the interconnected thin porous walls 31 and along their lengths to the outlet end face 33. Similarly 1ui~ entering the cells 34 passes into thy thin walls 31 and travels along their lengths past the plugs 36 and exits thy 10 filter 30b at the outlet end fact I This embodiment produces a very high initial . back pressure. over, the extensive filtering surface provided minimizes the rate of increase in back pressure due to solid particulate build-up.
All the conduit means 20 depicted thus far in describe lo in the invention have been tubular, extending substantially the length of the Jilter body 30 (kiwi or 30b) and surrounding it in close proximity, The term conduit means as used herein in referring to the invention is, however, of much broader scope. For example, the conduit means may comprise a first Z0 reservoir 60 for holding a contaminated fluid and a second reservoir 61 for collecting filtered fluid. The reservoirs are separated by a planar conduit t means or wall 50 into which the filter 30 or aye of Figs. l through 3 and 4 through S, - respectively is inserted as, for example! is depicted in Figs.
I 8 and 9, respectively Each filter aye and 30 it mounted within the ox nine 51 and with respect to planar conduit means 50 so that a significant portion or its spin 35 extends into Lo -;j3~3 the filtered fluid reservoir 61 (Fig. 8) or the contaminated fluid reservoir 60 I Fig . 9 ) .
In Fig. 8, the contaminated fluid aye and 37b enters the filter aye only through the inlet end face 32~ Again, all of the peripherally located cells are preferably sealed at the outlet end face 33 to form inlet cells and the remainder of the cells 34 are sealed at one of their two ends to form an arrangement of inlet and outlet cells. One such exemplary arrangement is depicted in Fig 5 buy there is virtually an infinite variety of plugging patterns which may be used Others are depicted, or example, in U.S. Patent 4,276,071 and in U.S. Patents Nos. 4,420,316; 4~417,908 and 4,416,676.

The contaminated fluid is filtered by passing from the port-furl located inlet cells trough the skin 35~ as is repro-sensed by the lined arrows aye, and across and through the thin walls 31 from the inlet to the outlet cells and through the outlet end face 33, which flow it represented by the lined arrow byway A portion of the filtered fluid may also pass from the filter 30 at the outlet end face 33 through the porous skin 35 and/or thin walls 31, as is represented by the lined arrow 38c. In Fig. 9 contaminated fluid inters the filter body 30 at the inlet end face 32 through the inlet cells and through the porous skin 35, as is represented by the lined arrows 7b and aye, respectively. filtered fluid exits the filter body 20 at the end face 33 through peripherally located and other outlet cells, as is represented by the lined arrows ~136638 38b and through the thin wills 31 and/or spin 35, as is wrapper sensed by the lined arrow 38c. If desired the filter 30b of Fig may ox substituted or the filter 30 in the embodiment depicted in Fig. 3. Barrier means have been omitted from both Figures for clarity In addition to the separate and distinct sealing means pa depicted in Fits. 1 through 6, it is envisioned that the invention may be used by forming a seal between the inner sun-face of the encircling conduit mean and the outer wall of a filter body. For example, a filter Cody may be provided with an integrally formed or attached protruding surface near one of its two end faces such as the protruding portion 60 of the outer surface 35' located near the inlet end faze 32 of the filter body aye' of Fig. or the truncated conical surface 61 located near the outlet end face 33 of the filter body 30 ' in Fig. 10. The inner surface I of an opening 51' through a planar conduit means 50' (Fig. g) and an inner surface 64 of a tubular conduit means 20' (Fig. 10~ are also suitably contoured to contact ably mate with the protrusions 60 and 61 of Figs. 9 and 10, respectively, provided to the filter bodies aye' and 30' and to form a seal there between which prevents contaminated - fluid from flowing past either jilter body I ' or aye' and into the filtered fluid. A pressure differential can be main twined between the contaminated and filtered fluids in Figs. 9 25 and 10 to keep the contoured portions 60 and 61 of the filters aye' and 30' centered and pressed against the contoured portion 63 and 64 of the conduit means So' and 20', respectively.

63~3 Alternatively or additionally, the surfaces 6Q, 61~ 53 and/or I may be coated with a f ill of suitable littoral to assure the formation of an adequate particulate barrier between 'eke conduit and filter.
S The descried apparatus may be fabricated f rum any materiels suitable it sufficiently durable, non-corrosive or chemically reactive, abrasive resistant, etch) for the filtering operation to be undertaken. Typically, the conduit moans may be fabricated from a conveniently formable or machine axle material such as metal, plastic, etc. Similarly, any of a variety of widely known materials and fabricating methods may be employed Jo provide suitable staling between the conduit means I or 50 and outer surface 35 of the filter body 30. The sealing means 40 may be such as to immobilize the filter body Jo 15 30 within the conduit means 20 and 50 or Jay be sufficiently pliable to allow some lateral and/or longitudinal movement of the filter body 30 with respect to the conduit means 20 and SO
In the latter case, additional support means such as thy pylons 41 of its 1 through 2, are desirably provided so as to main-lain the gap 39 bitterly the exterior surface of the filter skin and the inner surfaces of the conduit meals extending sub Stan-tidally along thy length of the filter to assure adequate space for fluid flow through and along the Quoter longitudinal surface of the fix ton. The matrix of thin walls 31 and porous skin 35 US of the filter may be formed from any of variety of materials including glasses, ceramics (typically crosstalk), metallic powders, resins or organic polymer, papers, textile ..abr1'cs (with or without fillers), etc. and various combinations there-of, such as cermets and glass-ceramic mixtures by a variety of methods depending upon the mutt selected. Honeycomb structures having the porous skin 35 and the kin porous inter-5 convected walls 31 necessary for preseason the invention arepre~erably fabricated from sinterable, finely divided particles Andre short length fibers of substances that yield a porous, sistered material after being fired to effect their sistering, especially metallic powders, ceramics, glass-ceramic, cermets, and other ceramic-based mixtures The sinkable materials can be formed into honeycomb structures by methods such as layering, described in U.S. Patents 3,112,184 and 3,444,~25, a pipe binding process wherein a large number of sinterable material pipes are bound together with sinterable materials to form a honeycomb structure or, preferably, by extrusion of : a plastically formable batch mixture of a sinterable material as is disclosed, for example, in U.S. Patents 3,790,654, 3,919,358, 4,008,033, and 4,364,888, assigned to the assignee hereof.

The honeycomb structure thus formed is fired to effect its tinkered condition as it disclosed, for example : in U.S. Patent 3~899,325. As desired, any suitable or convent tonal fugitive or combustible (burn-out) additive (besides volatizable plasticizer and binders used in the preparation of the formable mixture) can be dispersed within the formable and sinterable mixture so as to provide appropriate and adequate interconnected open porosity in the sistered material of the thin walls 31 and outer wall 35 of the filter body 30. Desirably, the thin walls 31 and outer wall US are formed monolithically by extrusion from the tame batch material in a single step with the interconnected open porosity extending between the thin walls 31 and outer wall 35.
The ends of the cells 34 may also be closed by plugging, covering or any other suitable technique and with any suitable material Preferably, plugs 36 are formed by charging plowable or plastically formable plugging material into selected cell ends at either or both end faces 32 and 33, in a manner as is disclosed in the aforesaid pending Canadian application Serial No. 380,875, and in published European patent application Serial No. 82/303724, Canadian application 405,931 and U.S. Patents Nos.
4,427,728 and 4~432,918, all assigned to the assignee ox this application. The referenced methods and apparatus may be utilized to plug green (i.e. dried but not sistered) or sistered honeycomb structures or other non-sinterable rigid honeycomb structures. The plugging material may then be allowed to dry, set or is sistered, etc. so a to form durable plugs 36 across the cell ends mechanically and/or chemically connected to the thin walls 31 forming the cells 34 and providing weals non per-Mobil to the solid particulate material being filtered.
A preferred use of the invention is as a diesel ox-hollowest gas particulate filtration system. The system comprises a tubular conduit means, or Cowan 20, such as is depicted in Jo 6~3~

jig. 1, which surrounds and holds the filter for mounting in the erlgine exhallst systernD The can 20 is similar to a oven tonal type emplaced for mounting catalytic converter honeycomb substrates in the exhaust systems of internal combustion engines, a is described in USE Patent 3~441~3~1s incorporated by refer-once t and can be fabricated in the manner described in that patent. Each filer body 30, aye or 30b is preferably formed from an extruded, swineherd ceramic honeycomb monolithic substrate which has been plugged with plastically formable an sistered ceramic materials. Extruded, ceramic honeycomb structures have in cordierite as its primary crystal phase, which is preferred for diesel exhaust particulate filtration and other moderately high temperature solid particulate filtering applications (approximately 1,OGO~C. or more) due to its low thermal expansion characteristics, may be provided in the manner described in the aforementioned Canadian apply Serial No. 380,875. Plugs 36 are formed from a material which has, in addition to the pro-piously recited characteristics of durability, chemical inert-news and/or non reactivity, etc., a coefficierlt of thermal 20 expansion which closely follows ( i.e. within about 10 parts per million) that of the honeycomb structure over the range of temperatures to which the plugs 36 and honeycomb strut Tory are exposed. Plug 36 may be formed from foam-typ~ ceramic cements which sinner and react into a primarily cordierite 25 crystal phase and which are thermally compatible with the aforesaid cordierit~ ceramic structures. These elements are described end claimed in U.S. Patent No. 4,297,140r - I

63~

filed July 3, 1980, which is assigned to the assignee of this application. A particular manganese-mag~esium composition of that foam-type cordierite Semite, which is preferred for use with diesel exhaust particulate filtering and other filtering applications hazing significant sodium ionic concentrations, as described in the aforesaid Canadian application Sexual No.
Roy As is described in Canadian application Serial No.
380,875 and U.S. Patent No. 4,297,140, the foam-type cordierite cement is used by charging a plastically formable batch of the cement into a previously sistered honeycomb structure and firing the structure and plugs to a temperature of about 1200C. to foam and stinter the cement oaring rigid plugs in the cell ends. Alternatively. a plugging material having a slight relative dimensional expansion with respect to a green, sinterable honeycomb structure after the plugging material and structure have been heated to a tempera-lure at which the structure is substantially sistered may be used, as is described and claimed in another U.S. Patent No 4~455,180, filed August 8, 1981 and assisted to the assignee of this application. Exemplary ;

compatible honeycomb structure and plugging material batch mixture compositions, which react to form primarily cordierite crystal phases when sistered and which may be used for diesel exhaust gas filtration, are described in that patent.
For diesel particulate filtering applications, the thin walls 31 are wormed in thicknesses or less than about lt.5 mm.

i' t (about 0~060 in o m1nimi~e filter volume and preferably be tweet about 9.25 an 0.76 mm. (about 0~10 and 0.030 in.). The outer wall 35 may lie within the same range of thicXne~ses at-though a greater thickness may be desired o'er the outer wall 35 than for the twirl walls 31 to strengthen the resulting filter. Open porosity of ho thin wall 31. and outer wall 35 is formed by pore having mean diameters of between about 1 and 60 microns desirably at least about 3.5 microns or more and preferably between about 10 and 50 microns. The volumetric open porosity of the thin walls 31 and outer wall 35 should also be greater than about US% of the wall bulk volume and is preferably at least about 40% or more to foster fluid flow through the longer wall dimensions. Volumetric open porosities greater than about 70% may result in walls to weak to withstand lo diesel exhaust operating conditions Useful transverse cross-sectional cellular densities are between about 10 and 300 cells/
inn (about I and 46~5 cells/cm.2~ and preferably between about 100 and 200 cells/in, 2 ( about 15 .. 5 and 31 cells/cm~ 2 ) .
Either of two types of sealing means may be desirably employed Boone the inner surface ox the can I and outer sun-face of the honeycomb jilter howdy 30. the first is a pliable, fibrous, ceramic-~ased material manufactured and supplied by the EM Corporation under the name Matt-mount'^ which expands with temperature upon first being heated to provide a constant pressure against the outer wall 35 o. the f titer The material may be installed by wrapping a narrow strip around the skin I

- I -of the filter 30 and witting the wrapped filter 30 into an appropriate filter hording section I or 23' of a can 200 The material may also be used to form the pylon support means I
previously described The structural integrity of the material it maintained up to a temperature of about 1200C. An alterna-live material is a heat resistant, fluorocarbon polymer coated, densely woven stainless steel mesh cord covered with a fiber-glass sleeve. Supplied under the brand name NovatemM by R & M
Industries, the material is widely used for the mounting of automotive catalytic converters end is presently supplied in bulk rolls of cord having a diameter ranging between .245 and ~330 inches (about 6 and 8 mm.). The cord is cut to length and jam fitted, either butted end to end or overlapped, to form an annular seal between the outer longitudinal wall 35 of the filter 30 Tao or 30b) and inner surface aye of the can I Positioning tabs 42 may also be provided, if desired, by welding appropriately formed steel members to the inner surface of the can 20~
While various embodiments of the invention and sup-gusted modifications thereto have teen described, it should be understood that other modifications could be made in the struck lure and arrangement of the described embodiments without de-parting from the scope of the invention which is more fully defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for filtering solid particulates from a fluid comprising:
a filter of honeycomb structure comprising:
a matrix of interconnected thin porous walls defining an inlet end face and an outlet end face and a multi-plicity of cells extending longitudinally between the two end faces, and a porous outer wall extending between the two end faces and around the matrix of thin walls and having an exterior surface forming an outer longitudinal surface of the filter, an inlet group of the cells each being open at the inlet end face and closed at the outlet end face, an outlet group of the cells each being closed at the inlet end face and open at the outlet end face, and the thin walls and the outer wall each containing interconnected open porosity of volume and size sufficient to enable the fluid to flow completely across the narrow dimensions of the walls and the outer wall and to restrain at least a significant portion of the particulates from flowing completely across the thin walls or the outer wall;
conduit means having an inner surface encircling the outer wall of the filter for transporting fluid containing the particulates to the filter and filter-ed fluid away from the filter;
sealing means between the conduit means inner surface and the filter outer wall encircling the filter for preventing the particulates from bypassing the filter between the conduit means inner surface and the filter outer wall, the barrier being sufficiently narrow at the filter to allow the fluid to pass along and through a substantial portion of the exterior surface of the outer wall.

2. The apparatus of claim 1 wherein the particulate barrier contacts the outer surface in the vicinity of only one of the two end faces.

3. The apparatus of claim 2 wherein all or substan-tially all of the cells around the periphery of the end faces are open at the one end face and closed at the remaining end face.

4. The apparatus of claim 1 wherein the particulate barrier is essentially impermeable to said fluid.

5. The apparatus of claim 1 wherein the interconnect-ed open porosity of the thin walls and skin is also of a vol-ume and size to enable the fluid to flow through the thin walls and outer surface in their longer dimensions while re-straining at least a significant portion of the particulates from passing completely through the thin walls or outer wall along any wall dimension.

6. The apparatus of claim 1 further comprising means for restricting the movement of said filter body with respect to said conduit means.

7. The apparatus of claim 1 wherein said filter is formed from ceramic materials.

8. The apparatus of claim 7 wherein said fluid is exhaust gas generated by a diesel engine said conduit means comprises an exhaust gas conduit extending from the engine a portion of the conduit comprising a housing containing the filter interposed across the exhaust gas path through the conduit and housing with the inlet end face of the filter facing an upstream portion of the gas path between the housing and engine, said particulate barrier being located near one end face of the filter and the cells located around the peri-phery of the end faces being closed near the remaining end face of the filter.

9. The apparatus of claim 1 wherein the open porosity of the outer wall is at least 25% of the outer wall bulk volume and is formed by pores having mean diameters greater than about 1 micron.

10. The filter of claim 9 wherein the open porosity of the outer wall and thin walls is about 40% or more of the bulk wall volume.

11. The filter of claim 10 wherein the thickness of the outer wall and the thickness of each thin wall is about 0.76 mm. or less.

12. The apparatus of claim 1 wherein said sealing means comprises a particulate barrier positioned in a gap between and in contact with said conduct means inner surface and said filter outer wall.

13. In a method of filtering solid particulates from a fluid comprising the steps of providing a filter body of honeycomb structure having a matrix of interconnected porous thin walls defining an inlet end face and an outlet end face and a plurality of cells extending through the structure between the two end faces, and a porous outer wall surrounding the thin walls and extending between the end faces, the thin walls and outer surface containing interconnected open porosity of a volume and size sufficient to enable the fluid to flow completely across or through the walls and outer surface along any of their dimensions and to restrain at least a significant portion of the particulates from passing completely across or through the thin walls or outer wall in any direction, an inlet group of the cells being open at the inlet end face and closed adjacent to the outlet end face and an outlet group of the cells being closed adjacent to the inlet end face and open at the outlet end face; conducting a fluid contaminated with solid particu-lates into the inlet end face of the filter body; filtering the solid particulates from the fluid by means of the thin walls; and conducting a filtered fluid away from the outlet end face of the filter body, the improvement comprising during the filtering step, the additional step of filtering the fluid through a substantial portion of the outer wall of the fil-ter body.