Gas separation – Combined or convertible – In motor vehicle
Reexamination Certificate
1999-12-23
2001-12-11
Simmons, David A. (Department: 1724)
Gas separation
Combined or convertible
In motor vehicle
C055S483000, C055S523000, C055S529000
Reexamination Certificate
active
06328777
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a filter system having a filter-system housing receiving a plurality of juxtaposed intrinsically stable filter elements made of a ceramic, in particular SiC, said elements comprising porous, longitudinal walls crossed by the medium being filtered.
DESCRIPTION OF THE RELATED ART
When filtering hot gases, for instance diesel engine exhaust gases or waste gases from large plants such as trash incinerators etc. ceramic tubular filter elements are being increasingly used which are fitted with porous, filtering outer walls being crossed by the material being filtered. Where a single filter element is insufficient, a plurality of such filter elements are juxtaposed and are then jointly crossed by such flows. Where such filter elements are in the form of candles and therefore their intrinsic stability is low or non-existent, they are slipped onto support pipes perforated by a pattern of holes (See German patent documents A 38 23 205; A 38 36 697 and C 40 26 375). If the filter elements are stable on their own, for instance being molded from sintered SiC, they are mounted inside the filter-system housing in mutually spaced manner, being affixed and held in place at their ends (European patent documents A 0 446 442; A 0 522 245; A 0 454 346; and A 0 336 883, FIG. 7).
The above described filter systems incur the drawback of excessive specific bulk. Furthermore, exchanging the filter elements is a difficult matter. Again, the filter elements—which are made of a highly brittle ceramic—are unprotected when being moved to or from the filter system. Affixation of the filter elements in part raises the danger that thermally caused changes in the dimensions of the filter-system housing shall entail stresses in the filter elements, and, in extreme cases, their destruction.
Moreover ceramic filter elements also of circular contour are known, which inside are partitioned, in checkerboard or honeycomb manner by porous, filtering longitudinal walls, into alternating inflow and outflow canals. The inflow canals are open at the inflow side and closed at the exhaust side, whereas the outflow canals are closed at the inflow side and open at the exhaust side (European patent document A 0 366 883 FIGS. 5 and 6 and U.S. Pat. No. 4,897,096). The specific bulk of such filter elements is much less and their intrinsic stability is comparatively high. The said documents do not disclose, or imply, arrays of such filter elements. However, if they are configured in the manner of the tubular filter elements, difficulties remain in installation and removal. Also, in view of their brittleness, there is risk of damage when moving them.
With respect to filter systems having filter elements entirely consisting of a porous ceramic and therefore being crossed by the gases in the axial direction, it is known to configure several such filter elements within a single housing of circular cross-section (WO93/13303) or of oval cross-section (U.S. Pat. No. 4,436,538). The cross-sections of the filter elements are quarter-circle or half-circle and these components are sealed from each other and relative to the outside by insulating layers consisting a heat-expanding material (WO93/13303). A multiple configuration of such assemblies of filter elements is not provided. This absence also applies to the version shown in U.S. Pat. No. 4,363,644 wherein the inside space of a cross-sectionally circular, ceramic support body is partitioned in part, a porous material being produced and sintered to the support body.
BRIEF SUMMARY OF THE INVENTION
The objective of the invention is to design a filter system having a plurality of filter elements, of which the filtering longitudinal walls are crossed by gases, in such manner that they may be easily installed and replaced and that they shall be protected against damage while being moved. Another objective is to install the filter elements in such manner as to be substantially sheltered from the filter-system housing's warping or stresses.
This problem is solved by the invention by the outer cross-section of the filter elements being rectangular and in that a plurality of filter elements is combined with others into a cross-sectionally rectangular sub-assembly of filter elements, each filter-component sub-assembly being mounted within a cassette case while forming a particular filter cassette, and in that the filter cassettes are exchangeably mounted inside the filter-system housing.
Accordingly the basic concept of the invention is to combine some of the filter elements into filter-component sub-assemblies and to mount such within one filter cassette each, which, as a unit, can be installed into and removed from the filter-system housing. As a result the filter elements may be configured very tightly. Installation and removal are simple and rapid. The cassette case protects the filter elements against damage both in installation and removal and when they are being moved. Warps and expansions of the filter-system housing are absorbed by the cassette case or even are shunted from it if appropriate supports are provided, as a result of which the filter elements per se are kept free from stresses. By combining a plurality of such filter cassettes, a filter system may be made almost arbitrarily large. High-grade steel is especially appropriate for the cassette housing.
The filter cassettes will be combined in especially compact manner if a filter cassette is flanked at least at two sides with a neighboring filter cassette in order to make the resultant cross-section rectangular.
In a preferred embodiment, the filter elements comprise in manner known per se adjacent and alternating inflow and outflow canals partitioned by the porous, filtering longitudinal walls, the inflow canals being open at the inflow side and closed at the exhaust side and the outflow canals being closed at the inflow side and open at the exhaust side. Appropriately the inflow and outflow canals are configured in checkerboard manner, allowing high efficiency in specific bulk relative to the filtering surfaces. The inflow and outflow canals shall be matched to the cross-sectional contour of the filter elements by themselves being cross-sectional rectangular, preferably square. The outer walls of the filter elements appropriately may be hermetic, though they should be at least impermeable to particles.
In an especially advantageous combination, a filter-component sub-assembly consists of four filter elements appropriately configured in such manner that neighboring filter elements are present at two sides of each filter element. It was found that a configuration of four filter elements offers a number of advantages. By such geometric interlocking, the filter elements are precluded from being forced out. Moreover the gap dimensions for the insulating layers can be observed more closely thereby. Size, weight and costs all are within a reasonable range. Simple cascading for electrical heating can be implemented by series connections.
In a further embodiment of the invention, the filter cassettes are supported in at least two mutually spaced cross-walls, though being axially affixed only to one. This kind of support prevents transmitting expansion or warping of the filter-system housing on the filter cassettes which thereby remain stress-free even when the gases being filtered undergo large temperature changes. In a development of this concept, the filter cassettes may be fitted with a flange resting against the inflow side of one of the cross-walls, and preferably the axial affixation of the filter cassettes shall be implemented by means of this flange. In this design the exhaust-side cross-wall need only be fitted with matching seating clearances for the filter cassettes. At the latter wall, axial affixation is neither required nor appropriate.
It is understood that the filter elements are protected best when the cassette cases enclose the filter-component sub-assemblies over their entire length.
Advantageously insulating layers are present between the filter elements and between
Benthaus Oliver
Best Walter
Schafer Wolfgang
Schumacher Uwe
Liniak, Berenato, Longacre & White LLC
Pham Minh-Chau T.
Simmons David A.
Thomas Josef Heimbach Gesellschaft mit beschrankter Haftung & Co
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