Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1998-06-22
2001-09-04
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S171000, C422S174000, C422S180000, C055S521000, C055SDIG003, C445S060000
Reexamination Certificate
active
06284201
ABSTRACT:
The invention relates to an apparatus for the catalytic purification of flowing gases, in particular exhaust gases of internal combustion engines, having a housing to be arranged in a gas flow path, which housing contains a gas-permeable support in the form of a textile sheet material made of heat-resistant fiber material onto which a catalytically active material is applied.
The catalytic converters conventional for the exhaust gas purification of motor vehicle engines, in particular internal combustion engines are composed throughout of ceramic monoliths in the form of extruded cellular bodies which are coated on the surfaces swept by the exhaust gas with a catalytically active material, in particular platinum. These mechanically sensitive monoliths are accommodated in metal housings in which they must be elastically supported, which is accompanied by certain problems. In order to obtain a sufficiently large surface area, before the application of the catalytically active material they must be coated with a so-called “washcoat”, which, however, rapidly alters at temperatures above 800° C. Because of this thermal sensitivity, these catalytic converters cannot be arranged directly on the engine. On the other hand, the arrangement at a relatively large distance from the engine, together with the considerable mass of the monoliths, is accompanied by the disadvantage that heating up the monoliths to the operating temperature after a cold start requires a relatively long time. During this heating-up period, the catalytic converter is thus active only to a limited extent. Since the exhaust gases essentially flow in laminar flow through the cellular body of the monolith, the conversion rate is also restricted on principle.
Austrian Patent 61 419, furthermore, discloses using filters for the purification of exhaust gases, in particular of internal combustion engines, which filters have fibers made of a heat-resistant polycrystalline material having a crystallite size between 50 and 500 angstroms. Polycrystalline aluminum oxide or zirconium oxide are preferred for this fibrous material. However, in principle, metal oxides having a temperature stability up to 900° C. can be used.
In order to decrease the temperature at which soot particles separated out from the exhaust gas stream are burnt, the fibers can be coated with a catalytic material, in particular silver, bismuth, lead, uranium, cobalt, etc. To remove undesirable gaseous components, for example carbon monoxide or hydrocarbons, from the exhaust gases it is also known, in the case of this filter, to coat zirconium oxide fibers with finely divided platinum.
The fibrous material is used in the filters in the form of loose staple fibers, paper, woven fabric, films, cardboard or felt, filter elements also being able to be used in which paper (or corrugated cardboard), or yarn, or felt produced from such fibrous material is loosely wound up to form a filter body through which gas flows. Filter bodies made of loosely packed fibrous material are problematic because the non-interlocked fibers become free with time, whereas in the case of fibers processed to form paper, felt, cloth or like linear textile sheet materials, either their resistance to flow is too high or there is the risk that the filters plug relatively rapidly. Moreover, the surface of the incorporated fibers is exposed to a very restricted extent, the exposed fiber surface being further increasingly reduced in operation. At any rate, catalytically active filters of this type have not hitherto achieved economic importance.
The object of the invention, in contrast, is to create an apparatus for the catalytic exhaust gas purification (“catalytic converter”) which can be used in particular in the exhaust gas purification of internal combustion engines and which features mechanical resistance with high activity.
To achieve this object, the apparatus according to the invention mentioned at the outset is characterized in that the support for the catalytically active material is a knitted fabric.
The fibrous material advantageously contains ceramic microfibers, which are taken to mean fibers having a diameter of 3 &mgr;m and more. In particular polycrystalline mullite fibers have proved to be expedient, but other heat-resistant fibrous materials are also suitable. Thus the fibrous material for certain application purposes can also contain carbon fibers or can be composed entirely of these. The surface area of the fibers of the fibrous material is expediently between 0.2 and 0.4 m
2
/g and above, without this range representing a restriction of the fibers usable in principle.
A knitted fabric whose fibers form the support for the catalytically active material offers, as has been shown, a high mass transfer to the fiber surfaces with a simultaneous outstanding hydraulic configuration. It has bulk elasticity and is insensitive to vibrations and pulsations of the gas flow. The fibers coated with the catalytic material are dimensionally pretensioned and firmly incorporated in the knitted fabric. Nevertheless, their surface is substantially open; they can move with respect to each other to a limited extent, so that stresses are reduced and damped. The extensively exposed fiber surface ensures a maximum catalytic activity.
The structure of the knitted fabric forms a versatile pore system in which resistance elements are contained, so that even in the case of laminar through-flow, extensive wall contact and thus high mass transfer results in all flow regions, as is essential for good catalytic activity. Within the knitted fabric itself, the flow path is branched several times with the result that the individual fibers supporting the catalytically active material are impinged by the flow over a large surface area.
Because of its special structure, the knitted fabric additionally ensures outstanding mixing of an exhaust gas stream linear with respect to concentration or temperature. From this there results a particular advantage in the case of multiple cylinder internal combustion engines and the so-called lambda 1 technology. Finally, such a knitted fabric has good noise insulation properties, it acting, moreover, as a filter for particulate pollutants, for example soot particles.
The good bonding of the fibers in the knitted fabric already mentioned has the effect that fiber fragments possibly occurring remain substantially anchored in the knitted fabric, while, on the other hand, progression of damage from one damaged site which has occurred virtually does not take place. Short fiber yarns can therefore also be used.
The knitted fabric can be made in at least a double-threaded manner from various fibrous materials of which the fibers of the one and/or of the other fibrous material can support the same or different catalytically active material. At least one metallic thread can also be worked into the knitted fabric, which metallic thread gives the knitted fabric, for example, an additional dimensional stability. It is also conceivable to work carbon fibers having an enlarged surface area (activated carbon fibers) into the knitted fabric, in order by this means to create the opportunity, for example during the cold start phase, of temporarily adsorbing unburnt hydrocarbons occurring and of desorbing again the substances adsorbed in this way in a subsequent period (peak emission).
For this purpose, the knitted fabric can contain electrically conducting fibers which are electrically conductively connected to connection means for an electric power source and which thus permit direct internal heating of the knitted fabric. However, this internal heating can be used not only for the desorption of adsorbed substances, but in particular, also, during the cold-start phase, to bring the knitted fabric containing the catalytically active material rapidly to the operating temperature. The electrically conducting fibers can be carbon fibers or metal fibers in the form of metal wires etc.
The carbon fibers, on their surface, can also bear an electrically insulating coating, for example SiO
2
. For t
Foley & Lardner
Tran Hien
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