Device for the purification of contaminated exhaust air through heterogeneous catalysis

A device for the purification of an exhaust gas containing at least one contaminant removable through heterogeneous catalysis and flowing through a chamber having an inlet and an outlet, comprises at least one disk structure positionable within the chamber and defining a central cavity alignable with the inlet of the chamber. The disk structure includes a non-metallic, gas-permeable and flexible carrier element comprising a band woven of glass fiber yarn. The yarn is formed of individual fibers coated with a layer of pulverized zeolitic material defining a molecular sieve and having a catalytic material, selected to act adsorptively upon the at least one contaminant, dispersed therein. The device further includes a heatable metallic woven band disposed in laminar relation with the carrier element, the metallic woven band and carrier element being wound spirally end-over-end, whereby exhaust gas flowing into the central cavity from the chamber inlet passes through the woven bands and the at least one contaminant is removed therefrom. A plurality of disk elements may be stacked and positioned within a cylindrical housing a having perforated sidewall, an inlet end, and a sealed end. Exhaust gas flows through the inlet and passes through the central cavities of the disk structures, the woven bands making up the disk structures, and perforated sidewall of the housing, respectively for subsequent flow through the chamber outlet. Adjacent pairs of disk elements may be wired in series in a star configuration to respective phases of a three-phase system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to air purification systems, and more particularly, 
to a device for the purification of contaminated exhaust air through 
heterogenous catalysis. 
2. Discussion of the Prior Art 
A device for conducting catalytic reactions is proposed in German 
specification DE AS 1003192. The carrier material is a wire, preferably 
made of a chrome-nickel alloy, which is coated with a thin, firmly 
adhering coat of a temperature-stable and highly porous oxide, e.g., 
aluminum oxide, or with a mixture of various oxides. The coating is 
subsequently impregnated with an active catalytic material, e.g., 
platinum. After undergoing this treatment, the coated wires are wound into 
flat coils and mounted in a coil holder. In the resulting arrangement of 
multiple connected coils, the individual flat coils are insulated 
electrically and in terms of contact by an intervening mica layer. 
Disadvantageously, such a coil arrangement is instable at a particular 
transfer cross section. The flat coils must therefore be carefully held by 
their outermost edge in the coil holder, so as to avoid sag when a coil is 
heated. The total area available for heterogeneous catalysis on each flat 
coil is limited, since the outer edge is covered by the coil holder. In 
addition, the mica strip between the two flat coils forms a blocking 
layer, so that only part of the surface of the flat coil located above the 
mica layer (seen in the flow direction) is involved in the catalysis. 
Larger cross sections cannot be produced in the suggested manner, since 
without an appropriate support the flat coil would sag from its own 
weight. Skilled personnel are needed to manufacture and handle the flat 
coils, because the wires are very thin and have a diameter of less than 
one mm. Another disadvantage is that the resistance wire is coated with 
the oxide layer before being wound, so that there is always a danger that 
the brittle film coating will partially flake off, possibly leading to 
shorting contacts in the turn area. 
A catalytic filter for diesel soot is proposed in published German 
specification DE 37 16 446 A1 in which a coating of metal-doped zeolite is 
applied to a permanent filter element, preferably a honeycomb body with 
reciprocally closed channels. The doped metal is preferably platinum. The 
suggested coating of the filter element serves to lower the ignition point 
for the thermal combustion of the adsorbed soot particles. In order to 
keep the required quantity of noble metal low, the noble metal is finely 
distributed by means of a zeolitic base. The effectiveness of this process 
must be questioned, since the dimensions of a soot particle are larger by 
a power of ten than the pore size of the zeolite used. This means that a 
large part of the applied noble metal cannot act catalytically, because 
the individual soot particles will not fit into the small pores and no 
contact is established with the doped noble metal particles located there. 
Furthermore, a large portion of the platinum is spatially fixed in the 
zeolite and cannot come into contact with the soot particles. 
A generic device for the purification of contaminated exhaust air is known 
from DE 43 39 025 A1. This device consists of a non-metallic, 
gas-permeable and windable carrier element which utilizes individual 
ceramic fibers coated with a layer of a material that acts in an 
adsorptive manner. The carrier material is connected sandwich-fashion to a 
heatable metallic woven band, which band is coated with catalytic 
material. The entire element is located in a housing equipped with an 
inlet and an outlet through which the contaminated gas can be introduced 
and the purified gas can be extracted. A disadvantage of this arrangement 
is the excessively small specific surface of the carrier element and the 
unfavorable placement of the catalytic material. 
A filter for diesel soot is disclosed in U.S. Pat. No. 5,180,409 which 
consists of a single-layer or multi-layer fabric of, preferably, ceramic 
yarn. For lower temperatures (between 330.degree. and 550.degree. C.) a 
glass fiber yarn can also be used. In order to reinforce the fabric, a 
flexible filling yarn is also woven into it. The fabric is not coated, and 
because of the large gaps between the individual yarn elements it is not 
suitable for use as an adsorbate. Furthermore, the filter cannot be 
regenerated and must be changed after a preset maximum pressure loss is 
reached. 
It is therefore an object of the present invention to provide a compact, 
easily fabricated device for the purification of contaminated exhaust air 
through heterogenous catalysis with prior adsorption and desorption, with 
which it is possible, in a regenerable fashion and without removing the 
filter element, to purify the gas contaminated with various constituents 
more efficiently and using less energy, compared to known units, even at 
fluctuating contaminant concentrations of less than 100 mg/cbm. 
SUMMARY OF THE INVENTION 
The aforementioned object, as well as others which will become apparent to 
those skilled in the art, are achieved in contrast to the known prior art, 
by an element in which the carrier material for the coating substances is 
a band woven of glass fiber yarn. The yarn is a filament yarn of 
individual glass fibers that is coated with a finishing in order to 
increase temperature stability. The advantage of the woven band 
configuration, compared to the known fabrics, is that the woven band has a 
larger active surface and greater gas permeability in the sense of a sharp 
deflection of the gas flow. If, in addition to this, the band is wound, 
surfaces are achieved which considerably exceed those of multiple fabric 
parts placed one atop the other. Moreover, it is possible, for example, by 
using a reel and a housing covering, to wind practically any desired 
diameter without the device becoming instable. It is desirable for the 
filament yarn to have a right/right weave structure. In contrast to 
activated charcoal, the suggested woven band is not combustible and will 
maintain its structure even at high temperatures (up to 700 degrees 
Celsius). 
In accordance with the present invention, the woven band which serves as 
the carrier material, together with the metallic woven band of the same 
width, is wound spirally end-over-end into a disk with an axial hole 
through the center. This disk is coated with a zeolitic molecular sieve 
that in itself is known; however, in contrast to the known prior art, the 
zeolitic molecular sieve is in pulverized form. 
In this pulverized form, the zeolitic molecular sieve has a considerably 
larger surface, compared to a known adsorber bed. Catalytic material, 
preferably platinum, is implanted by means of the known sol-gel process in 
the adsorptive layer. 
The use of a zeolitic molecular sieve applied to the carrier element as the 
adsorption medium in a timely distributed pulverized form, has several 
advantages over other known adsorptive materials. Adsorption is effective 
even at high temperatures, i.e., up to approximately 200.degree. C. 
Efficiency declines as temperatures rise, however, because the oscillation 
amplitude of the adsorbed contaminant molecule increases and once a 
certain temperature is reached the linkage forces are no longer sufficient 
and desorption occurs. Another advantage of the zeolitic molecular sieve 
utilized by the present invention lies in the fact that even the smallest 
concentrations of contaminants in the exhaust air to be purified are 
captured, in contrast to activated charcoal. In the case of activated 
charcoal, the adsorptive capacity rises to useful values only at higher 
concentrations. Because the zeolitic molecular sieve is a synthetically 
manufactured substance, it can be produced with precisely defined 
characteristics, including pore size, while activated charcoal has a 
distribution of pore sizes across several powers of ten. Furthermore, 
there are various types of molecular sieve with respect to the 
characteristic of being water-repellent (hydrophobic) or water-attracting 
(hydrophile), and deliberate advantage can be taken of these for the 
adsorption of various contaminants in the exhaust air mixture. The entire 
element can be coated optionally with various types of zeolite or with a 
mixture, whereby proportions may vary. The advantage of this is that the 
filter can be precisely matched to a particular type of contaminant. It is 
also possible to connect filters that have different types of zeolite in 
parallel or serial fashion, so that even a very complex mixture of various 
contaminants can be treated so as to eliminate these contaminants. 
The removal of adsorbed contaminants occurs via catalytic combustion, for 
which an active catalytic material is applied to the entire element after 
the adsorptive coating. The catalytic coating is applied via the known 
sol-gel process. Depending on the particular manufacturing conditions, 
gels with various characteristics are obtained. The homogeneous 
distribution of the initial components (e.g., platinum particles) is 
maintained during the gelling process. After drying, a SiO.sub.2 network 
forms in which the platinum particles are dispersed. 
By applying the catalytic material in this manner, the adsorptive effect of 
the entire element is increased, and the sites of adsorption and catalytic 
combustion are located directly next to one another. 
The entire coated element is heated in the known manner via a deformable 
heating element which is connected to a voltage source and forms, with the 
carrier element, a single unit. Preferably, this heating element is a 
metallic woven band of a highly temperature-stable material, e.g., a 
chrome-nickel alloy. The mesh size of this metallic woven band is 
preferably less than 1 mm, while the diameter of a single wire is 
preferably less than 0.3 mm. Because the metallic woven band is flexible, 
it can be folded sandwich-fashion into a tubular module or a box-type 
module. So that the process temperature required for catalytic combustion 
can be set, a temperature sensor can be attached to the heating element. 
Preferably, this is a thermocouple attached to the metallic woven band 
through laser welding. More advantageously, the heating is controlled by 
measuring the change in the electrical resistance of the element. 
Individual modules constructed as catalysts can be combined by serial or 
parallel connection into larger units. For this purpose, at least two and 
preferably up to six disks are placed on top of one another, separated by 
mica disks, in a cylindrical housing. The mica disks ensure that no 
electrical short circuits occur between the individual disks. The housing 
has a perforated inner and outer covering, so that the exhaust air to be 
purified can be fed without obstruction to the module and the purified air 
can be extracted. The gas is conducted in an essentially radial fashion 
from the inside to the outside, i.e., at right angles to the module axis. 
The front sides are provided with a lid which seals the two outermost 
disks and encompasses the inner and outer covering. 
The electrical connection of such a module calls for two disks at a time to 
be electrically connected in series. 
In addition to neutralizing odors from large-scale kitchens, concentrations 
of livestock, foodstuff and luxury-food production facilities and the 
pharmaceutical industry, this technique can remove the essential known 
combustible and organic substances. Given this broad application spectrum, 
it must be anticipated that the exhaust air to be purified will also be 
contaminated with solid dust particles. In addition, there may be 
components in the exhaust air which form ash particles during catalytic 
combustion. Such components must be removed in advance, so that the 
element does not become dirty or clogged after a short period of 
operation. It is therefore suggested that in these cases an appropriate 
separator be connected in front of the element. Separators for dust 
particles and for components that lead to ash particles are sufficiently 
known, so that a more detailed discussion of them is unnecessary. Here it 
must be noted that the exhaust air, particularly that from large-scale 
kitchens, may contain a very high proportion of steam. Because the 
saturation limit of the exhaust air for steam depends heavily on 
temperature, care must be taken to ensure that the temperature does not 
fall below the dew point on the way from the exhaust point to the 
separating element. Otherwise, the condensed water drops will form what 
amounts to a quasi-blocking layer on the adsorbate, making adsorption of 
the contaminants more difficult, if not impossible. 
The advantage of the device according to the invention can be seen in the 
fact that the device is constructed as a compact, stable adsorbate with a 
very large surface area, in which the adsorption point for the gaseous 
contaminant molecules to be separated and the location of catalytic 
combustion are the same. In addition, this device can be regenerated as 
often as desired, since the regeneration phase takes place in a 
temperature range which does not change or negatively effect the 
adsorbate. Another advantage of the suggested device is the temperature 
stability of its material in comparison to the known activated charcoal. 
The special measures needed during the desorption of contaminants adsorbed 
into activated charcoal can be omitted in the suggested device. The device 
is easily adapted to any type of contaminant composition, since in the 
zeolitic molecular sieve that is used the required pore size or the 
spectrum of desired pore sizes can be precisely set. Furthermore, a 
suitable zeolitic type in respect to the characteristic of 
water-repellency or water-rejection can be selected. 
The combination of a woven band as the carrier element with the coating of 
a zeolite and a catalytic material deposited via a sol-gel process permits 
a spectrum of applications ranging from odor neutralization of 
foul-smelling gaseous mixtures to purification of heavily-contaminated 
exhaust air. Depending on the particular requirement, the device can be 
miniaturized in order to permit easy installation in existing exhaust air 
conduits or, on the other hand, can be designed with dimensions allowing 
industrial use, e.g., in sewage treatment plants. Because the module 
constitutes a separate unit, it can be inserted and removed at any time to 
be tested or checked, without the entire unit having to be disassembled. 
Except for the electrical connections of the heating and temperature 
measurement elements and, possibly, several alignment or holding screws, 
no further assembly or disassembly is required. 
Other objects and features of the present invention will become apparent 
from the following detailed description considered in conjunction with the 
accompanying drawings. It is to be understood, however, that the drawings 
are designed solely for the purposes of illustration and not as a 
definition of the limits of the invention, for which reference should be 
made to the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic depiction in cross-section of a purification device 
constructed in accordance with an illustrative embodiment of the present 
invention. In this example, the sandwich-like carrier element 1, i.e., a 
weave consisting of glass fibers, and the metallic woven band 7 that 
functions as the heating element, are wound spirally into a tubular 
module. 
It will be readily apparent to those skilled in the art that such winding 
is possible only if both of the elements, i.e., the carrier element 1 and 
the heating element 2, are flexible. Such winding is not possible in many 
of the carrier elements commonly employed in prior art systems, such as 
honeycomb bodies, mineral wool, ceramic foam, and the like. For clarity, 
the individual winding layers are depicted in FIG. 1 at a distance from 
one another. In reality, however, the layers lie one atop the other with 
no space between them, in order to produce a disk that is compact. An area 
3 is left free in the center, to define a flow path for the gas supply. At 
each end of the heating element 2, a corresponding link 4, 5 is welded on, 
to define terminals connectable to a suitable voltage source. The entire 
element is coated with a zeolitic molecular sieve of a particular type, 
i.e., hydrophobic or hydrophilic or a mixture of both types. This 
adsorption layer is in turn impregnated with an active catalytic material, 
preferably platinum, via a sol-gel process. 
FIG. 2 shows a half-side longitudinal section and a half-side view of a 
module 13 with several disks. In the illustrated embodiment, a total of 
six disks 6.1-6.6 of the type shown in FIG. 1 are located in a housing. 
The individual disks 6.1-6.6, which lie one on top of the other, are 
separated from each other by the mica disks 7. This is to prevent an 
electrical short between the heating elements 2 of two neighboring disks, 
e.g., 6.1 and 6.2. The outer and inner sides of the disks 6.1-6.6 are each 
encompassed or covered by a perforated tin covering 8, 9. The connection 
on the front side is formed in each case by a lid 10, 11, which encircles 
the outermost disks 6.1-6.6 and also encompasses the outer covering 8 and 
inner covering 9. In each case, two adjacent disks (6.1 and 6.2, 6.3 and 
6.4, 6.5 and 6.6) are connected in series. These are connected, in each 
case, to one phase of a 400 V three-phase current network and connected in 
a star configuration. The hole 12 in the upper lid 10 serves for the 
attachment of the module 13, whereby a rod (not shown), having a threaded 
end of which can be connected to a bearing plate or other holding device 
(not shown), is extended through the hole 12. 
FIG. 3 is a schematic diagram of a complete set-up of a purification unit 
configured with the module 13 described in FIG. 2. By means of a 
ventilator 14 or a fan, the exhaust air to be purified is introduced via 
an inlet pipe 15. The exhaust air flows into a funnel-shaped chamber 16 
which, matching the opening 3 (FIG. 1) of the module 13, is closed at the 
top. In this configuration, exhaust air is forced by the ventilate fan 
into the inner space of module 13. 
As shown in FIG. 2, the opening by which exhaust air flows through module 
13 is closed off by lid 10. 
The purification system shown and described in FIG. 3 represents only one 
possible application of a module 13. For example, the module can be 
smaller or larger. A reversal of the air flow, i.e., from outside to 
inside, is also conceivable and useful for special applications. 
Thus, while there have been shown and described and pointed out fundamental 
novel features of the invention as applied to preferred embodiments 
thereof, it will be understood that various omissions and substitutions 
and changes in the form and details of the disclosed invention may be made 
by those skilled in the art without departing from the spirit of the 
invention. It is the intention, however, therefore, to be limited only as 
indicated by the scope of the claims appended hereto. 
The invention is not limited by the embodiments described above which are 
presented as examples only but can be modified in various ways within the 
scope of protection defined by the appended patent claims.