Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1998-08-26
2001-04-10
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S210500, C423S213200, C423S213500, C423S245300, C422S177000, C422S176000
Reexamination Certificate
active
06214305
ABSTRACT:
The invention relates to a method for the oxidation of carbon- and/or hydrocarbon- and/or organic compounds containing liquid or solid particulate contaminants in gas streams, more in particular on the diminishing, or the prevention of soot emission from diesel engines, comprising the treatment of the soot containing exhaust gasses prior to their emission to the open air.
Emission of gas streams which are contaminated with soot particles or with particles of solid or liquid hydrocarbon or organic compounds (for example oil or fat droplets) to the atmosphere is undesirable. This problem can be found in many places, such as in the oil processing industry and the like. It is known also that diesel engines show the disadvantage of a relatively high emission of soot particles. These soot particles have a negative influence on the environment and much research has been done already into the diminishing of the soot emission of diesel engines. A first possibility is to operate the engine at such conditions that the soot formation diminishes. In general this can be done at the expense of the capacity, the power and the fuel expenditure of the engine. An other possibility is the removal of the soot particles that are formed from the exhaust gasses.
However, in this last case one meets the difficulty that it is not easy to collect and to convert the often very fine particles.
The present invention aims at providing a method to diminish or even prevent the emission of such pollutants, by separating the solid or liquid particles from the exhaust gasses and by burning these after their separation through application of a non-selective oxidation catalyst (combustion catalyst) in the separator.
Therefor the invention relates to a method for the oxidation of carbon- and/or hydrocarbon- and/or organic compounds containing liquid or solid particulate contaminants in gas streams, comprising the treatment of said gas streams in a turbulent flow precipitator, of which at least part of the surface area shows catalytic activity for non-selective oxidation.
More in particular the invention relates to a method for the diminishing, or the prevention of soot emission of diesel engines, comprising the treatment of soot containing exhaust gasses prior to their emission in the open air in a turbulent flow precipitator, of which at least part or the surface area shows catalytic activity for non-selective oxidation.
The invention is based on the application or the principle of a specific separation system for the separation of very fine particles from gas streams, a ‘Turbulent Flow Precipitator’, as described for instance in the International patent application WO-A 93/15822, in combination with a catalytic combustion of the captured (soot) particles.
The separation is based on the phenomenon that a turbulent gas stream in a space, near to the walls of this space shows a zone of decreasing turbulence, known as the viscous border zone. In this zone particles can be captured and removed. According to the method described in said International patent application one obtains separation of particles of a dimension of 0.01 to 100 micrometer in a separator bat passing the turbulent as stream over a series of vertical plates, which form a number of vertical spaces with a chink (slit) form, which are in direct contact with the space in which the turbulent gas stream is contained.
The present invention is based on the insight that, it is possible to oxidize the mostly organic or soot particles, by bringing these in contact with a combustion catalyst (a non-selective oxidation catalyst) in said separation spaces of a slit (chink) form. It is known that for a good oxidation a good contact is necessary between the particles and the catalytically active material. In a separator of said type one obtains such a said good contact, especially if use is made of a preferred design of the separator and a preferred composition of the catalysts to be described later on.
According to the invention one takes care that in the separating spaces (slits/chinks), that is to say in the zone in which the main gas stream is not conveyed, a combustion catalyst is present. Herewith it is of importance that catalytically active surfaces are present in said slits/chinks. This surface can be provided by the surface of the plates, or as a packing in the slits/chinks.
The surface can already be catalytically active from origin or can be made active through the nature or the construction material of the plates or the packing (for instance copper). However, it is also possible to provide the catalytic activity by the application of a catalytically active material on said surface, for example as a wash coat.
Preferably the separator is provided with a packing, which exists of a metallic or ceramic support material, of which the surface already shows or gains catalytical activity for non-selective oxidation.
According to a preferred method of the invention one doesn't apply the design described above, but an improved design which is described in the Dutch patent application Nl 10-01963 of the same date. In this application an apparatus is described, which consists of at least a housing provided with an entrance duct for the gas stream to be purified on the one side (end) and a discharge (exit) duct for the purified gas stream on the other side (end), as well as at least one predominantly vertically placed convey channel for said gas stream, at which said apparatus is provided with means for the separation of the particles from said gas stream, which means are bounded to the convey channel, are in direct contact therewith and consist of a number of plates which are directed at an angle smaller than 90 degrees with the convey axis and where again and again two plates form a chink (crevice, slit), which is fit for separating and discharging the particles.
The conveying of the gas takes place either in upward or in downward direction, at which it is also possible to connect two or more vertically mounted pipe parts by bends of about 180 degrees, which shows as advantage that the system needs less height.
With a system as described above an optimal separation of the particles is obtained, while simple combustion of these particles is also possible, for instance by providing the surface of the plates, on which the particles fall, with a combustion catalyst. An other possibility is the application of a packing material consisting of a predominantly inert material, for instance a metal or a ceramic material, on the surface of which a catalytically active material is applied, or a packing material which itself shows catalytic activity. Under the influence of the gravitational force, or by mechanical vibrations, for instance resulting from the engine of a diesel vehicle, the particles will always move downward, so that the contact between the particles and the catalytically active surface is warranted almost always. It is known that in existing systems for the removal and combustion of soot from exhaust gasses the warranty of this contact is problematic.
The contact between the separated soot and the catalyst is an essential condition for a good combustion of the capured soot. This is decribed, among others, in publications of J.P.A. Neeft et al. In these references it is described that a good contact between the soot and the catalyst, as is obtained for instance by mixing of soot and catalyst in a ball mill, results in an appreciably (up to 200° C.) lower temperature of combustion than in case of bad contact as this results from mixing of soot and catalyst by shaking. Experiments, in which the combustion temperature was determined for soot, emitted by a diesel engine and captured on a ceramic filter provided with a layer of combustion catalyst, it was found that this temperature almost coincides with the combustion temperatures in case of bad contact.
As a packing material one can use almost any material that is resistant to the conditions prevailing at the oxidation. Examples are various kinds of fibres, (ceramic, metallic, glass), catalysts support part
Jelles Sietze Jelle
Makkee Michiel
Moulijn Jacob Adriaan
van Harderveld Ruud
Fink Edward M.
Griffin Steven P.
Michaelson Peter L.
Michaelson & Wallace
Technische Universiteit Delft
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