DE19640604A1 - Apparatus for purifying exhaust gases - Google Patents

Abstract

The apparatus for purifying gases comprises an existing apparatus for purifying gases, in which the large part of the conversion is shifted from the catalytically deactivated part into a still active part of the apparatus.

Description

The invention relates to a device according to the preamble of the saying 1.

Those processes are termed catalytic exhaust gas purification understood, in which the contaminating gaseous and vaporous substances (Pollutants) through chemical reaction on the surface of a solid auxiliary (Catalyst) can be converted into harmless substances.

Technical catalysts, hereinafter referred to as catalysts, exist therefore in the majority of highly porous materials that have a large surface for provide the chemical reaction. The catalyst is on following components:

• - carrier material (e.g. granules, monolith)
• - Intermediate layer or wash coat
• - Catalytically active component (e.g. platinum, rhodium).

Mass transfer and heat transfer between the gas space take place on the catalytic converter and catalyst instead. This allows the catalyst to be preheated Gas flow preheated to the necessary operating temperature or by the exothermic oxidation / combustion reaction warmed up catalyst surface be cooled [2].  

The mass transfer is divided into the mass transfer through the flow and the Wash coat towards the catalytically active component, the chemical reaction and the return transport of the resulting substances through the wash coat into the flow.

The catalytic converters are divided into two main types:

• - bulk catalyst (pellets, granules)
• - Parallel flow catalyst (channel catalyst, monolith).

A linear relationship is currently assumed for both types of catalysts between catalyst volume and catalyst activity. This connection applies to the parallel flow catalytic converter only to a limited extent. Because of very small The majority finds Reynolds numbers, usually less than 100, in the catalyst channels the conversion reactions in the inlet flow, d. H. with the three-way catalytic converter on the first few centimeters of the catalyst. Here the mass transfer takes place to Wash-Coat primarily convective. As soon as the flow in the channel is fully developed, the mass transport through the flow is only diffuse, i.e. much slower.

In the catalytic after-treatment of exhaust gases from stationary and non-stationary combustion engines based on the Otto principle Three-way catalytic converters and, for engines based on the diesel principle, oxidation catalytic converters analyzers used. These catalysts usually consist of one Channels with ceramic or metal supports on which the wash coat and the are applied catalytically active coating.

As the number of operating hours increases, the catalytic activity of Exhaust gas catalysts after, there is deactivation. This deactivation is called Catalytic converter aging. If the activity of the catalyst falls below one certain value, the catalyst must comply with emissions regulations be replaced.

The deactivation of catalysts is divided into four categories:

• - chemical deactivation
• - thermal deactivation
• - polluting deactivation
• - mechanical deactivation.

According to the current state of the art, the most common causes are Deactivation chemical and thermal deactivation.

The chemical deactivation is due to irreversible adsorption or reaction to the Surface of the catalytically active component, reduction of the catalytic Surface due to toxins and physical / chemical blockage of the pores attributed. The thermal deactivation is a result of sintering, Alloy formation as well as precious / non-precious metal interaction.

Both deactivation processes take place at the locations of the largest Conversion reactions, d. H. with parallel flow catalysts in the Inlet flow. This means that the deactivation in the flow direction of decreases front to back and perpendicular to it from the inside out.

If a catalyst no longer meets the required conversion rates, it will currently completely replaced. The deactivated catalysts are usually one Recycling process fed. With three-way catalytic converters for gasoline engines recycling mostly in grinding and melting to recover the Precious metals.

A disadvantage of the previous exchange of the entire parallel flow catalyst is the deactivated part of the catalyst is only the part that the flow as Inlet section required. The catalytically still active part becomes unnecessary Wisely fed into an energy-intensive recycling process early on.

The object of the invention is to fluidically deactivate the deactivated catalyst use and if necessary to convert that the inlet flow in the still active part of the catalyst falls.

This object is achieved by a catalyst with the features of claim 1 solved.

The advantages of the reactivated catalyst are:

• - Energy-saving "reactivation" of existing catalyst activity.
• - Avoidance of waste (ceramic carrier, wash coat, insulation material).
• - Conservation of raw materials and resources by reusing existing ones Catalysts.

A disadvantage of the "reactivation" is that the entire catalyst may be present is already partially deactivated and not the conversion rates of a new one Catalyst can be achieved.

example 1

Fig. 1 shows an axial section through a one-piece catalytic converter, such as is used for exhaust gas aftertreatment on an internal combustion engine. The flow is from right to left. After deactivation, the flow is simply from left to right, which z. B. can be achieved by turning the catalyst including casing / housing.

Example 2

The area of the inlet flow, ie the deactivated part, is separated off on a deactivated catalyst according to FIG. 1. The direction of flow can be maintained after the separation. Alignment of the remaining monolith on the rear edge of the catalyst housing is advantageous, FIG. 2.

Example 3

A sensible improvement of Examples 1 and 2 is a segmental arrangement of the remaining active catalyst monoliths, according to patent application 196 24 060.3, Fig. 3. It is also possible to combine catalyst segments from various deactivated catalyst monoliths to improve the conversion reactions.

Example 4

FIG. 4 shows an axial section through a one-piece exhaust gas catalytic converter which, after being deactivated by inserting a stem, directs the main exhaust gas flow to the channels on the outside of the catalytic converter which have not yet been deactivated.

Example 5

A useful improvement of the previous examples is the arrangement of the Monoliths in a housing that with a detachable connection for disassembly of the catalyst monolith is provided.

Claims (10)

1. Device for cleaning gases, characterized in that this device consists of an existing device for cleaning gases, in which the majority of the conversion is shifted from the catalytically deactivated part to the still active part of the device. 2. Device according to claim 1, characterized in that the shift in conversion by The flow direction is reversed. 3. Device according to claim 1, characterized in that the shift of the conversion by directing the flow into the still active edge region of the catalyst. 4. The device according to claim 1, characterized in that the shift in conversion by The deactivated part is separated. 5. The device according to claim 4, characterized in that the separated part between 0.5 mm and 0.99 times the length of the original catalyst monolith. 6. The device according to claim 1, characterized in that the device several catalyst carrier elements has elements that are serial with intermediate zones in between or parallel lel are arranged. 7. The device according to claim 6, characterized in that the individual elements from one Catalyst monoliths originate. 8. The device according to claim 5, characterized in that the individual elements from different Catalyst monoliths originate. 9. The device according to claim 1, characterized in that the catalyst housing with a detachable Connection for dismantling the catalyst is provided.   10. The device according to claim 1, characterized in that the interface of the catalyst housing to the Exhaust ducts is equipped with a detachable connection.