JP2598528Y2 - Diesel engine exhaust purification system - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas purification device for a diesel engine.

[0002]

2. Description of the Related Art An apparatus for purifying nitrogen oxides discharged from a diesel engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-149.
No. 317 and JP-A-63-100919, a reduction catalyst is provided in the middle of the exhaust passage.
In some cases, a reducing agent is added upstream of the reduction catalyst.

Conventionally, as shown in FIG. 7, for example, as shown in FIG. 7, a reduction catalyst 3 is interposed in an exhaust passage 2 of a diesel engine 1 and a part of light oil stored in a fuel tank 4 is removed. Some include an addition device 5 that adds a reducing agent upstream of the reduction catalyst 3 in the exhaust passage 2.
The reduction catalyst 3 is designed to decompose nitrogen oxides in the exhaust gas into nitrogen and oxygen by contacting the exhaust gas containing the nitrogen oxides in an oxidizing atmosphere or in the presence of a hydrocarbon (Japanese Unexamined Patent Publication (Kokai) No. Heisei 9 (1994) -207). 1-11-1809 reference).

[0004]

However, in such a conventional exhaust gas purifying apparatus for a diesel engine, when a reducing agent such as light oil is supplied, as shown by a solid line in FIG. In addition to the insufficient removal, there is a problem that the reducing agent is discharged without reacting.

[0005] The present invention focuses on the above problems, and aims at improving the reduction efficiency of nitrogen oxides and preventing the reducing agent from being discharged without being reacted.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a diesel engine exhaust purification system comprising: a reduction catalyst interposed in an exhaust passage; and means for adding light oil as a reducing agent upstream of the reduction catalyst. A zeolite catalyst is used as a pretreatment catalyst to catalytically crack the added light oil upstream of the reduction catalyst.
And is housed inside a casing that is shared with the reduction catalyst.

[0007]

[Function] Light oil added as a reducing agent is used for pretreatment catalyst and
And is catalytically decomposed by the zeolite catalyst to produce low molecular weight gaseous components. That is, since light oil is supplied to the reduction catalyst as a highly reactive gaseous component, the reduction efficiency of nitrogen oxides is improved, and light oil as a reducing agent passes through the reduction catalyst unreacted and is discharged to the outside. Can be suppressed.

[0008] The pretreatment catalyst reduces the calorific value of the exhaust gas of the engine.
The reaction that produces gaseous components of low molecular weight from light oil
Is promoted and the amount of heat generated in the reaction
Increase the temperature of the incoming exhaust gas. In other words, the pretreatment catalyst
The exhaust gas temperature of the engine is used for the activity of the
The heat of reaction of the pretreatment catalyst is also used for the activity.
Packing the catalyst and reduction catalyst inside one casing
As a result, the heat of reaction of the pretreatment catalyst suppresses heat radiation to the outside.
And can be efficiently used for the activity of the reduction catalyst .

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a diesel engine 1
The reduction catalyst 3 is interposed in the middle of the exhaust passage 2. The reduction catalyst 3 has a structure in which a base material such as alumina, silica, zeolite and the like and a catalyst material composed of a metal such as copper are supported on a honeycomb-shaped carrier, and in a oxidizing atmosphere or in the presence of a hydrocarbon, a nitrogen oxide is used. By contacting an exhaust gas containing (NOx), nitrogen oxides in the exhaust gas are decomposed into nitrogen and oxygen.

As a means for adding the reducing agent upstream of the reduction catalyst 3, an addition device 5 for adding a part of the light oil stored in the fuel tank 4 to the exhaust passage 2 upstream of the reduction catalyst 3 is provided.

A pretreatment catalyst 6 for catalytically decomposing a reducing agent is disposed immediately upstream of the reduction catalyst 3 in the exhaust passage 2. The pretreatment catalyst 6 is a zeolite catalyst (single zeolite or metal added).
The catalyst is formed into a honeycomb structure of an added zeolite catalyst, and catalytically decomposes high molecular weight components and aromatic components in light oil to generate highly reactive low molecular weight gaseous components.

In this embodiment, a pretreatment catalyst 6 and a reduction catalyst 3 are interposed at an interval inside a cylindrical casing 7.

Next, the operation will be described.

The light oil added as a reducing agent passes through the pretreatment catalyst 6 to generate a low molecular weight gaseous component from the light oil. By supplying light oil as a highly reactive low molecular weight gaseous component to the reduction catalyst 3, as shown by the dashed line in FIG. 2, the reduction efficiency of nitrogen oxides is improved, and the total hydrocarbon (THC) is increased. Can be promptly reduced to prevent the reducing agent from being discharged to the outside through the exhaust passage 2 without reacting. In this way, by passing gas oil through the pretreatment catalyst 6, the emission amount of nitrogen oxides and total hydrocarbons is reduced as compared with the case where, for example, propylene is added as a gaseous reducing agent as shown by the broken line in FIG. Can be suppressed equally.

The pretreatment catalyst 16 is used to generate heat of exhaust gas from the engine.
Depending on the amount of gasoline, it can produce gaseous components of low molecular weight from gas oil.
As a result, the temperature of the exhaust gas flowing into the reduction catalyst 3 can be increased by ΔT as compared with the conventional apparatus, as shown in FIG. In other words, before
The exhaust gas temperature of the engine is used for the activity of the treatment catalyst 16.
The reaction heat of the pretreatment catalyst 16 is also used for the activity of the reduction catalyst 3.
In this example, the pretreatment catalyst 16 and the reduction catalyst
3 in one casing 17.
As a result, the heat of reaction of the pretreatment catalyst 16 is reduced by suppressing heat radiation to the outside.
It can be used efficiently for the activity of the source catalyst 3. Then, by the increase in the temperature of the exhaust gas flowing into the reduction catalyst 3, the reduction efficiency of the nitrogen oxides can be increased as shown in FIG.

Thus, the calorie of the exhaust gas of the engine is
By promoting the reaction of the treatment catalyst 16 and increasing the temperature of the exhaust gas flowing into the reduction catalyst 3 by the reaction heat ,
The operating region in which the reduction catalyst 3 is activated can be expanded as shown in FIG.

As another embodiment, as shown in FIG. 6, a pretreatment catalyst section 16 and a reduction catalyst section 13 may be integrated and housed inside a cylindrical casing 17.

[0019]

As described above, the present invention relates to an exhaust gas purification apparatus for a diesel engine comprising: a reduction catalyst provided in an exhaust passage; and means for adding light oil as a reducing agent upstream of the reduction catalyst. , Zeolite as a pretreatment catalyst for catalytic cracking of added light oil upstream of the reduction catalyst
Since the catalyst is used and housed inside the casing that is shared with the reduction catalyst, the reduction agent can be prevented from being discharged without reacting, and the operating area in which the reduction catalyst is activated is expanded, and the nitrogen is reduced. The effect is obtained that the reduction efficiency of the oxide can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of exhaust gas concentration and the like.

FIG. 3 is a diagram showing characteristics of an inlet temperature of a reduction catalyst.

FIG. 4 is a graph showing characteristics of reduction efficiency of nitrogen oxides.

FIG. 5 is a diagram showing an operating region in which the catalyst is activated.

FIG. 6 is a configuration diagram showing another embodiment.

FIG. 7 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 Reference Signs List 1 diesel engine 2 exhaust passage 3 reduction catalyst 5 addition device (addition means) 6 pretreatment catalyst

Claims (1)

(57) [Scope of request for utility model registration] An exhaust gas purification apparatus for a diesel engine, comprising: a reduction catalyst interposed in an exhaust passage; and means for adding light oil as a reducing agent upstream of the reduction catalyst. Pre-treatment catalyst for catalytic decomposition on the upstream side
An exhaust purification device for a diesel engine, wherein a zeolite catalyst is used as a medium, and the zeolite catalyst is housed in a casing shared with a reduction catalyst.