Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1991-03-07
1993-01-19
Heller, Gregory A.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423212, B01J 800, C01B 1700
Patent
active
051805677
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an exhaust gas treating method of removing particulates and nitrogen oxides from exhaust gas discharged from a combustion engine such as a Diesel engine or the like.
2. Background Art
Exhaust gas discharged from a Diesel engine includes gas components such as nitrogen oxides (NOx), sulfur oxides, carbon monoxide and the like, and fine powder having a grain size of not greater than 1 .mu.m called particulates composed of soot (incomplete burnt carbon), soft or heavy hydrocarbon, sulfuric acid mist and the like.
The particulates are produced from the incomplete combustion of light oil serving as fuel of a Diesel engine or the like. The nitrogen oxides and the particulates are regarded as two primary causes of air pollution. It is therefore required to prevent the particulates and the nitrogen oxides from diffusing in the atmosphere.
In this connection, there are proposed various examples of a catalyst device of which catalyst filter carrying an oxidation catalyst is installed at the exhaust system of a Diesel engine so that the particulates from the Diesel engine come in contact with the catalyst filter, causing the particulates to be oxidized, decomposed and removed (See Japanese Unexamined Patent Publication 185425/1988, for example).
As a typical example of the catalyst device above-mentioned, there is known, as shown in FIG. 1, a catalyst filter F in which an oxidation catalyst is carried on a honeycomb structure 1 generally made of porous ceramics which has openings at the exhaust gas inlet side A and openings at the exhaust gas outlet side B, these openings at both sides A and B being alternately closed.
In the catalyst filter F, exhaust gas introduced from the inlet side A is forcibly passed through partition walls 2 made of porous ceramics and discharged outside from the outlet side B, as shown by arrows. When the exhaust gas is passed through the partition walls 2, particulates contained in the exhaust gas are caught by the partition walls 2 so that the particulates are oxidized and decomposed by the oxidation catalyst carried on the partition walls 2.
As the other primary cause of air pollution, nitrogen oxides which are to be removed by a reduction reaction, cannot be removed by the oxidation catalyst of the catalyst filter above-mentioned or the like. Accordingly, to remove both nitrogen oxides and particulates, both an oxidation catalyst and a reduction catalyst are required. This not only complicates the exhaust gas treating mechanism, but also involves the likelihood that the evacuation efficiency in a Diesel engine or the like is lowered.
In view of the foregoing, the present invention is proposed with the object of providing an exhaust gas treating method of readily and securely removing both nitrogen oxides and particulates contained in exhaust gas.
DISCLOSURE OF INVENTION
To solve the problems above-mentioned, the exhaust gas treating method in accordance with the present invention is characterized in that exhaust gas is passed through a catalyst layer at an areal velocity of 100 to 5000 m.sup.3 /m.sup.2. hr to selectively monoxide from particulates contained in the exhaust gas, so that the particulates are removed and nitrogen oxides contained in the exhaust gas are removed by the carbon monoxide thus produced.
According to the present invention having the arrangement above-mentioned, when exhaust gas is passed through the catalyst layer at the areal velocity above-mentioned, incompletely burnt carbon or hydrocarbon in particulates contained in the exhaust gas is partially oxidized to selectively produce carbon monoxide, causing the particulates to be removed. Further, the carbon monoxide thus produced causes nitrogen oxides in the exhaust gas to be reduced and removed as decomposed into nitrogen and water.
In the specification, the term of areal velocity refers to a value obtained by dividing a space velocity, i.e., the flow velocity of exhaust gas passing through the catalyst (in unit of hr.sup.-1), by the contact surfa
REFERENCES:
patent: 2975025 (1961-03-01), Cohn et al.
patent: 3929965 (1975-12-01), Kim et al.
patent: 4009242 (1977-02-01), Lauder et al.
patent: 4140749 (1979-02-01), Baresel et al.
patent: 4160805 (1979-07-01), Inaba et al.
Patent Abstracts of Japan, JP 63-242324 (A).
Nakatsuji Tadao
Yoshida Kimihiko
Yoshimoto Masafumi
Heller Gregory A.
Sakai Chemical Industry Co. Ltd.
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