JPH0671140A - Method and apparatus for treating nitrogen oxide - Google Patents

Abstract

PURPOSE:To remove and purify an exhaust gas with a simple and small constitution by using a compd. wherein gallium is a main ingredient as a catalyst and a hydrocarbon as a reduction gas and performing reduction reaction of nitrogen oxide at a specified temp. CONSTITUTION:Reduction reaction of nitrogen oxide is performed at 400-900 deg.C by using a compd. wherein gallium oxide (Ga2O3) is a main ingredient as a catalyst and a hydrocarbon as a reduction gas. In this case, nitrogen oxide is changed into nitrogen, carbon dioxide and water by reacting with the hydrocarbon based on a catalytic action. This reaction proceeds even when such a hydrocarbon with small number of carbon as methane is used as the reduction gas. As methane being an ingredient of city gas can be used when methane is used as the reduction gas, in a combustor using this as a fuel, it is possible to obtain an NOx-free clean gas by e.g. feeding methane in the exhaust gas in the combustor by making a combustor as a by-pass from the same city gas feeding source and introducing a gas in a mixed condition to a catalytic part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for treating nitric oxide, which is adopted for the purpose of detoxifying nitric oxide contained in exhaust gas from engines, boilers, and the like. The present invention relates to a method for treating nitric oxide which employs a selective reduction method in which nitric oxide is brought into contact with a catalyst together with a reducing gas to reduce it to nitrogen, and a nitric oxide treating apparatus using this method.

[0002]

2. Description of the Related Art This type of selective reduction method has been proposed for reducing nitrogen oxides to nitrogen (decomposing into nitrogen and oxygen) in an atmosphere in the presence of oxygen. Conventionally, in this method, a zeolite compound or the like is used as a catalyst,
Propane, propylene, etc. are used as the reducing gas. When this method is adopted, a reducing gas is supplied to the catalytic reaction part, and at the same time, nitric oxide to be treated is simultaneously supplied to purify the nitric oxide by reducing it.

[0003]

However, in the above-mentioned prior art, when zeolite or alumina is used as a catalyst, it is necessary to use a hydrocarbon having an abnormal carbon number of 3 as a reducing gas. That is, propane, propylene, etc. are used as the reducing gas,
For example, when using this for household combustion equipment,
It is necessary to provide a cylinder of propane, propylene or the like together with this device, which causes a problem that the device becomes complicated and the space required for the device becomes large.

Therefore, an object of the present invention is to use a lower hydrocarbon such as methane as a reducing gas in the selective reduction method. For example, even when used for household combustion equipment, the equipment is simple and small. By obtaining a nitric oxide treatment method that enables reduction treatment of nitric oxide (which eventually leads to removal and purification of exhaust gas) by simply configuring is there.

[0005]

[Means for Solving the Problems] To achieve this object
The characteristic means of the method for treating nitric oxide according to the present invention is a catalyst
Is gallium oxide (Ga₂O₃) Is the main compound
And the reducing gas is a hydrocarbon,
The reduction reaction of the above-mentioned nitric oxide by
There is something to do. Furthermore, the treatment of nitric oxide according to the invention
The characteristic configuration of the processing device is gallium oxide (Ga ₂O₃)
And a catalytic reaction part in which the compound to be distributed is disposed
Is equipped with a supply means for simultaneously supplying nitric oxide and hydrocarbons.
In addition, keep the catalytic reaction part at 400 to 900 ° C.
The warming means is provided, and its action and effect is
It is as follows.

[0006]

In other words, when the method for treating nitric oxide of the present application is used, the catalytic action of the compound containing gallium oxide (Ga ₂ O ₃ ) as the main component in the reaction part where nitric oxide is maintained at 400 to 900 ° C. , Reacts with hydrocarbons and changes into nitrogen, carbon dioxide, and water (where nitrogen is a reduction reaction). This reaction selectively proceeds even in the coexistence of oxygen. Here, the number of carbons is 3 as in the past.
When not only the above hydrocarbons but also hydrocarbons having a small amount of carbon such as methane are used as the reducing gas, the reaction proceeds. As a result, when this method is applied to, for example, exhaust gas containing nitric oxide, this exhaust gas is rendered harmless.

On the other hand, when the apparatus for treating nitric oxide according to the present invention is used, nitric oxide and hydrocarbons are supplied to the catalytic reaction section by the supply means and the above-mentioned reduction reaction is carried out.

[0008]

Therefore, by adopting the invention of the present application, it becomes possible to reduce nitric oxide even when methane or the like having a small carbon number is adopted as the hydrocarbon. Here, when methane is adopted as the reducing gas,
Since methane, which is a city gas component, can be used, in a combustor using this as a fuel, for example, by bypassing the combustor from the same city gas supply source and supplying methane into the exhaust gas of the combustor, NO by just guiding the gas to the catalyst
It is possible to obtain x-free clean gas. That is,
It is very easy to adapt to a combustor, and even in the device configuration, it is not necessary to separately install a cylinder of propane or the like, so that a space-saving exhaust gas purification system can be provided.

[0009]

Embodiments of the present application will be described with reference to the drawings. Figure
1 applies the invention of the present application to a gas engine heat pump
The configuration of the combustion / exhaust system 1 in the case of This moth
The gas engine 2 of the engine heat pump supplies the fuel gas.
Fuel gas p is supplied from the supply system 3 and the combustion air supply system 4, respectively.
Combustion air a is supplied. And inside the gas engine 2
Exhaust gas g containing nitric oxide generated by combustion of
It is discharged to the exhaust system 5. This exhaust system 5 has pellets
Gallium oxide (Ga) ₂O₃) Is the main component
The catalytic reaction part 6 in which the compound is disposed is interposed
It Also, when used, this catalytic reaction part 6 is suitable for reaction
The heat retention device 8 as a heat retention means for maintaining a high temperature
It is installed around the reaction section 6. Therefore, the catalytic reaction part
6 reacts with the heat of the exhaust gas g and the heat retention device 8
Maintained at a suitable temperature (where the exhaust from the gas engine
If the temperature of the gas is sufficiently high, this heat retaining device 8 is necessary.
It doesn't matter. ). On the other hand, gas as shown
Bypassing the engine 2, the reducing gas fuel gas p
Bypass system 9 that leads from the fuel gas supply system 3 directly to the exhaust system 5
Is provided. This bypass system 9 has a mass flow
A flow rate controller 10 such as a controller is provided,
The reducing gas (fuel that is supplied to the exhaust gas g from the bypass system 9
Gas) (the amount of reducing gas to exhaust gas) is controlled
It In operating conditions, exhaust gas containing nitric oxide is discharged.
The gas is purified by passing through the catalytic reaction unit 6 and discharged.
It is discharged to the air side 7. In this structure, the exhaust system 5,
The Y-pass system 9 and the flow rate controller 10 are used to
Elementary and reducing gas are supplied simultaneously. Therefore, this mechanism
Called supply means.

The operation of the above combustion / exhaust system 1 will be described below. First, an example in which methane (13A city gas) is used as the fuel gas (which also works as a reducing gas) will be described below. The gas engine 2 is burned in a state of oxygen excess (λ> 1) from the stoichiometric air-fuel ratio, and the temperature of the catalytic reaction part 6 is maintained at around 700 ° C. by this exhaust heat and the heat retention device 8. Fuel gas p under the conditions on the left
Table 1 shows the relationship between the mixture ratio (the ratio of the bypassed fuel to the amount of exhaust gas g), the purification rate of nitric oxide contained in the exhaust gas g, and the catalyst. (However, in this table, gallium oxide (Ga ₂ O ₃ ) having a particle size adjusted to 5 to 10 μm was used.
And the results of gallium oxide (Ga ₂ O ₃ ) which is a commercially available reagent whose particle size is not adjusted are shown. )

[0011]

[Table 1]

As a result, the removal rate of nitric oxide increased as the mixing ratio of methane as the reducing gas increased. In this state, the exhaust gas naturally contains nitrogen oxides, methane, oxygen, and carbon dioxide, and it can be seen that the selective reduction occurs because the nitrogen oxides are reduced. Here, the reaction of methane on the catalyst with respect to NO and NO ₂ as typical examples of nitric oxide in exhaust gas is described as follows.

[0013]

[Equation 1] 4NO + CH ₄ → 2N ₂ + CO ₂ + 2H ₂ O ……… 2NO ₂ + CH ₄ → N ₂ + CO ₂ + 2H ₂ O ………

By this reaction, NO is reduced and converted into nitrogen, carbon dioxide, and water to be rendered harmless.

In the above method for reducing nitric oxide,
The relationship between the reaction temperature and the reducing performance of nitric oxide will be described based on FIG. The device configuration used is similar to that of FIG. (In the figure, NO is representative of nitric oxide.) Conditions at the time of experiment NO concentration 500 ppm SV value (gas flow rate / reaction part volume) 20000 h ^-1 reducing gas methane (13A)
2500ppm In the coexistence of oxygen, hydrogen, carbon monoxide, carbon dioxide, and water (1) Change in reduction performance with temperature change In Fig. 2, the vertical axis shows the concentration of each gas and the horizontal axis shows the temperature of the reaction part. There is. NO is shown as a solid line and nitrogen is shown as a broken line. The reducing performance with temperature change will be described according to the temperature increase. The solid line shows the NO concentration, and the broken line shows the corresponding N ₂
The concentration is shown. (A) Almost no reaction occurs in the temperature range of 100 to 400 ° C. (B) NO decreases in the range of 400 to 900 ° C. and N ₂
It can be seen that is occurring. NOx can be purified by maintaining the temperature in the above range. Furthermore, in the temperature range of 700 ° C. or higher, the effect of reducing NOx decreased. Therefore, the optimum purification temperature for this catalyst is 60
The temperature is 0 to 700 ° C., and it is easy to apply to high temperature exhaust gas equipment.

[Other Embodiments] Other embodiments of the present application are listed below. (A) In the above-mentioned examples, gallium oxide (Ga ₂ O ₃ ) was mainly used as a catalyst, but yttrium,
It may be one carrying calcium or the like. Therefore, the compound according to the present invention is referred to as a compound containing gallium oxide (Ga ₂ O ₃ ) as a main component. Also, as the reducing gas,
Any hydrocarbon may be used.

(B) In the above embodiment, the compound was placed in a gas containing nitric oxide in the form of pellets.
This may be used after being formed into any shape such as a honeycomb shape.

(C) Further, in the above embodiment,
Although an example of the treatment of nitric oxide in the combustion / exhaust system 1 equipped with a gas engine is shown, the agricultural method of the present application can be used in any case such as treatment of nitric oxide in a plant. it can. Also in the embodiment, the reducing gas and the fuel gas supplied to the gas engine may be different. Further, as the flow rate controller, a needle valve, a capillary or the like can be adopted in addition to the mass flow controller.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exhaust gas purifying apparatus of the present application.

FIG. 2 is a diagram showing a reduced state of nitric oxide when methane is used as a reducing gas.

[Explanation of symbols]

 6 catalytic reaction part 8 heat retention means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Nakayama 4-1-2, Hiranocho, Chuo-ku, Osaka-shi, Osaka Prefecture Osaka Gas Co., Ltd.

Claims (2)

[Claims] 1. A method for treating nitric oxide by the selective reduction method, which comprises contacting nitric oxide with a reducing gas together with a catalyst to reduce the nitric oxide to nitrogen, wherein the catalyst comprises gallium oxide (Ga ₂ O ₃ ). In addition to being a compound containing the main component, the reducing gas is a hydrocarbon, and the reduction reaction of the nitric oxide by the reducing gas is 400 to
A method for treating nitric oxide at 900 ° C. 2. A catalytic reaction part (6) in which a compound containing gallium oxide (Ga ₂ O ₃ ) as a main component is arranged, and a supply means for simultaneously supplying nitrogen oxide and hydrocarbon to the catalytic reaction part. And further comprising the catalytic reaction part (6) of 400 to 900
A treatment apparatus for nitric oxide, which is provided with a heat retaining means (8) for holding at ℃.