JP2003074331A - Exhaust emission control device and exhaust emission treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of N2 O and increase the selectivity of N2 without lowering the purification rate of NOx in a precious metal catalyst. SOLUTION: In this method and device for denitration, a heat exchanger 2 is installed in a denitration catalyst 1 upstream of exhaust emission to control the temperature of the exhaust emission. A reducer is added to a rather low temperature exhaust emission, and then the exhaust gas is passed through the denitration catalyst 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide (NO) contained in exhaust gas generated from a combustion device such as a diesel engine or a gas engine for a moving body or stationary.
The present invention relates to a nitrogen oxide removing apparatus and method for reducing x) to convert it into harmless nitrogen.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purifying catalyst for gasoline automobiles and the like, a three-way catalyst having a high purifying performance at a theoretical air-fuel ratio and a lean region with excess oxygen (air-fuel ratio: A / F = 2
A NOx storage catalyst combined with a three-way catalyst is known so that NOx can be reduced even in 1). From the viewpoint of improving the fuel efficiency of automobiles, the latter has recently become the mainstream as an exhaust gas purification method. As the three-way catalyst, for example, A
γ-alumina (γAl ₂ O ₃ ) on a cordierite honeycomb substrate whose main component is an l ₂ O ₃ —SiO ₂ —MgO-based oxide.
It is well known that a carrier layer made of is formed and carries a noble metal such as platinum (Pt), palladium (Pd) and rhodium (Rh). As the NOx storage catalyst, it is well known that a carrier layer made of γ-alumina is formed on a cordierite honeycomb substrate and a platinum catalyst and an alkali metal, an alkaline earth metal, a rare earth metal or the like are supported on the carrier layer. The three-way catalyst simultaneously oxidizes unburned hydrocarbons (HC) and carbon monoxide (CO) and decomposes NOx at a stoichiometric air-fuel ratio (A / F = 14.6). On the other hand, the NOx storage catalyst positively oxidizes NO on the catalyst surface in the exhaust gas in the lean region, and then the nitrate ion (N
O ₃ ²⁻ ) is occluded, and when the occluded amount is saturated to some extent, the air-fuel ratio is temporarily made rich, so-called rich spike is performed to desorb and reduce NOx. Therefore, in the lean burn NOx storage catalyst, lean and rich air-fuel ratio control is essential during engine combustion. However, in general, when driving an automobile, especially in urban areas, since acceleration and deceleration are frequently performed, the air-fuel ratio changes frequently in the range from the stoichiometric air-fuel ratio to the lean state, and purification of NOx naturally occurs to some extent. From progressing,
It is considered as one of the practical purification methods.

On the other hand, the exhaust gas generated from a diesel engine generally has a higher oxygen concentration than the exhaust gas generated from a gasoline engine and always maintains a lean state. Therefore, it is possible to use a lean burn NOx storage catalyst for a diesel engine. However, the diesel engine has a problem that it is more difficult to control the air-fuel ratio than the gasoline engine, and the fuel efficiency is deteriorated. In particular, stationary diesel engines start and stop less frequently than automobile diesel engines, and in most cases operate in a steady load mode. Therefore, the conventional NOx storage catalyst that requires lean and rich air-fuel ratio control is not practical.

In addition, N in diesel engine exhaust gas
As a method of removing Ox, N using ammonia as a reducing agent is used.
There is an Ox selective reduction catalyst (SCR catalyst). However, in this case, ammonia as a reducing agent is subject to the regulation of deleterious substances and high-pressure gas, so that it is limited to use in a certain controlled area. There is also a method in which solid urea that is easy to handle is used as a reducing agent, and this is hydrolyzed into ammonia to denitrate. However, in this method, it is necessary to make the injection amount of urea smaller than the stoichiometric ratio of NOx in the exhaust gas so that ammonia does not slip from the outlet of the denitration catalyst, and there is a problem that the actual purification rate decreases. is there. Further, NOx sensors and ammonia gas sensors are installed before and after the catalyst, and it is necessary to control the injection amount of ammonia water or urea water while constantly monitoring the concentrations of NOx and ammonia in the exhaust gas. There is a problem that the sensor is expensive and not economical. In addition, ammonia,
Another problem when urea is used as a reducing agent is ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) produced by a reaction between sulfur and ammonia in exhaust gas, and acidic ammonium sulfate (NH ₄ HS).
O ₄ ) poisons the catalyst. In particular, when it is applied to a diesel engine, light oil or heavy oil containing more sulfur than gasoline is used as a fuel, and since the exhaust gas temperature is low, conditions for easily depositing ammonium sulfate or acidic ammonium sulfate are set.

In view of the conventional problems relating to the NOx purification method as described above, a number of NOx purification methods using a hydrocarbon derived from a fuel or an oxygen-containing organic compound such as alcohol as a reducing agent have been reported so far. ing. That N
Typical examples of Ox purification catalysts include Pt, Pd, Rh,
Examples thereof include noble metals such as Ag, transition metals such as Cu, Fe, Co, and V, and oxide-based catalysts selected from the group of Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , and zeolite.

[0006]

Among NOx purification catalysts that use hydrocarbon or an oxygen-containing organic compound such as alcohol as a reducing agent, transition metals such as Cu, Fe, Co and V,
And an oxide-based catalyst selected from the group of Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , and zeolite generally has a temperature of 400 ° C.
It is possible to exhibit high purification performance at or above or above 500 ° C. Therefore, under an exhaust gas condition where the exhaust gas temperature is relatively low, such as a diesel engine, the oxide catalyst cannot always exhibit sufficient performance. Further, there is a problem that NO ₂ is easily generated in the exhaust gas containing high temperature and excess oxygen, and as a result, the reaction selectivity to N ₂ is lowered.

On the other hand, Pt, Pd, Rh, Ag, etc.
Catalysts of noble metals are lower than those of the above transition metals and oxides.
Since the activity at temperature is relatively high, it is above 200 ℃ and below 400 ℃
It has a high purification effect at a relatively low temperature such as
It is considered to be a suitable purification catalyst for low temperature exhaust gas such as diesel
Has been. However, the issue of precious metal catalysts is NO
In the reduction reaction of x, N₂The question that O is also a byproduct at the same time
There is a problem. N₂O is still a subject of controlled emissions
Not yet, but in the future, substances that contribute to global warming and environmental pollutants
It is expected that it will be regulated as one of the
In the medium, N ₂The challenge is to suppress the generation of O
ing.

As a countermeasure for the above, Japanese Patent Laid-Open No. 2000-2111
Japanese Patent Laid-Open Publication No. P-A0
Installed NOx reduction catalyst consisting of t and Au, and exhaust gas outflow
N consisting of Rh and Ir supported on the metal oxide side₂O
Install a decomposition catalyst, N₂A method for decomposing O is disclosed
Has been. In this case, at least two types of exhaust gas treatment equipment
2 kinds of catalysts, one on the exhaust gas inflow side and the other on the exhaust gas outflow side
Since it is installed in a certain place, it has practical purification performance to some extent.
It is necessary to increase the catalyst volume in order to fill. Well
Also, in high temperature exhaust gas exceeding 300 ° C, N₂More than O
White NO₂Increases and N ₂O decomposition catalyst may not work
It In addition, R. Burch et al. Applied C
analysis B: Environmental 9
(1996) L19-L24, Pt / Al₂O₃For catalyst
When toluene is used as the reducing agent, N₂O is generated
It is reported that it is suppressed, but this is a clean model.
It has only been tested in Dellgas.

The present invention has been made in view of such circumstances, and even in the case of the same noble metal catalyst, NOx is used.
Suppresses the generation of N ₂ O without lowering the purification rate,
An object of the present invention is to provide a NOx purification device and method that improve the selectivity of N ₂ .

[0010]

[Means for Solving the Problems] To achieve the above object
First, the inventors of the present invention firstly conducted carbonization in various precious metal catalysts.
Hydrogen or a low-boiling oxygen-containing organic compound is used as a reducing agent,
A study on NOx reduction characteristics in diesel exhaust gas
However, it was found that there are the following general properties.
This will be described with reference to FIG.₂And N₂O yes
The deviation starts from low temperature and increases with temperature,
It decreases at a certain peak temperature. b) NO ₂Is N₂, N
₂It is generated on the relatively higher temperature side than O, and its peak temperature is
N₂, N₂Higher than O. Also, N₂, N₂O reaction selection
Properties and their peak temperatures depend on the precious metal, the type of support,
And N depends on the particle size of the noble metal, but N₂Towards the selectivity of
In order to raise the temperature, it is preferable to lower the temperature as much as possible.
Yes.

The characteristics of FIG. 1 are that NO--N ₂ O-- in the presence of O _2.
It is considered to be based on the thermodynamic equilibrium reaction in the gas phase of the NO ₂ system. In particular, it is presumed that the higher the activity of the catalyst, the closer the equilibrium composition of the reactant by the catalyst will be to the temperature from low temperature. A suitable temperature for the NOx purification characteristic is about 15
The range is 0 ° C to 320 ° C, and the more preferable range is 20 ° C.
It is 0 ° C or higher and 300 ° C or lower. If it exceeds 320 ° C., NO is easily oxidized on the catalyst and a large amount of NO ₂ is generated, which is not preferable. On the contrary, if the temperature is lower than 150 ° C., the NOx reduction rate is remarkably reduced, which is not practical. Also, N
_Although the method of controlling at a temperature slightly lower than the maximum peak temperature generated by ₂ , although the conversion rate to N ₂ is slightly lowered,
By-product of N ₂ O is remarkably suppressed, and it is the most effective means from the viewpoint of reaction selectivity of N ₂ .

Therefore, the above properties of the noble metal catalyst should be maximized.
According to the present invention, the denitration that contacts exhaust gas
A heat exchange means is provided in the exhaust gas upstream of the catalyst to control the exhaust gas temperature.
The exhaust gas temperature using the temperature detection means and the exhaust gas temperature control means
Is controlled to a temperature within a certain range, and optimal purification with various catalysts
It is characterized by making it a characteristic. Furthermore, specifically N
O ₂, N₂In order to suppress the by-product of O, the exhaust gas temperature is set to 150
It is preferable to control the temperature within the range of ℃ to 320 ℃.
In addition, the exhaust gas temperature is in the range of 200 ° C to 300 ° C.
It is more preferable to control.

Further, according to the present invention, as the reducing agent, a part of engine fuel is taken out and partially oxidized,
The oxygen-containing organic compound produced by the partial oxidation can be used. As a result, the apparatus can be made compact and the cost burden of the reducing agent can be reduced without newly installing a reducing agent storage container.

Further, the denitration catalyst of the present invention is already known as a catalyst having a high NOx purification rate, but in the present invention, it is limited to a catalyst having a relatively high N ₂ reaction selectivity particularly at a low temperature of 300 ° C. or lower. did. Among them, TiO ₂ , SiO ₂ , Z is used as a carrier.
At least one oxide selected from the group consisting of rO ₂ , Al ₂ O ₃ and zeolite or a composite oxide thereof is used, and Rh, Ru, and P and P are used as noble metals.
It is possible to provide a NOx purification device having a high N ₂ reaction selectivity in a catalyst using a multi-component metal or alloy in which t and Au are combined.

Further, according to the present invention, Pt, Rh, R
Among at least one metal or alloy catalyst selected from the group consisting of u, Pd, Ir, and Au, by making the primary particle diameter of these noble metal particles 10 nm or less, low temperature activity and reaction selectivity of N ₂ are achieved. Is further improved.

Further, according to the present invention, the oxidation catalyst and the dust trapping means, or the DPF (D) are provided on the exhaust gas upstream side of the heat exchanger or on the exhaust gas downstream side of the denitration catalyst.
iesel Particulate Filter)
By providing NOx, not only NOx but also unburned hydrocarbons (HC), carbon monoxide (CO) in diesel exhaust gas,
The present invention provides an exhaust gas purification system capable of simultaneously removing black smoke and particulate matter (PM). As the oxidation catalyst, γ-alumina, Pt supported on zeolite, and Pd-based catalyst can be used. As the dust collecting means or the DPF, an oxide-based or non-oxide-based porous material such as cordierite or SiC having high heat resistance and thermal shock resistance can be used, and its porosity depends on the dust collection efficiency. It is preferable that the porosity is 40% or more and 50% or less and the pore diameter is distributed in the range of several μm to 20 μm in order to increase the pressure drop and the pressure loss. Various dust trap filters can be applied as the dust collecting means.

Further, by providing the desulfurization device on the upstream side of the exhaust gas in front of the denitration catalyst, it is possible to suppress the deterioration of the denitration catalyst due to sulfur poisoning and to provide the NOx purification device which can maintain the stable purification performance for a long time. As a desulfurization device, there are a decomposition system by hydrogenation and an adsorption system by a zinc catalyst or the like, but any system is applicable.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. (Embodiment 1) FIG. 2 shows a schematic diagram of a basic exhaust gas purification method of this embodiment. This purification method is a denitrification method for reducing nitrogen oxides in combustion exhaust gas to harmless nitrogen by using at least one compound selected from hydrocarbons and oxygen-containing organic compounds as a reducing agent. A heat exchanger 2 which is a heat exchange means is provided in the exhaust gas upstream of the contacting NOx removal catalyst 1 to control the exhaust gas temperature to a substantially constant temperature, and then the reducing agent supply means 3 adds a reducing agent to the exhaust gas. However, it is characterized by efficiently reducing nitrogen oxides to nitrogen. The heat exchanger 2 may be a known one such as a shell tube type or plate type using a refrigerant such as water, or an air cooling type. Further, the temperature of the exhaust gas contacting with the denitration catalyst is controlled in the range of 150 to 320 ° C., and NO ₂ , N ₂
The feature is that the by-product of O can be suppressed. The heat exchange means for the exhaust gas is not necessarily limited to the heat exchanger. For example, the exhaust gas can be cooled to the above temperature range by supplying outside air on the exhaust gas inlet side of the denitration catalyst 1. As a method for controlling the temperature, a known method such as detecting the exhaust gas temperature with a thermocouple or a resistance temperature detector and controlling the flow rate of the refrigerant according to the detected temperature can be used. Further, in order to enhance the cooling efficiency of heat exchange, it is preferable to keep the distance between the engine and the denitration device as far as possible within the allowable range of the purification device.

(Embodiment 2) FIG. 3 shows a partial oxidation reactor 5 installed between the engine fuel tank 4 and the reducing agent supply means 3 in the exhaust gas purification method described in Embodiment 1.
The fuel supplied from the engine fuel tank 4 by the supply pump 6 is partially oxidized in the partial oxidation reactor 5, and the product produced by the partial oxidation is supplied through the reducing agent supply means to reduce NOx in the exhaust gas. Is the way. In order to prevent complete oxidation in the partial oxidation reactor, it is preferable to use gas phase oxidation without filling the oxidation catalyst. This is because the engine fuel loses its function as a reducing agent when it is completely oxidized.
By this method, although the fuel consumption is slightly deteriorated, it is not necessary to newly provide a space for storing the reducing agent, and the cost of the reducing agent is not newly added, which is economically advantageous.

The method of preparing the denitration catalyst used for the characteristic test in the purification method of Example 1 or Example 2 will be described below. The raw materials and preparation methods described in the examples do not particularly limit the scope of the present invention, and known noble metal catalysts disclosed so far can also be used.

(Example 3) 0.129 mol / l concentration
Tetraammineplatinic acid dichloride (Pt (NH ₃)_FourC
l₂) Liquid to silica (SiO 2₂), Anatase titania
(TiO₂), Γ-alumina (γAl₂O₃), And Zirco
Near (ZrO₂) Impregnated with the carrier powder in a predetermined amount at 120 ° C
After drying in air, bake in air at 300 ℃ for 2 hours.
2wt% Pt / SiO₂(Catalyst symbol P-1), 2 wt%
Pt / TiO₂(Catalyst symbol P-2), 2 wt% Pt / γ
Al₂O₃(Catalyst symbol P-3), and 2 wt% Pt / Zr
O₂A platinum catalyst of (Catalyst symbol P-4) was obtained. These
The rallyed product is a 6 mil / 400 cell honeycomb
-Coated on the gellite base material and dried, then at 700 ℃ for 5 hours
Firing was performed to manufacture a honeycomb-shaped denitration catalyst as a prototype. here,
The amount of Pt supported on the honeycomb substrate is both cost and performance.
Considering the above, it was set to 1 to 3 g / liter. Note that wt% is
The weight percentage is shown. Also, 6 mils / 400 cells means a wall
Has a thickness of 6/1000 inch (about 0.15 mm)
1 inch square (about 645 mm²) 400 per
Refers to a honeycomb with holes.

(Embodiment 4) Instead of the (Pt (NH ₃ ) ₄ Cl ₂ ) liquid which is the Pt raw material of Embodiment 3, 0.019mo
The method is the same as that described in Example 3 except that 1 / l of RhCl ₃ solution is used, and the catalyst obtained at this time is 1 wt.
% Rh / SiO ₂ (catalyst symbol R-1), 1 wt% Rh /
TiO ₂ (catalyst symbol R-2), 1 wt% Rh / γAl ₂ O
₃ (catalyst symbol R-3) and 1 wt% Rh / ZrO ₂ (catalyst symbol R-4).

(Embodiment 5) Instead of the (Pt (NH ₃ ) ₄ Cl ₂ ) liquid which is the Pt raw material of Embodiment 3, 0.0059 m
Example 3 except that IrCl ₄ solution of ol / l concentration was used
Is the same as the method described in, the catalyst obtained at this time,
2 wt% Ir / SiO ₂ (catalyst symbol I-1), and 2 w
t% Ir / TiO ₂ (catalyst symbol I-2).

Example 6 Pt (N) described in Example 3
The H ₃ ) ₄ Cl ₂ solution and the RhCl ₃ solution described in Example 4 were mixed with Pt.
And Rh were mixed at a ratio of 1: 1 in atomic ratio, and this mixed solution was impregnated with silica SiO ₂ and anatase-type titania TiO ₂ powder in predetermined amounts. The subsequent preparation method is the same as in Example 3. The catalyst obtained at this time is 2 wt%
_{(Pt-Rh) / SiO 2} ( Catalyst symbol PR-1), 2w
is t% (Pt-Rh) / TiO 2 ( catalyst symbol PR-2).

Example 7 RhCl described in Example 4
₃ liquid and the IrCl ₄ liquid described in Example 5 were mixed at an atomic ratio of Rh and Ir of 1: 1 and the mixed solution was mixed with silica S.
A predetermined amount of each of iO ₂ and anatase type titania TiO ₂ powder was impregnated. The subsequent preparation method is the same as in Example 3. The catalyst obtained at this time was 1 wt% (Rh-I
r) / SiO ₂ (catalyst symbol RI-1), 2 wt% (Rh
A -Ir) / TiO ₂ (catalyst symbols RI-2).

Example 8 The Rh solution was impregnated by the same method as described in Example 4 and calcined at 300 ° C. for 2 hours, after which a 0.0121 mol / l HAuCl ₄ solution and ammonium sulfite as a reducing agent were added. The aqueous solution was added so that the atomic ratio of Rh and Au was 9: 1, the temperature was kept at 60 ° C. to reduce the gold ion, and the gold ion was deposited on the carrier, then dried at 120 ° C., 300
Calcination was carried out for 2 hours. The catalyst obtained at this time was 1 wt.
A% (Rh-Au) / TiO 2 ( catalyst Symbol RA-1). The subsequent method of coating the honeycomb substrate is described in Example 3.
Is the same as.

Example 9 A solution of tetraethoxysilane and ethanol in a predetermined amount was mixed with a 0.129 mol / l concentration hexachloroplatinic acid (H ₂ PtCl ₆ ) aqueous solution and concentrated hydrochloric acid, and then tetraethoxy was added at room temperature. Hydrolyzes silane,
The gelled product is dried at 120 ° C and converted into xerogel,
Further, it was baked at 300 ° C. for 2 hours. The catalyst obtained at this time was 2 wt% Pt / SiO ₂ (catalyst symbol Psg-1).
Is. Further, instead of the H ₂ PtCl ₆ aqueous solution, 0.01
Using a 9 mol / l RhCl ₃ solution, it was prepared in the same manner as above. The catalyst at this time was 1 wt% Rh / SiO.
₂ (catalyst symbol Rsg-1). The subsequent method of coating the honeycomb substrate is the same as in Example 3. Further, the particle diameters of Pt and Rh obtained in this example were measured by X-ray diffractometry, and as a result, both were 6 to 10 nm. On the other hand, the particle diameters of the noble metals of the catalysts obtained by the impregnation methods of Examples 3 to 9 were all in the range of 10 to 30 nm.

(Example 10) Next, Examples 3 to 9 will be described.
In the purification method described in Example 1, using the prepared catalyst
Each catalyst performance when the test is performed will be described. Trial
The test method is a single cylinder diesel engine (bore φ
135 × stroke 140mm), engine rotation
Number 1800 rpm, fuel injection amount 80 mm³/ St,
Set the exhaust gas temperature at the engine outlet to 350-400 ° C and touch
The medium inlet temperature is 180, 200, and 2 depending on the heat exchanger.
The temperature was controlled at 50 ° C. The reducing agent is a hydrocarbon, propene
(C ₃H₆), The catalyst space velocity (SV) is 100
00h^-1And NO, NO in exhaust gas before and after catalyst
₂A NOx meter based on the Chemilumi method was used to measure
N at the catalyst outlet₂Non-dispersive infrared absorption method for measuring O
According to N₂, N₂O and NO₂The conversion rate to
Yes N₂Conversion rate [%] = (NO_in-(NO_out+ NO_{2 out}+2
× N₂O_out)) / NO _in× 100 N₂O conversion rate [%] = 2 × N₂O_out/ NO_in× 100 Where the subscript in is the amount of compound at the inlet,
out is the amount of compound at the outlet. Also, fuel injection
Mm used as a unit of radiation³/ St is the piston
Siri in one stroke from the intake process to the compression process
The amount of fuel injected into the chamber
It is a representation.

Table 1 shows NOx in each catalyst at that time.
The purification properties are indicated by the N ₂ conversion and the N ₂ O conversion defined above. The temperature in the table is the temperature of the exhaust gas at the outlet of the heat exchanger. Further, in the table, as a comparative example, the results when the heat exchanger is not used are also shown. In addition,
The catalyst temperature in the comparative example was almost the same as the exhaust gas temperature at the engine outlet of 350 to 400 ° C. The main exhaust gas composition measured at the catalyst inlet is as follows.
Exhaust gas _{composition: NO: 500~600ppm, O 2:} 8~
_{10%, CO 2: 10~12ppm,} CO: 50~10
0 ppm, H ₂ O: 5-8%, SO ₂ : 50-100 pp
m, balance N ₂ . Therefore, the supply amount of propene, which is a hydrocarbon reducing agent, is set to about 1000 ppm.

[Table 1] When the heat exchanger is not installed in the comparative example, both are
Low reaction selectivity of N _2, N ₂ and N ₂ O ratios are substantially equal. This is because the temperature of the catalyst layer is as high as about 350 ° C. or higher, so that the oxidation reaction of NO is promoted and the amount of NO ₂ produced increases, resulting in a decrease in the conversion rate to N ₂ . On the other hand, when a heat exchanger is installed and the temperature of the catalyst layer is controlled to 320 ° C. or lower, particularly 280 ° C., 230 ° C., and 180 ° C., the conversion rate to N ₂ increases with any catalyst. It can be seen that the reaction selectivity is also improved.
Among them, Rh-based catalysts (R-1 to 4, PR-1 to 2, RA
-1, Rsg-1), and a catalyst using TiO ₂ as a carrier, have relatively higher N ₂ reaction selectivity than other catalysts and have good performance in the purification method of the present invention. There is. In addition, the catalyst prepared by the sol-gel method (Psg-
In No. 1, Rsg-1), the denitration activity at a low temperature and the reaction selectivity of N ₂ are both improved as compared with the catalysts prepared by other impregnation methods. It can be said that this is due to the effect that the particle size of the noble metal particles is reduced to 10 nm or less and highly dispersed by the sol-gel method.

Example 11 A denitration catalyst (P-2, R-2) in the case of using ethylene (C ₂ H ₄ ) which is another hydrocarbon as a reducing agent in place of propene in Example 10.
Table 2 shows the results of purification characteristics of

[Table 2] As a result, it can be seen that even if ethylene is used as the reducing agent, high purification characteristics are exhibited by installing a heat exchanger, as in propene.

Example 12 In the case of using ethanol (C ₂ H ₅ OH), which is an oxygen-containing organic compound, instead of propene, which is a hydrocarbon, as a reducing agent in Example 10,
Table 3 shows the purification characteristic results of the denitration catalysts (P-2, R-2).

[Table 3] As a result, it can be seen that even when ethanol is used as the reducing agent, high purification characteristics are exhibited by installing the heat exchanger, as in the case of propene.

(Example 13) The results of the purification characteristics of the denitration catalysts (P-2, R-2) in the case of using a partially oxidized light oil instead of propene as the reducing agent in Example 10 are shown. It shows in Table 4. The reactor temperature at this time is
Although not particularly limited, if the temperature is raised too much, the complete oxidation of the gas oil proceeds and the function as a reducing agent is lost. Further, if the reactor temperature is too low, the light oil is less likely to be partially oxidized and directly injected into the exhaust gas flow path, and the purification performance is deteriorated.
A range of 500 ° C is preferred. Further, although the electric heater is used for heating the partial oxidation reactor here, exhaust heat of the engine exhaust gas may be used.

[Table 4] As a result, it can be seen that even if a reducing agent obtained by partially oxidizing light oil is used in the present invention, high purification characteristics are exhibited by installing a heat exchanger as in the case of propene.

Finally, an embodiment of the device of the present invention will be described with reference to FIG. First, the untreated exhaust gas 10 is generated from the engine 9. The engine 9 is connected to the engine fuel tank 4 via a fuel pump 8, and the engine fuel tank 4 is filled with light oil 7. The untreated exhaust gas 10 has its sulfur content removed by a desulfurizer 11 to become an exhaust gas A12, and the exhaust gas A12 has its soot dust removed by a soot and dust collecting means 13 to become an exhaust gas B14. The removal of the sulfur content and the removal of soot and dust contributes to the protection of each device and piping downstream of the exhaust gas, especially the denitration catalyst 1. The exhaust gas B14 is cooled by the heat exchanger 2 to become the exhaust gas C15. here,
In order to maintain the exhaust gas C15 at a preferable temperature of 150 to 300 ° C., the temperature of the exhaust gas C15 is measured by the temperature detection means 16 such as a thermocouple, and the measured temperature is input to the temperature control device 17 by the instrumentation line A20. , Refrigerant 19
The required opening of the flow rate adjusting valve 18 for adjusting the flow rate of the air is calculated by the temperature control device 17, and the operation result is the instrumentation line B2.
1 to output to the flow rate adjusting valve 18. Flow rate adjusting valve 18
The flow rate of the refrigerant 19 is increased by increasing the opening degree of the exhaust gas C15.
Needless to say, if the opening of the flow rate adjusting valve 18 is lowered, the flow rate of the refrigerant 19 decreases and the temperature of the exhaust gas C15 rises. On the other hand, the engine fuel tank 4
A part of the light oil 7 filled in is fed to the partial oxidation reactor 5 by the supply pump 6, and the light oil 7 is partially oxidized and becomes a reducing agent. This eliminates the need to provide a dedicated reducing agent tank and the need to supply a dedicated reducing agent, thereby increasing the degree of freedom in design and operation. The reducing agent is supplied into the exhaust gas C15 by the reducing agent supply means 3. The nitrogen oxides contained in the exhaust gas C15 react with the reducing agent by the denitration catalyst 1 to become harmless nitrogen gas, and are discharged as purified treated exhaust gas 22.

[0034]

According to the present invention, a heat exchanger is provided in the exhaust gas upstream of the noble metal catalyst which comes into contact with the combustion exhaust gas, particularly the exhaust gas from the diesel engine, and the exhaust gas temperature is set to 20.
By controlling the temperature in the range of 0 to 300 ° C. and adding a reducing agent for a hydrocarbon or an oxygen-containing organic compound, nitrogen oxides can be efficiently reduced to nitrogen.

[Brief description of drawings]

FIG. 1 is a graph used for explaining means for solving the problems in the present invention.

FIG. 2 is a schematic view of a nitrogen oxide purifying apparatus of the present invention used in Example 1.

FIG. 3 is a schematic diagram of a nitrogen oxide purifying apparatus of the present invention used in Example 2.

FIG. 4 is a flowchart showing a specific example of the present invention.

[Explanation of symbols]

1 DeNOx catalyst 2 heat exchanger 3 Reductant supply means 4 engine fuel tank 5 Partial oxidation reactor 6 supply pumps 7 light oil 8 fuel pump 9 engine 10 untreated exhaust gas 11 Desulfurization equipment 12 Exhaust gas A 13 Dust collection means 14 Exhaust gas B 15 Exhaust gas C 16 Temperature detection means 17 Temperature control device 18 Flow control valve 19 Refrigerant 20 Instrumentation line A 21 Instrumentation line B 22 Treated exhaust gas

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 B01D 53/36 101A ZAB 102B 102H (72) Inventor Shuji Fujii 1-chome, 8-chome, Kanazawa-ku, Yokohama-shi, Kanagawa Address 1 Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory (72) Inventor Yuichiro Murakami 12 Nishiki-cho, Naka-ku, Yokohama-shi Kanagawa F-term (reference) 3R091 AA18 AB02 AB05 AB11 AB13 BA14 CA08 CA18 EA17 GA16 GB05W GB06W GB07W GB09X GB10X HA08 HA16 4D048 AA06 AB02 AB07 AC02 AC09 BA03X BA06X BA07X BA08X BA11Y BA30X BA31Y BA32Y BA33X BA34X BA41X BA42X BB02 BB17 BC01 BC04 CC31 CC47 CC54 CC61 CD01 CD03 DA08 CD10 CD10

Claims (14)

[Claims] 1. A denitration catalyst in contact with exhaust gas, a heat exchange means provided on the exhaust gas upstream side of the denitration catalyst, and a reducing agent supply means provided between the heat exchange means and the exhaust gas passage of the denitration catalyst. A denitration device for nitrogen oxides in exhaust gas, which is characterized in that 2. The temperature of the exhaust gas is 200 ° C. or higher and 300.
The denitrification device for nitrogen oxides in exhaust gas according to claim 1, further comprising a temperature control means capable of controlling within a range of ℃ or less. 3. The reducing agent supply means comprises a fuel storage device connected to the combustion device, a reducing agent injection means, and a partial oxidation reactor installed between the fuel storage device and the reducing agent injection means. 3. The method according to claim 1 or 2, wherein
A denitrification device for nitrogen oxides in exhaust gas according to 1. 4. The denitration catalyst is TiO ₂ , SiO ₂ , Z
A carrier containing at least one single oxide selected from the group consisting of rO ₂ , Al ₂ O ₃ and zeolite, or a composite oxide thereof, and Pt, Rh, Ru, Pd, I
4. A denitration device for nitrogen oxides in exhaust gas according to claim 1, comprising an active component which is at least one metal or alloy selected from the group consisting of r and Au. 5. The denitration device for nitrogen oxides in exhaust gas according to claim 4, wherein the primary particle diameter of the active ingredient is 10 nm or less. 6. An oxidation catalyst, a dust collecting means and a DPF (Diesel Particulate) on the exhaust gas upstream side of the heat exchange means or on the exhaust gas downstream side of the denitration catalyst.
6. A denitration device for nitrogen oxides in exhaust gas according to claim 1, wherein any one or more of the following) are provided. 7. The denitrification device for nitrogen oxides in exhaust gas according to claim 1, wherein a desulfurization device is provided on the exhaust gas upstream side of the heat exchange means. 8. The nitrogen in the exhaust gas according to claim 1, wherein the reducing agent is at least one compound selected from hydrocarbons and oxygen-containing organic compounds. Oxide denitration equipment. 9. A heat exchange step of exchanging heat of exhaust gas, a reducing agent supply step of supplying a reducing agent to the exhaust gas after heat exchange, and a denitration step of bringing the exhaust gas after adding the reducing agent into a denitration catalyst. A method for denitrifying nitrogen oxides in exhaust gas, comprising: 10. The method for denitrifying nitrogen oxides in exhaust gas according to claim 9, further comprising a temperature control step of controlling the exhaust gas temperature after heat exchange in the range of 150 ° C. or higher and 300 ° C. or lower. 11. The nitrogen oxide in the exhaust gas according to claim 9, wherein at least one compound selected from hydrocarbons and oxygen-containing organic compounds is used as the reducing agent. Denitration method. 12. The oxygen-containing organic compound produced by the partial oxidation of the fuel of the combustion apparatus, the partial oxidation of the fuel, and the partial oxidation, is used as the reducing agent. 12. The method for denitrifying nitrogen oxides in exhaust gas according to any one of 11 above. 13. The method according to claim 9, wherein one or both of a catalytic oxidation treatment step and a dust removal step are performed on the exhaust gas upstream side of the heat exchange step or the exhaust gas downstream side of the denitration step. A method for denitrifying nitrogen oxides in exhaust gas according to claim 1. 14. The desulfurization process is performed on the upstream side of the exhaust gas in the heat exchange process.
3. A method for denitrifying nitrogen oxides in exhaust gas according to any one of 3).