JP2003080033A - Method for denitrifying exhaust gas and system therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out effective denitration with little nitrous oxide as a by- product even in the low temperature region of about 100-300 deg.C when NOx is removed from exhaust gas. SOLUTION: In a method for denitrating NOx-containing exhaust gas, the proportion of NO2 contained in the exhaust gas is increased with an oxidizing agent or an oxidation catalyst, an organic nitrogen compound having a nitrile group is added as a reducing agent to the exhaust gas and denitration by reduction of the NOx is carried out in the presence of a denitration catalyst in the temperature region of 100-300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas denitration method and system for removing nitrogen oxides in combustion exhaust gas, and more particularly, to nitrogen oxides contained in combustion exhaust gas, for example, exhaust gas of a marine diesel engine. (NOx)
The present invention relates to an exhaust gas denitration method and system for removing carbon dioxide using a catalyst and a reducing agent.

[0002]

2. Description of the Related Art As is well known, flue gas of marine diesel engines contains nitrogen oxides such as nitric oxide and nitrogen dioxide. The agent was used to decompose into harmless nitrogen (N ₂ ) and water.

Conventionally, in the denitration method of reducing carbon monoxide (NO) or carbon dioxide (NO ₂ ) in combustion exhaust gas to nitrogen in the presence of a catalyst using hydrocarbons or alcohols as a reducing agent, zeolite is used as a denitration catalyst. There have been used those in which metals such as Pt and Cu are supported, and those in which metals such as Cu and Co are supported on alumina. Using these catalysts, hydrocarbons contained in the combustion exhaust gas, hydrocarbons newly injected into the exhaust gas, alcohol, etc. as a reducing agent,
Nitrogen monoxide and nitrogen dioxide in flue gas were reduced to nitrogen for denitration.

[0004]

However, in the above-mentioned denitration treatment using hydrocarbons, alcohols, etc. as a reducing agent, each catalyst has its own temperature range in which it exhibits high activity for the denitration reaction. When the temperature of the exhaust gas at the inlet of the denitration catalyst deviates from this range, nitric oxide and nitrogen dioxide in the exhaust gas are hardly removed.

When an organic nitrogen compound having a nitrile group is used as a reducing agent, nitrous oxide (N ₂₎ which is one of the factors of global warming is shown in the following reaction formulas.
O) was a by-product.

NO + CH ₃ CN + O ₂ → N ₂ O + CO ₂ + H ₂ O The present invention has been made to solve the above problems.
In the method for denitration of combustion exhaust gas containing nitrogen oxides, after increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas with an oxidizing agent or an oxidation catalyst, an organic nitrogen compound is added to the combustion exhaust gas as a reducing agent to remove the denitration catalyst. An object of the present invention is to provide an exhaust gas denitration method capable of removing nitrogen oxides in a low temperature range and reducing byproduct of nitrous oxide by performing a denitration treatment by reducing the nitrogen oxides in the presence. .

Further, according to the present invention, in a method for denitrifying combustion exhaust gas containing nitrogen oxides, an oxidizing means for increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas with an oxidant or an oxidation catalyst, and a downstream of this oxidizing means. Denitration by adding organic nitrogen compound having a nitrile group to the combustion exhaust gas as a reducing agent and performing denitration treatment by reducing the nitrogen oxides in the presence of a denitration catalyst in a temperature range of 100 ° C to 300 ° C. It is an object of the present invention to provide an exhaust gas denitration system capable of removing nitrogen oxides in a low temperature range and reducing byproduct of nitrous oxide by adopting the configuration including the means.

[0008]

According to a first aspect of the present invention, in a method for denitrifying combustion exhaust gas containing nitrogen oxides, after increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas with an oxidant or an oxidation catalyst, An exhaust gas denitration method is characterized in that an organic nitrogen compound is added to a combustion exhaust gas as a reducing agent, and denitration treatment is performed by reducing the nitrogen oxide in the presence of a denitration catalyst.

A second aspect of the present invention is a denitration system for denitration of combustion exhaust gas containing nitrogen oxides, and an oxidizing means for increasing the proportion of nitrogen dioxide contained in the combustion exhaust gas with an oxidizing agent or an oxidation catalyst, and this oxidation. The organic nitrogen compound having a nitrile group is added as a reducing agent to the combustion exhaust gas, which is disposed on the downstream side of the means, and denitration is performed by reducing the nitrogen oxides in the presence of a denitration catalyst in a temperature range of 100 ° C to 300 ° C. An exhaust gas denitration system characterized by comprising denitration means for performing treatment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An exhaust gas denitration method and system according to the present invention will be described. The present invention is not limited to the embodiments below. In the denitration reaction by hydrocarbon (HC), the following reactions generally proceed. NO + HC + O ₂ → N ₂ + CO ₂ + H ₂ O (1) HC + O ₂ → CO ₂ + H ₂ O (2) For example, the exhaust gas from the engine also contains a hydrocarbon component and is used as it is as a reducing agent. Although a method can be considered, the amount of hydrocarbons in the exhaust gas is very small, and it is necessary to positively add a reducing agent and perform efficient denitration by combining the catalyst and the reducing agent. Also,
It requires a reducing agent that promotes the positive reaction of the above (1) and suppresses the side reaction of the above (2), and the reaction (2) that only burns proceeds by simply adding a large amount of hydrocarbons. Will end up. Therefore, in the formula (1), the catalyst and the reducing agent which is a hydrocarbon are selected so as to promote the positive reaction of reducing NO to nitrogen gas even in the presence of oxygen.

In the present invention, examples of the organic nitrogen compound added as the reducing agent include nitrile organic nitrogen compounds such as acetonitrile, acrylonitrile, benzonitrile, and propionitrile. By using these organic nitrogen compounds, NOx can be effectively removed from the exhaust gas even in a low temperature range of about 250 ° C. It is considered that the reason why the nitrile compound is excellent as the reducing agent is that the nitrile group promotes the reduction reaction of NO as a reaction intermediate in the reaction of the above formula (1). Therefore, it is preferable to add a compound having a nitrile group, such as acetonitrile, as a reducing agent.

In the present invention, the oxidizing agent is HCl.
O_Four, HClO_Three, HClO_Two, HClO, H_TwoO_Two，
O_ThreeAt least one of the above. Also acid
As the oxidization catalyst, Al_TwoO_Three, SiO_Two, ZrO_Two, T
iO_Two, A group consisting of metallosilicates and zeolites
At least one carrier selected from among MnO_Two, Ag _Two
O, CO_ThreeO_Four, CoO, In_TwoO_Three, Mn_TwoO_Three, C
eO_Two, Ce_TwoO_Three, RuO_Two, Pt, Ru, Rh, I
at least 1 selected from the group consisting of r, Ag and Pd
The thing carrying the active species of a seed | species is mentioned.

In the present invention, used when performing denitration treatment
The denitration catalyst used is Al_TwoO _Three, SiO_Two, Zr
O_Two, TiO_Two, From metallosilicates and zeolites
At least one carrier selected from the group consisting of Pt and R
u, Rh, Ir, Pd, Cu, Co, Fe, Ag, M
less selected from the group consisting of n, Ni, Zn and In
Both include one carrying one active species.

In the present invention, the denitration treatment is 100 to
It is performed in the temperature range of 300 ° C. The reason for this is that denitrification treatment cannot be performed below 100 ° C., and if it exceeds 300 ° C., the amount of nitrous oxide by-product increases.

In the present invention, the ratio of the nitrogen dioxide is 80% or less of the total NOx (NO + NO ₂ ) at the denitration catalyst inlet. This is because if the proportion of nitrogen dioxide exceeds 80%, the denitration performance will be reduced. The ratio of nitrogen dioxide is more preferably 60% or less.

[0016]

EXAMPLES Examples of the present invention will be described below. (Example 1) (Preparation of catalyst 1): First, water glass No. 1 (SiO ₂ : 3)
0%): 5616 g is dissolved in water: 5429 g, and this solution is referred to as solution A. On the other hand, aluminum sulfate: 718.9 g, ferric chloride: 110 g, calcium acetate: 47.2 g, sodium chloride: 262 g, concentrated hydrochloric acid: 2020 g are dissolved in water: 4175 g, and this solution is designated as solution B.
Subsequently, the solution A and the solution B were supplied at a constant ratio to form a precipitate, which was sufficiently stirred to obtain a slurry having a pH of 8.0.
Next, this slurry was charged into a 20-liter autoclave, 500 g of tetrapropylammonium bromide was further added, and hydrothermal synthesis was carried out at 160 ° C. for 72 hours, followed by washing with water and drying, and further firing at 500 ° C. for 3 hours. The crystalline silicate 1 was obtained. This crystalline silicate is represented by the following composition formula in terms of the oxide molar ratio (excluding the water of crystallization).

0.5Na ₂ O ・ 0.5H ₂ O ・ (0.8Al ₂ O ₃・ 0.2Fe
₂ O ₃ · 0.25CaO) · 25SiO _{2 The} above crystalline silicate 1 is a 4N NH ₄ Cl aqueous solution 40
NH ₄ ion exchange was carried out with stirring at ℃ for 3 hours. Next, after ion exchange, it was washed, dried at 100 ° C. for 24 hours, and then baked at 400 ° C. for 3 hours to obtain an H-type crystalline silicate 1.

(Catalystization) First, to 100 g of the above H-type crystalline silicate 1, alumina sol: 3 g, silica sol: 55 g (SiO ₂ : 20 g) and water: 200 g were added as a binder and sufficiently stirred to wash coat. For slurry. Subsequently, a cordierite monolith substrate (for a 400-cell grid) was immersed in the slurry and taken out, and then excess slurry was blown and dried at 200 ° C. Here, the coating amount is 20 per liter of the substrate.
0 g was carried, and this coated product was designated as honeycomb coated product 1. Next, chloroplatinic acid (H ₂ PtCl ₆ · H ₂ O: 4.
The honeycomb coated article 1 was dipped in 39 g / 100 cc: H ₂ O) and impregnated for 1 hour, and then the liquid adhering to the wall of the substrate was wiped off and dried at 200 ° C. Further, firing was performed at 500 ° C. to obtain a honeycomb catalyst 1.

(Preparation of Catalysts 2-18) In the method for synthesizing the crystalline silicate 1 in the preparation of the above-mentioned honeycomb catalyst 1, cerium chloride, titanium chloride, and antimony chloride were used instead of calcium acetate as Fe ₂ O in terms of oxides. Crystalline silicates 2 to 4 were prepared by repeating the same operation as in crystalline silicate 1 except that the same molar number as ₃ was added. The composition of these crystalline silicates is represented by the following composition formula in terms of the oxide molar ratio (dehydrated form). 0.5Na ₂ O ・ 0.5H ₂ O ・ (0.2Fe ₂ O ₃・ 0.8Al ₂ O ₃・ 0.25M
O) .25SiO ₂ However, M is Ce, Ti, Sb.

Using the above crystalline silicates 2 to 4, the H-type crystalline silicates 2 to 2 are processed in the same manner as the honeycomb catalyst 1.
No. 4 was obtained, and this silicate was further coated on a cordierite monolith substrate by the same steps as in the preparation of the honeycomb catalyst 1, to obtain honeycomb coated products 2 to 4. Next, it was immersed in a chloroplatinic acid aqueous solution and treated in the same manner as the honeycomb catalyst 1, to obtain honeycomb catalysts 2 to 4.

Further, the crystalline silica of the honeycomb catalyst 1 is
Γ-Al instead of_TwoO_Three, Θ-Al_TwoO_Three,
ZrO_Two, TiO_Two, TiO_Two・ ZrO_Two, SiO_Two・
Al _TwoO_Three, Al_TwoO_Three・ TiO_Two, SO_Four/ Zr
O_Two, SiO_Two, Y-type zeolite, X-type zeolite, Z
SM-5 type zeolite, mordenite and silicalite
Platinum is loaded in the same manner as catalyst 1 using
Cam catalysts 5 to 18 were obtained.

(Catalysts 19 to 22): Further, in the preparation method of Catalyst 1, crystalline silicate 1 was used, and palladium nitrate, rhodium chloride, ruthenium chloride, and iridium chloride were used in the same manner as in Catalyst 1 in place of chloroplatinic acid. To obtain honeycomb catalysts 19 to 22.

(Catalysts 23 to 27): In the preparation method of Catalyst 1, crystalline silicate 1 was used, and manganese nitrate, silver nitrate, cobalt nitrate, indium chloride and cerium nitrate were used in place of chloroplatinic acid, each metal or metal. The honeycomb catalysts 23 to 27 were obtained in the same manner as in the catalyst 1 by immersing the oxide in an amount of 1% by weight based on the carrier.

(Catalyst 27-40): Honeycomb catalyst 1
In place of the crystalline silicate 1 of γ-Al ₂ O ₃ , θ
_{-Al 2 O 3, ZrO 2,} TiO 2, TiO 2 · ZrO
₂ , SiO ₂ · Al ₂ O ₃ , Al ₂ O ₃ · TiO ₂ , S
O ₄ / ZrO ₂ , SiO ₂ , Y-type zeolite, X-type zeolite, ZSM-5 type zeolite, mordenite, and silicalite were used to carry platinum in the same manner as in Catalyst 1 to prepare honeycomb catalysts 28 to 41. Obtained.

Example 2 Using the honeycomb catalysts 1 to 41 prepared in Example 1, two of them were arranged in series as shown in FIG. 1 and a denitration activity evaluation test was conducted. The evaluation condition is a simulation of exhaust gas from a diesel engine, and the gas conditions before the catalyst A are described below.

<Gas condition before catalyst A> NO: 1000
ppm, SO ₂ : 1000 ppm, O ₂ : 15%, CO
₂ : 5%, H ₂ O: 5%, N ₂ : balance, GHSV:
5000h ^-1 , gas amount 110NL / h, <others> NO oxidation catalyst amount: 11.7cc, catalyst layer temperature: 250 ° C added acetonitrile: 1600ppm DeNOx catalyst amount: 11.7cc catalyst layer temperature: 100 ° C, 200 ° C, 300 C. The denitration rate is represented by the following formula. Denitration rate (%) = (1−outlet NOx concentration / inlet NOx concentration) × 100 Activity evaluation results are shown in Tables 1 and 2 below using each honeycomb catalyst.

[0027]

[Table 1]

[0028]

[Table 2]

In Table 1, the honeycomb catalyst 23 is selected as the oxidation catalyst A, and the honeycomb catalysts 1 to 22 are selected as the denitration catalyst B. Further, in Table 2, the honeycomb catalysts 24 to 41 are selected as the oxidation catalyst A, and the honeycomb catalyst 1 is selected as the denitration catalyst B.

(Embodiment 3) Under the same test conditions as in Embodiment 2.
The type of reducing agent using honeycomb catalysts 1 and 23
I examined the effect of. Instead of acetonitrile,
Ronitrile (CH _TwoCHCN), benzonitrile (C₆
H₅CN), propionnitrile (C_TwoH ₅CN)
The activity was evaluated by adding 3200 ppm in terms of Cl.
Value test was conducted. Table 3 below shows the activity evaluation results.
You

[0031]

[Table 3]

Example 4 As shown in FIG. 2, the oxidizing agent adding apparatus 1 and the denitration catalyst B were arranged in series, and the influence of the type of oxidizing agent was examined. As an added oxidant, instead of the oxidation catalyst, H
ClO ₄ , HClO ₃ , HClO ₂ , HClO, H ₂ O
₂ and O ₃ were added at 500 ppm and an activity evaluation test was conducted. Table 4 below shows the activity evaluation results. However, the gas conditions in the former stage of the oxidizing agent adding device are as follows.

<Gas condition before oxidizer addition device> NO:
1000 ppm, SO ₂ : 1000 ppm, O ₂ : 5
%, CO ₂ : 5%, H ₂ O: 5%, N ₂ : balance, G
HSV: 5000 h ^-1 , gas amount 110 NL / h, <Others> 1600 ppm of acetonitrile was added after the addition of the oxidizing agent. DeNOx catalyst amount: 11.7 cc Catalyst layer temperature: 100 ° C, 200 ° C, 300 ° C The denitration rate is represented by the following formula. Denitration rate (%) = (1-outlet NOx concentration / inlet NOx concentration) × 100

[0034]

[Table 4]

From the test results shown in Table 1, Table 2, Table 3 and Table 4 above, after increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas with the oxidizing agent or the oxidizing catalyst in the preceding stage of the denitration catalyst, By adding a reducing agent having a nitrile group as a hydrocarbon to the exhaust gas, 100 to 300 ° C
It was found that NOx can be efficiently removed with almost no N ₂ O by-produced in the temperature range of 1. Therefore,
It has become clear that the problem of the denitration method using an organic nitrogen compound, which has conventionally required a high temperature of about 300 ° C. and the problem of by-product of nitrous oxide, can be solved.

FIG. 3 shows a schematic structure of the exhaust gas denitration system according to this embodiment. In FIG. 3, reference numeral 11 indicates a combustion engine such as a marine diesel engine. This combustion engine 11
An oxidizer 12 for increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas containing nitrogen oxides from the combustion engine 11 with an oxidant (or an oxidation catalyst) is connected to the.
In this oxidizing device 12, an oxidizing agent such as HClO ₄ is sprayed, and NO in the combustion exhaust gas supplied from the combustion engine 11 is oxidized to NO ₂ .

On the downstream side of the oxidizing device 12, there is arranged a denitration device 13 in which a catalyst, for example, alumina (Al ₂ O ₃ ) carrying platinum (Pt) is filled. The flue gas supplied from the oxidizer 12 side has a denitration device 13
Nitrogen compounds having a nitrile group on the upstream side of (CH ₃
CN) is added as a reducing agent, and the denitration device 13 performs denitration treatment by reducing nitrogen oxides in the presence of a denitration catalyst in a temperature range of 100 ° C. to 300 ° C. to obtain nitrogen (N ₂ ).

Thus, the exhaust gas denitration system according to the present invention
In the system, the combustion exhaust gas is placed between the combustion engine 11 and the denitration device 13.
The ratio of nitrogen dioxide contained in oxygen
It has a structure in which an oxidizing device 12 for increasing the amount of medium is arranged.
Therefore, CH is added to the combustion exhaust gas. _ThreeAdd CN as reducing agent
The presence of a denitration catalyst in the temperature range of 100 ° C to 300 ° C
By performing denitration treatment by reducing the nitrogen oxides,
This makes it possible to remove nitrogen oxides at low temperatures and
It is possible to reduce the by-product of nitric oxide, and it is also desirable to remove nitrogen oxides.
Appropriate temperature range (especially lower limit) from the conventional lower limit of 250 ℃ to 1
Can be extended to 00 ℃.

(Comparative Example) Catalyst No. When 23 is used only as the denitration catalyst B (that is, when the oxidation catalyst A is not used), the denitration rate is 10% and N ₂ O is 200 ° C.
The amount of by-product was 80 ppm.

[0040]

As described in detail above, according to the exhaust gas denitration method of the present invention, the effect of the reducing agent promotes the denitrification decomposition of nitrogen oxides in the combustion exhaust gas into nitrogen and water. can do. Further, according to the method of the present invention, when removing NOx from the exhaust gas of a diesel engine or the like, nitrous oxide is hardly produced as a by-product, and
Effective denitration treatment can be performed even in a low temperature range of about 300 ° C. Further, the suitable temperature for removing nitrogen oxides can be widened as compared with the conventional case. Further, also in the exhaust gas denitration system according to the present invention, the same effect as the denitration method can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram in the case of performing denitration using two types of honeycomb catalysts in an exhaust gas denitration method according to a second embodiment.

FIG. 2 is an explanatory diagram in the case of performing denitration using an oxidizing agent addition device and one type of honeycomb catalyst in the exhaust gas denitration method according to Example 4.

FIG. 3 is a schematic explanatory diagram of an exhaust gas denitration system according to the present invention.

[Explanation of symbols]

1 ... Oxidizer addition device, 11 ... Combustion engine, 13 ... Oxidizer, 14 ... Denitration device.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 29/44 B01J 29/88 A 29/88 F01N 3/08 B F01N 3/08 DG 3/10 A 3/10 3/28 301E 3/28 301 B01D 53/36 102G (72) Inventor Shigeru Nojima 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute F-term (reference) 3G091 AA04 AA18 AA28 AB02 AB04 BA04 BA14 BA39 CA16 CA21 FA02 FA04 FA12 FA13 FB02 FB10 FC04 FC07 GA06 GB01W GB01X GB05W GB06W GB07W GB09X GB10W GB10X GB16X HA10 4D048 AA06 AB31 BAX BA31XXBAX BA31XXBAX BA07XBAX BA07X BA07X BA07X BA07X BA07X BB02 4G069 AA03 AA08 BA01B BA02B BA04B BA05B BA07B BC09B BC18B BC26B BC43B BC50B BC66B BC70B BC71B BC72B BC75B CA02 CA03 CA07 CA08 CA13 DA06 EA19 FA02 FA03 FB14 ZA03B ZA06B ZA11B ZA36B ZA37B ZB01 ZB06 ZB09

Claims (9)

[Claims] 1. A method for denitrifying combustion exhaust gas containing nitrogen oxides, wherein the ratio of nitrogen dioxide contained in the combustion exhaust gas is increased by an oxidizing agent or an oxidation catalyst, and then an organic nitrogen compound is added as a reducing agent to the combustion exhaust gas. The exhaust gas denitration method is characterized by performing denitration treatment by reducing the nitrogen oxides in the presence of a denitration catalyst. 2. The exhaust gas denitration method according to claim 1, wherein the organic nitrogen compound is an organic nitrogen compound having a nitrile group. 3. The exhaust gas denitration method according to claim 1, wherein the denitration catalyst is used in a temperature range of 100 to 300 ° C. 4. The exhaust gas denitration method according to claim 1, wherein the ratio of the nitrogen dioxide is 80% or less of the total NOx (NO + NO ₂ ) at the denitration catalyst inlet. 5. The oxidizing agent is HClO ₄ , HCl
The exhaust gas denitration method according to any one of claims 1 to 4, which is at least one of O ₃ , HClO ₂ , HClO, H ₂ O ₂ , and O ₃ . 6. The oxidation catalyst is Al_TwoO_Three, Si
O_Two, ZrO_Two, TiO _Two, Metallosilicates and zeo
At least one carrier selected from the group consisting of lights
To MnO_Two, Ag_TwoO, Co_ThreeO_Four, CoO, In_Two
O_Three, Mn_TwoO_Three, CeO_Two, Ce_TwoO_Three, RuO_Two，
From the group consisting of Pt, Ru, Rh, Ir, Ag and Pd
It carries at least one selected active species.
In any one of Claim 1 thru | or 4 characterized by the above-mentioned.
Exhaust gas denitration method described. 7. The exhaust gas denitration method according to any one of claims 1 to 4, wherein the organic nitrogen compound is acetonitrile, acrylonitrile, benzonitrile, or propionitrile. 8. When performing denitration treatment, A is used as a denitration catalyst.
Pt, Ru, Rh, Ir, Pd, C on at least one carrier selected from the group consisting of 1 ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , metallosilicate and zeolite.
5. At least one active species selected from the group consisting of u, Co, Fe, Ag, Mn, Ni, Zn and In is contained therein, according to any one of claims 1 to 4. Exhaust gas denitration method described. 9. In a denitration system for denitration of combustion exhaust gas containing nitrogen oxides, an oxidizing means for increasing the ratio of nitrogen dioxide contained in the combustion exhaust gas with an oxidizing agent or an oxidation catalyst, and a downstream side of the oxidizing means. Denitration means for performing denitration treatment by adding an organic nitrogen compound having a nitrile group to a combustion exhaust gas as a reducing agent and reducing the nitrogen oxide in the presence of a denitration catalyst in a temperature range of 100 ° C to 300 ° C. An exhaust gas denitration system comprising: