JP3254040B2 - DeNOx treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration method capable of removing nitrogen oxides (hereinafter abbreviated as NOx) in exhaust gas with high efficiency.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides (NOx) in exhaust gas, a catalytic ammonia reduction method in which NOx and ammonia (NH ₃ ) are catalytically reacted to decompose into nitrogen and water is widely used. I have. This method requires a denitration catalyst for accelerating the reaction, and many researches on catalyst development have been made so far.

[0003]

Recently, NOx emission regulations have become stricter. Particularly in large cities, there has been a demand for reducing the NOx emission concentration from a chimney to about 0.06 ppm corresponding to the atmosphere. . In the denitration method by catalytic reduction using NH ₃ , the reaction proceeds according to the following equation, and NOx is decomposed into N ₂ . 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O In the conventional method, almost the same amount of NH ₃ was added as in the above equation to perform denitration. However, in the boiler exhaust gas,
Due to the influence of the degree of mixing of NO and NH ₃ and the decomposition of NH ₃ , 100% denitration cannot be carried out according to the above reaction formula, the reaction rate is about 80 to 90%, and the unreacted NO is several ppm to
0 ppm was emitted as it was. On the other hand, NH ₃
Although it is possible to increase the decomposition rate of NO by adding more than the same amount of O, there is a problem that unreacted NH ₃ is discharged into the atmosphere. Therefore, there is a preferable NOx emission concentration reduction method. Did not.

An object of the present invention is to solve the problems of the prior art and to provide a denitration method capable of decomposing NOx with high efficiency without releasing unreacted NH ₃ into the atmosphere. And

[0005]

The present invention provides a method for removing nitrogen oxides by introducing a nitrogen oxide-containing exhaust gas into a denitration reactor filled with a denitration catalyst and contacting the exhaust gas with the denitration catalyst in the presence of ammonia. A denitration catalyst layer is installed on the exhaust gas inflow side, and a denitration reactor with an ammonia decomposition catalyst layer is installed on the exhaust gas outlet side. Decomposing, a denitration treatment method of exhaust gas to decompose excess ammonia in the subsequent stage, wherein the ammonia decomposition catalyst,
In the dehydrated state, (1.0 ± 0.6) R ₂ O · [aM ₂
O ₃ · bAl ₂ O ₃ ] · cMeO · ySiO ₂ (wherein,
R: alkali metal ion and / or hydrogen ion; M: at least one element selected from the group consisting of group VIII elements of the periodic table, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium; Me: alkali Earth element, a + b = 1.0, a ≧ 0, b ≧ 0, c ≧ 0, y / c
> 12, y> 12), and Table 1
Exhaust gas which is a catalyst comprising a crystalline silicate having an X-ray diffraction pattern shown in the above, containing at least one or more of copper, cobalt, nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements This is a denitration treatment method.

[0006] In the method of the present invention, the denitration reactor is discharged.
NH on gas inlet side_ThreeSelective decomposition of NOx in the presence of NO
A denitration catalyst is provided, and NH is reacted with NOx or more_ThreeWith
To sufficiently decompose NOx. On the other hand, on the exhaust gas outlet side
Has NH_ThreeBy installing a decomposition catalyst, unreacted NH_ThreeIs
Harmless N_TwoAnd H_TwoDecomposes into O. 2NH_Three+ 3 / 2O_Two → N_Two+ 3H_TwoO According to the method of the present invention, the denitration catalyst and NH_ThreeAfter cracking catalyst
NOx or NH on the downstream side _ThreeIs hardly discharged,
It is possible to perform denitration at a rate.

As the denitration catalyst used in the former stage, a titania catalyst supporting vanadium, tungsten, or the like is suitable, and it is preferable to form and install it in a honeycomb shape.

The NH ₃ decomposition catalyst installed at the subsequent stage is dehydrated (1.0 ± 0.6) R ₂ O. [aM ₂ O _3.
bAl ₂ O ₃ ] .cMeO.ySiO ₂ (wherein, R is an alkali metal ion and / or a hydrogen ion, M is a group VIII element in the periodic table, a rare earth element, titanium, vanadium, chromium, niobium, antimony and gallium. At least one element selected from the group consisting of: Me: alkaline earth element, a +
b = 1.0, a ≧ 0, b ≧ 0, c ≧ 0, y / c> 12,
y> 12) and a crystalline silicate having an X-ray diffraction pattern shown in Table 1 among copper, cobalt, nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements. It is a catalyst containing at least one or more kinds.

[0009]

[Table 1] VS: Very strong (X-ray source: Cu) S: Strong M: Intermediate W: Weak

This catalyst converts NH ₃ into N ₂ at a temperature range of 100 to 600 ° C. without deterioration over a long period of time.
Can be decomposed into This catalyst has a feature that it does not generate any by-products such as NO, NO ₂ and N ₂ O by decomposition of NH ₃ , and can be selectively converted to N ₂ . This catalyst is preferably provided in a honeycomb form by a wash coat method or a solid method. As a particularly preferred embodiment, the substrate is used in a form coated on a substrate such as cordierite molded into a honeycomb shape.

[0011]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples. (Preparation of catalyst) Ammonia reduction denitration catalyst (denitration catalyst) is prepared by using vanadium pentoxide (V ₂ O) on a titania (TiO ₂ ) carrier.
₅ ) 2 wt%, tungsten trioxide (WO ₃ ) 8 w
3mm □ pitch, 1mm wall thickness of powder catalyst loaded with t%
What was shape | molded in the honeycomb shape of this was used. This honeycomb catalyst is referred to as Catalyst A.

As the ammonia decomposition catalyst, a crystalline silicate type catalyst having the composition shown in Table 2 in terms of the molar ratio of oxides and having the crystal structure having the X-ray diffraction pattern shown in Table 1 was used. A powder of these catalysts is applied to a cordierite honeycomb substrate having a shape similar to that of the above-mentioned denitration catalyst.
Coating was carried out by a wash coat method so that the amount was g / m ² . These honeycomb catalysts were designated as catalysts B to N.

[0013]

[Table 2]

(NOx removal test) A denitration catalyst layer 2 (catalyst A) is provided on the exhaust gas inflow side (front stage) of the vertical denitration reaction test apparatus 1 shown in FIG. 1, and an ammonia decomposition catalyst is provided on the exhaust gas outlet side (rear stage). The layers 3 (the catalysts B to N) were placed so that each volume became 27 ml. In this test apparatus, a test gas having the following composition was applied in the directions of arrows X and X to SV = 16300.
h ^-1 (gas amount: 440 Nl / h) and heated by the electric furnace 4 to adjust the temperatures of the denitration catalyst layer and the ammonia decomposition catalyst layer to 300 to 400 ° C. and 200 to 400 ° C., respectively.
A denitration test was carried out while the temperature was kept at a temperature in the range of ° C. <Test gas composition> NO 50 ppm NH ₃ 100 ppm CO ₂ 7% H ₂ O 6% O ₂ 14.7% N ₂ remaining Between the former catalyst layer and the latter catalyst layer (gas A) and the latter catalyst Sample gas on the downstream side (gas B) of the bed,
NOx (NO + NO ₂ ) and NH ₃ at each position
Was determined. DeNOx catalyst A and ammonia decomposition catalyst B
Table 3 shows the measurement results obtained by changing the temperature of each catalyst layer. Table 4 shows the results obtained by measuring the temperatures of the denitration catalyst layer and the ammonia decomposition catalyst layer at 350 ° C. and 300 ° C., respectively, and using the catalysts C to N as the ammonia decomposition catalyst.

[0015]

[Table 3]

[0016]

[Table 4]

[0017] Table 3 and from the results of Table 4, the method of the present invention, a high denitration rate of approximately 99% in the previous stage of the denitration catalyst layer can be obtained, the use of NH ₃ in 2 molar ratio with respect to NOx, It can be seen that the excess NH ₃ is almost completely decomposed in the subsequent ammonia decomposition catalyst layer, and the denitration is further advanced in the subsequent catalyst layer, and the NOx concentration is further reduced. Note that NOx was used for gases A and B.
(NO + NO _2), but analysis of the N ₂ O is also performed other than N ₂ O
It was confirmed that there was almost no by-product.

[0018]

According to the method of the present invention, there is no danger of leaking NH ₃ from the exhaust gas containing NOx, and the efficiency of N 2 is increased with high efficiency.
Ox can be decomposed and removed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of a denitration treatment method according to the method of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/00 B01D 53/86

Claims (1)

(57) [Claims] 1. A method for removing a nitrogen oxide by introducing a nitrogen oxide-containing exhaust gas into a denitration reactor filled with a denitration catalyst and bringing the exhaust gas into contact with the denitration catalyst in the presence of ammonia. A denitration reactor having an ammonia decomposition catalyst layer is installed on the exhaust gas outlet side, and ammonia is added to the nitrogen oxides in an earlier stage in a reaction equivalent amount or more to decompose the nitrogen oxides. A method for denitration of exhaust gas, wherein the ammonia decomposition catalyst is dehydrated (1.0 ± 1.0%).
0.6) R ₂ O · _{[aM 2 O 3 · bAl 2 O} 3 ] · cM
eO · ySiO ₂ (wherein, R is an alkali metal ion and / or a hydrogen ion, M is a member selected from the group consisting of a group VIII element of the periodic table, a rare earth element, titanium, vanadium, chromium, niobium, antimony, and gallium. Or more elements, Me: alkaline earth element, a + b = 1.0, a ≧
0, b ≧ 0, c ≧ 0, y / c> 12, y> 12) and a crystal having an X-ray diffraction pattern shown in Table 1 described in the detailed description of the invention. A method for denitrifying exhaust gas, which is a catalyst comprising at least one of copper, cobalt, nickel, iron, zinc, manganese, chromium, an alkaline earth element and a rare earth element in a crystalline silicate.