JPH11267459A - Reducing method of nitrogen oxide and so3 in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease both of NOx concn. and SO3 concn. in an exhaust gas by adding ammonia to the exhaust gas containing NOx and SO3 and then, bringing the exhaust gas into contact with a SO3 reducing catalyst and a denitration catalyst to reduce the NOx and the SO3 in the exhaust gas. SOLUTION: In a process to selectively decompose NOx into nitrogen and water in order to prevent NOx and SO3 present in a combustion exhaust gas such as a boiler from being exhausted into the air, after ammonia is added to the exhaust gas, the exhaust gas is brought into contact with a SO3 reducing catalyst and a denitration catalyst to reduce the NOx and the SO3 in the exhaust gas. As the SO3 reducing catalyst, a catalyst prepared by carrying ruthenium on a carrier comprising titania or alumina is used. As the denitration catalyst, a catalyst prepared by adding vanadia, tungsten oxide or molybdenum oxide on a carrier made of titania is used. The SO3 reducing catalyst and the denitration catalyst may be a same material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the combustion exhaust of a boiler or the like.
Nitrogen oxides (NO_X) And SO _ThreeReturn of
Original processing method.

[0002]

From the viewpoint of prevention of the Related Art Air pollution, as a method for preventing the discharge of the NO _X in the air generated from boilers and various combustion furnaces, with the addition of ammonia in the exhaust gas contacts the denitration catalyst Then, a denitration method of selectively decomposing NO _X into nitrogen and water is applied.

[0003]

However, the above denitration method
When the method is used, poor fuel such as heavy oil and
Exhaust gas generated by burning the fuel contains a large amount of sulfur oxides (S
O_X). SO _XAmong them, SO_ThreeIs corrosive
It is a gas, and sulfuric acid or acid is added to the downstream air preheater or electric dust collector.
Condensed in the form of volatile ammonium sulfate, etc., causing corrosion and clogging.
You. In addition, in the combustion of poor fuel oil,
What is SO_ThreeMay be emitted in large quantities. Furthermore, denitration
At this time, on the denitration catalyst, SO_TwoSO
_ThreeOxidation to SO_ThreeThe concentration increases. Therefore,
The present inventors have found that nitrogen oxides and SO_ThreeTogether
As a result of studying the method of
Was.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for reducing nitrogen oxides and SO _{3 in} exhaust gas, comprising the steps of:
_X) and after the addition of ammonia to the exhaust gas containing SO _3, the exhaust gas is contacted with the SO ₃ reduction catalyst and the denitration catalyst, which comprises reducing nitrogen oxides and SO ₃ in the exhaust gas (Claim 1). The SO ₃ reduction catalyst contains, for example, Ru (ruthenium) as an active metal (claim 2). The SO ₃ reduction catalyst and the denitration catalyst may be the same substance. The above SO ₃
As a reduction catalyst and the above denitration catalyst, SO ₃
A catalyst carrying a reduction catalyst may be used (claim 4).

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In both the SO ₃ reduction catalyst and the denitration catalyst used in the present invention, ammonia effectively acts as a reducing agent. Therefore, by bringing the exhaust gas to which ammonia is added into contact with these catalysts, SO ₃ becomes SO ₂
And NO _x is reduced to nitrogen (N ₂ ).

As the SO ₃ reduction catalyst, for example, titania (TiO ₂ ), alumina (Al ₂ O ₃ ), silica (S
a carrier composed of at least one selected from the group consisting of iO ₂ ), zirconia (ZrO ₂ ), silicalite, and metallosilicate, and a carrier having ruthenium (Ru) as an active metal supported on the carrier. be able to.
Here, silicalite is a silicate composed of only Si and O having a pentasil-type crystal structure.

Metallosilicate is a crystalline silicate having an X-ray diffraction pattern shown in Table 1 below and expressed by the molar ratio of oxide in a dehydrated state and having the following chemical formula. (1 ± 0.8) R ₂ O · [aM ₂ O ₃ · bM'O · cA
l ₂ O ₃ ] · ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, and M is selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium. M ′ is an alkaline earth metal ion of any of magnesium, calcium, strontium and barium, and a, b and c are a> 0, 20> b ≧ 0 , A + c = 1
And y is 3000>y> 11. )

[0008]

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

As the denitration catalyst used in the present invention, generally,
Tania (TiO_Two) As active metal
Nazia (V_TwoO_Five), Tungsten oxide as co-catalyst
(WO _Three) Or molybdenum oxide (MoO)_Three)
Use a catalyst. SO_ThreeThe reduction catalyst and the denitration catalyst are connected in series.
Deploy. The order of arrangement is arbitrary, but in general,
SO_ThreeIt is better to place the reduction catalyst on the front side
If you supply a lot of near_ThreeThe reduction activity is higher
Is preferred. SO_ThreeBoth the reduction catalyst and the deNOx catalyst
Honeycomb shape with low pressure loss in gas processing
Preferably.

In the present invention, a catalyst having both a denitration ability and an SO ₃ reducing ability can be used. This catalyst
For example, it can be prepared by supporting Ru having SO ₃ reducing ability on a denitration catalyst. The SO ₃ reduction reaction by the SO ₃ reduction catalyst using ammonia as a reducing agent is as follows:
It is expressed by the following equations (1) and (2). 3SO ₃ + 2NH ₃ → 3SO ₂ + N ₂ + 3H ₂ O (1) 2SO ₃ + 2NH ₃ + ／ O ₂ → 2SO ₂ + N ₂ + 3H ₂ O (2) The amount of Ru to be supported is 0.0 per 100 parts by weight of the carrier.
It has an activity of at least 02 parts by weight, and preferably has a high activity of at least 0.02 parts by weight. Examples of a method for supporting Ru on a carrier include an impregnation method and an ion exchange method.

On the other hand, the denitration reaction by the denitration catalyst is represented by the following equation. 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (3) When there is a large amount of NO _{2 in} NO _X , it is expressed by the following equation. 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (4)

The amount of vanadia (V ₂ O ₅ ) supported on the carrier as a denitration catalyst is generally from 0 to 15 parts by weight per 100 parts by weight of the carrier. In addition, even when vanadia does not exist at all, there is a temperature range in which the activity is obtained. The amount of tungsten oxide to be added as a co-catalyst (WO ₃₎ or molybdenum oxide (MoO _3), the per carrier 100 parts by weight and 0-25 parts by weight.

In the present invention, the reducing agent for SO ₃ and NO _x
Are both ammonia. Therefore, it is preferable that the addition amount of ammonia is larger than that in the case of a general denitration apparatus, and is set to 0.8 or more in a molar ratio of NH ₃ / NO _X. Further, in order to obtain a high SO ₃ reduction rate and a high denitration rate, the amount of added ammonia may be increased.

[0014]

EXAMPLES Hereinafter, the effects of the present invention will be clarified with reference to specific examples of the present invention. Example 1 (Preparation of SO ₃ reduction catalyst) Ruthenium chloride (RuCl ₃ ) was added to anatase type titania powder containing 10 parts by weight of tungsten oxide (WO ₃ ) per 100 parts by weight of titania (TiO ₂ ). Impregnate with the aqueous solution,
1 part by weight of Ru per 100 parts by weight of anatase titania powder is supported on the powder, and after evaporation and drying, 500 parts by weight
C. for 5 hours to prepare a powdery catalyst (No. 1). Water was added to the powder catalyst (No. 1), and wet ball milling was performed to obtain a wash coat slurry. Next, a cordierite monolith substrate (7.4 mm pitch, wall thickness 0.6 mm) was immersed in the slurry,
Dry at ℃. The coating amount of the powder catalyst (No. 1) was 200 g per 1 m ² of the surface area of the base material, and the obtained coating was used as a honeycomb SO ₃ reduction catalyst (No. 1).

(Preparation method of denitration catalyst) Anatase type titani
A (TiO_Two) Powder of ammonium metavanadate (N
H _ThreeVO_Three) And ammonium paratungstate ((N
H_Four)_TenH_TenW₁₂O₄₆・ 6H_TwoO) Methylamine aqueous solution
100 parts by weight of TiO._TwoHit, V _TwoO
_Five0.6 parts by weight, WO_Three8 parts by weight, and dried by evaporation.
After solidification, heating and baking were performed at 500 ° C. for 5 hours. Got
The powder was used as a powder denitration catalyst (No. 1). Powder denitration catalyst
(No. 1) clay as inorganic binder
Add cellulose acetate as binder and knead
After that, an integrated extruded catalyst (7.4 mm pitch, 1 m wall thickness)
m). After molding, microwave drying is performed and 50
It was baked at 0 ° C. for 5 hours to remove the organic binder. Get
The honeycomb catalyst thus obtained is referred to as a honeycomb denitration catalyst (No. 1).
Was.

(Denitration Test) As shown in FIG. 1, the above-mentioned honeycomb SO ₃ reduction catalyst (No. 1) was installed in the first stage, and the above-mentioned honeycomb de-NOx catalyst (No. 1) was installed in the second stage, and a denitration test was conducted. . The test conditions are as follows. Gas composition _{NO: 150ppm, NH 3: 200ppm} , SO 2:
2,000 ppm, SO ₃ : 100 ppm, O ₂ : 1.
3%, H ₂ O: 10% Test conditions Gas amount: 27 Nm ³ / h, temperature: 380 ° C., linear velocity:
3.3 Nm / s Catalyst shape: SO ₃ reduction catalyst 6 × 6 cells, 870 mm
(1) DeNOx catalyst 6 x 6 cells, 870mm (3)

FIG. 1 shows the layout of the catalyst, and Table 2 shows the composition of the gas at the outlet of the catalyst. In FIG. 1, the exhaust gas is a honeycomb SO.
₃ Reduction catalyst (No. 1), honeycomb denitration catalyst (No.
1), the honeycomb denitration catalyst (No. 1), and the honeycomb denitration catalyst (No. 1). The measurement values shown in Table 2 were obtained using gases collected at points A, B, C, and D in FIG. From Table 2, the SO ₃ concentration in the exhaust gas after passing through the three denitration catalysts is determined by the honeycomb SO ₃ reduction catalyst (N
o. It can be seen that the SO ₃ concentration in the exhaust gas before introduction into 1) is lower. That is, even after passing through a series of catalyst layers,
SO ₃ does not increase, and only NO _X can be significantly reduced. As described above, in the existing denitration apparatus, it is possible to realize a denitration apparatus that suppresses the generation of SO ₃ with only a slight modification of installing the SO ₃ reduction catalyst before the denitration catalyst.

Example 2 Instead of the honeycomb denitration catalyst (No. 1), a honeycomb SO was used.
_A denitration test was performed in the same manner as in Example 1 except that ₃ reduction catalyst (No. 1) was arranged. Also in this case, as shown in Table 2, not only the concentration of SO _{3 in} the gas but also the concentration of nitrogen oxides decreased. That is, the honeycomb SO ₃ reduction catalyst (No. 1) also functions as a denitration catalyst. Thus, in the present invention, the SO ₃ reduction catalyst and the denitration catalyst
The same substance may be used.

Example 3 Denitration was carried out in the same manner as in Example 1 except that three honeycomb denitration catalysts (No. 1) were arranged at the front stage and one honeycomb SO ₃ reduction catalyst (NO. 1) was arranged at the rear stage. The test was performed.

Example 4 The powdery catalyst of the SO ₃ reduction catalyst used in Example 1 (No.
1) was replaced with the honeycomb denitration catalyst (No. 1) used in Example 1.
1) The coating was performed on the upper surface so that the addition amount was 200 g per 1 m ² of the honeycomb surface area. This coating is applied to the honeycomb SO ₃
It was set as a reduction catalyst (No. 2). Four honeycomb SO ₃ catalysts (No. 2) were arranged in series similarly to Example 1, and a denitration test was performed. This embodiment is an example in which a catalyst obtained by supporting an SO ₃ reduction catalyst on a denitration catalyst is used as the SO ₃ reduction catalyst and the denitration catalyst. In Example 4, the case where the inlet ammonia concentration was 200 ppm and the case where the ammonia concentration was 250 ppm were used.
Each of the ppm cases was tested. FIG. 1 shows the arrangement of the catalysts in each of the above examples, and Table 2 shows the composition of the gas at the catalyst outlet.

[0021]

[Table 2]

From Table 2, it can be seen that in all of Examples 1 to 4, the SO ₃ concentration in the exhaust gas is reduced and a high denitration rate is obtained.

[0023]

According to the method of the present invention, both the concentration of nitrogen oxides and the concentration of SO _{3 in} exhaust gas can be reduced.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of the present invention.

[Explanation of symbols]

1 Honeycomb SO ₃ reduction catalyst (No. 1) 2, 3, 4 Honeycomb denitration catalyst (No. 1)

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01D 53/36 102A

Claims (4)

[Claims] [Claim 1] After adding ammonia to the exhaust gas containing nitrogen oxides and SO _3, the exhaust gas is contacted with the SO ₃ reduction catalyst and a denitration catalyst, nitrogen oxides and SO ₃ in the exhaust gas recirculation A method for reducing nitrogen oxides and SO ₃ in exhaust gas. 2. The method according to claim 1, wherein said SO ₃ reduction catalyst contains Ru. 3. The method according to claim 1, wherein the SO ₃ reduction catalyst and the denitration catalyst are the same substance. 4. The method according to claim 1, wherein a catalyst obtained by supporting an SO ₃ reduction catalyst on a denitration catalyst is used as the SO ₃ reduction catalyst and the denitration catalyst.