JPH10225620A - Method for reducing sulfur trioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce and remove the SO3 discharged from a boiler waste gas by bringing the combustion gas admixed with ammonia into contact with an Ir carrying catalyst. SOLUTION: Three parts of alumina sol, 55 parts of silica sol and 200 parts of water are added as a binder to 100 parts of H-type metallosilicate and sufficiently agitated to obtain a slurry for a wash coat. Subsequently, a monolithic substrate for cordierite is dipped in the wash-coat slurry, brought out and then dried at 200 deg.C after the excess slurry is swept off. The coat is deposited by 200g per 1 of the substrate to obtain a honeycomb coat. The honeycomb coat is dipped in iridium chloride (2.88g IrCl4 .H2 O/200cc of H2 O) and impregnated for 1hr, the liq. depositing on the substrate wall is scraped off, and the coat is dried at 200 deg.C. The coat is then purged with a nitrogen atmosphere at 500 deg.C to obtain a honeycomb catalyst. The SO3 discharged from the boiler waste gas, etc., is removed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a method for reducing and removing the SO ₃ discharged from the boiler exhaust gas or the like.

[0002]

The NH ₃ with Related Art denitration catalyst as a method for preventing the NO _x generated from the viewpoint of preventing air pollution from boilers and various combustion furnaces to catalytically nitrogen and water by adding to the exhaust gas The selective contact / reduction method that decomposes is widely applied to any exhaust gas of gas, oil and coal. In the denitration method, in the exhaust gas to burn inferior fuel oils such as heavy oils and orimulsion as fuel containing a large amount of SO _x. Among SO _x , SO ₃ is a corrosive gas, and is supplied to an air preheater or an electrostatic precipitator downstream thereof with sulfuric acid or ammonium sulfate (hereinafter abbreviated as ammonium sulfate) or ammonium ammonium sulfate (hereinafter abbreviated as acid ammonium sulfate).
Etc., condensing in the form, etc., causing corrosion and clogging. Further, when the load on the boiler or the like increases, a large amount of mist such as ammonium sulfate is instantaneously discharged from the chimney in a large amount, and the white colored exhaust gas is discharged.

[0003]

Although SO _x in the exhaust gas due to combustion of the invention Problems to be Solved inferior fuel oil is almost SO _2, there is a case where a large amount of SO ₃ is discharged by the combustion method. Further, on the denitration catalyst, SO ₂ + ／ O ₂ → SO ₃
The disadvantage that the SO ₃ concentration increases due to the side reaction of.

In order to solve the above-mentioned problems, the present inventors have intensively developed a catalyst for reducing and removing generated SO _3, and found that a catalyst supporting iridium has desired characteristics. They have found and completed the present invention.

[0005]

That is, the present invention provides (1)
A method of reduction treatment SO ₃ from flue gas containing SO _3, SO _3, characterized in that contacting the flue gas with the addition of ammonia to the catalyst carrying Ir
The reduction treatment method and (2) the carrier of the Ir-supporting catalyst is composed of at least one selected from the group consisting of titania, alumina, silica, zirconia, silicalite and metallosilicate. The SO ₃ reduction treatment method according to the above (1).

The combustion exhaust gas containing SO ₃ to be treated in the present invention may be one containing a component acting as a reducing agent for SO ₃ , such as carbon monoxide or hydrocarbon, in the combustion exhaust gas. It may not be included.

[0007] In the present invention, titania, alumina, silica, zirconia, silicalite and metallosilicate are used as a carrier for supporting Ir. Here, silicalite is a silicate composed of only pentasil-type Si and O, and metallosilicate has an X-ray diffraction pattern shown in Table A below, and shows a molar ratio of oxide in a dehydrated state. And is a crystalline silicate having the following chemical formula.

[0008]

Embedded image (1 ± 0.8) R ₂ O. [aM ₂ O ₃ .bM ′
O · cAl ₂ O ₃ ] · ySiO ₂ (where R is
Is an alkali metal ion and / or hydrogen ion, M is VIII
Group element, rare earth element, at least one or more element ions selected from the group consisting of titanium, vanadium, chromium, niobium, antimony and gallium, M 'is an alkaline earth metal ion of magnesium, calcium, strontium, barium, a > 0, 20> b ≧ 0, a + c = 1,
3000>y> 11. )

[0009]

[Table 1]

(Action) As shown in JP-A-6-296870, a catalyst in which Ir is supported on a specific carrier can use carbon monoxide and hydrocarbons in exhaust gas as reducing agents even in an atmosphere where oxygen is excessive. Although the present invention can reduce nitrogen oxides, the present inventors have found that ammonia, which is a reducing agent for nitrogen oxides (NO _x ), can also reduce SO ₃ by using the above catalyst. Is completed. The reduction reaction of SO ₃ using ammonia is as follows.

[0011]

Embedded image 3SO ₃ + 2NH ₃ → 3SO ₂ + N ₂ + 3H ₂ O

As the amount of added ammonia increases, the SO
The removal rate of ₃ is higher. The amount of ammonia is 1 ppm or more,
Preferably 10 ppm or more is desirable.

The amount of iridium to be carried is 0.002 wt%
The above-mentioned activity is obtained, but preferably 0.02 wt% or more has a high activity. The method of supporting iridium on the carrier may be an impregnation method, an ion exchange method, or the like.

Further, in order to treat both NO _x and SO ₃ in the combustion exhaust gas, a honeycomb-shaped denitration catalyst (for example, Ti
By coating the catalyst powder used in the present invention on a catalyst composed of O ₂ -WO ₃ -V ₂ O ₅ ), it is possible to remove both NO _x and SO ₃ using ammonia.

[0015]

EXAMPLES Hereinafter, specific examples of the present invention will be described to clarify the effects of the present invention.

(Example 1) (Preparation method 1 of catalyst) ○ (Synthesis of metallosilicate): Water glass No. 1 (SiO
₂ : 30%): 5616 g was dissolved in 5429 g of water,
This solution is referred to as solution A. On the other hand, water: 4175 g, aluminum sulfate: 718.9 g, ferric chloride: 110 g,
Calcium acetate: 47.2 g, sodium chloride: 262
g, concentrated hydrochloric acid: 2020 g, and this solution is referred to as solution B. The solution A and the solution B are supplied at a constant rate to form a precipitate, and the mixture is sufficiently stirred to obtain a slurry having a pH of 8.0. This slurry was charged into a 20-liter autoclave, and 500 g of tetrapropylammonium bromide was further added. Hydrothermal synthesis was performed at 160 ° C. for 72 hours. After the synthesis, the resultant was washed with water and dried. Get 1. The metallosilicate 1 is represented by the following composition formula in terms of the molar ratio of the oxide (omitting the water of crystallization), and the crystal structure is shown in Table A by X-ray diffraction.

[0017]

Embedded image 0.5Na ₂ O · 0.5H ₂ O · [0.8Al
₂ O ₃ .0.2Fe ₂ O ₃ .0.25CaO] .25S
iO _{2 The} above metallosilicate was added to a ₄ NH ₄ Cl aqueous solution at 80 ° C., ion-exchanged twice for 3 hours or more, washed with water and dried.
After firing at 500 ° C. for 3 hours, an H-type metallosilicate 1 was obtained.

○ (catalyzed): Next, alumina sol: 3 parts, silica sol: 55 parts (SiO ₂ : 20) as a binder for the above 100 parts of H-type metallosilicate 1.
%) And water: 200 parts and sufficiently stirred to obtain a slurry for washcoat. Next, a monolith base material for cordierite (a grid of 400 cells) was immersed in the above slurry, taken out, and then sprayed with excess slurry and dried at 200 ° C. The coating amount is 200 g per 1 liter of the base material. next,
Iridium chloride (IrCl ₄ .H ₂ O: 2.88 g / H
₂ O: 200 cc), the honeycomb coated article 1 was immersed and impregnated for 1 hour, and the liquid adhering to the substrate wall was wiped off.
Dried at 00 ° C. Next, at 500 ° C. in a nitrogen atmosphere, 12
A time purge process was performed to obtain a honeycomb catalyst 1.

The metallosilicate in Preparation method 1 of the above catalyst
In the method for synthesizing salt 1, instead of ferric chloride,
Baltic, ruthenium chloride, rhodium chloride, lanta chloride
, Cerium chloride, titanium chloride, vanadium chloride, chloride
Chromium, antimony chloride, gallium chloride and niobium chloride
Are converted to Fe_TwoO_ThreeAdd the same number of moles as
The same operation as for metallosilicate 1 was repeated except for
Metallosilicates 2-12 were prepared. These crystal structures
The structure is shown in Table A above by X-ray diffraction.
The composition is represented by the molar ratio of oxides (dehydrated form),
(1 ± 0.8) R _TwoO ・ (0.2M_TwoO_Three・ 0.8Al
_TwoO_Three・ 0.25CaO) ・ 25SiO_TwoIt is. here
R is Na and H, M is Co, Ru, Rh, La, C
e, Ti, V, Cr, Sb, Ga, Nb. these
The composition of the metallosilicate is shown in Table B below.

In the preparation method 1 of the above catalyst, the same operation as that of the metallosilicate 1 was carried out except that magnesium acetate, strontium acetate and barium acetate were each added in the same molar amount as CaO in terms of oxide in place of calcium acetate. Repeatedly, metallosilicates 13 to 15 were prepared. The crystal structures of these metallosilicates are those shown in Table A above by X-ray diffraction, and their compositions are expressed in terms of the molar ratio of oxides (dehydrated form) to 0.5 Na ₂ O
・ 0.5H ₂ O ・ (0.2Fe ₂ O ₃・ 0.8Al ₂ O
A ₃ · 0.25MeO) · 25SiO _2. Where M
e is Mg, Sr, Ba.

The above metallosilicates 2 to 15 were converted into the H-form in the same manner as in the above-mentioned catalysis, and further coated on a cordierite monolith substrate to obtain honeycomb coated products 2 to 15. Next, it was immersed in an iridium chloride aqueous solution to obtain honeycomb catalysts 2 to 15 in the same manner as in Preparation method 1 described above.

(Catalyst Preparation Method 2) TiO ₂ (Mc-90, manufactured by Ishihara Sangyo), γ-Al ₂ O ₃ (manufactured by Sumitomo Chemical), Si
Each of O ₂ (Fuji Silysia Chemical), ZrO ₂ (JGC Chemicals), and silicalite (Mobile) powders was used as a carrier, and an iridium chloride (IrCl ₄ .H ₂ O) aqueous solution was used. .6 wt%.
After evaporating to dryness, baking was performed at 500 ° C. for 12 hours in a nitrogen atmosphere. 200 g of this powder catalyst was supported per liter of cordierite honeycomb substrate of 400 cell lattice, and honeycomb catalysts 16 to 20 were obtained. The honeycomb catalysts 1 to 20 are also shown in Table B.

[0023]

[Table 2]

(SO_ThreeReduction test of the catalyst)
Using the obtained honeycomb catalysts 1 to 20, SO_ThreeReduction test
Test was carried out. The test conditions are as follows. ○ (gas composition) NO: 150ppm, SO_Two: 2000 ppm, S
O_Three: 100 ppm, NH _Three: 800 ppm, O_Two:
0.4%, H_TwoO: 10%, N_Two: Residual ○ (test conditions) Gas amount: 512 Nl / h, catalyst amount: 15.4 cc (16
mm x 16 mm x 60 mm: 12 cells x 12 cells), G
HSV (gas amount per catalyst volume): 33300 h^-1,
AV (gas amount per catalyst surface area): 14.8 m^Three/ M
^Twoh, temperature: 400 ° C. SO of catalysts 1 to 20_ThreeThe reducing activity is shown in Table C. Note that S
O_ThreeArsenazo III method using mini-spiral tube
Was analyzed by

[0025]

[Table 3]

Example 2 In the SO ₃ reduction test of Example 1, the NH ₃ concentration was 400 ppm, 800 ppm,
An SO ₃ reduction test was performed at 1200 ppm. Further, under the same conditions as in Example 1, the O ₂ concentration was set to 0.2 to 1.0.
At 0%, a SO ₃ reduction test was performed. The above test was carried out using the catalyst 1 of Example 1, and the SO ₃ reduction activity was measured in Table D.
Shown in

[0027]

[Table 4]

(Example 2) V ₂ O ₅ : 0.6 as a component
%, WO ₃ : 8%, TiO ₂ as a main component, and a 7.4 mm pitch honeycomb catalyst (wall thickness 1 mm) is used as a base material. The base material was coated with the powdered catalyst 1 shown in Example 1 at 100 g / m ² per base material surface area (50 g / l per honeycomb volume). This catalyst is referred to as catalyst 21. Using this catalyst, a SO ₃ reduction test was performed under the following test conditions with the same gas composition as in Example 1. ○ (Test conditions) Gas amount: 512 Nl / h, catalyst amount: 30.8 cc (16
mm x 16 mm x 120 mm: 2 cells x 2 cells), GH
SV: 16700 h ^-1 , temperature: 400 ° C. Table ₃ shows the SO ₃ removing activity and NO _x removing activity of the catalyst 21.

[0029]

[Table 5] From this result, the catalyst 21 can remove both nitrogen oxides (NO _x ) and sulfur trioxide (SO ₃ ).

[0030]

As described in detail in the above embodiments, harmful SO ₃ can be reduced and removed by the method of the present invention.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Kazumasa Uchihashi 1-1, Akunouramachi, Nagasaki City, Nagasaki Prefecture Inside Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard

Claims (2)

[Claims] 1. A method for producing SO ₃ from combustion exhaust gas containing SO ₃
A method for reducing SO ₃ , wherein the combustion exhaust gas obtained by adding ammonia to a catalyst supporting Ir is brought into contact with the catalyst. 2. The catalyst carrier for supporting Ir is titania,
Alumina, silica, zirconia, silicalite and SO ₃ reduction processing method according to claim 1, characterized in that constructed than from the group consisting of metallosilicate of one or more selected.