JP2002126536A - Oxidation resistant and corrosion resistant metal substrate, catalyst for nitrogen oxide removal, and waste gas cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidation resistant and corrosion resistant metal substrate capable of preventing diffusion of iron ion from itself into a catalyst component in a high temperature range to prevent the decrease of nitrogen oxide removal efficiency and suppressing the increase of oxidation ratio of SO2 contained in a waste gas to prevent corrosion of appliances on the downstream side, to produce a catalyst using the substrate for nitrogen oxide removal by ammonia contact reduction, and to provide a waste gas cleaning method. SOLUTION: The oxidation resistant and corrosion resistant metal substrate (1) is a substrate produced by forming a dense titania layer (5) on the surface of a metal substrate by applying a titanium peroxide solution or its sol. The catalyst for nitrogen oxide removal is a catalyst produced by forming a catalyst layer (2) on the surface of the oxidation resistant and corrosion resistant metal substrate (1). The waste gas cleaning method (3) is a method for removing nitrogen oxides from a waste gas by bringing the waste gas at 350-600 deg.C into contact with the catalyst for nitrogen oxide removal in ammonia atmosphere. The waste gas cleaning method is also a method (4) for removing nitrogen oxides from a sulfur oxide- containing waste gas by bringing the waste gas into contact with the catalyst for nitrogen oxide removal in ammonia atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation-resistant and corrosion-resistant metal substrate, a catalyst for denitration, and a method of purifying exhaust gas, and more particularly, to 500 to 65 exhausted from a gas turbine.
Oxidation-resistant and corrosion-resistant metal substrate capable of preventing formation of an oxide film or acid corrosion even when used for processing exhaust gas at a high temperature of 0 ° C. or exhaust gas containing SO ₂ or the like. The present invention relates to a denitration catalyst having high denitration performance even in a high temperature range and a method of purifying exhaust gas using the denitration catalyst.

[0002]

2. Description of the Related Art In recent years, power generation has been decentralized, and many gas turbines using various exhaust gases as driving sources have been constructed in place of conventional large-scale thermal power generation. Since these gas turbines are often constructed in an urban area or a suburban area, it is necessary to suppress nitrogen oxides (NOx) contained in exhaust gas to a low level. To remove NOx in the exhaust gas in this case,
If a waste heat recovery boiler (HRSG) is installed downstream of the gas turbine, the exhaust gas temperature will be around 350 ° C,
NH widely used for flue gas denitration of conventional boilers
₃ Catalytic reduction denitration method can be applied, but when HRSG is not installed, the exhaust gas temperature is 500 ~ 650 ℃
, And there is a problem that the denitration catalyst used in the conventional NH ₃ catalytic reduction denitration method cannot be used.

[0003] Particularly, stainless steel (SUS) is used as a base material for a catalyst.
When a metal substrate is used, iron ions (Fe ions) move from the metal substrate to the denitration catalyst component and the N
Since H ₃ is decomposed to generate NOx, a high denitration rate cannot be obtained. For example, a catalyst body in which a denitration catalyst component is directly supported (or coated) on the surface of a conventional metal substrate is heated to 350 ° C.
When used at the above high temperature, as shown in FIG. 2, an oxide film 3 is formed between the metal substrate 1 and the catalyst component layer 2, and Fe ions gradually diffuse into the catalyst component layer 2 via the oxide film 3. I do. When the content of Fe ions in the catalyst component increases,
Since NH ₃ added as a reducing agent is decomposed to generate N ₂ or NO as shown in the following formulas (1) and (2), high denitration performance could not be obtained. 2NH ₃ + 3 / 2O ₂ → N ₂ + 3H ₂ O NH ₃ + 5 / 2O ₂ → NO + 3 / 2H ₂ O (2)

[0004] For this reason, aluminum spraying is performed on a metal substrate (Japanese Patent Application Laid-Open No. Sho 52-14658), or an intermediate coating layer of silica and inert titania is formed on the metal substrate to form Fe.
There has been proposed a method for preventing a decrease in the denitration rate in a high temperature range by preventing the transfer of ions to the catalyst component (Japanese Patent Laid-Open No. 6-246176). However, although the above-mentioned aluminum spraying and the formation of the intermediate coating layer made of inorganic particles can reduce the decrease in the denitration rate due to the transfer of Fe ions from the metal substrate, the intermediate coating layer is not dense, As shown in FIG. 3, the oxide film 3 is formed in the cracks of the intermediate layer 4 formed between the metal substrate 1 and the catalyst component layer 2 when exposed to Fe ions gradually migrated and diffused into the catalyst component, and it was not possible to completely prevent a decrease in the denitration rate. Also,
Since the connection between the metal substrate 1 and the intermediate layer 4 is not always sufficient, there is a problem that the intermediate layer 4 is easily peeled off from the metal substrate 1.

[0005] Further, when used in an acidic atmosphere containing sulfur oxides (SOx) in the exhaust gas or during the heat treatment process during the production of the catalyst, acid corrosion of the metal substrate occurs in a temperature range of 400 ° C or less, and Similarly, Fe ions easily move into the catalyst component, and SO ₂ in the exhaust gas is oxidized to SO ₃ due to the presence of the Fe ions, and the SO ₃ tends to corrode downstream equipment.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to prevent the formation of an oxide film on a metal substrate used for a denitration catalyst and the prevention of acid corrosion.
Thereby preventing a decrease in the denitrification rate by preventing the diffusion of the catalyst component of iron ions from the substrate in a high temperature range, preventing the corrosion of downstream equipment by suppressing the increase in the oxidation rate of SO ₂ contained in the exhaust gas An object of the present invention is to provide an oxidation-resistant and corrosion-resistant metal substrate that can be used, a catalyst for ammonia catalytic reduction denitration using the same, and a method for purifying exhaust gas.

[0007]

The invention claimed in the present application to solve the above-mentioned problems is as follows. (1) An oxidation-resistant and corrosion-resistant metal substrate comprising a metal substrate surface coated with a titanium peroxide solution or a sol thereof to form a dense titania layer. (2) The oxidation-resistant and corrosion-resistant metal substrate according to (1), wherein the titanium peroxide solution or the sol thereof contains inert inorganic fine particles. (3) A denitration catalyst comprising a catalyst layer formed on the surface of the oxidation-resistant and corrosion-resistant metal substrate according to (1) or (2). (4) The denitration catalyst according to (3), wherein the catalyst layer contains an oxide of titanium and tungsten as a catalyst component. (5) The denitration catalyst according to (3), wherein the catalyst layer contains an oxide of titanium, molybdenum, and navadium as a catalyst component.

(6) An exhaust gas at 350 to 600 ° C. is brought into contact with the denitration catalyst according to any one of (3) to (5) in an ammonia atmosphere to remove nitrogen oxides from the exhaust gas. Characteristic method of purifying exhaust gas. (7) An exhaust gas containing sulfur oxides is brought into contact with the denitration catalyst according to any one of (3) to (5) in an ammonia atmosphere to remove nitrogen oxides in the exhaust gas. Exhaust gas purification method.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Oxidation resistance and corrosion resistance in the present invention
Metal substrate has a dense titania layer on the metal substrate surface
You. This dense titania layer provides a layer of titanium dioxide on the surface of the metal substrate.
Tan (formula weight: H _FourTiO_Five) Solution or titanium peroxide
Some or all of the solution aggregated into a sol
(Hereinafter, these may be simply referred to as titanium peroxide.)
After coating, dry, if necessary
It can be formed by firing at a temperature of 500 ° C.
Wear.

The titanium peroxide used in the present invention is obtained as a yellow solution by reacting hydrogen peroxide on metatitanic acid or orthotitanic acid obtained by hydrolyzing titanium sulfate, titanium alkoxide or the like. This titanium peroxide is also called pertitanic acid or peroxotitanic acid, and is a compound represented by TiO ₃ .2H ₂ O or H ₄ TiO ₅ . The titanium peroxide solution can be used as it is for coating the metal surface, but when the titanium peroxide solution is left for a long time or heated, a part of the solution is condensed or hydrolyzed to form a sol-like material that exhibits a paste-like state. Become. The sol is well compatible with metals and is particularly advantageous for coating metal surfaces.

From the viewpoint of the effect of the present invention, the amount of titanium peroxide supported on the surface of the metal substrate is 0 to 50 as titanium oxide.
g / m ² , more preferably 0.1 to ²⁰ g / m ^2.
m ² . In addition, 0 g / m ² as titanium oxide is 0 g / m ^2.
Means an effective amount close to Also, in the titanium peroxide solution,
In order to increase the thickness of the coating layer and to prevent the movement of Fe ions, it is preferable to mix inert inorganic fine particles. As the inert inorganic fine particles, for example, a titanium oxide powder having a low specific surface area and an inert surface, which has been treated at a high temperature such as a chlorine method. The method of coating the titanium peroxide solution is not particularly limited, and for example, a known coating method such as a method of dipping a metal substrate in a liquid containing titanium peroxide or a sol thereof, and a method of spraying can be used. There is no particular limitation on the metal substrate used in the present invention,
In addition to nets and wire nets obtained by metal lath processing of stainless steel (SUS), flat plates such as SUS, mild steel, and aluminum may be used.

The denitration catalyst of the present invention is obtained by forming a catalyst layer on the surface of an oxidation-resistant and corrosion-resistant metal substrate having the above-mentioned dense titania layer. The catalyst components used in the catalyst layer include titanium (Ti), molybdenum (Mo), tungsten (W),
A known catalyst component composed of an oxide such as vanadium (V) is used. In particular, for the denitration of exhaust gas in the high temperature region at the gas turbine outlet, it is preferable to use a catalyst containing Ti and W oxides and a catalyst containing Ti and Mo and / or V oxides that are less deteriorated at high temperatures. These catalysts are supported on a metal substrate by a known method such as a method in which the catalyst component is applied in a paste form to the metal substrate or a wash coating in which the metal component is immersed in a liquid in which the catalyst component is dispersed in a slurry form. It can be performed using a preparation means. Further, a binder such as silica sol or titania sol or a strength member such as inorganic fiber can be added to the catalyst component.

FIG. 1 is an explanatory sectional view of a denitration catalyst according to an embodiment of the present invention. The denitration catalyst is made of a metal substrate 1
And a transparent and dense titania layer 5 formed by coating titanium oxide or titanium peroxide sol on the surface of the metal substrate 1, and a catalyst component layer 2 formed on the surface of the titania layer 5. . The thin film of the titania layer 5 formed on the surface of the metal substrate 1 is composed of a titanium oxide film and a titanium oxide layer formed of titanium peroxide, and is extremely dense. No oxide film is formed on the surface of the substrate even if is exposed for a long time. Therefore, after passing through the oxide film,
The phenomenon that ions move to the catalyst component layer 2 and lower the denitration rate can be greatly suppressed. The dense titania layer 5 can also reduce the acid corrosion of the metal substrate in a temperature range of 400 ° C. or less in an atmosphere of an acidic gas such as SOx. When the metal substrate is corroded by the acid, Fe ions move into the catalyst component in the same manner as when a catalyst is used at a high temperature, and the activity of oxidizing SO ₂ in the exhaust gas to SO ₃ increases, which adversely affects downstream equipment. Become like In the present invention, the dense titania layer 5 formed on the surface of the metal substrate
Since acid corrosion of the metal substrate can be suppressed, it is also possible to suppress a temporal increase in the oxidation rate of SO ₂ contained in the exhaust gas.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 Titanium tetrabutoxide (Ti (C ₄ H ₉ O) ₄ )
A mixed solution of 50 g and 50 g of ethanol was poured into 300 g of water made alkaline with ammonia and hydrolyzed to form a precipitate of orthotitanic acid (Ti (OH) ₄ ). The precipitate formed was separated by a centrifugal separator, washed three times with water, finally washed with ethanol, and air-dried to obtain orthotitanic acid powder. The obtained orthotitanic acid powder was placed in a 500 cc beaker, and 30% aqueous hydrogen peroxide was added little by little to completely dissolve the orthotitanic acid particles to produce a yellow transparent titanium peroxide solution. The obtained titanium peroxide solution was SUS4
The surface of 30 plates (0.2 mm thick, 20 mm wide, 100 mm long) was applied with a brush, air-dried, and fired at 500 ° C. to obtain the oxidation-resistant and corrosion-resistant metal substrate of the present invention. The amount of titanium peroxide supported on this substrate was 2.6 g / m ² as TiO ₂ .

Comparative Example 1 The SUS430 plate used in Example 1 was fired at 500 ° C. without applying a titanium peroxide solution to obtain a comparative metal substrate.

<Oxidation Resistance Test of Metal Substrate> The metal substrates obtained in Example 1 and Comparative Example 1 were placed in the air at 550 ° C. for 300 minutes.
After holding for a time, the state of formation of the oxide film was observed. As a result, despite the fact that the metal substrate obtained in Example 1 on which the titanium peroxide film was formed was exposed to the high temperature of 550 ° C. for a long time, the metal luster was maintained, and the formation of the oxide film was recognized. I couldn't. On the other hand, the surface of the comparative metal substrate on which the titanium peroxide film was not formed had a brown-violet color and was covered with the oxide film. From the above results, it was confirmed that the titanium peroxide film formed on the metal substrate of the present invention forms a dense titania layer to prevent oxidation of the metal surface and suppress the formation of an oxide film.

Example 2 While stirring the titanium peroxide solution obtained in Example 1,
The mixture was heated on a bath to obtain a paste-like titanium peroxide sol. This zo
SUS430 plate as in Example 1
After that, air-dry and further bake at 500 ° C for 2 hours to
An oxidation-resistant and corrosion-resistant metal substrate covered with a tin film was obtained.
The amount of titanium peroxide supported on this substrate was TiO 2 _TwoAs 20
g / m^TwoMet. Separately, the acid obtained by the sulfuric acid method
Titanium (specific surface area 250m^Two/ G, SO _FourContent 1.
8% by weight) aqueous solution of ammonium metatungstate
(WO_ThreeContent of 50% by weight) and the atomic ratio of Ti to W (T
i / W) is 95/5, and then water is added.
In addition, the mixture was kneaded to obtain a paste-like catalyst precursor. This page
Rolled catalyst catalyst precursor into sheet with thickness of about 3mm
And then cut into 20 mm squares.
Paste on the edible metal substrate, air-dry and bake at 550 ° C
The catalyst for denitration of the present invention was obtained.

Comparative Example 2 A denitration catalyst was produced in the same manner as in Example 2 except that the titanium peroxide film was not formed on the metal substrate.

<Test for Transferring Fe Ions to Catalyst Layer> The catalyst sheet for denitration obtained in Example 2 and Comparative Example 2 was heated in the atmosphere at 600 ° C. for 1000 hours and then adhered to a metal substrate. Was removed, and the Fe content of each catalyst sheet surface in contact with the metal substrate and the Fe content of the unused catalyst sheet surface were measured by X-ray fluorescence analysis.
The results are shown in Table 1. In the denitration catalyst obtained in Example 2, the Fe content in the catalyst component showed only a slight increase as compared with that of the unused catalyst. It was confirmed that the movement was extremely small. On the other hand, in the catalyst obtained in Comparative Example 2, it was found that the Fe content in the catalyst component was significantly increased. From the above results, it was confirmed that according to the denitration catalyst using the metal substrate on which the titanium peroxide film was formed, the thermal diffusion of Fe ions into the catalyst component could be effectively prevented.

[0020]

[Table 1]

Example 3 A net obtained by subjecting a SUS430 steel plate having a thickness of 0.2 mm to metal lath processing was immersed in a titanium peroxide sol solution prepared in the same manner as in Example 2, and excess sol was air blown. Then, the metal lath surface was air-dried and covered with a titanium peroxide film. The supported amount of this titanium peroxide was about 10 g / m ² as TiO ₂ . On the other hand, an aqueous solution of ammonium metatungstate (WO ₃ content 50% by weight) was added to titanium oxide (specific surface area 250 m ² / g, SO ₄ content 1.8% by weight) obtained by the sulfuric acid method, After adding so that the atomic ratio (Ti / W) becomes 95/5, water was added and kneaded with a kneader to form a paste. An inorganic fiber (fiber flux, manufactured by Toshiba Monoflux) was added to this paste in an amount of 20% by weight based on the total amount of titanium oxide, and mixed uniformly to obtain a coating paste. The obtained paste for application is placed on the surface of the metal lath on which the titanium peroxide film is formed, and the resultant is passed through a rolling roller to apply a catalyst to the mesh and the surface of the metal lath, air-dried, and then fired at 550 ° C. for 2 hours. A catalyst for denitration was obtained.

Example 4 In Example 3, the titanium oxide sol was mixed with titania for pigment (CR50, manufactured by Ishihara Sangyo Co., Ltd.) synthesized by the chlorine method as inert fine particles, and the weight ratio of TiO ₂ to CR50 (TiO ₂ ) in the sol was changed. _A catalyst for denitration was produced in the same manner as in Example 3 except that a titanium peroxide sol solution added so that ( ₂ / CR50) became 1/4 was used.

Comparative Example 3 A denitration catalyst was produced in the same manner as in Example 3 except that no titanium peroxide film was formed on the metal lath surface.

<Denitration rate test> The denitration catalysts obtained in Examples 3 and 4 and Comparative Example 3 were treated at 600 ° C. in the same manner as in Example 2.
For 1000 hours to perform a heat resistance test. The denitration performance at 550 ° C. of the catalyst after the heat resistance test and the unused catalyst not subjected to the heat resistance test was examined under the conditions shown in Table 2. The results are summarized in Table 3. In the denitration catalysts of Examples 3 and 4, high values were obtained for both the initial denitration rate of the unused catalyst and the denitration rate after the heat test (after aging). In the catalyst of Comparative Example 3, the initial denitration rate was low, and the denitration rate after the heat test was also significantly reduced. From the above results, it was confirmed that the denitration catalyst of the present invention can effectively prevent a decrease in denitration performance due to Fe ion transfer at a high temperature. Further, since the catalysts of Examples 3 and 4 had the same denitration performance even after the heat resistance test, it was found that the same effect could be obtained by mixing inactive fine particles with titanium peroxide.

[0025]

[Table 2]

[0026]

[Table 3]

Example 5 In Example 3, ammonium molybdate and ammonium metavanadate powder were replaced by an aqueous solution of ammonium metatungstate in the atomic ratio of Ti: Mo: V (Ti
/ Mo / V) was adjusted to 96/3/1 to prepare a catalyst paste in the same manner as in Example 3. The paste was applied to a metal lath on which a titanium peroxide film was formed, and then dried. At 500 ° C. for 2 hours to obtain a denitration catalyst.

Comparative Example 4 A denitration catalyst was produced in the same manner as in Example 5 except that the titanium oxide film was not formed on the metal lath processing mesh.

<Corrosion Resistance Test> In order to simulate low-temperature corrosion that occurs during the denitration of the exhaust gas from an oil-fired boiler, the denitration catalysts manufactured in Example 5 and Comparative Example 4 were diluted with sulfuric acid to SO _4.
%, And kept for 3 days under a humid condition of 90% humidity. Using the catalyst after the corrosion test and the unused catalyst, Table 4
The exhaust gas was circulated under the following conditions, and the oxidation rate of SO _{2 in} the exhaust gas was measured. The results obtained are shown in Table 5, but the denitration catalyst obtained in Example 5, less oxidation rate of SO ₂ in the catalyst in both the post-catalyst and corrosion test unused, was used as a denitration catalyst base It was found that the increase in the oxidation rate of SO ₂ due to acid corrosion of the metal can be suppressed.

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

According to the oxidation-resistant and corrosion-resistant metal substrate of the present invention, the substrate has a dense titania layer formed of a titanium peroxide solution or a sol thereof on its surface, so that it can be used in a high temperature range. Even when used, an oxide film can be prevented from being formed on the surface thereof, and even when used for treating exhaust gas containing an acidic gas, corrosion of the metal surface can be prevented. Therefore, the denitration catalyst using the oxidation-resistant and corrosion-resistant metal substrate is treated with NH3 at a high temperature range of 350 to 600 ° C.
_{(3) Even} when used as a catalyst in the catalytic reduction denitration method, it is possible to prevent the transfer of Fe ions from the metal to the catalyst component, and to prevent a reduction in the denitration rate. It becomes possible. Also, even when used for treating exhaust gas containing acidic gas, acid corrosion of the metal substrate can be prevented, so that oxidation of SO ₂ contained in the exhaust gas can be prevented, and as a result, corrosion due to SO _{3 in} equipment downstream of the denitration apparatus can be reduced. can do.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a denitration catalyst according to an embodiment of the present invention.

FIG. 2 is an explanatory sectional view of a conventional denitration catalyst.

FIG. 3 is an explanatory cross-sectional view of another conventional denitration catalyst.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal substrate, 2 ... Catalyst component layer, 3 ... Oxide film, 4 ... Intermediate layer, 5 ... Dense titania layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/36 102D (72) Inventor Naomi Imada 3-36 Takara-cho, Kure-shi, Hiroshima Babcock-Hitachi Kure Kenkyu In-house F-term (reference) 4D048 AA06 AB02 AB03 BA07X BA23X BA26X BA27X BA41X BB03 BC01 BC10 4G069 AA03 AA08 AA11 BA04A BA04B BA18 BA37 BB04A BB04B BB20C BC50A BC50B BC54A BC54B BC59 CA03 CA06 EC06 BC08

Claims (7)

[Claims] 1. An oxidation-resistant and corrosion-resistant metal substrate comprising a metal substrate surface coated with a titanium peroxide solution or a sol thereof to form a dense titania layer. 2. The method according to claim 1, wherein the titanium peroxide solution or the sol thereof contains inert inorganic fine particles.
2. The oxidation-resistant and corrosion-resistant metal substrate according to 1. 3. A denitration catalyst comprising a catalyst layer formed on the surface of the oxidation-resistant and corrosion-resistant metal substrate according to claim 1. 4. The catalyst layer according to claim 3, wherein the catalyst layer contains titanium and tungsten oxides as a catalyst component.
The catalyst for denitration described in 1. 5. The denitration catalyst according to claim 3, wherein the catalyst layer contains an oxide of titanium, molybdenum and vanadium as a catalyst component. 6. A denitration catalyst according to claim 3, wherein an exhaust gas at 350 to 600 ° C. is brought into contact with an ammonia atmosphere to remove nitrogen oxides from the exhaust gas. Exhaust gas purification method. 7. A denitration catalyst according to claim 3, wherein an exhaust gas containing sulfur oxides is brought into contact with an ammonia atmosphere to remove nitrogen oxides in the exhaust gas. Exhaust gas purification method.