JP3234239B2 - Method for removing nitrogen oxides from high-temperature exhaust gas and catalyst for removal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a catalyst for removing nitrogen oxides from exhaust gas, and more particularly to a method for suitably removing nitrogen oxides from high-temperature exhaust gas such as exhaust gas at the outlet of a gas turbine. The present invention relates to a removing method and a removing catalyst.

[0002]

2. Description of the Related Art A method for removing nitrogen oxides from exhaust gas and
Therefore, ammonia (NH _Three) After injection the catalyst
So-called catalytic ammonia reduction
The original method is widely used. The catalyst used in this method
Conventionally, (1) titanium oxide (TiO)_Two) To vanadium
(V), tungsten (W), molybdenum (Mo), iron
(Fe) and other elements (JP-B-52-69)
No. 54, Japanese Patent Publication No. 52-22839, etc.)
(2) Zeo that carries copper (Cu), iron (Fe), etc.
Light catalysts (Japanese Patent Publication No. 54-8351 etc.)
Used.

[0003] To mitigate the peak of the recent power demand, but installation of the gas turbine generator is increasing, the gas turbine outlet temperature is 100 to 200 ⁰ C about hot compared to like 500 to 600 ⁰ C and the boiler flue gas In some cases, the catalyst used must have excellent heat resistance and a high denitration rate in a high temperature range. Therefore, a denitration apparatus using a TiO ₂ -WO ₃ -based catalyst or an Fe-substituted zeolite catalyst which relatively satisfies this requirement among the above-mentioned catalysts is about to be put into practical use.

[0004]

SUMMARY OF THE INVENTION Among the above prior arts,
Those using TiO ₂ -WO ₃ catalyst is excellent in heat resistance, 500 to 600 ⁰ C is characterized to maintain for a long time stable denitration performance, but the catalytic activity in this temperature range is low, the boiler flue gas denitration In this case, there is a problem that two to three times the amount of the catalyst must be used.

Moreover, those using Fe-substituted zeolite although superior in 500 to 600 ⁰ C activity, of high strength poor moldability zeolite difficult to obtain, there is a problem with long-term stable operation Was. Further, when an attempt is made to obtain high strength by using an inorganic binder, there has been a problem that the high-temperature activity is reduced due to the reaction with zeolite, and the feature of being excellent in high-temperature activity is not utilized.

An object of the present invention show excellent activity and strength against high temperature exhaust gas of 500 to 600 ⁰ C, including gas turbine outlet gas, nitrogen oxide removal method and a catalyst for removing the high temperature exhaust gas Is to provide.

[0007]

[Means for Solving the Problems In order to achieve the above-mentioned problems
The invention claimed in the present application is as follows. (1) For exhaust gas containing nitrogen oxides at a high temperature of 500 ° C or higher,
In a method for removing nitrogen oxides from exhaust gas, which comprises mixing ammonia as a reducing agent and contacting it with a catalyst to reduce nitrogen oxides, a composition comprising Fe-substituted zeolite as a first component and an oxide of titanium and tungsten as the catalyst. things were the second component, the weight of both ratio (first component / second generation minute) 1
A method for removing nitrogen oxides from high-temperature exhaust gas, wherein a mixture obtained by mixing and sintering so as to be 9/1 to 9/1 is used . (2) In (1), the zeolite is mordenite.
Of removing nitrogen oxides from high-temperature exhaust gas
Law. (3) In a catalyst for removing nitrogen oxides in a high-temperature exhaust gas in which a nitrogen oxide-containing exhaust gas of 500 ° C. or more is catalytically reduced with ammonia, Fe carrying 0.2 to 5% by weight of Fe is used.
A catalyst for removing nitrogen oxides from high-temperature exhaust gas, which is obtained by mixing a substituted zeolite with an oxide of titanium and tungsten and calcining the mixture . (4) In a catalyst for removing nitrogen oxides in a high-temperature exhaust gas in which a nitrogen oxide-containing exhaust gas of 500 ° C. or more is catalytically reduced with ammonia, an iron compound solution is kneaded with a hydrogen-substituted zeolite, or impregnated in the zeolite and dried. -Tungsten mixed with the calcined Fe-substituted zeolite and the metatitanate slurry obtained by the sulfuric acid method so that the atomic ratio of Ti / W becomes 9/1 to 99/1 , and then dried and calcined titanium・ Mix with tungsten oxide
A catalyst for removing nitrogen oxides in high-temperature exhaust gas, which is obtained by calcining . (5) In a catalyst for removing nitrogen oxides in a high-temperature exhaust gas in which a nitrogen oxide-containing exhaust gas is catalytically reduced with ammonia,
And Fe-substituted zeolite, after adding inorganic fibers to the mixture of titanium-tungsten oxide, by adding water and kneaded, after applying this metal substrate, the inorganic fiber woven fabric or mesh-like body, made by drying and baking A catalyst for removing nitrogen oxides from a high-temperature exhaust gas, characterized in that:

[0008]

The Fe-substituted zeolite among the above catalysts is 500
600 acts as a highly active catalyst component ⁰ C. TiO
₂ -WO ₃ based composition, acts as an inorganic binder having the activity of improving the strength at the time of molding of the Fe-substituted zeolite. Further, the inorganic fibers are dispersed in the catalyst to contribute to the improvement of the strength, and also help the formation of pores in the catalyst, and have the effect of improving the activity.

Therefore, the catalyst of the present invention has the following excellent properties.
It has features. (A) The denitration activity at 500 to 600 ° C. is equivalent to that of the Fe-substituted mordenite, and is about twice as high as the activity of the TiO ₂ —WO ₃ based catalyst. (B) The strength of the molded catalyst is equivalent to that of TiO ₂ -WO _3, and a strength having no practical problem can be obtained. Further, since the reaction between zeolite and TiO ₂ -WO ₃ can be almost ignored, there is almost no phenomenon of the collapse of the zeolite structure and the decrease in activity at high temperatures as seen in a zeolite molded catalyst using a viscous mineral or the like as a binder .

A brief description will be given of how the inventors have completed the present invention. 550 to 600 ⁰ C for having the highest denitrification rate in a high temperature range is Fe substituted mordenite, have not found to be comparable thereto. That is, the Ti-W catalyst has the second highest activity after the Fe-substituted mordenite, but about one third of the Fe-substituted mordenite. Cu-mordenite is also known as a denitration catalyst, which has a high activity in a low temperature range but has a low activity at a high temperature. Further, Ni in the zeolite, Pd, I tried to test for those carrying Co, to generate NOx by oxidizing the NH ₃ as a reducing agent in a high temperature range, rather NOx increases. Further, there is a problem that Zn has almost no activity and Ag is expensive.

Next, the properties required as a reinforcing material of the Fe-substituted zeolite include the following. (1) It is easy to become fine particles and does not sinter at high temperatures. (2) Not deteriorating by reacting with zeolite. (3) Sulfation by SOx in the gas must not occur. (4) The compound itself exhibits NH ₃ decomposition activity and does not cause a decrease in the denitration rate.

As a result of testing various materials, Ti
O ₂ easily sinters and decomposes NH ₃ to produce N ₂ O. WO ₃ does not easily become fine particles and has no binding property. In addition, it reacts with zeolite and deteriorates.
Co and Fe decompose NH ₃ remarkably and generate NOx. SiO ₂ and Al ₂ O ₃ show high NH ₃ decomposition activity because a small amount of Fe in Fe-mordenite moves to these. Moreover, it turned out that it becomes tattered if it uses it for a long time at high temperature. Ti—Fe has a high NH ₃ decomposition activity,
Above 50 ⁰ C, NOx increases conversely. Ti-Mo is
550-600 ⁰ When used in C is MoO ₃ there is a problem that evaporates. For the reasons described above, it has been found that those which can be used as the reinforcing aid are extremely limited. Among them, acid clay and activated clay gave relatively good results, but they were found to have a problem of sulfation.

FIG. 1 shows a flow chart for carrying out the denitration method according to the present invention. 500 to 650 ⁰ C of the exhaust gas discharged from the gas turbine 1, after NH ₃ 4 is injected, those that have been filled by combining the plate-shaped catalyst according to the present invention or a honeycomb shape molded Although guide the filling layer 2 He
NOx in the exhaust gas is reduced by NH ₃ by a catalytic action, converted into N ₂ and H ₂ O, and removed. The exhaust gas that has passed through the catalyst layer is discharged from the chimney 3 as it is, or guided to a waste heat recovery boiler (HRSG) for effective use as needed.

The catalyst layer shown in FIG. 1 is filled with a catalyst comprising the Fe-substituted zeolite according to the present invention and the TiO ₂ -WO ₃ composition described above, and its shape is plate-like, honeycomb-like, or It may be granular as long as the gas passing pressure loss permits.
Usually, a plate-shaped or honeycomb-shaped product is used in a state where the catalyst surface is arranged parallel to the flow direction.

The Fe-substituted zeolite used for these catalysts is an aqueous solution of iron chloride, iron nitrate, iron sulfate or an iron salt of various organic acids and a hydrogen-substituted zeolite, preferably a hydrogen-substituted mordenite (Si / Al atomic ratio: about 20%). 35) and after the water was kneaded while evaporating a paste in a kneader in which a heating equipment and by baking after drying 300 to 600 ⁰ C a part or all of the hydrogen in the zeolite with Fe Obtained by substitution. Fe supported on zeolite
The proportion is 0.2~5wt _^0/0, especially 0.5~2w
t _^0/0 with high activity, of high durability can be obtained. On the other hand, T
The iO ₂ -WO ₃ composition is obtained by converting a tungsten compound which generates WO ₃ by sintering ammonium paratungstate, tungstic acid or the like into a metatitanate slurry manufactured by a sulfuric acid method with a Ti / W atomic ratio of 9/1 to 99 /. After adding at a ratio of 1, the mixture was heated and kneaded with a heating kneader, dried, and dried at 250.
600 obtained by firing at ⁰ C.

The Fe-zeolite obtained by the above method and T
The iO ₂ -WO ₃ composition is ground, if necessary, for 200 minutes.
After the powder is reduced to a mesh size or less, the mixing ratio of the two is 10
/ 90-90 / 10 and mixed with SiO ₂
-Al ₂ O ₃ system 5~40wt inorganic fibers _^0/0 after the addition is while adding water and kneaded by a kneader to form a paste moisture of about 40 _^0/0. This paste a metal substrate, or applied or coated on the inorganic fiber woven fabric or catalyst support substrate made of a mesh-like body, after being formed into a honeycomb shape by an extrusion molding machine, and fired in a dry and 500 to 650 ⁰ C , Used as a catalyst.

The features of the catalyst according to the present invention are as described above.
Modification of each operation is included in the scope of the present invention, in which the Fe-substituted zeolite and the TiO ₂ -WO ₃ composition are used in a mixed form.

[0018] In 500 ⁰ NH ₃ reduction of nitrogen oxides in C or more high temperature, the NH ₃ to be used, and those used in the denitration reaction of (1), is decomposed by (2) N
Some generate O. In other words, both reactions are competing reactions, and promoting the reaction of equation (1) and minimizing the reaction of equation (2) are the key points in high-temperature denitration.

[0019] NH_Three+ NO + ／ O_Two→ N_Two+ 3 / 2H_TwoO ... (1) NH_Three+ 3 / 4O_Two → NO + 3 / 2H_TwoO (2) Fe-zeolite, especially Fe-mordenite is represented by the formula (1)
Has a remarkably high reaction activity, and the equation (2) can be ignored.
e-Al_TwoO_Three, Fe-silica, etc., have the reaction of formula (2)
It is the subject. Therefore, the strength of Fe-mordenite is increased.
When using various binders to improve the
The decomposition reaction of the formula (2) proceeds easily due to the catalytic action.
Above, the structure of zeolite is destroyed and Fe-Al_TwoO_Three, F
e-SiO _TwoProduces a similar compound and reduces equation (1)
On the other hand, the reaction of the formula (2) is increased. This is high temperature
It is considered to be the main cause of
High strength Fe-zeo by using hard-to-repel material for binder
500 to get a light molded body⁰Practical denitration of C or more
It depends on what you can do.

The present inventors have searched for such substances, and as a result, most of the substances show high activity in the reaction of (2) or cause structural destruction by reaction with zeolite, I came to the conclusion that I couldn't. The most effective means is to use a TiO ₂ -WO ₃ catalyst which is originally excellent in the reaction activity of (1), has relatively few side reactions of (2), and has sufficient binding strength for practical use as a binder. -It was found that the zeolite was shaped, and the catalyst of the present invention was completed. That is, Ti
The O ₂ -WO ₃ catalyst is not only inert to the side reaction of (2), but also hardly reacts with zeolite, and is extremely easily atomized as compared with zeolite particles. It was confirmed that the molded article had excellent properties indicating the strength of the molded article.

Thus, a high-strength catalyst can be realized without deteriorating the excellent high-temperature activity of Fe-zeolite.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples. Example 1 100 g of H-type mordenite having an Si / Al atomic ratio of 23 (TSZ-650 manufactured by Toyo Soda, average particle size of 9 μm)
Is converted to iron nitrate (Fe (NO ₃ ) ₃ .9H ₂ O) 21.7
g was dissolved in 265 g of water, and the mixture was evaporated to dryness with stirring. After 2h drying obtained paste at 130 ⁰ C, and 2hr calcined at 500 ⁰ C in an electric furnace at atmospheric pressure, Fe-
Mordenite was prepared.

On the other hand, metatitanic acid slurry (manufactured by Ishihara Sangyo prepared by sulfuric acid method, TiO ₂ content 30 wt ^_0/0,
Ratio of SO ₄ with respect to TiO ₂ 10wt _^0/0) 100
0 g of ammonium paratungstate (5 (NH ₄ ) ₂ O)
_{· 12WO 3 · 5H 2 O)} 51.5g was added, to the water evaporated while heating and kneading, dried 550 130 ⁰ C ⁰ C
For 2 hours in the air. The obtained powder was ground with a hammer mill and used as a binder.

The Fe-mordenite obtained by the above method
50g powder and TiO_Two-WO_ThreeMix 50g of composition
Then, 30 inorganic fibers (kaolin type, fiber diameter 3μ) were added to this.
g and 80 g of water, and kneaded to obtain a uniform paste.
I got the quality. E glass yarn (wire diameter 9μ, 2000 /
Yarn) is woven at 10 stitches per inch to form a SiO
_TwoAnd TiO_TwoCoating with catalyst component mainly composed of
Later 5⁰/₀HCl water to reduce Ca in the glass to 30%.⁰/
₀What removed (inorganic fiber base material) two upper and lower layers
A pair of upper and lower rolling rollers sandwiching the catalyst paste between
While pressing to a thickness of 1.1 mm with
A paste was applied. The obtained plate catalyst was air dried to 600⁰C
For 2 hours. Example 2 Fe-Mo in Example 1
The amount of iron nitrate used in the preparation of rudenite was 7.2 g
A catalyst was prepared in the same manner as described above. Examples 3 to 6 Fe-mordenite and TiO of Example 1_Two-WO_Threecomposition
The mixing ratio of 50/50 is 90/10, 70/30, 3
Change the catalyst to 0/70, 10/90 and adjust the catalyst in the same way.
Made. Comparative Examples 1 and 2 Fe-mordenite alone of Example 1 and TiO_Two-W
O_ThreeA plate catalyst was prepared with the composition alone. Comparative Examples 3 to 5 TiO in Example 1_Two-WO_ThreeBen instead of composition
Tonite (made by Toyo Bentonite), acid clay (Kisida
) And activated clay (Kishida Chemical)
Prepared.

[0025] For catalysts of Examples 1-6 and Comparative Examples 1-5, the denitration activity and the bending strength in the case of 300h held in the initial and 600 ⁰ C as measured under the conditions of Table 1 and Table 2. The results obtained are shown in Table 3.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

Comparative Example 1, which is a simple catalyst of Fe-mordenite, has high denitration performance but little strength. T
Comparative Example 2, which had only the iO ₂ -WO ₃ catalyst, had a high strength of 60%.
Although the activity change by the heat test at 0 ° C. is small, the absolute value of the denitration activity is significantly smaller than that of Fe-mordenite. Furthermore, clay minerals that using the binder initial activity of Comparative Examples 3 to 5, but also excellent strength, 600 ⁰ C-
The activity was significantly reduced by the heat resistance test of 300 hours, and was lower than that of Comparative Example 2.

On the other hand, all of Examples 1 to 6 according to the present invention are excellent in strength and denitration activity before and after the heat resistance test, and are clearly excellent catalysts. Further, there was no significant difference in the performance between Examples 1 and 2 in which the Fe content in Fe-mordenite was changed.
-It is clear that it does not depend on the Fe content of the mordenite. On the other hand, from the results of Example 1 and Examples 3 to 6,
The mixing ratio of Fe-mordenite and TiO ₂ -WO ₃ is as follows:
If the amount of Fe-mordenite is too large, it is disadvantageous in strength,
Conversely, it indicates that an increase in TiO ₂ -WO ₃ is disadvantageous in terms of denitration activity, and the mixing ratio of the two is desirably set to 70/30 to 30/70.

FIG. 2 shows Example 1 and Comparative Example 2.
And the activity and strength of the case where the catalyst of Comparative Example 3 was held at 600 ⁰ C plots the results measured over time. Not only is the catalyst of Example 1 according to the present invention will now excellent point of the active intensity, it can be seen that to maintain a high denitrification performance and strength at high temperatures of 600 ⁰ C.

[0032]

According to the present invention, it is possible to realize a denitration apparatus using a catalyst having a long high denitrification rate and strength under high temperature of 500 ⁰ C, 500-60 gas turbine outlet
0 ⁰ becomes possible denitrification of C exhaust gas and less catalyst without cooling. This not only simplifies the process itself, but also has the effect of reducing the amount of catalyst used and achieving a high denitration rate.

[Brief description of the drawings]

FIG. 1 is a system diagram of an apparatus provided with a nitrogen oxide removing catalyst according to the present invention in a gas turbine exhaust gas passage.

2 is a graph showing changes with time of the intensity and the denitrification rate in the 600 ⁰ C for example and the comparative example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas turbine, 2 ... Catalyst, 3 ... Chimney, 4 ... Ammonia.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-68120 (JP, A) JP-A-63-126560 (JP, A) JP-A-50-140362 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/94 B01D 53/86

Claims (5)

(57) [Claims] To 1. A 5 00 ° C. or higher high-temperature nitrogen oxide-containing exhaust gas, ammonia as a reducing agent are mixed, the nitrogen oxide removal method of the catalyst and is contacted with the exhaust gas to reduce nitrogen oxides, the As a catalyst, Fe-substituted zeolite is used as a first component, and a composition comprising an oxide of titanium and tungsten is used as a second component, and the two are in a weight ratio (first component / second component).
A method for removing nitrogen oxides from high-temperature exhaust gas, characterized by using a mixture which has been mixed and calcined so as to be 1/9 to 9/1 in 1 minute . 2. The method according to claim 1, wherein the zeolite is mordenite. 3. A catalyst for removing nitrogen oxides in a high-temperature exhaust gas in which a nitrogen oxide-containing exhaust gas at 500 ° C. or higher is catalytically reduced with ammonia, comprising a Fe-substituted zeolite supporting 0.2 to 5% by weight of Fe; A catalyst for removing nitrogen oxides in high-temperature exhaust gas, which is obtained by mixing and sintering tungsten oxide. 4. A catalyst for removing nitrogen oxides in a high-temperature exhaust gas by catalytically reducing a nitrogen oxide-containing exhaust gas of 500 ° C. or higher with ammonia, wherein an iron compound solution is kneaded with a hydrogen-substituted zeolite or after impregnation with the zeolite. , Dried and calcined Fe-substituted zeolite, and a meta-titanate slurry obtained by a sulfuric acid method containing a tungsten compound with Ti
/ Atomic ratio of W is after mixing <br/> case such that the ratio of 9/99/1, and a titanium-tungsten oxide was dried and calcined mixed, characterized by comprising by firing Catalyst for removing nitrogen oxides from high-temperature exhaust gas. 5. A nitrogen oxide removing catalyst of the hot flue gas nitrogen oxide-containing exhaust gas catalytic reduction with ammonia, and the Fe-substituted zeolite, after adding inorganic fibers to the mixture of titanium-tungsten oxide, water A catalyst for removing nitrogen oxides from high-temperature exhaust gas, which is kneaded, applied to a metal substrate, a woven fabric made of inorganic fiber or a net , dried and fired.