JPH09155155A - Denitration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the denitration of NOx -containing gas such as exhaust gas and to enhance a denitration ratio. SOLUTION: A denitration agent obtained by supporting a metal on zeolite and NOx -containing gas are subjected to catalytic reaction in the coexistence of a reducing agent and the reducing agent is sprayed on the NOx -containing gas to be allowed to coexist. At this time, as the reducing agent, a mixture of ammonium acetate and acetic acid is used and an (ammonium acetate/acetic acid) value using a mol ratio is set to 1.5 or more. Pref., the (ammonium acetate/acetic acid) value is set to (7/3)-4. Further, pref., the concn. of the reducing agent is set to 7-9(mol/l).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for removing NO _x , for example, a technology for removing NO _x contained in smoke emitted from an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Conventional NO _x processing technology is required in various fields. For example, NO _x existing in exhaust gas of a diesel generator or the like is harmful to humans and causes acid rain, so that it is desired to effectively treat NO _x in the exhaust gas.

Examples of such NO _x removal methods include a three-way catalyst method used in automobiles (gasoline vehicles) and a selective catalytic reduction method using ammonia.

However, in the above-mentioned three-way catalyst method, particularly when denitration of exhaust gas with excess oxygen is carried out, the deterioration of the catalyst progresses and the life of the catalyst is shortened.

Further, in the selective catalytic reduction method using ammonia, harmful and dangerous ammonia gas is used, so that it is necessary to handle it with caution. Furthermore, since the reduction catalyst is deteriorated by other components in the exhaust gas, it is necessary to replace the catalyst, which is economically disadvantageous when a particularly expensive noble metal-based catalyst is used.

Therefore, for example, Japanese Patent Laid-Open No. 63-283727.
As disclosed in the publication, a method of contacting a zeolite containing various metals with a gas containing NO _{x in} the presence of hydrocarbons has been studied and has already been put to practical use. The Japanese Patent Application No. 5-178670 filed by the present applicant also discloses a technique for denitration by contacting a catalyst supporting cobalt on zeolite with NO _x gas in the presence of a reducing agent such as carboxylic acid or its ammonium salt. It is shown. A schematic explanatory view of a denitration device according to this technique is shown in FIG. In this figure, 1
Is a denitration device, 2 is an introduction pipe, 3 is a discharge pipe, 4 is a honeycomb,
5 is a spray nozzle.

The NO _x containing gas such as exhaust gas is introduced into the introduction pipe 2
Is introduced into the denitration device 1 through the spray nozzle 5
The reducing agent is sprayed by. NO sprayed with reducing agent
_{The x-} gas is exhausted through the exhaust pipe 3 after being denitrated by contacting with the honeycomb denitration agent honeycomb 4.

[0008]

However, in this denitration technique, there may be variations in the outlet NO _x concentration after denitration.

For example, using the apparatus shown in FIG. 1, using (ammonium acetate 6 mol + acetic acid 6 mol) / l as a reducing agent, and using a one-fluid nozzle at a position away from the honeycomb as shown in FIG. When the reducing agent is sprayed, as shown in Table 1, the outlet NO _x concentration varies.

[0010]

TABLE 1 reducing agent flow outlet concentration of NO _x (l / hr) (ppm) 1 150~350 2 100~300 present invention has been made under the above background, contacting the NO _x gases into zeolite catalyst In the technology of performing denitration, the task is to stabilize the denitration rate.

[0011]

In order to solve the above problems SUMMARY OF THE INVENTION The present invention, together with contacting reacting denitrating agent and NO _x containing gas obtained by the metal is supported the zeolite in the presence of a reducing agent, In the method of causing the reducing agent to coexist by spraying the reducing agent on a NO _x- containing gas,
The value of (ammonium acetate / acetic acid) was calculated by using a mixture of ammonium acetate and acetic acid as the reducing agent and by using a molar ratio.
It is characterized by being 1.5 or more.

Preferably, the above (ammonium acetate / acetic acid)
The value of is (7/3) to 4. Further, the concentration of the reducing agent is preferably 7-9 (mol / l).

[0013] In denitration method of contacting reacting a denitrating agent obtained metal is supported with the zeolite and NO _x containing gas in the presence of a reducing agent, a mixture of acetic acid ammonium acetate as a reducing agent, spraying them Then, the coexistence of a reducing agent improves the denitration rate.

In this case, the ratio of ammonium acetate to acetic acid becomes a problem. In such a denitration method, when the component ratio of ammonium acetate is increased, the reducing agent is smoothly sprayed and the denitration is stably performed. Therefore, the residual NO _x concentration after the NO _x removal treatment becomes small and , Its variation is also small. Since acetic acid is an essential component, be sure to add it.

Further, when the concentration of the reducing agent becomes high, its viscosity also becomes high, and there are problems such as spray failure and nozzle clogging. Preferably, by setting the concentration of the reducing agent to 7 to 9 (mol / l), stable denitration is performed, and residual NO after the denitration is performed.
_{As the x} concentration becomes smaller, the variation becomes smaller.

If the contact time between the honeycomb and the exhaust gas is too short, the denitrification rate will be affected. Therefore, the contact time is preferably 1 second or longer. As a method of spraying the reducing agent, for example, the wide-angle one-fluid nozzle or the two-fluid nozzle (70 ° to 180 °) used in the above-described example is used for the spraying.
The spraying of the reducing agent is preferably performed in the reverse method of the flow of exhaust gas.

The temperature of the denitration device is preferably 40.
The temperature is 0 ° C to 450 ° C.

The present invention will be described in more detail below.

V, C on a carrier such as zeolite or alumina
When a metal (active metal) such as r, Cu, Fe, Mo, W, Mn, Mg, Ru, and Rh is supported, active points are expressed and a denitration action is obtained.

However, when denitration is carried out by catalytically reacting with the exhaust gas of a diesel engine using a denitration agent in which a metal is supported on a carrier such as zeolite as described above, the denitration performance deteriorates.

The cause is S contained in the exhaust gas.
It can be mentioned that O _x gas (sulfur sulfide) coats the surface of zeolite and also reacts with the catalytically active metal to become a catalyst poison.

On the other hand, when a reducing agent is allowed to coexist during the contact reaction between the NO _x gas and the denitration agent, the SO _x gas reacts preferentially with the hydrocarbon. Therefore, the SO _x gas is suppressed from coating the surface of the zeolite, which also suppresses the reaction of the carrier such as zeolite or alumina with the active metal.

As the above-mentioned zeolite, it is preferable to use an alkali metal-type zeolite, particularly Na-containing X-type zeolite, Na-containing Y-type zeolite, Na-containing mordenite, and (K, Na, C).
It is preferable to use type A zeolite containing at least one of a).

As the active metal supported on this zeolite, cobalt is preferably used. There are various methods for supporting the active metal, but preferably the zeolite is immersed in a metal salt solution having a predetermined concentration, and the active metal such as cobalt is sufficiently diffused in the pores of the zeolite. After checking, evaporate the metal salt solution as it is, or
Alternatively, the immersed zeolite is pulled out and taken out from the aqueous solution, and then the water contained in the zeolite is removed.

By thus bringing the metal salt and the zeolite into contact with each other, ion exchange or the like occurs, and the active metal is supported on the zeolite. In the present specification, the state in which the active metal and the zeolite are physically or chemically integrated is described as carrying, not limited to such ion exchange.

The salt of the active metal is not particularly limited as long as it does not inhibit denitration, and for example, nitrates, acetates and the like are used.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, it is considered that the conventional reducing agent has too high a concentration and a high viscosity, so that the denitration rate may vary due to defective spraying or nozzle clogging. Therefore, denitration was performed by changing the composition and concentration of the reducing agent, and the denitration rate of each reducing agent was measured. The details are shown below.

In this example, an experiment was conducted using a 100 kW class diesel engine generator. Table 2 shows the specifications of the diesel engine generator.

[0029]

Shown Table 2] A schematic illustration of a gas flow rate 600 Nm ³ / hr exhaust gas pipe diameter 150mm inlet concentration of NO _x 1000ppm denitration system in FIG. Exhaust gas is
It is introduced from the side of the denitration equipment and exhausted from the side. In addition, in this figure, as in FIG. 1, reference numerals 1 to 3 denote a denitration device, an introduction pipe, and a discharge pipe, respectively, which are not shown, but a honeycomb 4 is provided in the denitration device 1.
In addition, 6 is a generator and 7 is a muffler, respectively.

The zeolite catalyst was produced as follows. First, 30% of clay and glass fibers were mixed and kneaded with powder of Na-containing Y-type zeolite (NaY-type zeolite: manufactured by Tosoh Corporation, HSZ-320NAA), and then formed into a honeycomb shape.

The honeycomb was dried for one day in the sun, dried at 50 ° C. for 10 hours and at 100 ° C. for 5 hours, and then calcined at 750 ° C. for 2 hours to obtain a catalyst base material.

Next, 500 (ml) of a 0.1 (N) acetic acid aqueous solution was added to 500 (ml) of a 0.6 (mol / l) ammonium acetate aqueous solution.
Was added to make 1 liter, and cobalt nitrate was added to this mixed aqueous solution to prepare a solution having a concentration of 0.1 (mol / l) (cobalt nitrate 0.05 mol impregnation).

The above honeycomb formed body was immersed in this aqueous cobalt solution for 2 hours to obtain a cobalt-containing zeolite by ion exchange. At this time, the pH of the aqueous cobalt solution was about 4.4.

After that, the honeycomb was taken out, washed with pure water, immersed in pure water for 30 minutes to remove impurities, and the honeycomb was dried at 150 ° C. for 8 hours to obtain a zeolite denitration agent.

The zeolite catalyst thus obtained was used as a honeycomb in the denitration system of FIG. 2 to denitrate the diesel engine while spraying the reducing agent. On this occasion,
A wide-angle one-fluid nozzle was used as a spraying device for the reducing agent.
Note that this spraying device was installed at a position away from the honeycomb, as in FIG.

Table 3 shows the concentration and component ratio of each reducing agent used in this system.

[0037]

[Table 3] For each reducing agent, denitration was performed with a spray flow rate of 1 or 2 (l / hr). Table 4 shows the results.

[0038]

[Table 4] From Table 4, it is shown that, in each of the reducing agents 1 to 5, the outlet NO _x concentration is lower than that in the conventional example, the denitration rate is improved, and the variation is small.

In particular, referring to Test Examples 1 to 3, the reducing agent 1 has the lowest concentration and good results are obtained. Further, when the ratio of acetic Ammon and acetic acid is constant, it is understood that the outlet concentration of NO _x becomes higher as the reducing agent concentration becomes higher. As the outlet NO _x concentration increases, the concentration variation tends to increase. It is considered that this is because good spraying could not be performed because the reducing agent concentration became high and the viscosity became high.

Therefore, it is preferable that the reducing agent concentration is not too high. From this example, it is shown that the concentration of the reducing agent is lower than the conventional value, preferably about 9 (mol / l).

Further, comparing reducing agents 1, 4, and 5, when the reducing agent concentration was fixed at 9 (mol / l), the test example 1 in which the ratio of ammonium acetate to acetic acid was 7: 3 This ratio is 1
It is shown that the concentration of outlet NO _x is lower than that in Test Example 4 in which the ratio is 0: 0 and Test Example 5 in which the ratio is 6: 4.

From this, it is considered that the ratio of ammonium acetate to acetic acid affects the spray state, and the optimum ratio of ammonium acetate: acetic acid is within the range of 10: 0 to 6: 4.
Particularly, in this example, it is shown that good results are obtained when the ratio is 7: 3.

Next, the concentration of the reducing agent is 9 (mol / l) as it is.
As a result, the denitration ratio of the reducing agent 6 was measured with the ratio of ammonium acetate: acetic acid being 8: 2. Further, in order to confirm the influence of the concentration of the reducing agent, the denitration rate was also measured for the reducing agent 7 having an ammonium acetate: acetic acid ratio of 8: 2 and a reducing agent concentration of 12 (mol / l). Table 5 shows the concentrations and compositions of these reducing agents.
Shown in

[0044]

[Table 5] For each reducing agent, denitration was performed with a spray flow rate of 1 or 2 (l / hr). Table 6 shows the results.

[0045]

[Table 6] From this result, assuming that the concentration of the reducing agent is 9 (mol / l) and the ratio of ammonium acetate and acetic acid is 8: 2, the ratio is 7: 3.
It is shown that the denitrification rate is higher and the variation is smaller than that of the above.

From the above results, the concentration of the reducing agent is 9 (mol /
l) or less is preferable. Further, as a matter of course, the concentration of the reducing agent is preferably higher than the value required to obtain the action as the reducing agent. For example, if the concentration of reducing agent is 7
It is preferably (mol / l) or more. Therefore, the concentration of the reducing agent is preferably 7 (mol / l) to 9 (mol / l).

Further, as shown by the above denitration results, the ratio of ammonium acetate: acetic acid is 6: 4 to 10: 0,
It is preferably 7: 3 to 8: 2. That is, the value of (ammonium acetate / acetic acid) is 1.5 or more, preferably (7
/ 3) to 4. Acetic acid is an essential component and must be added.

In particular, in this example, as shown in FIG. 2, an inclined portion was provided after the introduction of the exhaust gas to make the exhaust gas uniform so that the exhaust gas could flow uniformly through the denitration device. Further, as in this embodiment, it is preferable that the exhaust gas is introduced from the side of the denitration device and exhausted from the side.

The spray position is 300 mm to 3 mm from the honeycomb.
It is preferable to carry out from a place 000 mm away. The diameter of the pipe that introduces the exhaust gas into the denitration equipment is 80 mm to 150 mm
It is preferable that

[0050]

As described above, according to the present invention,
The reducing agent can be sprayed stably and good denitration performance can be obtained.

In particular, by reducing the concentration of the reducing agent and setting the ratio of ammonium acetate to acetic acid to 7: 3, the viscosity of the reducing agent becomes low, and the spray failure of nozzles, clogging, etc. are suppressed, which is excellent. You will be able to spray. Therefore, the concentration of NO _{x at} the outlet is reduced and the variation in the value is also reduced, so that denitration can be stably performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a denitration device.

FIG. 2 is an explanatory diagram of a denitration system.

[Explanation of symbols]

 1 ... Denitration device 2 ... Introducing pipe 3 ... Exhaust pipe 4 ... Honeycomb 5 ... Spray nozzle

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location F01N 3/28 301 B01D 53/36 102C 102D (72) Inventor Masamichi Kuramoto 2 Osaki, Shinagawa-ku, Tokyo No. 1-17 Incorporated company Shameidensha (72) Inventor Kazutoshi Kamura 2-11-17 Osaki, Shinagawa-ku, Tokyo Incorporated company Meidensha (72) Inventor Yoshihiko Asano 2-1-117 Osaki, Shinagawa-ku, Tokyo No. Stock Company Shameidensha

Claims (3)

[Claims] 1. A a denitrating agent and NO _x containing gas obtained by supporting a metal causes a contact reaction in the presence of a reducing agent in the zeolite, the by spraying the reducing agent to NO _x containing gas In the method of allowing a reducing agent to coexist, a mixture of ammonium acetate and acetic acid is used as the reducing agent, and the value of (ammonium acetate / acetic acid) is calculated using a molar ratio.
A denitration method characterized by being 1.5 or more. 2. The value of (ammonium acetate / acetic acid) is (7)
/ 3) -4. The denitration method according to claim 1, wherein 3. The denitration method according to claim 1, wherein the concentration of the reducing agent is 7 to 9 (mol / l).