JP2003260331A - Reducing agent composition for denitrification of flue gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducing agent composition for denitrification of a flue gas, the composition which is excellent in the ability for generating ammonia NH<SB>3</SB>to decrease the harmful effect by excess water, which can be massproduced and stably supplied, and which realizes denitrification even in a temperature range from 200°C to 300°C. <P>SOLUTION: The reducing agent composition 6 for the denitrification of the flue gas comprises an aqueous solution essentially comprising urea CO(NH<SB>2</SB>)<SB>2</SB>and contain ammonia NH<SB>3</SB>as an accessory component. The concentration of urea CO(NH<SB>2</SB>)<SB>2</SB>is controlled to 76.9 mass% maximum and in the range of >32.5 mass% and ≤76.9 mass%, while the concentration of the ammonia NH<SB>3</SB>is specified to ≥1 mass% and ≤15 mass%. The composition is injected to the exhaust gas 1 from an exhausting system of a diesel engine 2 or the like prior to a catalyst 12 so as to produce ammonia NH<SB>3</SB>gas as the reducing agent, and thereby, nitrogen oxides NOX in the exhaust gas 1 are reduced into nitrogen N and removed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reducing agent composition for flue gas denitration. That is, the present invention relates to a reducing agent composition for flue gas denitration, which can generate ammonia gas that reduces and removes nitrogen oxides in exhaust gas.

[0002]

BACKGROUND OF THE INVENTION Technical Background Exhaust gas from an internal combustion engine, such as a diesel engine, contains nitrogen oxides NOx. Such nitrogen oxide NOx is harmful if it is directly discharged to the outside air, and its removal is an important theme. Therefore, various types of dry flue gas denitration (from the exhaust gas in the presence of a catalyst to NOx
SCR denitration), which is referred to as flue gas denitration or denitration in the present specification, has been developed and used. And as this type of denitration technology, ammonia N
It is widely practiced to reduce and remove nitrogen oxide NOx to nitrogen N under a catalyst by using H ₃ gas as a reducing agent. As the reducing agent, ammonia NH ₃ is the most direct, but the reducing agent composition is widely used because it has many technical, safety and legal restrictions. That is, a reducing agent composition that generates ammonia NH ₃ gas,
The nitrogen oxide NOx was injected into the exhaust gas to generate ammonia NH ₃ gas as a reducing agent, thereby reducing and removing the nitrogen oxide NOx.

<< Prior Art >> First, as a prior art,
An aqueous solution of 32.5 mass% urea CO (NH ₂ ) ₂ was commonly used as a reducing agent composition for this type of flue gas denitration. See, for example, JP-A-9-150037 and JP-A-10-174841. Urea CO (N
H ₂ ) ₂ has an excellent ability to generate ammonia NH ₃ gas, has high solubility in water, has no toxicity, etc., and is optimal and practical for this type of reducing agent composition. And
An aqueous solution containing 32.5% by mass of urea CO (NH ₂ ) ₂ , which is a eutectic composition (eutectic composition) of urea CO (NH ₂ ) and water, is generally used as this type of reducing agent composition. It is used and its freezing point is -12 ° C to -13 ° C. That is, the aqueous solution of urea CO (NH ₂ ) _{2 having} such a composition is a liquid without being crystallized or solidified from −12 ° C. to −13 ° C. This type of reducing agent composition is stored in a tank at room temperature and is pumped by a liquid to be injected, and in particular, in order to avoid crystallization and solidification in the winter, such urea CO (NH ₂ ) An aqueous solution containing 32.5% by mass of ₂ has been generally used in the past.

<< Prior Art >> Further, as the prior art,
Compounds other than urea CO (NH ₂ ) ₂ and their aqueous solutions
It was sometimes used as a reducing agent composition for this type of flue gas denitration. For example, ammonium carbamate Ammo
A nium carbamate (manufactured by PUReM), a buret (urea dimer), a combination of alcohol as a reduction aid, and the like were sometimes used.

[0005]

<Problem to be Solved by the Invention><FirstProblem> The following problems have been pointed out in such a conventional example. First, 32.5 mass% urea CO
Regarding the above-mentioned conventional reducing agent composition for flue gas denitration using (NH ₂ ) _{2, in addition} to the problem that the concentration of urea CO (NH ₂ ) ₂ is low and the ability to generate ammonia NH ₃ gas is low, It has been pointed out that there is a problem that water becomes excessive and causes various problems. That is, theoretically, a reaction formula for generating ammonia NH ₃ gas as a reducing agent composition, CO
In (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ , 1
One mole of urea CO (NH ₂ ) ₂ which reacts with 23.1% by weight of water in a 1: 1 molar composition is 76.9% by weight. On the other hand, this reducing agent composition contains 32.5% by mass.
Of urea CO (NH ₂ ) ₂ and 67.5% by mass of water, a large amount of 1 mol or more of water is excessive.

In addition to the excess water, the water brought into the exhaust gas together with the generated ammonia NH ₃ gas has caused various harmful effects. a. Excessive water injected into the exhaust gas lowers the temperature of the exhaust gas due to the heat of vaporization, thereby reducing the reduction rate of the nitrogen oxide NOx by the ammonia NH ₃ gas and denitrifying efficiency. The problem was pointed out. The temperature of the exhaust gas is about 400 ° C to 450 ° C during normal operation. b. It has been pointed out that the excess water injected into the exhaust gas dilutes the nitrogen oxide NOx, thereby reducing the reduction rate of the nitrogen oxide NOx, and also from this aspect, denitration efficiency is deteriorated. It was c. Excess water injected into the exhaust gas increases the amount of gas due to vaporization,
Therefore, the space velocity (SV) of the exhaust gas is increased in the denitration reactor equipped with the catalyst. As a result, it has been pointed out that the residence time of the exhaust gas in the denitration reactor is shortened, and the reduction efficiency of the nitrogen oxide NOx, that is, the denitration efficiency is sharply deteriorated.

<< Second Problem >> Secondly, urea C
The reducing agent composition for flue gas denitration of the prior art, which uses a compound other than O (NH ₂ ) ₂ , is as follows.
For example, since it is an extremely special compound such as ammonium carbamate, it is difficult to mass-produce it industrially, and it is difficult to stably supply it.
Also, for example, when alcohol is used as a reduction aid,
It has been pointed out that it is highly flammable and dangerous, and that it has a detrimental effect on denitration, especially on the catalyst.

<Third Problem> Thirdly, the above-mentioned conventional technique, that is, the reducing agent composition for flue gas denitration of this type of conventional example is used only during normal operation of a diesel engine or the like. It was That is, during normal operation, the temperature of the exhaust gas is in the temperature range of about 400 ° C to 450 ° C. At such a high temperature, urea CO (N
H ₂ ) _{2 and the} like generate ammonia NH ₃ gas, so that denitration, that is, reduction of nitrogen oxide NOx has been performed. On the other hand, when the operation is started or the operation is changed, it takes 3 minutes to 5 minutes.
The temperature of the exhaust gas is in the temperature range of about 200 ° C. to 300 ° C. for about a minute. At such a relatively low temperature, urea CO (NH ₂ ) _{2 and the} like have a low ability to generate ammonia NH ₃ gas, so that denitration, that is, nitrogen oxide NO
The reduction of x was practically not performed. in this way,
In this type of conventional example, it has been pointed out that denitration is not performed at the time of starting the operation and the exhaust gas is discharged to the outside air while containing harmful nitrogen oxides.

<Regarding the present invention> The reducing agent composition for flue gas denitration of the present invention has been made in view of the above circumstances in order to solve the problems of the above-mentioned conventional examples. The greatest feature is that it consists of an aqueous solution in which ammonia is used in combination as an auxiliary component. And
The concentration of urea is more than 32.5% by mass to 76.9% by mass or less, the concentration of ammonia is 1% by mass to 15% by mass, and the ammonia gas, which is a reducing agent of nitrogen oxides, is injected into the exhaust gas. Is generated. Therefore, the present invention is, firstly, excellent in the ability to generate ammonia gas, in which adverse effects due to excess water are reduced, secondly, mass production and stable supply are possible, and thirdly, a temperature range of 200 ° C to 300 ° C. The purpose of the present invention is to propose a reducing agent composition for flue gas denitration, which also realizes denitration.

[0010]

<< About Each Claim >> The technical means of the present invention for solving such a problem are as follows. First, claim 1 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 1 is
An aqueous solution containing urea as a main component and ammonia as a secondary component. Claim 2 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 2 is an aqueous solution containing the urea as a main component and the ammonia as an auxiliary component according to claim 1, and reduces nitrogen oxides in exhaust gas. , Ammonia gas that is a reducing agent to be removed can be generated. Claim 3 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 3 is characterized in that, in claim 2, the concentration of the urea is at most 76.9% by mass. Claim 4 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 4 is characterized in that, in claim 3, the concentration of the urea is more than 32.5 mass% to 76.9 mass% or less. .

Claim 5 is as follows. That is, the reducing agent composition for flue gas denitration of claim 5 has the ammonia concentration of 1% by mass or more to
It is characterized by being 15 mass% or less. Claim 6 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 6 can be injected into the exhaust system of a diesel engine before the catalyst according to claim 2, and the ammonia gas is generated based on the injection. And reducing and removing nitrogen oxides in the exhaust gas to nitrogen,
Is characterized by. Claim 7 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 7 is the same as that of claim 6, in which the temperature of the exhaust gas exceeds 300 ° C.
It can be used not only during normal operation at 0 ° C. to 450 ° C., but also at operation start-up or operation fluctuation when the temperature of the exhaust gas is about 200 ° C. to 300 ° C. . Claim 8 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 8 is the reducing agent composition according to claim 6, which uses a heating means such as a heater and the like.
It is characterized by being heated to about 80 ° C. or higher.

<Regarding Operation> The present invention is configured as described above, and is as follows. This reducing agent composition for flue gas denitration consists of an aqueous solution containing urea as a main component and ammonia as an auxiliary component. Urea concentration is 32.5% by mass
The super-maximum is 76.9% by mass, and the concentration of ammonia is 1% by mass or more and 15% by mass or less. Then, it is injected in front of the catalyst to the exhaust system of a diesel engine or the like to generate ammonia gas as a reducing agent to reduce and remove nitrogen oxides in the exhaust gas.

Therefore, firstly, this reducing agent composition has a high concentration of urea as a main component, is excellent in the ability to generate ammonia gas, and reduces excess water. That is, in the reaction formula of ammonia gas generation, urea having a 1: 1 molar composition is 76.9% by mass and water is 23.1% by mass, but the concentration of urea exceeds 32.5% by mass and 76. It is approaching 9% by mass, the water concentration is approaching 23.1% by mass, and the excess water is reduced accordingly. As a result, the excess water is less likely to be injected into the exhaust gas, and a. Exhaust gas temperature reduction, b. Dilution of nitrogen oxides, c. The increase in the space velocity (SV) of the exhaust gas and the like also decrease. Therefore,
A reduction in the reduction rate of nitrogen oxides is avoided, and the denitration efficiency is kept high.

Secondly, this reducing agent composition has a simple and easy composition with urea as a main component and ammonia as an auxiliary component.

Thirdly, since the reducing agent composition is mainly composed of high concentration urea, the temperature of exhaust gas is 400 to 450 ° C. during normal operation of a diesel engine or the like.
It excels in the ability to generate ammonia gas in a high temperature range. Therefore, in this high temperature range, the nitrogen oxides in the exhaust gas are reliably reduced and removed, and denitration is performed.
At the same time, since ammonia is used as an auxiliary component, the temperature of the exhaust gas is 200 ° C when the operation is started or when the operation fluctuates.
Even in a low temperature range of about 300 ° C, the ammonia gas generation ability is excellent. Therefore, even in this low temperature range, the nitrogen oxides in the exhaust gas are reliably reduced and removed, and denitration is performed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments of the invention shown in the drawings. Figure 1, Figure 2,
FIG. 3 serves to explain the embodiment of the present invention. And
FIG. 1 is a system explanatory diagram of an exhaust system, FIG. 2 is a solubility graph, and FIG. 3 is a ammonia generation capacity graph.

<< Regarding the Exhaust System >> First, the exhaust system will be described with reference to FIG. Diesel engines are widely used in automobiles, power generation, ships, locomotives, aircraft, various machines, and others. In the exhaust gas 1 emitted from the internal combustion engine such as a diesel engine, and further in the exhaust gas 1 emitted from the gas turbine, nitrogen oxides N
Ox, carbon monoxide CO, hydrocarbon HC, carbon particles PM,
Etc. are contained. According to the present invention, the exhaust gas 1
Flue gas denitration (denitrification) technology that removes the nitrogen oxides NOx contained in it, that is, SCR (Selective Catalytic Re
duction) Denitration technology. The purpose of the invention is to reduce and remove nitrogen oxide NOx, which is a harmful pollutant, from the exhaust gas 1 and discharge it to the outside air, thereby protecting the human body and environment and contributing to pollution prevention.

First, in the illustrated example, the diesel engine 2 is supplied with fuel 4 from the fuel tank 3, and the diesel engine 2 discharges exhaust gas 1. Exhaust gas 1
Is in the temperature range of about 200 ° C. to 300 ° C. for about 3 to 5 minutes when the diesel engine 2 starts operation or changes in operation, and is in the temperature range of about 400 ° C. to 450 ° C. during normal operation. And, in the exhaust pipe 5 of this exhaust gas 1,
An injection nozzle 7 for the reducing agent composition 6 and a denitration reactor 8 are sequentially provided.

The injection nozzle 7 is made of, for example, an injector and is attached to the exhaust pipe 5. Then, the reducing agent composition 6 is supplied from the storage tank 8 via a pump, and the reducing agent composition 6 is sprayed onto the exhaust gas 1. The denitration reactor 9 is interposed in the exhaust pipe 5. Then, the reducing catalyst 12 is adhered and coated on the cell wall 11 of the porous honeycomb core 10, or the catalyst 12 itself is molded into the shape of the porous honeycomb core 10 is used. As the catalyst 12, vanadium compound, titanium oxide, zeolite or the like is used. The exhaust system is like this.

<< Reducing agent composition 6 >> The reducing agent composition 6 for flue gas and flue gas used as described above will be described below.
This will be described with reference to FIGS. 1, 2 and 3. Reducing agent composition 6
Is injected from the injection nozzle 7 to the exhaust gas 1 of 200 ° C. or higher in the exhaust pipe 5, so that the ammonia NH ₃ gas as a reducing agent is immediately supplied in the upstream side of the denitration reactor 9 and in the denitration reactor 9. Occur. The generated ammonia NH ₃ gas is converted into nitrogen oxide NOx in the exhaust gas 1, that is, nitrogen oxide NO and nitrogen dioxide NO ₂ in harmless nitrogen N and water under the catalyst 12 according to the chemical formula 1 or 2 below. H ₂ O
And reduce, remove, transform, and convert.

[0021]

[Chemical 1]

[0022]

[Chemical 2]

Now, the reducing agent composition 6 for generating ammonia NH ₃ gas has the following composition. The reducing agent composition 6 for flue gas denitration contained a high concentration of urea CO (NH ₂ ) ₂ as a main component and ammonia NH ₃ as an auxiliary component, and contained a low concentration of ammonia NH ₃ as an auxiliary component. , Consisting of an aqueous solution. A composition in which ammonium carbonate (NH ₄ ) ₂ CO ₃ or the like is added as a sub-component in addition to ammonia NH ₃ is also possible. First, urea CO (NH ₂ ) _{2 which} is the main component,
The reducing agent composition 6 contains more than 32.5% by mass to 76.9% by mass or less, that is, 76.9% by mass at maximum,
It is at least 32.5 mass%. 76.9% by mass
In the above, although excess water is not generated corresponding to a 1: 1 molar composition with water, the freezing point becomes relatively high. Also, 40% by mass to 5
About 0% by mass is easy to handle and can be said to be the most practical because the amount of excess water is relatively small and the freezing point is lower than that of 76.9% by mass. And urea CO (N
H ₂ ) ₂ has a high solubility in water and a temperature of 400 ° C. to 4 ° C.
In the temperature range of about 50 ° C., it has excellent ammonia NH ₃ gas generation characteristics and is not toxic. Ie urea CO
(NH ₂ ) ₂ generates ammonia NH ₃ gas and carbon dioxide CO ₂ based on the hydrolysis reaction according to the chemical formula of the following chemical formula ₃ .

[0024]

[Chemical 3]

Next, the auxiliary component ammonia NH ₃ (aqueous ammonia) is contained in the reducing agent composition 6 in an amount of 1% by mass or more to 1% by mass or more.
5 mass% or less is contained. And ammonia NH
₃ (ammonia water) generates ammonia NH ₃ gas based on evaporation and vaporization, and exhibits a function of being excellent in ammonia NH ₃ gas generation characteristics particularly in a temperature range of 200 ° C to 300 ° C. By the way, when the content is less than 1% by mass, the amount of ammonia NH ₃ gas generated in the temperature range of 200 ° C. to 300 ° C. of the reducing agent composition 6 is insufficient. 15 above
If the content exceeds 10% by mass, the solubility in water decreases when the temperature rises, so ammonia NH with odor
_A large amount of ₃ gas is generated, which is not suitable for practical use.

<< Data >> Solubility in water,
The generation capacity of ammonia NH ₃ gas will be described based on the data. First, in FIG. 2, the reducing agent composition 6 having various compositions that can be industrially used, and the composition of urea CO
Solubility data for (NH ₂ ) _{2 and} other water are shown along with temperature changes. As can be understood from this data, urea CO (NH ₂ ) ₂ generally has the highest solubility, is easy to handle, and is suitable as the main component of the reducing agent composition 6. Ammonium hydrogen carbonate NH ₄ HCO ₃ , burette, ammonia NH ₃ (ammonia water), ammonium carbonate (NH ₄ ) ₂ CO _3, etc. are generally inferior in solubility to urea CO (NH ₂ ) ₂ . . Urea CO (NH ₂ ) ₂ can be dissolved at about 70 ° C. in 76.9% by mass, which is a 1: 1 molar composition with water, and can be handled as a liquid as it is at about 70 ° C. or higher. At about 40 ° C. or higher, it can be dissolved at about 60% by mass and can be handled as a liquid, and at −12 ° C. to −13 ° C., 32.5% by mass becomes the melting point.

Next, referring to FIG. 3, for various industrially usable reducing agent compositions 6, ammonia N per 100 g was used.
The data of the generated amount g of H ₃ gas (deammonified state) is shown together with the concentration change in the composition of urea CO (NH ₂ ) _{2 and} other aqueous solutions. Temperature setting is 4
The temperature is set to 00 ° C to 450 ° C. As can be understood from this data, urea CO (NH ₂ ) ₂ generally has a large amount of ammonia NH ₃ gas generation and is suitable as the reducing agent composition 6. Ammonia NH ₃ (ammonia water) generates a large amount of ammonia NH ₃ gas, but as shown in FIG. 2 above, the solubility in water decreases when the temperature rises, and therefore the amount that is not dissolved in water during storage is Is vaporized and vaporized to generate a large amount of ammonia NH ₃ gas accompanied by a foul odor, which is not suitable as the main component of the reducing agent composition 6. However, ammonia NH ₃ (ammonia water) with a low concentration of 1% by mass to 15% by mass produces little ammonia NH ₃ gas even if the temperature rises, and can be put to practical use.

<< Regarding Operation and the Like >> The present invention is configured as described above. Therefore, it becomes as follows.
The reducing agent composition 6 for flue gas denitration is urea CO (N
H ₂ ) ₂ as a main component and ammonia NH ₃ as a subcomponent, and an aqueous solution containing ammonia NH ₃ as a subcomponent. The maximum concentration of urea CO (NH ₂ ) ₂ is 7
For example, it is more than 32.5 mass% to 76.9 mass% or less. Ammonia NH ₃ concentration is 1% by mass
It is not less than -15% by mass. Then, the reducing agent composition 6 is injected before the catalyst 12 to the exhaust gas 1 of 200 ° C. or higher in the exhaust system of the diesel engine 2 or the like, and immediately produces ammonia NH ₃ gas as a reducing agent. , Nitrogen oxide NOx in exhaust gas 1, that is, nitrogen oxide N
O and nitrogen dioxide NO ₂ are reduced to nitrogen N and removed (see FIG. 1, chemical formula 1, chemical formula 2).

Then, this reducing agent composition 6 for flue gas denitration
Becomes the following first, second, and third. First, the reducing agent composition 6 contains urea CO (NH ₂ ) ₂ which is the main component.
Has a high concentration of more than 32.5% by mass to 76.9% by mass or less, and is dissolved in water at a high concentration. Therefore, excellent generation capability of the reducing agent serving ammonia NH ₃ gas, while generating ammonia NH ₃ gas at a high conversion, the excess water is being reduced. That is, theoretically, in the reaction formula for generating ammonia NH ₃ gas by the hydrolysis reaction, 1: 1
The molar composition of urea CO (NH ₂ ) ₂ is 76.9% by mass,
Water is 23.1% by mass, but in reality, in this reducing agent composition 6, the concentration of urea CO (NH ₂ ) ₂ was 32.
It exceeds 5% by mass and approaches the concentration of 76.9% by mass, and the concentration of water approaches the concentration of 23.1% by mass, and the excess water is reduced accordingly.

As a result, excess water in the reducing agent composition 6 is less likely to be injected and introduced into the exhaust system of the exhaust gas 1 by that amount. So a. Excessive water is injected into the exhaust gas 1 and the reduction in the temperature of the exhaust gas 1 due to the heat of vaporization is also reduced. Therefore, the reduction rate (denitration rate) of the nitrogen oxide NOx by the ammonia NH ₃ gas is
It also reduces the reduction. b. Excessive water is injected into the exhaust gas 1 and the dilution of the nitrogen oxide NOx in the exhaust gas 1 is also reduced, thereby reducing the reduction rate (denitration rate) of the nitrogen oxide NOx by the ammonia NH ₃ gas. The number of accidents is reduced. c. Excessive water is injected into the exhaust gas 1 and is injected and vaporized to increase the amount of gas, and thus decrease the space velocity (SV) of the exhaust gas 1 in the denitration reactor 9. Therefore, the residence time of the exhaust gas 1 in the denitration reactor is maintained without being shortened. As a result, when this reducing agent composition 6 is used, the reduction efficiency (denitration efficiency) of the nitrogen oxide NOx is maintained high.

Secondly, this reducing agent composition 6 contains urea CO
(NH ₂ ) ₂ is the main component, and ammonia NH ₃ (ammonia water) is the auxiliary component. Since it has such a simple composition, it can be easily produced, supplied and obtained.

Thirdly, the reducing agent composition 6 has a high concentration of urea CO (NH ₂ ) ₂ as a main component. Therefore, during normal operation of the diesel engine 2 and the like, effective denitration is performed. That is, in the high temperature range where the temperature of the exhaust gas 1 exceeds 300 ° C. and is about 400 ° C. to 450 ° C., the ability to generate the ammonia NH ₃ gas as a reducing agent is excellent, and the ammonia NH ₃ gas is converted at a high conversion rate. NOx in the exhaust gas 1 as it is generated
Is reliably reduced and removed. At the same time, the reducing agent composition 6 contains ammonia NH ₃ (ammonia water) as an auxiliary component. Therefore, effective denitration is performed even when the diesel engine 2 or the like is started or changes in operation. That is, the temperature of the exhaust gas 1 is 200 ° C to 300 ° C.
Even at relatively low temperature range of approximately ° C., has excellent generation capability of the reducing agent serving ammonia NH ₃ gas, since the generation of ammonia NH ₃ gas at a high conversion rate, the exhaust gas 1
The nitrogen oxide NOx therein is surely reduced and removed.

By the way, in order to prevent the reducing agent composition 6 from crystallizing and solidifying (especially, as the concentration of urea CO (NH ₂ ) ₂ approaches 76.9% by mass, the solidifying point rises). Tank 8 for heating or a heating means such as a heater is attached in front of the tank 8 to reduce the reducing agent composition 6 in storage at 60 ° C to
Heat to above 80 ° C. By thus providing the heating means, crystallization and solidification at room temperature, especially in winter, can be reliably prevented.

[0034]

EXAMPLES Examples of the present invention will now be described.
Ku. The reducing agent composition 6 of the present invention, that is, urea CO (N
H_Two)_TwoWith ammonia as the main component_Three(ammonia
200 ° C. for the reducing agent composition 6 containing water as an auxiliary component
Under the temperature of ammonia NH_ThreeThe ability to generate gas
Tested First, regarding the test conditions,
Ri. ○ In Fig. 1, the diesel engine 2 and the exhaust pipe 5
Turn off and include nitrogen oxide NOx instead of exhaust gas 1
Unheated air was supplied to the exhaust pipe 5. With this,
The catalyst 12 was removed from the denitration reactor 9. They are,
Differentiated from the reduction reaction of nitrogen oxide NOx,
A NH_ThreeIt depends on the purpose of verifying only the gas generation capacity. ○ Heating air is 1Nm in standard state conversion^Three/ Min, temperature
Set to 200 ℃. The reducing agent composition 6 of the example is shown in Tables 1 and 2 below.
Sea urchin, CO (NH _Two)_TwoIs 73.3 mass% (molar ratio
45%), ammonia NH_ThreeIs 2.3% (molar ratio
5% in units), water H_TwoO is 24.4 mass% (molar ratio unit
50%). The reducing agent composition 6 of the comparative example is shown in Tables 1 and 2 below.
Sea urchin, CO (NH _Two)_TwoIs 76.9 mass% (molar ratio
50% in units), water H_TwoO is 23.1% by mass (molar ratio simple
50%) (ammonia not included, urea only
Aqueous solution). ○ And in FIG. 1, the exhaust pipe 5 is provided by the injection nozzle 7.
At a rate of 3.69 g / min for the heated air inside,
Example 6 reducing agent composition 6 and Comparative example reducing agent composition 6
Were sequentially ejected.

[0035]

[Table 1]

[0036]

[Table 2]

In FIG. 1, the heated air in a gas state was sampled before the position where the catalyst 12 of the denitration reactor 9 was located. ○ Then, the temperature of the collected heated air was converted into 1 Nm ³ / min, and the concentration of the contained ammonia NH ₃ gas was
It was measured in the unit g / Nm ³ · min. The results are shown in Table 3 below. That is, it was verified that the reducing agent composition 6 of the example generated twice the amount of ammonia NH ₃ gas as compared with the comparative example (aqueous solution containing urea alone without ammonia). As described above, the reducing agent composition 6 has an excellent ability to generate ammonia NH ₃ gas as a reducing agent even in a relatively low temperature range of 250 ° C.,
Effective denitration can be carried out.

[0038]

[Table 3]

[0039]

<Features of the Invention> As described above, the reducing agent composition for flue gas denitration according to the present invention is prepared from an aqueous solution in which urea as a main component and ammonia as a subcomponent are used in combination. The greatest feature is.
The concentration of urea is more than 32.5% by mass to 76.9% by mass or less, the concentration of ammonia is about 1% by mass to 15% by mass, and it is injected into the exhaust gas to serve as a reducing agent of nitrogen oxides. Generating ammonia gas.
Therefore, the following effects are exhibited.

<< Regarding the First Effect >> First, the harmful effects of excess water are reduced. That is, this reducing agent composition has a high concentration of urea, is excellent in the ability to generate ammonia gas as a reducing agent, and is reduced in excess water, so that excess water is rarely introduced into the exhaust gas exhaust system. . There, a. Exhaust gas temperature drop,
b. Dilution of nitrogen oxides, c. Space velocity of exhaust gas (S
V) increase, etc. are prevented. Therefore, as compared with the above-described conventional example of this type, a reduction in the reduction rate of nitrogen oxides is avoided, and the reduction efficiency of nitrogen oxides, that is, the denitration efficiency is excellent.

<< Second Effect >> Secondly, mass production and stable supply are possible. That is, the reducing agent composition has a simple and easy composition containing urea as a main component and ammonia as an auxiliary component, is industrially produced, and can be stably supplied. That is, unlike the conventional example of this type using ammonium carbamate or the like, mass production and stable supply are not difficult, and the cost is excellent. Further, unlike the case where alcohol is used as a reduction aid, it does not adversely affect denitration, especially the catalyst.

<< Third Effect >> Thirdly, 200 ° C.
Denitration is realized in the temperature range of up to 300 ° C. That is, this reducing agent composition contains ammonia as an auxiliary component and is excellent in the ability to generate ammonia gas as a reducing agent even in the temperature range of 200 ° C to 300 ° C. Therefore, during normal operation of a diesel engine or the like, that is, in the high temperature range of the exhaust gas temperature of about 400 ° C to 450 ° C,
Not only is reliable denitration performed, but also at the time of operation start-up or operation fluctuations, that is, the temperature of the exhaust gas is 200 ° C to 300 ° C.
Effective denitration can be realized even in a relatively low temperature range. As in the conventional example of this kind described above, denitration is not performed for about 3 to 5 minutes at the time of starting the operation, etc., and exhaust gas containing harmful nitrogen oxides is directly discharged to the outside air. Certainly prevented. As described above, the effects of the present invention are remarkably large, such that all the problems existing in this type of conventional example are solved.

[Brief description of drawings]

FIG. 1 is a system explanatory diagram of an exhaust system, which is used to explain an embodiment of the invention, regarding a reducing agent composition for flue gas denitration according to the present invention.

FIG. 2 is a graph showing the solubility of the reducing agent composition, which is used for the description of the embodiment of the present invention.

FIG. 3 is a graph showing the ammonia generating ability of the reducing agent composition, which is used for explaining the embodiment of the present invention.

[Explanation of symbols]

1 exhaust gas 2 diesel engine 3 fuel tank 4 fuel 5 exhaust pipe 6 reducing agent composition 7 injection nozzle 8 tanks 9 Denitration reactor 10 Honeycomb core 11 cell wall 12 catalyst

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/20 B01D 53/34 ZAB 3/24 53/36 101Z F term (reference) 3G091 AA18 AA28 AB05 BA14 CA05 CA17 GA06 GB01W GB09W GB10W 4D002 AA12 AC10 BA06 CA11 DA07 DA57 DA70 GA01 GB03 GB08 4D048 AA06 AB02 AC03 AC04

Claims (8)

[Claims] 1. A reducing agent composition for flue gas denitration, which comprises an aqueous solution containing urea as a main component and ammonia as a subcomponent. 2. The reducing agent composition for flue gas denitration according to claim 1, comprising an aqueous solution containing urea as a main component and ammonia as a secondary component, and nitrogen oxides in exhaust gas. A reducing agent composition for flue gas denitration, which is capable of generating ammonia gas which is a reducing agent for reducing and removing hydrogen. 3. The reducing agent composition for flue gas denitration according to claim 2, wherein the concentration of the urea is at most 76.9% by mass. Reducing agent composition. 4. The reducing agent composition for flue gas denitration according to claim 3, wherein the urea concentration is more than 32.5% by mass.
A reducing agent composition for flue gas denitration, which is 76.9% by mass or less. 5. The flue gas denitration according to claim 2, wherein the concentration of the ammonia is 1% by mass or more and 15% by mass or less. Reducing agent composition. 6. The reducing agent composition for flue gas denitration according to claim 2, which is used for an exhaust system of a diesel engine,
A reducing agent for flue gas denitration, characterized in that it can be injected before the catalyst, and the ammonia gas is generated based on the injection to reduce and remove nitrogen oxides in the exhaust gas to nitrogen. Composition. 7. The reducing agent composition for flue gas denitration according to claim 6, wherein the temperature of the exhaust gas exceeds 300 ° C. 4
It can be used not only during normal operation of about 00 ° C to 450 ° C, but also during start-up or operation fluctuation when the temperature of the exhaust gas is about 200 ° C to 300 ° C.
A reducing agent composition for flue gas denitration. 8. The reducing agent composition for flue gas denitration according to claim 6, wherein a heating means such as a hitter is used,
A reducing agent composition for flue gas denitration, which is heated to about 80 ° C. or higher.