JP2003269141A - Reducer composition for flue gas denitrification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducer composition for flue gas denitrification firstly having excellent generation capability of ammonia NH<SB>3</SB>and capable of reducing adverse effect due to excessive water, secondly capable of avoiding crystallization and coagulation, thirdly mass-producible and stably suppliable, and fourthly capable of realizing denitrification in a region of 200-300°C. <P>SOLUTION: This reducer composition 6 for flue gas denitrification contains urea CO(NH<SB>2</SB>)<SB>2</SB>as a main ingredient, and ammonium carbonate (NH<SB>4</SB>)<SB>2</SB>CO<SB>3</SB>as a sub-ingredient. The concentration of urea CO(NH<SB>2</SB>)<SB>2</SB>is 32.5-76.9 mass%. The concentration of ammonium carbonate (NH<SB>4</SB>)<SB>2</SB>CO<SB>3</SB>is 15-25 mass%. The reducer composition is spouted to an exhaust gas 1 of an exhaust system of a diesel engine 2 or the like before a catalyst 12 to generate ammonia NH<SB>3</SB>of a reducer, so that nitrogen oxides NOX in the exhaust gas 1 are eliminated by reducing them to nitrogen N. <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 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 oxides NOx to nitrogen N under a catalyst by using H ₃ 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,
The reducing agent composition that generates ammonia NH ₃ is injected into the exhaust gas containing the nitrogen oxide NOx, and ammonia NH ₃ that is the reducing agent is generated to reduce and remove 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 , has a high solubility in water, has no toxicity, etc., and is optimal and practical for this type of reducing agent composition. 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 ) ₂ and water, is used as the reducing agent composition of this type. It is generally 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 >> Next, as the prior art,
An aqueous solution of urea CO (NH ₂ ) _{2 having} a high concentration of more than 32.5% by mass, for example, 40% by mass, has also been used as a reducing agent composition for flue gas denitration. For example, JP-A-8
See Japanese Patent No. 252429. That is, as the concentration of urea CO (NH ₂ ) ₂ in the aqueous solution becomes higher, the ability to generate ammonia NH ₃ as a reducing agent improves,
It is excellent as a reducing agent composition of this type. Incidentally, in the present theory, ammonia NH ₃ is generated by hydrolysis, and in the reaction formula CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ , water and urea CO (NH ₂ ) ₂ having a 1: 1 molar composition are ,
76.9 mass%, and water H ₂ O is 23.1 mass%. Therefore, a reducing agent composition having a high concentration of urea CO (NH ₂ ) ₂ is used while preventing the above-mentioned crystallization and solidification at room temperature, especially in winter by providing a heating means. Was there.

<< Prior Art >> Furthermore, as a 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.

[0006]

<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 reducing agent composition for flue gas denitration of the prior art, which uses an aqueous solution containing (NH ₂ ) ₂ , urea CO (NH
₂ ) In addition to the problem that the concentration of ₂ is low and the ability to generate ammonia NH ₃ is low, it has been pointed out that there is a problem that water becomes excessive and various adverse effects occur. That is, theoretically, in the reaction formula for generating ammonia NH ₃ as a reducing agent composition, CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ , 1 mol of 23.1 mass% water and 1: 1 mol composition The amount of 1 mol of urea CO (NH ₂ ) ₂ that reacts with is 76.9% by mass. On the other hand, this reducing agent composition is 32.
Since it is composed of 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 becomes excessive.

In addition to the excess water, the water brought into the exhaust gas system together with the generated ammonia NH ₃ causes various harmful effects. a. Excess water injected into the exhaust gas lowers the temperature of the exhaust gas due to the heat of vaporization, so that ammonia NH ₃
It has been pointed out that the reduction rate of the nitrogen oxide NOx due to the above-mentioned is reduced and the denitration efficiency is deteriorated. Note that the temperature of the exhaust gas is 400 ° C. during normal operation.
It is about 450 ° C. b. Excess water injected into the exhaust gas causes nitrogen oxide NO
It has been pointed out that there is a problem in that x is diluted and the reduction rate of the nitrogen oxide NOx is reduced, which also deteriorates the denitration efficiency. c. Excess water injected into the exhaust gas increases the amount of gas by vaporization, thereby increasing the space velocity (SV) of the exhaust gas 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.

<Regarding Second Problem> Secondly, for example, urea CO (NH ₂ ) ₂ having a high concentration of 40% by mass was used.
It has been pointed out that the conventional reducing agent composition for flue gas denitration has problems of crystallization and solidification when stopped. That is, since the reducing agent composition is provided with a heating means, crystallization and solidification are prevented during continuous operation. However, when the operation is stopped and the heating means is stopped, the reducing agent composition is crystallized and solidified at room temperature. Then, once crystallized and solidified, even after trying to re-dissolve by driving the heating means, the crystallized and solidified reducing agent composition has low thermal conductivity and no convective heat transfer. It has been pointed out that it is not easy and takes a long time, and thus it is not easy to handle.

<< Third Problem >> Thirdly, 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.

<Regarding Fourth Problem> Fourth, the above-mentioned conventional technology, 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. Was there. That is, during normal operation,
The temperature of the exhaust gas is in the temperature range of about 400 ° C to 450 ° C. And, at such a high temperature, urea CO
(NH ₂ ) _{2 and the} like generate ammonia NH _3, and as a result, 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 , and thus denitration, that is, reduction of nitrogen oxide NOx has not been actually performed. Thus, in this type of conventional example, denitration is not performed at the time of starting the operation,
It has been pointed out that 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 ammonium carbonate is used as a sub ingredient in combination. Then, the concentration of urea is more than 32.5% by mass to 76.9% by mass or less, the concentration of ammonium carbonate is 15% by mass to 25% by mass, and it is injected into the exhaust gas to serve as a reducing agent of nitrogen oxides. Generating ammonia. Therefore, the present invention is, firstly, excellent in the ability to generate ammonia, the adverse effects caused by excess water are reduced, secondly, crystallization and solidification can be avoided, and thirdly, mass production and stable supply are possible, Fourth, 20
It is an object of the present invention to propose a reducing agent composition for flue gas denitration, which also realizes denitration in the temperature range of 0 ° C to 300 ° C.

[0012]

<< 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 ammonium carbonate as a secondary component. Claim 2 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 2 is the reducing agent composition according to claim 1, which is an aqueous solution containing the urea as a main component and the ammonium carbonate as a secondary component, and removes nitrogen oxides in exhaust gas. It is characterized in that ammonia, which is a reducing agent for reduction and removal, can be generated. Claim 3 is as follows. That is, this claim 3
The reducing agent composition for flue gas denitration is characterized in that the concentration of the urea is 76.9% by mass at maximum. Claim 4 is as follows. That is,
The reducing agent composition for flue gas denitration according to claim 4 is the method according to claim 3.
In the above, the concentration of the urea exceeds 32.5 mass% to 76.
It is 9 mass% or less.

Claim 5 is as follows. That is, the reducing agent composition for flue gas denitration according to claim 5 is characterized in that, in claim 2, the concentration of the ammonium carbonate is 15% by mass or more and 25% by mass or less. Claim 6 is as follows. That is, this claim 6
The reducing agent composition for flue gas denitration according to claim 2 can be injected into the exhaust system of a diesel engine before the catalyst, and the ammonia is generated based on the injection to generate the ammonia in the exhaust gas. The nitrogen oxides of 1 are reduced to nitrogen and removed. Claim 7 is as follows.
That is, the reducing agent composition for flue gas denitration according to claim 7 is the exhaust gas not only in the normal operation in which the temperature of the exhaust gas exceeds 300 ° C. to about 400 ° C. to 450 ° C. It is characterized in that it can be used even when the gas temperature is about 200 ° C. to 300 ° C. when the operation is started or when the operation is changed. Claim 8 is as follows.
That is, the reducing agent composition for flue gas denitration according to claim 8 uses the heating means such as a heater according to claim 6,
It is characterized by being heated to about 50 ° C. to 60 ° C. or higher.

<Regarding Operation> Since the present invention is configured as described above, it is as follows. This reducing agent composition for flue gas denitration consists of an aqueous solution containing urea as a main component and ammonium carbonate as an auxiliary component. Urea concentration is 32.5
The content is more than 7% by mass and at most 76.9% by mass, and the concentration of ammonium carbonate is 15% by mass or more and 25% by mass or less. Then, it is injected in front of the catalyst to an exhaust system such as a diesel engine to generate ammonia 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, and reduces excess water. That is, in the reaction formula of ammonia generation, urea having a 1: 1 molar composition is 76.
Water is 23.1% by mass at 9% by mass, but the concentration of urea exceeds 32.5% by mass and approaches 76.9% by mass, and the concentration of water is 23.1% by mass. %, Excess water is being reduced. 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 maintained high.

Secondly, since the reducing agent composition is prepared by adding ionic dissociative ammonium carbonate to an aqueous solution of nonionic urea, the freezing point is lowered and crystallization,
The speed of coagulation is also reduced. Therefore, although it has a high concentration of urea as its main component, it is difficult to crystallize and solidify, and it can be handled in a liquid state at room temperature, and it is possible to open the way to store it in a tank as it is and to pump and inject it. Of course, in order to surely prevent crystallization and solidification, a heating means may be additionally provided to heat at about 50 ° C. to 60 ° C. or higher. Thirdly, this reducing agent composition is composed of urea as a main component and ammonium carbonate as a secondary component, and has a simple and easy composition.

Fourthly, since the reducing agent composition contains urea in a high concentration as a main component, 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 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 ammonium carbonate is used as an auxiliary component, the temperature of the exhaust gas is 200 when the operation is started or changed.
Even in a low temperature range of about 300 ° C to 300 ° C, the ammonia generation ability is excellent. Therefore, even in this low temperature range,
Nitrogen oxides in the exhaust gas are surely reduced, removed, and denitrated.

[0018]

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.

<< 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 >> Hereinafter, the reducing agent composition 6 for flue gas and flue gas used as described above will be described.
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, and thus ammonia, which is a reducing agent immediately vaporized and gasified in the upstream side of the denitration reactor 9 and in the denitration reactor 9. Generates NH ₃ . Under the catalyst 12, the generated ammonia NH ₃ 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 H according to the following chemical formula. It is reduced, removed, converted and converted into ₂ O.

[0023]

[Chemical 1]

[0024]

[Chemical 2]

The reducing agent composition 6 for generating ammonia NH ₃ has the following composition. The reducing agent composition 6 for flue gas denitration has a high concentration of urea CO (NH ₂ ) ₂ as a main component and a low concentration of ammonium carbonate (NH ₄ ) ₂ CO ₃ as a secondary component. Ammonium carbonate (NH ₄ )
_It consists of an aqueous solution containing ₂ CO ₃ . As an accessory ingredient,
In addition to ammonium carbonate (NH ₄ ) ₂ CO ₃ , a composition in which aqueous ammonia or the like is added is also possible. First, urea CO (NH ₂ ) ₂ as the main component was added to the reducing agent composition 6 in an amount of 3
More than 2.5% by mass to 76.9% by mass or less, that is, 7 at maximum
Contains 6.9% by mass, at least 32.5% by mass
Is over. At 76.9% by mass, an excessive amount of water is not generated corresponding to a 1: 1 molar composition with water, but the freezing point becomes relatively high. In addition, about 40% by mass to 50% by mass, the amount of excess water is relatively small, and the freezing point is lowered as compared with the case of 76.9% by mass, which is easy to handle and can be said to be the most practical. Urea CO (NH ₂ ) ₂ has high solubility in water, excellent generation characteristics of ammonia NH ₃ in the temperature range of about 400 ° C. to 450 ° C., and is not toxic. That is, urea CO (NH ₂ ) ₂ is converted into ammonia NH ₃ based on the hydrolysis reaction according to the following chemical formula.
And carbon dioxide gas CO ₂ is generated.

[0026]

[Chemical 3]

Next, ammonium carbonate (NH
_Four)_TwoCO_ThreeIs 15% by mass or more in the reducing agent composition 6.
Contained in an amount of up to 25% by mass (calculated as anhydrous salt). That
Ammonium carbonate (NH_Four)_TwoCO_ThreeAnti-pyrolysis
Ammonia NH_ThreeOccurs, especially from 200 ° C
Ammonia NH in the temperature range of 300 ° C_ThreeOccurrence characteristics
Demonstrate the function of being excellent. Furthermore, carbonated ammonium
Mu (NH_Four)_TwoCO_ThreeIs urea CO (NH_Two)_TwoSolidification of
It also exerts the function of lowering points. By the way, the above 15 qualities
When the amount is less than 200%, the reducing agent composition 6 has a temperature of 200 ° C to 300 ° C.
Ammonia NH in the temperature range of ℃_ThreeInsufficient amount generated
Together with urea CO (NH _Two)_TwoLack of freezing point lowering function
To do. If it exceeds 25% by mass, it will dissolve in water at room temperature.
There is a problem with the solution. About 20% to 23% by mass,
The most practical. Ammonia NH_ThreeAnd carbon dioxide CO
_TwoThe chemical formula for generating
It In addition, ammonium carbonate (NH_Four)_TwoCO_ThreeIs
Normally, it is handled as a monohydrate salt, but here it is treated as a water-soluble salt.
An anhydrous salt is used to distinguish it from the liquid.

[0028]

[Chemical 4]

<< Data >> Solubility in water,
The generation capacity of ammonia NH ₃ will be described based on the data. First, FIG. 2 shows a composition of urea CO (N
H ₂ ) _{2 and} other water solubility data are shown along with temperature changes. As can be understood from this data, urea CO (NH ₂ ) ₂ is generally the most soluble and therefore easy to handle, and the reducing agent composition 6
Suitable as the main component of. Ammonium hydrogen carbonate NH
₄ HCO ₃ , burette, aqueous ammonia, 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 water at 76.9% by mass, which has a 1: 1 molar composition, 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.
At −13 ° C., the freezing point is where 32.5% by mass melts. Ammonium carbonate (NH ₄ ) ₂ CO ₃ has a solubility of about 35.8 mass% at 0 ° C or higher.

Next, FIG. 3 shows various industrially usable return types.
Ammonia NH per 100 g of the base composition
_ThreeThe amount of generated g (deammonified state) data is
Urea CO (NH)_Two)_TwoIn other aqueous solutions
It is shown together with the change in concentration. Temperature setting is 400 ℃
~ 450 ° C. As can be understood from this data
And urea CO (NH_Two)_TwoBut in general, ammonia
NH_ThreeSince a large amount is generated, it is suitable as a reducing agent composition.
As shown in Fig. 2 mentioned above, the temperature of ammonia water rises.
In case of storage, the solubility in water will decrease.
The part that is not dissolved in water evaporates and vaporizes, causing a foul odor.
Ammonia NH_ThreeThe problem is that a large amount of gas is generated
Yes, it is not suitable for practical use. Ammonium carbonate (NH
_Four)_TwoCO_ThreeIn the temperature range of 200 ° C to 300 ° C
Ammonia NH_ThreeThe ability to generate
Looking at ammonia NH _ThreeHas a low ability to generate
Not suitable for the main component of things.

<< 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 ammonium carbonate (NH ₄ ) ₂
It is composed of an aqueous solution containing ammonium carbonate (NH ₄ ) ₂ CO ₃ as a sub-component such as CO ₃ as a sub-component.
The maximum concentration of urea CO (NH ₂ ) ₂ is 76.9% by mass.
Is 32.5 mass% to 76.9 mass% or less. The concentration of ammonium carbonate (NH ₄ ) ₂ CO ₃ is 1
It is 5% by mass or more and 25% by mass or less. The reducing agent composition 6 is used in an exhaust system 2 such as a diesel engine 2.
The exhaust gas 1 above 00 ° C. is injected before the catalyst 12 and immediately produces ammonia NH ₃ as a reducing agent (see Chemical formulas ₃ and 4), so that nitrogen oxide NOx in the exhaust gas 1 is generated. That is, nitrogen oxide NO 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, third and fourth. First
In addition, the reducing agent composition 6 contains urea CO (N
The concentration of H ₂ ) ₂ exceeds 32.5% by mass to 76.9% by mass.
It is as high as below, and it is highly soluble in water. Therefore, the ability to generate ammonia NH ₃ as a reducing agent is excellent, ammonia NH ₃ is generated at a high conversion rate, and excess water is reduced. That is, theoretically, in the reaction formula for generating ammonia NH ₃ by a hydrolysis reaction, urea CO (NH ₂ ) ₂ having a 1: 1 molar composition is 76.9% by mass, and water is 23.1% by mass. In practice, this reducing agent composition 6
In, the concentration of urea CO (NH ₂ ) ₂ exceeds 32.5% by mass and approaches the concentration of 76.9% by mass,
The concentration of water approaches that amount of 23.1% by mass, and the amount of 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 temperature of the exhaust gas 1 is not lowered due to heat of vaporization, which reduces the reduction rate (denitration rate) of the nitrogen oxide NOx by the ammonia NH _3. Things also decrease. 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. It also reduces the number of accidents. 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.

Second, the reducing agent composition 6 contains urea CO (NH ₂ ) _{2 as} a main component and ammonium carbonate (NH ₄ ) ₂ CO ₃ as a subcomponent. Then, by adding ammonium carbonate (NH ₄ ) ₂ CO ₃ , first, the freezing point is lowered to a lower temperature and the crystallization temperature is lowered, and further, the progress speed of crystallization and solidification is lowered, It takes time to solidify and solidify. That is, urea CO (NH ₂ ) ₂ has a nonionic bond / covalent bond (nonionic crystallinity), whereas ammonium carbonate (NH ₄ ) ₂ CO ₃ has an ionic dissociation property. Therefore, a nonionic urea aqueous solution is added to an ionic dissociative ammonium carbonate (NH ₄ ) ₂
When CO ₃ is added, the freezing point of urea CO (NH ₂ ) ₂ is lowered and the solidification speed is lowered.

Therefore, this reducing agent composition 6 has a composition of 32.5
Urea CO with high concentration of over 7% to 76.9% by mass
Although it contains (NH ₂ ) ₂ as a main component, it is difficult to crystallize and solidify and can be handled in a liquid state at room temperature.
It can be stored in the tank 8 as it is, and the way can be opened by sending and jetting the liquid with the pump. The higher the concentration of urea CO (NH ₂ ) ₂ , the higher the freezing point and the
The higher the concentration of H ₄ ) ₂ CO _3, the lower the freezing point. Of course, in order to more reliably prevent the crystallization and solidification of the reducing agent composition 6, (especially urea CO (NH ₂ ) ₂
Since the freezing point rises as the concentration of the reducing agent approaches 76.9% by mass, a tank 8 for storage or a heating means such as a heater is provided in front of the tank 8 to reduce the amount of the reducing agent composition 6 during storage to 50%.
You may make it heat to about 60 to 60 degreeC or more. In this case, added ammonium carbonate (NH ₄ )
Due to the synergistic action with ₂ CO ₃ , crystallization and solidification are reliably prevented. Further, this reducing agent composition 6 has a slow progress rate of crystallization and solidification even if the possibility of crystallization and solidification occurs in cold regions, winter, etc. due to, for example, the stoppage of operation. In many cases, crystallization and solidification can be avoided by restarting the operation. Further, even if it is crystallized or solidified, it can be redissolved within a relatively short time by heating.

Thirdly, the reducing agent composition 6 contains urea CO
(NH ₂ ) ₂ as a main component and ammonium carbonate (N
The H _{4) 2} CO ₃ made as a sub-component. Since it has such a simple composition, it can be easily produced, supplied and obtained.

Fourthly, 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 a high temperature range in which the temperature of the exhaust gas 1 exceeds 300 ° C. and is about 400 ° C. to 450 ° C., the ability to generate ammonia NH ₃ as a reducing agent is excellent, and ammonia NH ₃ is generated at a high conversion rate. Therefore, the nitrogen oxide NOx in the exhaust gas 1 is reliably reduced and removed. Along with this, this reducing agent composition 6
Contains ammonium carbonate (NH ₄ ) ₂ CO ₃ as a subcomponent. Therefore, effective denitration is performed even when the diesel engine 2 or the like is started or changes in operation.
That is, even in a relatively low temperature range where the temperature of the exhaust gas 1 is approximately 200 ° C. to 300 ° C., the ability to generate ammonia NH ₃ as a reducing agent is excellent, and ammonia NH ₃ is generated at a high conversion rate. The nitrogen oxide NOx in the exhaust gas 1 is reliably reduced and removed.

[0038]

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 ammonium carbonate (NH_Four)_Two
CO_ThreeRegarding the reducing agent composition 6 containing as an auxiliary component, 250
Ammonia NH at a temperature of ℃_ThreeThe ability to generate
Strike. First, the test conditions are as follows. ○ 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 ability to generate. ○ Heating air is 1Nm in standard state conversion^Three/ Min, temperature
Set to 250 ℃. The reducing agent composition 6 of the example is shown in Tables 1 and 2 below.
Sea urchin, CO (NH _Two)_TwoIs 56.6 mass% (molar ratio
40% in units), ammonium carbonate (NH_Four) _TwoCO_Three
22.2% (10% in molar ratio unit), water H_TwoO is 2
1.2% by mass (50% in terms of molar ratio). Carbonic acid
MONMONIUM (NH_Four)_TwoCO_ThreeIs equivalent to anhydrous salt. 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%) (ammonium carbonate-free, urea
Only aqueous solution). ○ And in FIG. 1, the exhaust pipe 5 is provided by the injection nozzle 7.
At a rate of 4.24 g / min with respect to the heated air inside,
Example 6 reducing agent composition 6 and Comparative example reducing agent composition 6
Were sequentially ejected.

[0039]

[Table 1]

[0040]

[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, by converting the collected heated air to ^{1 Nm} 3 / min, the concentration of ammonia NH _3, which is contained, was measured in ^{g /} Nm 3 · min. The results are shown in Table 3 below.
It became as shown in. That is, it was verified that the reducing agent composition 6 of the example generated 3 times the amount of ammonia NH ₃ as compared with the comparative example (aqueous solution containing urea alone without ammonium carbonate). Thus, this reducing agent composition 6
Has excellent ability to generate ammonia NH ₃ as a reducing agent even in a relatively low temperature range of 250 ° C., and can effectively perform denitration.

[0042]

[Table 3]

[0043]

As described above, the reducing agent composition for flue gas denitration according to the present invention is used in combination with urea as a main component and ammonium carbonate as a subcomponent. Is the greatest feature. And
The concentration of urea is more than 32.5% by mass to 76.9% by mass or less, the concentration of ammonium carbonate is about 15% by mass to 25% by mass, and ammonia, which is a reducing agent for nitrogen oxides, is injected into exhaust gas. Is generated. 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 as a reducing agent, and is reduced in excess water, so that excess water is rarely brought into the exhaust system of exhaust gas. 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, crystallization,
Coagulation can also be avoided. That is, since the reducing agent composition is formed by adding ammonium carbonate to the urea aqueous solution, the freezing point is lowered and the crystallization temperature is lowered, and the progress speed of crystallization and solidification is lowered and the time is extended. Therefore, although this reducing agent composition has a high concentration of urea as a main component, it does not easily crystallize and solidify at normal temperature (except in extremely cold regions and winter), and can be handled in a liquid state. Storage in tanks and pumping liquids,
It also becomes possible to avoid problems with the injection. Of course, when the storage tank is provided with a heating means, crystallization and solidification can be more reliably prevented. As described above, crystallization and solidification are prevented not only during normal operation but also during operation stop, operation restart, and the like, and handling is easier than in the conventional examples of this type described above.

<< Third Effect >> Thirdly, mass production and stable supply are possible. That is, this reducing agent composition has a simple and easy composition containing urea as a main component and ammonium carbonate 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.

<< Fourth Effect >> Fourthly, 200 ° C.
Denitration is realized in the temperature range of up to 300 ° C. That is, this reducing agent composition has ammonium carbonate as an auxiliary component and is excellent in the ability to generate ammonia 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, denitration is surely performed, and at the time of operation start or operation fluctuation, that is, exhaust gas. Temperature is 200 ℃ ～ 30
Effective denitration is realized even in a relatively low temperature range of about 0 ° C. 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

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3G091 AA02 AA03 AA04 AA05 AA06                       AA18 AB04 BA14 CA17 GA06                       GB03W GB09W GB10W                 4D002 AA12 AC10 BA06 CA11 DA07                       DA16 DA57 DA70 GA01 GB03                       GB08                 4D048 AA06 AB02 AC03 AC08 BB02

Claims (8)

[Claims] 1. A reducing agent composition for flue gas denitration, which comprises an aqueous solution containing urea as a main component and ammonium carbonate as a subcomponent. 2. The reducing agent composition for flue gas denitration according to claim 1, comprising an aqueous solution containing the urea as a main component and the ammonium carbonate as a secondary component, wherein nitrogen oxidation in exhaust gas is carried out. A reducing agent composition for flue gas denitration, which is capable of generating ammonia as a reducing agent for reducing and removing substances. 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 reducing agent composition according to claim 2, wherein the concentration of the ammonium carbonate is 15% by mass or more and 25% by mass or less. A reducing agent composition for denitration. 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 composition for flue gas denitration, characterized in that it can be injected before the catalyst, and the ammonia is generated based on the injection to reduce and remove nitrogen oxides in the exhaust gas to nitrogen. object. 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 and the temperature is 50.degree.
A reducing agent composition for flue gas denitration, which is heated to about 60 ° C. or higher.