JP2005288397A - Tail gas denitrification apparatus using urea water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tail gas denitrification apparatus removing harmful components of nitrogen oxides in tail gas exhausted from a diesel engine, a gas engine, a gas turbine, a boiler, or a heating furnace, using urea water as a reducing agent, preferably used for purifying tail gas, using a hydrolysis reactor for promoting hydrolysis of urea water, or a cyclone. <P>SOLUTION: The hydrolysis reactor is provided between a urea water pouring part and a denitrification reactor, for hydrolyzing by the temperature and moisture possessed by the tail gas itself in a tail gas passage. The cyclone is installed between the urea water pouring part and the denitrification reactor, efficiently hydrolyzing urea water even with a short tail gas pipe, or the cyclone is installed between the urea water pouring part and the denitrification reactor, for holding a hydrolysis catalyst component on its inner face for promoting hydrolysis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses urea water as a reducing agent to remove nitrogen oxides, which are harmful components in exhaust gas discharged from diesel engines, gas engines, gas turbines, boilers, heating furnaces, and the like (hereinafter referred to as engines). The present invention relates to an exhaust gas denitration apparatus using a hydrolysis reactor or a cyclone container for promoting the hydrolysis of urea, which is preferably used for purification of exhaust gas.

Nitrogen oxides in exhaust gas discharged from automobiles and various factories are one of the main causes of photochemical smog.
As an effective removal method, a denitration method using a denitration reactor containing a denitration catalyst containing ammonia (NH ₃ ) as a reducing agent has a simple reaction principle and is easy to handle without generating harmful by-products. So far it has been widely used.

The chemical formula of the decomposition reaction by ammonia such as nitrogen monoxide and nitrogen dioxide representing nitrogen oxides in exhaust gas is as follows.

尚、これまでは該還元剤として液化アンモニアまたはアンモニア水（通常は２５％濃度程度）を使用しているが、該液化アンモニアまたは該アンモニア水から発生するアンモニアガスは人体にとって著しく有害であるばかりでなく爆発の危険性があり、これらの還元剤を人工密集地などに設置する民生用並びに自動車用の脱硝装置に適用することは極めて難しい。

Until now, liquefied ammonia or aqueous ammonia (usually about 25% concentration) has been used as the reducing agent, but the ammonia gas generated from the liquefied ammonia or aqueous ammonia is not only harmful to the human body. There is no danger of explosion, and it is extremely difficult to apply these reducing agents to consumer and automobile denitration equipment installed in artificial crowded areas.

Therefore, as an alternative reducing agent that is safe and easy to handle and generates ammonia gas by decomposition, there is a method in which urea, which is an ammonia compound, is decomposed into ammonia (gas) and carbon dioxide (gas) as shown in the following formula. .

ここで、尿素を用いる方法として、固体の尿素は吸湿性が高く取扱いが困難であるばかりでなく、還元剤は別途設けられる制御装置によって所定量を供給する必要があるが定量供給する手段が複雑となるために、固体のままで用いるのではなく専ら尿素水（通常３２％〜４０％濃度程度）を排ガス流路に直接注入して流路内でアンモニアを発生させ、または別途設けられた尿素気化器を設けてアンモニアガスを発生させて脱硝作用に寄与させる方法が提案されている。（特開平１１−１７１５３５号公報及び特開２００４−８６７号公報）

Here, as a method using urea, not only solid urea is hygroscopic and difficult to handle, but a reducing agent needs to be supplied in a predetermined amount by a separate control device, but the means for quantitative supply is complicated. Therefore, urea water (usually about 32% to 40% concentration) is not directly used as a solid, but is directly injected into the exhaust gas passage to generate ammonia, or urea provided separately A method of providing a vaporizer and generating ammonia gas to contribute to denitration has been proposed. (Japanese Patent Laid-Open Nos. 11-171535 and 2004-867)

FIG. 4 shows a method in which urea water is directly injected into the exhaust gas flow path and is naturally converted into ammonia in the flow path.
However, conditions for realizing sufficient conversion from urea water to ammonia by the method of directly injecting urea water into the exhaust gas flow path (time for converting urea water droplets to ammonia gas in the exhaust gas flow path or required exhaust gas The length of the flow path) varies greatly depending on the size of the urea water droplets injected into the exhaust gas flow path by the injection means and the temperature and flow rate of the exhaust gas, but in any case, the natural conversion will result in sufficient ammonia. Since a necessary and sufficient exhaust gas flow path length required for the conversion is required, application of a denitration apparatus using urea water is often impossible due to restrictions on arrangement.
As an example, FIG. 1 shows the results of a test conducted to confirm the conversion time to ammonia gas depending on the size of urea water droplets.

From FIG. 1, even when the droplet diameter is sprayed at a diameter of about 100 microns with a spray nozzle by an injection means that is considered to be sprayed relatively finely, the exhaust gas temperature is 220 ° C. This shows that the residence time required for the urea water in the exhaust gas to sufficiently convert to ammonia is about 0.23 seconds.
This means that when the exhaust gas flow rate is 50 m / s, the exhaust gas passage needs to be as long as about 12 m. Therefore, the arrangement of the urea water injection part and the denitration reactor into the exhaust gas passage is greatly restricted. This arrangement is practically impossible.

On the other hand, a method of introducing ammonia decomposed using an alkali metal system proposed in Japanese Patent Application Laid-Open No. 11-171535 as a decomposition catalyst to a denitration reactor is based on the fact that a part of the alkali is accompanied by ammonia. Since the denitration catalyst accommodated in the inside is poisoned by the alkali and causes significant catalyst deterioration, the function of the original denitration catalyst is impaired even if it has a hydrolysis action, which is not preferable in terms of the denitration apparatus configuration.

On the other hand, Japanese Patent Application Laid-Open No. 2004-887 proposes to install a urea vaporizer separately from the exhaust gas flow path system. This method not only requires a separate high-temperature heat source and temperature control inside the carburetor, but also when the amount of urea spray required due to sudden load fluctuations of the engine etc. changes significantly from these system mechanisms. It is conceivable that sufficient responsiveness to the required amount of ammonia is not ensured.

Sufficiently convert urea water to ammonia in the exhaust gas flow path system, shorten the conversion time, and shorten the required flow path length between the urea water injection part and the denitration reactor in the exhaust gas flow path. In addition to reducing the restrictions on the placement of urea water injection section and denitration reactor in the exhaust gas flow path, the conversion efficiency of urea water to ammonia is increased, the components are simple, the denitration equipment is easy to arrange, and the denitration efficiency is high Realize denitration equipment.
Further, a denitration apparatus having excellent responsiveness to steep load fluctuations (changes in exhaust gas amount, NOx, etc.) of an engine or the like is realized.

Composition selected from one or more of zeolite, alumina, and titania having urea hydrolysis ability built into the hydrolysis reactor, or among titania-vanadium, titania-vanadium-tungsten, titania-tungsten Spherical, columnar, cylindrical, etc. pellet-type or honeycomb-type decomposition catalyst composed of one or more of the above decomposition catalysts in the exhaust gas flow in the exhaust gas flow path between the reducing agent injection part and the exhaust gas denitration reactor Directly arranged, urea water injected into the exhaust gas flow path from the reducing agent injection part is continuously hydrolyzed in the hydrolysis reactor with abundant moisture originally contained in the combustion exhaust gas, and ammonia And the ammonia is supplied to the denitration reactor.

FIG. 2 shows the results of tests conducted for confirming the conversion time of urea water to ammonia gas when a titania-vanadium-based decomposition catalyst was used.
From this result, the conversion time was about 0.017 seconds at an exhaust gas temperature of 220 ° C., and the conversion time under the same other conditions without a cracking catalyst in FIG. 1 was about 0.23 seconds. It turns out that it is shortened to 7%.
This is because the length of the exhaust gas flow path from the urea injection section to the denitration reactor can be shortened to about 7% compared to the case without a cracking catalyst, so the restrictions on the arrangement of the denitration device are remarkably eased and the installation space is reduced. The denitration equipment can be installed even under severe conditions.

In this case, if the AV value indicating the unit catalyst amount of the cracking catalyst is 2000 Nm ³ / h · m ² or less in order to secure an effective conversion rate to ammonia gas, the conversion rate to ammonia gas is about 40%. This is practical because it can be secured. (See Figure 3)
Here, the AV value is expressed by the following equation as a characteristic value indicating the amount of the decomposition catalyst with respect to the exhaust gas amount.
In addition, since the decomposition catalyst has various unit surface areas (geometric surface area per unit volume) depending on the geometric shape forming the catalyst shape, the unit surface area is taken into consideration.

In addition, in order to efficiently complete the hydrolysis by securing the retention time in the exhaust gas of urea water injected from the reducing agent injection part into the exhaust gas flow path and ensuring the effective contact area for hydrolysis of urea water droplets A cyclone container designed to give a cyclone action to the exhaust gas flow is arranged, and urea water injected into the exhaust gas flow path from the reducing agent injection part is continuously contained in the cyclone container by the moisture originally contained in the combustion exhaust gas. In particular, urea is hydrolyzed to generate ammonia, and the ammonia is supplied to the denitration reactor.

In addition, in order to efficiently complete the hydrolysis by securing the retention time in the exhaust gas of urea water injected from the reducing agent injection part into the exhaust gas flow path and ensuring the effective contact area for hydrolysis of urea water droplets A composition selected from one or more of zeolite, alumina, and titania having urea hydrolytic ability, or a decomposition catalyst comprising one or more of titania-vanadium, titania-vanadium-tungsten, and titania-tungsten Injecting a reducing agent directly into the exhaust gas flow in the exhaust gas flow path with a hydrolysis reactor designed to give a cyclone effect to the exhaust gas flow coated with the inner surface or the molded catalyst catalyst on the inner surface The urea water injected into the exhaust gas flow path from the section is continuously hydrolyzed by the hydrolysis reactor with the water originally contained in the combustion exhaust gas. To generate ammonia so as to supply the ammonia denitration reactor was.

  Due to the above-described effects, a denitration apparatus using urea water can be employed even when an effective exhaust pipe space cannot be secured, and a safe and inexpensive denitration apparatus can be provided and is currently applied. This contributes to the spread of denitration equipment for small engines that are not installed.

Embodiments of the present invention will be described based on examples with reference to the drawings.
FIG. 5 shows a configuration of a denitration apparatus provided with a hydrolysis reactor as a basis of the present invention.
A composition selected from one or more of zeolite, alumina, and titania having hydrolytic ability built in a hydrolysis reactor, or a titania-vanadium system, titania-vanadium-tungsten system, titania-tungsten system Spherical, columnar, cylindrical, etc. pellet-type or honeycomb-type decomposition catalysts composed of one or more decomposition catalysts are directly put into the exhaust gas flow in the exhaust gas passage between the reducing agent injection section and the exhaust gas denitration reactor. The urea water injected into the exhaust gas flow path from the reducing agent injection part is continuously hydrolyzed in the hydrolysis reactor by the abundant moisture contained in the combustion exhaust gas, and ammonia is The ammonia is supplied to the denitration reactor.

Since the exhaust gas itself usually has a temperature of 200 to 500 ° C. and a water content of usually 5 to 12% by volume with respect to the total amount of the exhaust gas, the hydrolysis reactor reacts with the catalytic action of the decomposition catalyst from the injected urea water. The ammonia decomposed inside the gas flows into the denitration reactor and contributes to the denitration action.
FIG. 6 shows a configuration of a denitration apparatus in which a cyclone container according to the present invention is arranged.
The injected urea water is naturally hydrolyzed in the exhaust gas flow by the temperature and moisture of the exhaust gas itself, but the size of the urea water droplets injected into the exhaust gas and the temperature of the exhaust gas itself In order to effectively convert to ammonia by such means, the residence time of the necessary urea in the exhaust gas usually requires 0.1 seconds or more. Incidentally, when the flow velocity in the exhaust pipe is 50 m / s, the length of the exhaust pipe from the ammonia injection part to the denitration reactor needs to be 5 m or more.

Therefore, if the cyclone container is used, the residence time of the exhaust gas can be extended, and at the same time the urea solid mass is larger than the exhaust gas molecules, so that urea is temporarily trapped in the inner periphery of the cyclone container and the urea residence Is further preserved.

14 and 15 show the structure of another hydrolysis reactor of the present invention.
In addition to the action and effect of the cyclone container of FIG. 6, a composition selected from at least one of zeolite, alumina, and titania having urea hydrolytic ability, or titania-vanadium-based, titania-vanadium-tungsten-based, titania- By making the hydrolysis reactor having a cyclone effect by coating the inner surface of the cyclone vessel with a decomposition catalyst composed of one or more of tungsten-based or placing a molded catalyst catalyst on the inner surface, the exhaust gas flow from the reducing agent injection part The urea water injected into the passage is continuously hydrolyzed in the hydrolysis reactor by the water originally contained in the combustion exhaust gas to generate ammonia, and the ammonia is supplied to the denitration reactor. To do.

Incidentally, according to the method of FIG. 6 and FIGS. 14 and 15, it is possible to avoid the problem that the decomposition catalyst of the hydrolysis reactor according to the method of FIG. 5 is clogged by foreign matters such as soot flying from the upstream and iron rust. I can do it.

FIG. 5 shows a first embodiment of the present invention.
A hydrolysis reactor (12) is installed between the urea water injection part (9) and the denitration reactor (10) in the exhaust gas flow path (3) of the engine or the like (1).
In the hydrolysis reactor, a composition selected from one or more of zeolite, alumina, and titania having urea hydrolysis ability, or one of titania-vanadium, titania-vanadium-tungsten, and titania-tungsten is used. Spherical, columnar, cylindrical, etc. pellet-type or honeycomb-type decomposition catalysts composed of cracking catalysts composed of more than seeds are incorporated in the exhaust gas flow path system so as to be in direct contact with the exhaust gas.

The injected urea water generates ammonia in the hydrolysis reactor (12) by the temperature of the exhaust gas and the moisture originally contained in the combustion exhaust gas, and supplies the ammonia to the denitration reactor (10). .
According to this method, a separately provided hydrolysis reactor method proposed in JP-A-5-15739, JP-A-11-319483, JP-A-2004-867 and JP-A-11-171535 are proposed. Compared with an indirect hydrolysis reactor that uses only the temperature of the exhaust gas, the temperature of the exhaust gas and the water originally contained in the exhaust gas directly act in the hydrolysis reactor (12). The conversion from ammonia to ammonia can be performed efficiently, and at the same time the response time can be shortened, and the load of the engine etc. (1) changes sharply and the amount of exhaust gas discharged from the engine etc. and the nitrogen in the exhaust gas The responsiveness of the ammonia supply is important when an appropriate denitration action is required against the fluctuation of oxides, but the response time is significantly shortened. It is very practical result apparatus on the Hydrolysis of the urea water and simple with it.

FIG. 6 shows a second embodiment of the present invention.
A cyclone container (14) is installed between the urea water injection section (9) and the denitration reactor (10) in the exhaust gas flow path (3) of the engine or the like (1).
8 to 13 show various structures of the cyclone container (14).
The inflowing exhaust gas (6) is arranged so as to flow in the tangential direction into the body (16) of the cyclone body (15). The effluent exhaust gas (7) may be tangential as shown in FIG. 8 or axial as shown in FIG.

The exhaust gas flowing into the cyclone container (14) is decelerated and given a swirling flow (17), stays in the cyclone container and stays in the cyclone container, and drops of urea water having a mass larger than the exhaust gas molecules that have been with the exhaust gas flow until then. Is temporarily attached to the inner surface of the cylinder (16) by centrifugal force due to the swirling flow of exhaust gas under the conditions of exhaust gas temperature and water replenishment, and then flows out as ammonia gas after elapse of the residence time required for hydrolysis. It flows out to the denitration reactor (10) together with the exhaust gas (7).

14 and 15 show a third embodiment of the present invention.
The exhaust gas that has flowed into the cyclone vessel is decelerated and swirled to stay, and the urea water droplets that have a larger mass than the exhaust gas molecules that existed with the exhaust gas flow up to that point are the temperature and hydration conditions of the exhaust gas. The denitration reactor (10) together with the effluent exhaust gas (7) becomes ammonia gas after a residence time required for hydrolysis for a while due to centrifugal force caused by the swirling flow of the exhaust gas. As shown in the second embodiment, the liquid flows out toward this direction.
Here, in the third embodiment, in order to promote hydrolysis, a coating film (27) or a decomposition catalyst molded body (28) of a decomposition catalyst having a high hydrolysis capacity of urea is arranged on the inner surface of the cyclone container body (15). Is.

FIG. 10 shows a perspective view of the internal structure of the cyclone container in which a swivel guide plate (18) is provided inside the cyclone container main body (15) to maintain the swirling force of the exhaust gas.
As mentioned above, it cannot be overemphasized that this invention is widely applicable to the denitration apparatus formed by inject | pouring urea water directly into an exhaust gas flow path, without being limited to the said Example.

The test result which confirmed the time required for the conversion of the urea water to ammonia which becomes the 1st ground of this invention is shown. The test result which confirmed the time which conversion of urea water to ammonia in the presence of the cracking catalyst used as the 2nd grounds of this invention is shown. The test result which confirmed the time which conversion to ammonia with respect to the decomposition catalyst AV value used as the 3rd grounds of this invention is shown. The prior art is shown. The 1st Example using the hydrolysis reactor in this invention is shown. The 2nd Example using the cyclone container in this invention is shown. The schematic diagram of the behavior in the exhaust gas flow path of the sprayed urea water droplet is shown. The structure of a cyclone container is shown. 2 shows another structure of a cyclone container. The perspective view of the cyclone container which provided the turning guide plate inside is shown. The AA cross section of the cyclone container of FIG. 8 is shown. FIG. 10 shows a BB cross section of the cyclone container of FIG. 9. FIG. 9 shows another structure in the cyclone container of FIG. The structure which provided the decomposition catalyst coating film in the cyclone container inner surface is shown. The structure which provided the decomposition catalyst shaping | molding body in the cyclone container inner surface is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine etc. 2 Exhaust gas 3 Exhaust gas flow path 4 Exhaust gas pipe 5 Exhaust gas pipe required length 6 Inflow exhaust gas 7 Outflow exhaust gas 8 Moisture in exhaust gas 9 Urea water injection part 10 Denitration reactor 11 Denitration catalyst 12 Hydrolysis reactor 13 Decomposition catalyst 14 Cyclone Container 15 Cyclone body 16 Cyclone cylinder 17 Exhaust gas swirl flow 18 Swirling guide plate 19 Urea water tank 20 Urea aqueous solution 21 Urea water supply pump 22 Urea water injection nozzle 23 Urea water supply pipe 24 Urea water spray droplet 25 Partially evaporated water Urea water 26 Urea 27 Decomposition catalyst coating film 28 Decomposition catalyst molded body 29 High temperature exhaust gas 30 Ammonia gas

Claims (3)

A flow path for nitrogen oxide-containing exhaust gas, an injection section provided with an injection nozzle for injecting a nitrogen oxide reducing agent into the flow path, and a denitration catalyst provided on the downstream side of the injection section for the reducing agent In the exhaust gas denitration apparatus having a built-in denitration reactor, a composition selected from one or more of zeolite, alumina, and titania having urea hydrolysis ability in the exhaust gas flow path between the reducing agent injection section and the denitration reactor Or pellet-type or honeycomb-type hydrolysis composed of one or more hydrolysis catalyst components of titania-vanadium, titania-vanadium-tungsten, titania-tungsten, etc. catalyst (hereinafter, referred to as decomposition catalyst) a pressurized to AV value in the exhaust gas flow of the exhaust gas flow path has a built-in said cracking catalyst becomes 2000Nm 3 / h ^· m ² or less By placing a decomposition reactor, the reducing agent to generate ammonia from the urea water injected from the injection unit denitration apparatus that supplies the ammonia denitration reactor. A flow path for nitrogen oxide-containing exhaust gas, an injection section provided with an injection nozzle for injecting a nitrogen oxide reducing agent into the flow path, and a denitration catalyst provided on the downstream side of the injection section for the reducing agent In the exhaust gas denitration apparatus having a built-in denitration reactor, a container having a cyclone effect is disposed in the exhaust gas flow path between the reducing agent injection unit and the denitration reactor, and the urea water injected from the reducing agent injection unit A denitration apparatus that generates ammonia and supplies the ammonia to a denitration reactor. A flow path for nitrogen oxide-containing exhaust gas, an injection section provided with an injection nozzle for injecting a nitrogen oxide reducing agent into the flow path, and a denitration catalyst provided on the downstream side of the injection section for the reducing agent In the exhaust gas denitration apparatus having a built-in denitration reactor, a composition selected from one or more of zeolite, alumina, and titania having urea hydrolysis ability in the exhaust gas flow path between the reducing agent injection section and the denitration reactor Or a hydrolytic catalyst having a cyclone effect in which a cracking catalyst comprising at least one of titania-vanadium, titania-vanadium-tungsten, titania-tungsten is coated on the inner surface or a molded product of the decomposition catalyst is disposed on the inner surface. A decomposition reactor is arranged so that ammonia is generated in the hydrolysis reactor from the urea water injected from the reducing agent injection section, and the ammonia is supplied to the denitration reactor. Denitration equipment.

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