WO2013088850A1

WO2013088850A1 - Aqueous urea-spraying structure

Info

Publication number: WO2013088850A1
Application number: PCT/JP2012/078166
Authority: WO
Inventors: 重樹岡崎
Original assignee: 日立造船株式会社
Priority date: 2011-12-13
Filing date: 2012-10-31
Publication date: 2013-06-20
Also published as: JP2013124555A; CN103890335A; DK201470377A; CH707487B1; CN103890335B; KR102001477B1; KR20140105435A; JP5753485B2; DK178838B1

Abstract

[Problem] To limit the generation of by-products even when the proportion of SO₃ contained in the exhaust gas is high or when the aqueous urea is sprayed in a reduced exhaust gas temperature region. [Solution] An aqueous urea-spraying structure capable of supplying ammonia to an SCR catalyst (6a) of a denitrogenation reactor (6) of an exhaust gas-cleaning device (7) equipped with a denitrogenation reactor (6) provided between an exhaust manifold (3) that collects exhaust gas exhausted from exhaust connection tubes (2) that are connected to the exhaust ports (1a) of an engine (1), and an exhaust pathway (5) upstream of a turbine (4a) of a turbocharger (4). An evaporation tube (10) connected to a branching pipe (9) branching from a gas supply pathway (8) downstream from the compressor (4b) of the turbocharger (4) is disposed inside the exhaust manifold (3) and a nozzle (11) that sprays aqueous urea into the air passing through the evaporation tube (10) is provided. [Effect] The present invention prevents corrosion and occlusion of the exhaust pathway and is also able to maintain favorable SCR catalyst performance.

Description

Urea water spray structure

The present invention is an exhaust gas that purifies by reacting nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas discharged from an internal combustion engine with a reducing agent under a selective reduction catalyst (hereinafter referred to as “SCR catalyst”). The present invention relates to a spray structure of urea water in a purification device.

A denitration reactor equipped with an SCR catalyst is installed downstream of the exhaust pipe of the engine, and ammonia gas is added as a reducing agent to the exhaust passage upstream of the denitration reactor, so that NOx in the exhaust gas is removed in the denitration reactor. A technique for purification is disclosed (Patent Document 1).

However, since ammonia gas and ammonia water are highly toxic and dangerous, and have problems such as odor, there are severe restrictions on mounting them on ships. Therefore, conventionally, in an exhaust gas purification apparatus using an SCR catalyst, chemically stable urea is used as a reducing agent precursor, stored in a tank in a state of urea water, and upstream of the denitration reactor using a nozzle. Many configurations have been adopted in which spraying is performed in the exhaust passage on the side (for example, Patent Document 2).

In the case of the above configuration, the urea water sprayed from the nozzle into the exhaust passage is hydrolyzed as shown in the following formula (1) before reaching the SCR catalyst if the temperature in the exhaust passage is sufficiently high, Ammonia gas (NH ₃ ) is generated.
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂ ... (1)

The ammonia gas generated by the hydrolysis is supplied to the SCR catalyst, whereby a denitration reaction such as the following formulas (2) and (3) is performed between ammonia and NOx in the exhaust gas on the SCR catalyst, NOx is decomposed into nitrogen and water and detoxified.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (3)

Thus, in the exhaust gas purification apparatus using the SCR catalyst, when urea water is used for safety reasons, the hydrolysis reaction of the above formula (1) is surely performed while the sprayed urea water flows in the exhaust passage. Need to be done. Therefore, conventionally, for example, in the NOx soot purifying device of Patent Document 2, a muffler is provided as a means for promoting the generation of ammonia between the urea water addition nozzle and the NOx soot catalytic converter.

Conventionally, for example, in a four-cylinder marine diesel engine 102 having an exhaust manifold 101 as shown in FIG. 2, a nozzle for spraying urea water provided in the exhaust passage 104 upstream of the turbine 103 a of the turbocharger 103. An evaporation pipe 107 for promoting hydrolysis of urea water sprayed from the nozzle 105 may be provided between the 105 and the SCR catalyst 106.

However, in the case of a diesel engine using heavy fuel oil such as C heavy oil that contains a large amount of sulfur in the fuel, the ratio of SO ₃ contained in the exhaust gas increases. When ammonia produced by hydrolysis of SO ₃ and urea water is brought into contact, salts such as ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and acidic ammonium sulfate (NH ₄ HSO ₄ ) are produced as by-products. When these by-products are deposited in the exhaust passage, they cause corrosion and blockage of the exhaust passage, and when they are deposited on the SCR catalyst, there is a problem that the catalytic activity of the SCR catalyst is lowered.

In particular, when a configuration such as the muffler of Patent Document 2 or the evaporation pipe 107 of FIG. Since urea water is sprayed in the region where the temperature of the exhaust gas is lowered, mist of urea water adheres to the wall surface and the wall surface temperature is lowered, so that a by-product is easily generated. For example, even in an engine that does not use C heavy oil, urea water adheres to the wall surface and the wall surface temperature decreases, so that hydrolysis of urea water does not proceed and cyanuric acid is generated as a by-product, and the exhaust passage goes to the exhaust passage. Cause accumulation of water.

In the case of using a configuration such as the evaporation pipe 107 in FIG. 2, ammonia generated by hydrolysis of urea water is not uniformly diffused in the exhaust gas, and is supplied to the SCR catalyst 106 in a nonuniform state. In addition, the progress of the denitration reaction of the above formulas (2) and (3) may be insufficient.

Japanese Utility Model Publication No. 2-115912 JP 2003-293739 A

Since the conventional exhaust gas purifying apparatus uses a fuel containing a large amount of sulfur, the temperature of the exhaust gas is lowered by spraying urea water in an atmosphere where the ratio of SO ₃ contained in the exhaust gas is high, ammonium sulfate, Byproducts such as acidic ammonium sulfate are likely to be produced. Further, in the conventional exhaust gas purifying apparatus, the sprayed urea water adheres to the wall surface, so that by-products such as cyanuric acid are easily generated. The problem to be solved by the present invention is that the above-mentioned by-products have caused problems such as corrosion and blockage of the exhaust passage and degradation of the performance of the SCR catalyst.

The urea water spray structure of the present invention is
An exhaust gas purification apparatus having a denitration reactor provided between an exhaust manifold that collects exhaust gas discharged from an exhaust communication pipe connected to an exhaust port of an engine and an exhaust passage upstream of a turbine of a turbocharger A urea spray structure capable of supplying ammonia to the SCR catalyst of the denitration reactor,
In the exhaust manifold, an evaporation pipe connected to the branch pipe branched from the air supply passage on the downstream side of the turbocharger compressor is disposed, and
The most important feature point is that the evaporation pipe is provided with a nozzle for spraying urea water to the air introduced into the evaporation pipe through the branch pipe.

In the urea water spray structure of the present invention, an evaporation pipe connected to a branch pipe branched from an air supply passage on the downstream side of a turbocharger compressor is arranged in an exhaust manifold, and urea water spray and ammonia are arranged in the evaporation pipe. To complete hydrolysis. High-temperature air compressed by a compressor passes through the inside of the evaporation pipe, but this air is not introduced into the intake port of the engine and does not contain SO _3. Even when used, the production of by-products such as ammonium sulfate and acidic ammonium sulfate can be suppressed.

In addition, in the urea water spray structure of the present invention, the wall surface of the evaporation pipe provided in the exhaust manifold is sufficiently heated by the high-temperature exhaust gas immediately after being discharged from the exhaust communication pipe, and the temperature is also increased in the region where the urea water is sprayed. Therefore, it is possible to prevent the formation of by-products such as cyanuric acid. Also, even if a by-product is generated and adheres to the wall surface of the evaporation tube when the engine is in a low load state, the wall surface of the evaporation tube becomes hot again if the engine is in a high load state. Temporarily adhered by-products can be decomposed.

Therefore, according to the present invention, generation of by-products such as ammonium sulfate, acidic ammonium sulfate, and cyanuric acid can be suppressed, corrosion and blockage of the exhaust passage can be prevented, and the performance of the SCR catalyst can be maintained well.

It is a figure explaining an example of composition of an exhaust gas purification device which has urea water spray structure of the present invention. It is the schematic which showed the structure of the conventional marine diesel engine.

The present invention provides an exhaust gas purifying apparatus in which, when the proportion of SO ₃ contained in the exhaust gas is high, or even when urea water is sprayed in a region where the temperature of the exhaust gas is lowered, secondary substances such as ammonium sulfate, acidic ammonium sulfate, and cyanuric acid are used. The purpose of suppressing the production of products,
An exhaust gas purification apparatus having a denitration reactor provided between an exhaust manifold that collects exhaust gas discharged from an exhaust communication pipe connected to an exhaust port of an engine and an exhaust passage upstream of a turbine of a turbocharger A urea spray structure capable of supplying ammonia to the SCR catalyst of the denitration reactor,
In the exhaust manifold, an evaporation pipe connected to the branch pipe branched from the air supply passage on the downstream side of the turbocharger compressor is disposed, and
This is realized by adopting a urea water spraying structure in which a nozzle for spraying urea water to the air introduced into the evaporation pipe through the branch pipe is provided in the evaporation pipe.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIG. In FIG. 1, reference numeral 1 denotes a 4-cylinder marine diesel engine to which the urea water spray structure of the present invention is applied, which is discharged from an exhaust communication pipe 2 connected to an exhaust port 1a provided in each cylinder head. An exhaust manifold 3 that collects high-temperature exhaust gas and guides it to an exhaust passage 5 upstream of the turbine 4 a of the turbocharger 4 is provided. The main part of the urea water spray structure of the present invention is mounted inside the exhaust manifold 3, is continuously disposed in the exhaust manifold 3, and is a denitration reactor provided between the exhaust passage 5 on the upstream side of the turbine 4 a. 6 constitutes an exhaust gas purification device 7. Reference numeral 4b denotes a compressor of the turbocharger 4, and 8 denotes an air supply passage through which air compressed by the compressor 4b is sent.

Inside the exhaust manifold 3, an evaporation pipe 10 connected to a branch pipe 9 branched from a branch portion 8a of an air supply passage 8 on the downstream side of the compressor 4b is disposed. The evaporation pipe 10 has one end connected to the branch pipe 9 and the other end opened to the exhaust manifold 3 through the ejection hole 10a.

Reference numeral 11 denotes a nozzle for spraying urea water to the air introduced into the evaporation pipe 10 through the branch pipe 9. The air passing through the evaporation pipe 10 is compressed by the compressor 4b and is in a high temperature state, but this air is not introduced into the intake port of the engine 1 and does not contain SO ₃ . The urea water spray structure of the present embodiment introduces high-temperature air that does not contain SO ₃ into the evaporation pipe 10 and promotes hydrolysis of urea water by spraying urea water on the air in the evaporation pipe 10. Even when a fuel containing a large amount of sulfur is used, it is possible to suppress the generation of by-products resulting from the reaction between ammonia and SO ₃ .

Here, the position where the nozzle 11 is provided is a region where the evaporation pipe 10 exists in the exhaust manifold 3 (an area other than A) rather than the area where the evaporation pipe 10 protrudes outside the exhaust manifold 3 (area A). ) Is preferable. This is because the wall surface of the evaporation pipe 10 can always be kept at a high temperature by direct contact with the high-temperature exhaust gas immediately after being discharged from the exhaust port of the exhaust communication pipe 2, so that the production of by-products due to the low temperature can be suppressed.

More specifically, the evaporation pipe 10 is arranged so that the longitudinal direction of the evaporation pipe 10 is parallel to the direction in which the exhaust ports of the exhaust communication pipe 2 connected to the exhaust port 1a of each cylinder of the engine 1 are arranged. Above, the position of the nozzle 11 may be determined so that the region B where the urea water sprayed from the nozzle 11 flows faces the exhaust port of the exhaust communication pipe 2.

The SCR catalyst 6a that selectively reduces and removes NOx soot that is contained in the exhaust gas discharged from the engine 1 and causes environmental pollution such as acid rain and photochemical smog is interposed in the denitration reactor 6. As the SCR catalyst 6a, for example, a desired catalyst such as a metal oxide catalyst such as alumina, zirconia, vanadia / titania or a zeolite catalyst may be used, and these catalysts may be combined. Further, the SCR catalyst 6a may be carried on a catalyst carrier having a honeycomb structure, for example, or may be charged in a cylinder and caged. The urea water spray structure of the present invention supplies ammonia in a completely hydrolyzed state to the SCR catalyst 6a.

In this embodiment, a hydrolysis catalyst 12 for promoting the hydrolysis of urea water is provided inside the evaporation pipe 10 and downstream of the nozzle 11 so as to further increase the efficiency of hydrolysis. The hydrolysis catalyst 12 may be any catalyst that has an action of promoting ammonia generation. For example, a desired catalyst such as a titanium oxide catalyst or an alkali metal catalyst can be used.

Further, in this embodiment, an ejection hole 10a for ejecting ammonia generated by hydrolysis of urea water toward the SCR catalyst 6a is provided on the downstream side of the hydrolysis catalyst 12 of the evaporation pipe 10. Therefore, the ammonia gas generated by hydrolysis in the evaporation pipe 10 is ejected at a high pressure into the exhaust gas in the exhaust manifold 3 through the small-diameter ejection hole 10a, and is sufficiently diffused in the exhaust gas. Therefore, the progress of the denitration reaction does not become insufficient.

In the present embodiment, since the evaporation pipe 10 including the nozzle 11 and the hydrolysis catalyst 12 is incorporated in the exhaust manifold 3, the evaporation pipe is provided in the exhaust passage 5 on the upstream side of the turbine 4a. Space saving can be achieved compared with the conventional apparatus. Further, in this embodiment, the exhaust passage leading to the turbocharger 4 can be shortened as compared with the conventional device in which the exhaust manifold and the exhaust pipe are arranged side by side, thereby reducing the loss of air pressure in the exhaust passage. This is also advantageous.

13 indicates an air cooler provided in the air supply passage 8. The air compressed by the compressor 4b rises in temperature and tends to expand. However, if expanded, the density of the air decreases and the amount of air decreases. 1 is supplied with air.

In the urea water spray structure of the present invention, when the air cooler 13 is provided in the air supply passage 8, the position where the branch pipe 9 is branched from the air supply passage 8 (the position of the branch portion 8 a) is upstream of the air cooler 13. Is preferred. This is because, in the present invention, feeding hot air to the evaporation pipe 10 is advantageous in promoting hydrolysis of urea water.

14 denotes a receiver tank provided on the downstream side of the air cooler 13. When the engine 1 starts to use air, the air is quickly supplied from the receiver tank 14, and when the pressure in the receiver tank decreases thereafter, the decrease is replenished by supply from the compressor 4b. Even when a large amount of air exceeding the capacity is needed instantaneously, the air supply is kept short.

As described above, in the urea water spray structure of the present invention, the evaporation pipe connected to the branch pipe branched from the air supply passage on the downstream side of the compressor of the turbocharger is arranged in the exhaust manifold, Since the hydrolysis to ammonia is completed by spraying urea water, it is possible to suppress the formation of by-products such as ammonium sulfate and acidic ammonium sulfate even when using a fuel containing a large amount of sulfur. Moreover, since the wall surface of the evaporation pipe provided in the exhaust manifold is sufficiently heated by the high-temperature exhaust gas immediately after being discharged from the exhaust communication pipe, the temperature does not become insufficient even in the area where the urea water is sprayed, such as cyanuric acid. It is possible to prevent the formation of by-products.

The present invention is not limited to the above-described embodiments, and it is needless to say that the embodiments may be appropriately changed within the scope of the technical idea described in each claim.

For example, in the above-described embodiment, a configuration in which a constant amount of air is introduced from the air supply passage 8 through the branch pipe 9 to the evaporation pipe 10 is shown. However, depending on the sea area where the ship travels, denitration processing by the SCR catalyst 6a may be performed. Since there is a case where it is not necessary, by providing a switching valve in the branch portion 8a, the inlet of the branch pipe 9 is sealed as necessary, and if no denitration treatment is required, all air is sent to the air cooler 13. You may comprise.

The urea water spray structure of the present invention can be applied not only to marine diesel engines but also to automobile diesel engines.

DESCRIPTION OF SYMBOLS 1 Engine 1a Exhaust port 2 Exhaust communication pipe 3 Exhaust manifold 4 Turbocharger 4a Turbine 4b Compressor 5 Exhaust passage 6 Denitration reactor 6a SCR catalyst 7 Exhaust gas purification device 8 Supply passage 9 Branch pipe 10 Evaporating pipe 10a Ejection hole 11 Nozzle 12 Water Decomposition catalyst 13 Air cooler

Claims

An exhaust gas purification apparatus having a denitration reactor provided between an exhaust manifold that collects exhaust gas discharged from an exhaust communication pipe connected to an exhaust port of an engine and an exhaust passage upstream of a turbine of a turbocharger A urea spray structure capable of supplying ammonia to the SCR catalyst of the denitration reactor,
In the exhaust manifold, an evaporation pipe connected to the branch pipe branched from the air supply passage on the downstream side of the turbocharger compressor is disposed, and
A urea water spray structure characterized in that a nozzle for spraying urea water to high-temperature air introduced into the evaporation pipe through the branch pipe is provided in the evaporation pipe.
The urea water spray structure according to claim 1, wherein the nozzle is provided in a region where the evaporation pipe is present in the exhaust manifold.
The urea water spray structure according to claim 1 or 2, wherein a hydrolysis catalyst for accelerating hydrolysis of urea water is provided inside the evaporation pipe and downstream of the nozzle.
4. The urea according to claim 3, wherein an ejection hole for ejecting ammonia generated by hydrolysis of urea water toward the SCR catalyst is provided downstream of the hydrolysis catalyst in the evaporation pipe. Water spray structure.
The air cooler is provided in the air supply passage, and a position where the branch pipe is branched from the air supply passage is located upstream of the air cooler. Urea water spray structure.