JPH06101454A - Exhaust gas purifying device for diesel engine - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purifying device which is designed to achieve efficiently denitration of exhaust gas from a diesel engine without forming the particulates of a catalyst surface, in a denitration system wherein exhaust gas is brought into contact with a catalyst. CONSTITUTION:Exhaust gas exhausted from an engine is guided to an exhaust gas purifying device 1. The exhaust gas purifying device 1 is provided, in order, from a position situated upper stream of the flow of exhaust gas with a secondary air feed port 2, a gasifying combustion chamber 3 for light oil, and a catalyst layer 5. The gasifying combustion chamber 3 is served to burn light oil, fed for denitration of exhaust gas, right before the catalyst layer 5. The combustion chamber comprises a protector 6 having structure wherein a cover part arranged on the upper stream side in a direction crossing an exhaust gas flow passage is provided and a release part is provided on the downstream side, a partition plate 10 arranged in the protector 6 and to the vicinity of a pipe 8 for feeding light oil and a tip nozzle 7, a globe plug 11, and a cylindrical mesh part 12 made of a metal. In the catalyst layer 5, a denitrided catalyst (magnetite) is sintered on a carrier of honeycomb structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying device for a diesel engine.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides (hereinafter sometimes referred to as NOx) in exhaust gas discharged from a combustion device, a method that has been put to practical use in a large boiler or the like has conventionally used ammonia as a reducing agent. Using Cr ₂ O ₃ , Mn ₂ O ₃ ,
In the presence of a non-metallic oxide catalyst such as V ₂ O ₅ , CuO, Fe ₂ O ₃ , CoO, etc., this is added to the exhaust gas and reacted with the nitrogen oxides in the exhaust gas to make NOx harmless. There is a method of decomposing it into nitrogen and oxygen. However, since this denitrification method uses ammonia, which is a harmful substance, there are legal restrictions on its handling, and it has only been used in a stationary large-scale exhaust gas denitration device.

However, in the midst of calls for air pollution and environmental protection, NOx in exhaust gas emitted from diesel combustion devices such as urban cogeneration systems or diesel vehicles cannot be ignored. , The development of the effective removal means is desired.

Oxygen having a high concentration of 9 to 13% remains in the exhaust gas discharged from the diesel combustion device. Also, the concentration of sulfur oxides in this exhaust gas is 100 to 500 p.
In some cases, the soot concentration is as high as pm and the soot concentration is as high as 10 to 100 mg / m ³ . Further, there is a feature that the exhaust gas temperature is as low as 200 to 600 ° C. NOx that meets such exhaust gas conditions and is economically viable
Development of reduction reaction system is necessary.

As a method for treating exhaust gas of the diesel combustion apparatus, the present inventors first added a reducing agent composed of a hydrocarbon or alcohol and secondary air to the combustion exhaust gas in the presence of magnetite to produce nitrogen oxides in the combustion exhaust gas. An exhaust gas denitration method for removing nitrogen at a high rate was developed (JP-A-3-20705).
No. 4). As shown in FIG. 8, the patent application invention has a reducing agent supply pipe 3 such as light oil on the upstream side of the magnetite catalyst layer 35 in which exhaust gas from a diesel engine is constantly flowing.
No. 6 in the exhaust gas is reduced when the reducing agent and the secondary air are supplied to the No. 6 and the secondary air supply pipe 37, respectively, and they are brought into contact with the magnetite catalyst layer 35.

[0006]

However, in the above-mentioned patent application invention, since a reducing agent such as light oil is added or injected directly to the place where exhaust pressure is applied, a large amount of reducing agent is required.
Also, the particulates (SO
F: soluble organic fraction
n, ISOF: insoluble organicf
Raction) is formed on the catalyst surface of the catalyst layer 35, and the denitration performance may decrease.

Therefore, an object of the present invention is to supply a reducing agent such as light oil and secondary air to the upstream side of the catalyst part and to contact the magnetite catalyst with the denitration system without forming the particulates on the catalyst surface without forming particulates. An object of the present invention is to provide an exhaust gas purifying device that efficiently achieves denitration of exhaust gas from an engine.

[0008]

The above objects of the present invention can be achieved by the following constitutions. That is, on the upstream side of the catalyst portion for denitration of the exhaust gas discharge flow path, a reducing agent vaporization combustion chamber in which a reducing agent vaporization chamber and a protector that does not affect the vaporization and combustion of the reducing agent by the exhaust gas flow are integrated. Is an exhaust gas purifying device for a diesel engine.

Magnetite (Fe ₃ O ₄ ) as a denitration catalyst
To use. The magnetite can be obtained by sintering magnetite. The magnetite is used in a shape having a large contact area with the exhaust gas. For example, granules, pellets,
It can be used in the shape of a honeycomb-shaped product. As the hydrocarbon used as the reducing agent, light oil, heavy oil, paraffins such as benzine, methane, ethane, propane and n-hexane, olefins such as ethylene and propylene, and alcohols such as methanol can be used alone or as a mixture. .

In order to improve the combustibility of the reducing agent or the denitration reaction of the exhaust gas, secondary air is introduced into the exhaust gas discharge passage, but the amount used is 7 to 13% by volume of the exhaust gas.
Used in. If it is outside this range, the denitrification rate will be poor. The denitration reaction temperature in the catalyst layer of the present invention is 400 ° C to 700 ° C, preferably 450 ° C to 500 ° C. Above 700 ° C,
The magnetite changes to hematite and the catalytic activity is lost. If the temperature is lower than 400 ° C, the reaction efficiency will decrease,
The reduction rate of NOx becomes worse.

Since the denitration device of the present inventors has a simple structure, it can be installed in the exhaust gas discharge part of a mobile diesel combustion device or an urban stationary diesel combustion device. It is especially suitable for exhaust gas from diesel vehicles.

[0012]

[Function] When a reducing agent composed of hydrocarbon or alcohol and secondary air (oxygen) are added to combustion exhaust gas and brought into contact with magnetite (Fe ₃ O ₄ ), NOx in the exhaust gas is reduced to nitrogen. . The mechanism of the reduction reaction of NOx to nitrogen is not completely clear. However, it has been confirmed that the denitration catalytic reaction of magnetite hardly progresses in the absence of a reducing agent and oxygen.

Further, when the reducing agent such as light oil or heavy oil is burned with high efficiency at the place where the exhaust gas of the diesel engine is constantly flowing, the particulate matter on the catalyst surface is removed, and the diesel engine is cleaned while cleaning the catalyst surface. It is possible to efficiently achieve denitration of the exhaust gas.

According to the configuration of the present invention, the reducing agent is vaporized in the reducing agent vaporizing chamber provided on the upstream side of the catalyst portion in which the exhaust gas is arranged in the exhaust passage. At this time, the exhaust gas of the diesel engine is discharged, and the reducing agent can be vaporized and burned without trouble by a protector for preventing the combustion state of the vaporization chamber from being disturbed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust gas purifying apparatus for a diesel engine of the present embodiment. FIG. 1 (a) is a conceptual diagram thereof, FIG. 1 (b) is a front view of the vaporization combustion chamber, and FIG. 1 (c) is a vaporization combustion chamber. The side view of each is shown. Exhaust gas discharged from the engine is guided to the exhaust gas purification device 1. In the exhaust gas purifying apparatus 1, a secondary air supply port 2, a vaporizing combustion chamber 3 for a reducing agent (light oil as a fuel is used in this embodiment), and a catalyst layer 5 are arranged in this order from the upstream side of the flow of exhaust gas. . The secondary air supply port 2 is provided to supply the air for burning the fuel. Further, the vaporization combustion chamber 3 is for burning light oil supplied for denitration of exhaust gas immediately before the catalyst layer 5, has a cover portion on the upstream side in the direction crossing the exhaust gas flow passage, and has a downstream side. A protector 6 having a structure having an open portion, and a light oil supply pipe 8 having a tip nozzle 7 in the central portion of the exhaust gas flow passage cross section inside the cover portion of the protector 6 and the tip nozzle 7 are provided in the vicinity thereof. Partition plate 10 and the partition plate 1
Glow plug 11 arranged in the cover portion on the side opposite to the light oil supply pipe 8 through 0, and a cylindrical metal mesh arranged so as to surround these light oil supply pipe 8, partition plate 10 and glow plug 11. And a part 12. The cover of the protector 6 is provided to prevent vaporized light oil from being affected by the exhaust gas flow. Further, in the catalyst layer 5, a denitration catalyst (magnetite) is sintered on a honeycomb-structured carrier arranged on the entire surface of the exhaust gas passage of the exhaust gas purifying apparatus 1.

When light oil is supplied from the light oil supply pipe 8, the light oil drops on the partition plate 10 and then touches the mesh portion 12. At this time, the mesh part 12 is made up of 80 glow plugs.
Since it is heated to 0 to 1000 ° C, the mesh part 12
The light oil vaporizes above and is ignited by the high temperature of the exhaust gas (about 300 ° C. or higher) to burn the particulates adhering to the catalyst surface of the catalyst layer 5 to keep the surface of the catalyst layer 5 clean. At this time, the mesh portion 12 has a function of preventing the exhaust gas from being caught in the opening of the protector 6, and also has a function of uniformly dispersing the ignition of the light oil in the cross-sectional direction of the exhaust gas flow, so that the light oil is used as the protector. Fires evenly throughout 6 Exhaust gas flow rate 48 x 1
The NO reduction rate was 13% at 0 ⁶ cm ³ / hr, exhaust gas space velocity of 0.0105, catalyst (component) weight of 140 g, and light oil addition amount of 24 ml / min.

Further, instead of the protector 6 having the opening shown in FIG. 1 on the downstream side of the exhaust gas flow path, a cylindrical protector 13 is used as shown in FIG. 2, and the protector 6 on the side facing the catalyst layer 5 is used. The cylindrical protector 13 may be provided with pores 14. In this way, the flame ignited by the light oil burned in the vaporization combustion chamber 3 is blown out from the pores 14 to the catalyst layer 5 with a penetrating force, the direction of the flame can be determined, and the protector 6 having an opening is formed. Compared to (Fig. 1), it consumes less fuel.

In the case of FIG. 1, since a part of the exhaust gas collides with the end surface of the catalyst layer 5 and returns to the mesh portion 12 of the vaporization combustion chamber 3 as a reflected wave, the amount of light oil to be added is increased to produce a reflected wave. Although it is necessary to generate a flame axis exceeding the above, the use of the protector 13 with pores shown in FIG.
Although the gas oil vaporized from No. 4 is jetted and spontaneously ignited at the exhaust gas temperature, the protector 13 has a shield structure, so that the amount of gas oil to be added can be reduced.

Specifically, in the case of the exhaust gas purifying apparatus 1 having the structure shown in FIG. 1, the amount of fuel oil (light oil) added was 24 ml / min and the NO reduction rate was 12%. The structure of Fig. 2 has a fuel oil addition of 1.5 m
The reduction rate was 13% at 1 / min. However, the operating conditions of the engine were the same in all cases. Further, since the addition amount of fuel oil could be reduced, the total increase of unburned hydrocarbons was 3850 ppm in the case of FIG. 1, whereas it was 650 ppm in the case of FIG. 2 and could be minimized.

As shown in FIG. 3, the secondary air (O ₂ ) required for vaporizing and burning the combustion oil (light oil) is directly vaporized through a stainless thin tube 16 provided upstream of the catalyst layer 5. It is also possible to adopt a structure in which the combustion chamber 3 is introduced. Incidentally. The broken lines shown in FIGS. 2 and 3 represent the inflowing exhaust gas dispersion plate 15. In the vaporizing combustion chamber 3 having the structure shown in FIGS. 1 and 2, the oxygen concentration is diluted with the inert gas (exhaust gas) because the secondary air is introduced into the exhaust gas. At this time, it was necessary to introduce an excessive amount of air to obtain the oxygen concentration necessary for vaporized combustion, but in the structure shown in FIG. 3, as shown below, the NO _x reduction effect is not affected. The amount of secondary air introduced can be reduced. 1 and 2 system ... Secondary air volume: 50 liters / m
in NO reduction rate: 12.8% System of FIG. 3 Secondary air amount: 1-2 liter / min NO reduction rate: 13.4%

Further, as shown in FIG. 4, the vaporization combustion chamber portion is divided into a ceramic vaporization chamber 17 and a gas chamber 18 having a high heat insulation effect, and the combustion chamber portion is made independent of the secondary air insertion portion to obtain the secondary air. By directly pumping the gas to the gas chamber 18,
The vaporization density of light oil becomes uniform and the combustion flame becomes stable. Therefore, the heat distribution in the catalyst layer 5 became uniform, and the direct decomposition efficiency of NO in the exhaust gas could be improved. As shown in the enlarged detailed view of the vaporization combustion chamber portion in FIG. 4, the tip nozzle 7 of the gas oil supply pipe 8 of the vaporization combustion chamber is opened to the ceramic vaporization chamber 17 surrounded by the ceramic member 19. The ceramic vaporization chamber 17 is composed of a cylindrical protector 13 having a secondary air inlet 20. The lower part of the ceramic vaporization chamber 17 is the plug 1
1, and a jet port 21 of vaporized light oil 21 is provided on the side surface of the cylindrical protector 13 opposite to the secondary air introduction port 20.
Is provided.

The results of comparing the temperature of the upstream portion of the catalyst layer 5 (the measurement portion is the central portion of the catalyst layer) under the same test conditions are shown below. 3 system ... 499 ° C. FIG. 4 system ... 520 ° C. Thus, in the system of FIG. 3, since the vaporization chamber and the gas chamber are integrated, vaporization of light oil is affected by the amount of secondary air and vaporized. The density became non-uniform and the combustion flame was intermittent and not stable, but in the system shown in FIG. 4, the heat distribution in the catalyst layer 5 was uniform, and a stable combustion flame could always be obtained.

In addition, in the systems shown in FIGS. 1 to 4, even if an attempt is made to reignite the extinguished vaporization combustion chamber 3 again at the temperature of only the exhaust gas, ignition may not occur easily due to engine load fluctuations and the like. It was Therefore, as shown in FIG. 5, a combustion hood 22 is provided on the upstream side of the catalyst layer 5, and a secondary air supply hole 24 is opened in the combustion hood 22 to increase the oxygen concentration necessary for re-ignition of light oil. . At this time, it is necessary to provide a glow plug 25 for re-ignition of light oil in the combustion hood 22 for re-ignition of light oil. Further, a punch metal 26 for preventing backflow of exhaust gas can be installed on the end surface of the combustion hood 22. According to visual inspection, FIG.
It was confirmed that the re-ignition of light oil was reliably and instantaneously adopted by adopting the structure of.

Further, in the case of the system of FIG. 5, the secondary air was sent along the inner wall of the combustion hood 22, but in this case, when operating for a long time, the heat of the inner wall of the combustion hood 22 heats the secondary air. As a result, the air density was reduced, and oxygen could not be taken into the combustion flame, resulting in extinction. Therefore, as shown in FIG. 6, a nozzle hood 28 is provided so that the direction of the secondary air supplied into the combustion hood 22 is in the same direction as the combustion flame, and the secondary air introducing pipe 29 is provided in the nozzle hood 28. It is also possible to adopt a configuration in which the hood 28 is connected so as to open. In the case of the system shown in FIG. 6, the secondary air flows so as to wrap around the combustion flame ejected from the vaporized fuel injection nozzle 30 of the vaporization combustion chamber 3, and the secondary air is sent in the direction coaxial with the combustion flame. As a result, it is possible to take in oxygen required for continuous combustion, and a combustion chamber that does not extinguish flames even during long-term operation. Regarding the other structures, the structure in which the glow plug 25 for re-igniting the fuel in the combustion hood 22 and the vaporization combustion chamber 3 are the same as in the case of FIG.

As shown in FIG. 7, when a mesh 31 made of metal such as platinum is installed at the tip of the vaporized fuel injection nozzle 30, air turbulence occurs in the gap between the mesh parts or the flame kernel stabilizes. As a result, air can be taken into the combustion flame, and the flame will not be extinguished even if it is operated for a long time with the amount of light oil being reduced.

Further, an exhaust gas introduction guide 32 is provided between the combustion hood 22 and the catalyst layer 5 (not shown) so that the exhaust gas from the engine flows along the outer wall of the combustion hood 22 before the exhaust gas reaches the catalyst layer. By inducing the exhaust gas from the engine to come into contact with the exhaust gas, the exhaust gas from the engine is always discharged through the combustion flame, and the particulates in the exhaust gas on the catalyst layer are surely combusted. The Bosch smoke concentration was 26% when the guide 32 was not provided, but decreased to 24% when the guide 32 was installed.

[0027]

EFFECTS OF THE INVENTION According to the present invention, by providing a chamber in the exhaust gas passage of a diesel engine, which can surely vaporize the reducing agent and combust the reducing agent, the particulate matter on the catalyst surface can be prevented. While being effectively removed and the catalyst surface can be cleaned, denitration of exhaust gas of a diesel engine can be efficiently achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing an exhaust gas purification apparatus.

FIG. 2 is a diagram showing an exhaust gas purification apparatus.

FIG. 3 is a diagram showing an exhaust gas purification apparatus.

FIG. 4 is a cross-sectional view of a fuel vaporization combustion chamber of an exhaust gas purification device.

FIG. 5 is a diagram showing an exhaust gas purification apparatus.

FIG. 6 is a diagram showing an exhaust gas purifying apparatus.

FIG. 7 is a diagram showing an exhaust gas purification apparatus.

FIG. 8 is a diagram showing an exhaust gas purifying apparatus of a conventional technique.

[Explanation of symbols]

1 ... Exhaust gas purifying device, 3 ... Vaporizing combustion chamber, 5 ... Catalyst layer, 6
…protector

Claims (1)

[Claims] 1. A reducing agent comprising a reducing agent vaporization chamber and a protector that are not affected by the exhaust gas flow to vaporize and burn the reducing agent on the upstream side of the catalyst for denitration in the exhaust gas discharge channel. An exhaust gas purification device for a diesel engine, which is provided with a vaporization combustion chamber.