JP2003176711A - Exhaust emission control method and device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate particulates and nitrogen oxide included in exhaust gas from a diesel engine. <P>SOLUTION: Exhaust gas is introduced through a combustion catalyst layer 8 to a fiber layer 5. Fuel 60 is supplied to the combustion catalyst layer to cause catalyst combustion, so that the particulates collected to the fiber layer 5 are burnt and eliminated. The exhaust gas is then introduced to a denitration catalyst layer 16 to be catalytically cracked by ammonium obtained by decomposition of urea in an urea decomposition catalyst layer 17. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing particulate matter (hereinafter referred to as particulates) and nitrogen oxides contained in diesel engine exhaust gas.

[0002]

2. Description of the Related Art Reduction of particulate matter contained in diesel engine exhaust gas has come to be taken up as a social problem. Further, not only exhaust gas from diesel engine but also reduction of nitrogen oxides emitted from internal combustion engine has become a social problem.

Of the above two substances, regarding reduction of nitrogen oxides, urea, urea aqueous solution, ammonia,
It is known to denitrate using an aqueous ammonia solution.
On the other hand, regarding the removal of particulates, there is a method of carrying a combustion catalyst on a metal fiber filter, a honeycomb filter, or these filters to collect the particulates and remove them by burning. Nikkei Ecology is a method of treating nitrogen oxides and particulates separately, or a method of simultaneously removing nitrogen oxides and particulates.
It is described in the August 2000 issue.

A method for purifying exhaust gas by attaching a catalyst to a fibrous body is described in JP-A-2000-354738.

[0005]

The ignition temperature of particulates contained in diesel engine exhaust gas is about 250 ° C. for high-boiling organic components and soot (carbonaceous matter).
Is 550 ° C. or higher. Therefore, in the method of collecting the particulates with a filter or the like and burning and removing the collected particulates, it is necessary to heat the exhaust gas to the combustion temperature of the particulates. As a method for heating the exhaust gas to a high temperature, there are a method using an electric heater, a method using catalytic combustion, and the like. In the catalytic combustion method, if the catalyst is heated to a predetermined temperature, the exhaust gas temperature can be raised to the particulate combustion temperature by supplying fuel to the catalyst and burning it.

The present invention is to provide an effective method for burning off particulates by catalytic combustion. Further, it is to make it possible to effectively use the heat contained in the exhaust gas of the diesel engine for heating the combustion catalyst. Another object of the present invention is to provide an industrially promising method and apparatus for removing nitrogen oxides contained in exhaust gas by using ammonia obtained by urea decomposition as a reducing agent.

[0007]

According to the present invention, diesel engine exhaust gas is introduced into a trapping layer containing a combustion catalyst and a fibrous body, the particulate matter is trapped by the fibrous body, and the particulate matter is introduced into the trapping layer. A fuel is externally added to the exhaust gas, the fuel is burned by the combustion catalyst, and the particulate matter trapped in the fibrous body is burned by the combustion heat.

Further, the exhaust gas from which the particulate matter has been removed by passing through the trapping layer is introduced into a denitration catalyst layer, and ammonia obtained by decomposing urea by a urea decomposition catalyst is denitration catalyst. The nitrogen oxide contained in the exhaust gas introduced into the bed is catalytically decomposed by the ammonia.

In carrying out the method of the present invention, it is desirable to provide a heat pipe in the trapping layer so that the heat radiating portion side of the heat pipe comes into contact with the combustion catalyst. Then, the diesel engine exhaust gas is introduced to the heat radiating portion side after passing through the heat absorbing portion side of the heat pipe,
Accordingly, it is desirable to transfer the retained heat of the exhaust gas of the diesel engine to the heat radiating portion of the heat pipe to heat the combustion catalyst to the activation temperature.

The combustion catalyst can be supported on the adsorbent. An example of this adsorbent with a catalyst is a zeolite adsorbent or an activated alumina adsorbent to which a catalyst is attached. The fibrous body means an aggregate of many fibers. As the fiber body, it is desirable to use a silica fiber body or a metal fiber body. The combustion catalyst and the fibrous body may be formed in separate layers, or both may be mixed to form a mixed layer.

The heat pipe is provided to transfer the heat of the engine exhaust gas to the combustion catalyst and heat the combustion catalyst. By heating the combustion catalyst with exhaust gas heat,
The fuel added to the exhaust gas can be rapidly catalytically burned. The particulate heat is burned by the combustion heat generated by the catalytic combustion. As a heat source for heat transfer of the heat pipe, it is desirable to use exhaust gas in a high temperature region near the engine, and it is preferable to introduce the exhaust gas into the heat absorbing portion (evaporating portion) of the heat pipe.

The fibrous body from which the particulates have been burned and removed is regenerated and the particulate collecting ability is enhanced again. One or more heat pipes can be provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows the structure of a diesel engine exhaust gas purifying apparatus used in an embodiment of the present invention. The high temperature exhaust gas discharged from the diesel engine 9, for example, the exhaust gas at 350 ° C., is partially or entirely introduced into the trapping layer 4. In FIG. 1, the collection layer 4 is provided with three heat pipes 1. The inside of the collection layer 4 is partitioned into two chambers by a non-perforated plate 6. An aperture plate 7 is further provided in one chamber in the collection layer 4, and a fiber layer 5 made of a fibrous body and a combustion catalyst layer 8 made of a combustion catalyst are laminated in two layers there. The size of the holes of the aperture plate 7 is set so that the fibrous body and the combustion catalyst do not pass but the exhaust gas passes. The heat absorption part 2 of the heat pipe 1 is located in a room in which the fibrous body and the combustion catalyst are not filled, out of the two rooms in the collection layer 4, and the heat dissipation part 3 is located in the other room.

The exhaust gas 50 is supplied to the heat absorbing section (evaporating section) 2 of the heat pipe 1 located in a region partitioned by the non-perforated plate 6 of the trapping layer 4. As a result, the medium sealed in the heat pipe 1 is heated and evaporated, and the heat radiating unit (condensing unit) 3
The heat is transferred to and the temperature of the heat radiation part 3 is heated and maintained at the temperature of the exhaust gas. The heat radiated from the heat radiating portion 3 heats the combustion catalyst filled in the heat radiating portion region.

The temperature of the exhaust gas 50 is lowered by heating the endothermic portion 2 of the heat pipe, becomes the exhaust gas 51 and leaves the trapping layer 4, and is then filled with the combustion catalyst of the trapping layer 4 again. Introduced into the room. Then, the particulates contained in the exhaust gas are collected in the fibrous body. By adding the fuel 60 to the exhaust gas 51, the combustion catalyst layer 8
Combustion occurs in the exhaust gas and the exhaust gas is heated to a higher temperature. The exhaust gas heated to this high temperature burns off the particulates collected in the fibrous body and regenerates the fibrous body. To supply the fuel 60 to the exhaust gas 51, the fuel 60 in the fuel storage tank 12 is supplied to the valve 11 by the oil feed pump 10.
It is carried out by supplying via. The fuel 60 is adjusted and supplied to a temperature at which the particulates can burn.

The exhaust gas from which the particulates have been removed in the trapping layer 4 exits the trapping layer 4 and becomes the exhaust gas 53 which is introduced into the denitration layer 15. The denitration layer 15 is provided with a denitration catalyst layer 16 filled with a denitration catalyst and a urea decomposition catalyst layer 17. Since the reduction of nitrogen oxides contained in the exhaust gas is performed using ammonia as a reducing agent, a system for supplying the urea aqueous solution 61 to the urea decomposition catalyst layer 17 is provided. The urea aqueous solution 61 is supplied from the urea aqueous solution storage tank 18 to the urea decomposition catalyst layer 17 via the valve 14 by the water supply pump 13. As a result, the urea aqueous solution 61 is decomposed into ammonia, and the nitrogen oxides contained in the exhaust gas 53 are reduced and removed by the ammonia while passing through the denitration catalyst layer 16.
The treated exhaust gas 54 is discharged to the outside of the denitration layer 15.

The combustion catalyst layer 8 may be made of palladium-based metal or platinum-based metal, but is not limited thereto. Further, the urea decomposition catalyst layer 17 and the denitration catalyst layer 16 can use a catalyst supporting a metal such as titania or tungsten, but the catalyst is not limited thereto.

In this embodiment, the heat pipe 1 capable of heat transfer of exhaust gas is installed, and the exhaust gas in the high temperature region near the engine is taken out to heat the combustion catalyst layer 8 arranged in the trapping layer 4. Therefore, as long as the fuel 60 is supplied to the exhaust gas 51, the catalytic combustion can be performed at any time, and the particulates collected in the fiber layer 5 can be burned and removed.

According to the first embodiment, the combustion catalyst layer 8 arranged in the trapping layer 4 is always made uniform at a predetermined temperature by utilizing the heat of the exhaust gas taken out immediately from the diesel engine 9 in which the temperature change is small due to the load fluctuation. It has the effect of heating. Therefore, if the fuel 60 is supplied, the trapped particulates can be burned and removed at any time, and the trapping layer 4 can be regenerated. Further, by appropriately selecting the temperature of the exhaust gas taken out immediately from the engine and transferring the heat by the heat pipe 1, there is an effect that the exhaust gas 53 passing through the trapping layer 4 can be maintained at a predetermined temperature at which denitration is possible. Further, since heating means such as an electric heater is not required and fuel is not required except for burning particulates, running cost can be reduced and operability and operability can be improved.

(Embodiment 2) FIG. 2 shows a structure of an engine exhaust gas purifying apparatus in which the heat pipe 1 is not provided and a combustion catalyst layer 28 is further provided above the denitration layer 15.

In FIG. 2, the exhaust gas 55 discharged from the diesel engine 9 is introduced into the collection layer 4 from above.
The introduced exhaust gas 55 is heated to a predetermined temperature, for example, 300 ° C. by the combustion catalyst layer 8 which has been heated in advance by means such as an electric heater. When burning the particulates, fuel 60 is added to the exhaust gas 55 by the same operation as in the first embodiment.
Is supplied to burn the fuel 60 in the combustion catalyst layer 8, and the particulate heat is burned and removed by the combustion heat. Except for the combustion of particulates, the exhaust gas 55 is supplied to the upper portion of the denitration layer 15 via the fiber layer 5 while being maintained at 300 ° C.

In the second embodiment, the combustion catalyst layer 28 is further provided on the urea decomposition catalyst layer 17 above the denitration catalyst layer 16, and the combustion catalyst layer 28 heated by the exhaust gas 58 is provided.
Fuel 60 is supplied to the valve via valve 19. The fuel 60 is burned by the combustion catalyst layer 28, which heats the exhaust gas 58 to a higher temperature. Using this high temperature heat, nitrogen oxides are reduced by ammonia and decomposed and removed into nitrogen. Ammonia production is described in Example 1.
Is the same as. The exhaust gas 54 from which the nitrogen oxides have been removed is discharged to the outside of the denitration layer 15.

The exhaust gas 55 introduced can be heated by heating the combustion catalyst layer 8 by means of an electric heater or the like. Since the urea decomposition catalyst layer 17 and the denitration catalyst layer 16 can be heated to denitration conditions by heating the exhaust gas 55, the denitration layer 1
The installation of the combustion catalyst layer 28 in 5 can be omitted.

Also in this embodiment, if the combustion catalyst layer 8 is heated by means such as an electric heater and the fuel 60 is supplied during combustion, the collected particulates can be burned and removed,
The fibrous body of the collection layer 4 can be regenerated. Further, the combustion catalyst layer 28 provided in the denitration layer 15 is heated to a predetermined temperature by means such as an electric heater, the fuel 60 is supplied and burned, and the heat raises the urea decomposition catalyst layer 17 to a predetermined temperature. it can. As a result, the urea aqueous solution 61 is easily decomposed into ammonia, and nitrogen oxide can be reduced and removed by the generated ammonia.

[0025]

According to the present invention, it is possible to construct an industrially feasible system in which particulates contained in exhaust gas of a diesel engine are burned and removed by using a combustion catalyst and nitrogen oxides are decomposed by ammonia. Further, it is possible to construct a system in which the heat of exhaust gas near the engine outlet is used to heat the combustion catalyst.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a diesel engine exhaust gas purification apparatus showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a diesel engine exhaust gas purification apparatus showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heat pipe, 2 ... Heat absorption part, 3 ... Heat dissipation part, 4 ... Collection layer, 5 ... Fiber layer, 6 ... Non-perforated plate, 7 ... Perforated plate, 8, 28
... Combustion catalyst layer, 9 ... Diesel engine, 15 ... Denitration layer, 16 ... Denitration catalyst layer, 17 ... Urea decomposition catalyst layer.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) B01D 53/86 ZAB F01N 3/24 E F01N 3/08 L 3/24 3/28 301C 3/36 C 3 / 28 301 D 3/36 B01D 46/42 B 53/36 ZABC // B01D 46/42 B (72) Inventor Shinichi Ichikawa 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Electric Power & Electric Co., Ltd. In the development laboratory (72) Inventor Takashi Fujimura 3-2-2, Sachimachi, Hitachi, Ibaraki F-term in Hitachi Engineering Service Co., Ltd. (reference) 3G090 AA01 AA02 BA01 CB00 EA01 EA02 3G091 AA18 AB13 BA00 BA14 BA15 BA19 CA01 CA03 CA17 CA18 GB01W GB06W GB07W GB10W GB17X GB17Y 4D019 AA01 BA02 BA05 BB13 BC05 BC07 CB02 CB04 CB09 4D048 AA06 AA14 AA18 AB01 AB02 AB05 AC02 AC03 AC04 CC41 CC53 CC61 EA04 4D05 8 JA60 MA41 MA42 MA44 SA08 TA02 TA06 UA30

Claims (7)

[Claims] 1. A method of removing particulate matter contained in a diesel engine exhaust gas, wherein the diesel engine exhaust gas is introduced into a trapping layer containing a combustion catalyst and a fibrous body to collect the particulate matter with the fibrous body. Then, a fuel is externally added to the exhaust gas introduced into the trapping layer, the fuel is burned by the combustion catalyst, and the particulate matter trapped in the fibrous body is burned by the heat of combustion. A method for purifying exhaust gas from a diesel engine, characterized by: 2. The method according to claim 1, wherein the exhaust gas from which the particulate matter has been removed by passing through the trapping layer is introduced into a denitration catalyst layer, and urea is decomposed by a urea decomposition catalyst. A method for purifying a diesel engine exhaust gas, which comprises introducing ammonia into the denitration catalyst layer to catalytically decompose nitrogen oxides contained in the exhaust gas with the ammonia. 3. The heat pipe according to claim 1, wherein a heat pipe is provided in the trapping layer so that a heat radiating portion side of the heat pipe comes into contact with the combustion catalyst, and the diesel engine exhaust gas is passed through a heat absorbing portion side of the heat pipe. A method for purifying exhaust gas of a diesel engine, characterized in that the heat retained by the exhaust gas of the diesel engine is transferred to the heat radiating portion of the heat pipe to heat the combustion catalyst. 4. The method for purifying exhaust gas from a diesel engine according to claim 1, wherein the combustion catalyst is supported on an adsorbent. 5. A device for removing particulate matter contained in a diesel engine exhaust gas, a trapping layer containing a combustion catalyst and a fibrous body, and a fuel addition system for adding fuel to the exhaust gas introduced into the trapping layer. The exhaust gas is introduced into the collection layer to collect and remove particulate matter, the fuel added to the exhaust gas is burned by the combustion catalyst, and the combustion heat collects in the collection layer. A diesel engine exhaust gas purification device, characterized in that the collected particulate matter is burned and removed. 6. The denitration catalyst layer according to claim 5, which catalytically reduces nitrogen oxides contained in the exhaust gas discharged from the trapping layer with ammonia, and the ammonia used in the denitration catalyst layer to decompose urea into urea. And a urea decomposition catalyst layer for production by the method for purifying diesel engine exhaust gas. 7. The heat pipe according to claim 5, wherein a heat pipe is provided inside the trapping layer so that a heat radiating portion of the heat pipe comes into contact with the combustion catalyst, and the diesel engine exhaust gas passes through the heat absorbing portion side of the heat pipe. A purification device for a diesel engine exhaust gas, characterized in that the heat retained by the diesel engine exhaust gas is used for heating the combustion catalyst so that the heat is introduced into the heat radiating section side.