JPH07243322A - Nox reducing device for engine - Google Patents

Abstract

PURPOSE:To reduce NOx in a specified wide temperature range stably and more effectively by combining two catalysts whose adaptive temperatures are different from each other in an exhaust system. CONSTITUTION:An NOx catalyst 13 and an NOx catalyst 23 are provided in series in the exhaust pipe 12 of an engine 10, and injection nozzles 16, 26 capable of injecting hydrocarbon system liquid 20 toward a catalyst are provided in the exhaust pipe 12 of the gas upstream side of each catalyst. The liquid 20 is supplied to those injection nozzles 16, 26 by a hydrocarbon system liquid supplying means 19. Temperature sensors 14, 24 are arranged on entrances of the catalysts 13, 23 so as to detect the temperature of exhaust gas in the exhaust pipe 12. In a controller 30, regulating valves 18, 28 are opened/closed according to a catalyst entrance temperature especially, and amounts for supplying the liquid 20 into the injection nozzles 16, 26 are regulated, on the basis of detecting outputs of a rotation sensor 22, a load sensor 25, the temperature sensors 14, 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reducing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art As a device for reducing this type of NOx,
An apparatus using a monolith catalyst made of copper ion-exchanged zeolite is known. This copper ion exchanged zeolite is N
It is a substance in which Na ions of a-type ZSM-5 zeolite are ion-exchanged with Cu ions, and a copper ion-exchanged zeolite catalyst is a copper ion-exchanged ZSM on the surface of a honeycomb-shaped monolith carrier made of a ceramic material such as cordierite.
-5 It is made by coating zeolite. When oxygen and hydrocarbon coexist on the copper ion-exchanged zeolite catalyst, the selective reduction of NOx efficiently and catalytically proceeds in the temperature range of the exhaust gas temperature of mainly 350 to 400 ° C.,
Enables purification of exhaust gas from diesel engines, lean-burn gasoline engines, etc.

[0003]

However, while the copper ion-exchanged zeolite catalyst has a high NOx selective reduction function, it has a drawback that the NOx selective reduction rate becomes low when the exhaust gas temperature is 350 ° C. or lower and 450 ° C. or higher. It was An object of the present invention is to provide a NOx reduction device for an engine, which is stable in a wide temperature range of 250 to 550 ° C. and more efficiently reduces NOx by combining two catalysts having different compatible temperatures in an exhaust system. To do.

[0004]

A structure of the present invention for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The NOx reduction device of the present invention includes a first NOx catalyst 13 provided in an exhaust pipe 12 of an engine 10 and the catalyst 1
No. 2 provided in the exhaust pipe 12 on the exhaust gas downstream side from No. 3
x catalyst 23, a first injection nozzle 16 provided at the inlet of the first NOx catalyst 13 and capable of injecting the hydrocarbon liquid 20 toward the catalyst 13, and an inlet of the second NOx catalyst 23 provided at the inlet of the second NOx catalyst 23 Second injection nozzle 26 capable of injecting the liquid 20 by means of the above, and a hydrocarbon-based liquid supply means 19 for supplying the liquid 20 to the injection nozzles 16 and 26 via the first and second adjusting valves 18 and 28, respectively. With. Further, the NOx reduction device of the present invention includes a rotation sensor 22 for detecting the rotation speed of the engine 10 and the engine 10.
Load sensor 25 for detecting the load of the first NOx catalyst 1
First temperature sensor 14 for detecting the temperature of the exhaust gas at the inlet of No. 3
And a second temperature sensor 24 for detecting the temperature of the exhaust gas at the inlet of the second NOx catalyst 23, the rotation sensor 22, the load sensor 25, the first temperature sensor 14 and the second temperature sensor 24.
The first and second regulating valves 18, 28 are opened and closed based on the detection output of the first and second injection nozzles 16, 16 for the liquid 20.
And a controller 30 that adjusts the supply amount to the device 26.

[0005]

The liquid 20 is injected from the injection nozzle 16 when the engine 10 is in a medium load, the rotation speed thereof is in the middle and high speed range, and the exhaust gas temperature at the inlet of the first NOx catalyst 13 is 250 to 350 ° C. NOx in the exhaust gas is reduced to N ₂ by the NOx catalyst 13. The exhaust gas temperature further rises due to the heat generated by the reduction reaction at this time. When the exhaust gas temperature at the inlet of the second NOx catalyst 23 is 350 to 550 ° C., the liquid 20 is injected from the injection nozzle 26, and NOx in the exhaust gas is reduced to N ₂ by the NOx catalyst 23.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIG. 1, a diesel engine 10
An exhaust pipe 12 is connected to the exhaust manifold 11. A first NOx catalyst 13 and a second NOx catalyst 23 are provided in the exhaust pipe 12 from the engine side. First NOx
The catalyst 13 is a monolith catalyst and has a honeycomb-shaped monolith carrier 13a made of cordierite or alumina. The monolithic carrier 13a contains, as catalytically active components, one or more metal oxides selected from the group consisting of zeolite, alumina, zirconia, and titania, and In, Fe, which are supported by the metal oxides. Sm, G
One or more metals selected from the group consisting of a, Co and Cu are supported. In this example, a cordierite monolithic carrier is coated with a zeolite catalyst carrying indium.

The second NOx catalyst 23 is also a monolith catalyst and has a honeycomb-shaped monolith carrier 23a made of cordierite or alumina. This monolith carrier 23
In a, as catalytically active components, zeolite, alumina,
One or more metal oxides selected from the group consisting of zirconia and titania and Cu or Co supported on the metal oxides are supported. In this example, a cordierite monolithic carrier is coated with a zeolite catalyst carrying cobalt. This indium-supported zeolite catalyst or cobalt-supported zeolite is Na-type ZSM
-5 It is a substance obtained by ion exchange of Na ion of zeolite with In ion or Cu ion. The injection nozzle 16 is provided with NOx in the exhaust pipe 12 on the exhaust gas upstream side of the first NOx catalyst 13.
An injection nozzle 26 is provided toward the NOx catalyst 23 in the exhaust pipe 12 on the exhaust gas upstream side of the second NOx catalyst 23 provided toward the catalyst 13.

A supply pipe 17 is connected to the injection nozzle 16, and the supply pipe 17 is connected via a regulating valve 18 and a pump 19 to a tank 21 containing a hydrocarbon liquid 20. In this example, the regulating valve 18 controls the liquid 2 to the injection nozzle 16.
It is a three-way valve that regulates the supply of 0
0 is light oil. A return pipe 17a connected to the tank 21 is connected to the adjusting valve 18. When the adjusting valve 18 is closed, the liquid 20 discharged from the pump 19 is returned to the return pipe 1
The liquid 20 is returned to the tank 21 through 7 a, and when opened, the liquid 20 is supplied to the injection nozzle 16. A supply pipe 27 is connected to the injection nozzle 26, and the supply pipe 27 is connected to a tank 21 containing the hydrocarbon liquid 20 via a regulating valve 28 and the pump 19. In this example, the adjustment valve 28 is a three-way valve that adjusts the supply amount of the liquid 20 to the injection nozzle 26. The adjusting valve 28 includes a return pipe 27 connected to the tank 21.
a is connected. The liquid 20 discharged from the pump 19 is returned to the tank 21 through the return pipe 27a when the adjustment valve 28 is closed, and supplies the liquid 20 to the injection nozzle 26 when opened.

A temperature sensor 14 for detecting the exhaust gas temperature is provided at the inlet of the NOx catalyst 13 near the injection nozzle 16, and a temperature sensor 24 for detecting the exhaust gas temperature is provided at the inlet of the NOx catalyst 23 near the injection nozzle 26. It is provided. The detection outputs of these temperature sensors 14 and 24 are connected to the control input of a controller 30 composed of a microcomputer. The controller 30 is connected to the rotation sensor 22 that detects the rotation speed of the engine 10 and the detection outputs of the load sensor 25 that detects the load of the engine 10. The load sensor 25 detects the displacement amount of the load lever of the fuel injection pump (not shown) in this example. The control output of the controller 30 is connected to the regulating valves 18, 28 and the pump 19. The controller 30 includes a memory 31. In the memory 31, the engine rotation, the engine load,
A map of the injection amount of the hydrocarbon liquid 20 according to the exhaust gas temperature or the like at the NOx catalyst inlet is stored in advance.

The operation of the NOx reducing device having such a configuration will be described. First, when the engine 10 has a light load and is operating in a low speed range, the exhaust gas temperature discharged from the exhaust manifold 11, that is, the exhaust gas temperature detected by the temperature sensor 14 is 2
When the temperature is 50 to 350 ° C., the controller 30 operates the pump 19 based on the stored contents of the memory 31 to open the adjusting valve 18. As a result, the liquid 20 is ejected from the ejection nozzle 16. Since the indium-supported zeolite catalyst has a high NOx selective reduction function at 250 to 350 ° C., NOx contained in the exhaust gas that has passed through the NOx catalyst 13 is reduced to N ₂ with high efficiency.

The exhaust gas temperature detected by the temperature sensor 24 is 3
When the temperature is less than 50 ° C., the controller 30 closes the adjusting valve 28, but when the exhaust gas temperature rises due to the heat generated by the reduction reaction of the NOx catalyst 13 and the temperature sensor 24 detects a temperature in the range of 350 to 550 ° C., the controller 30 adjusts. Open the valve 28. As a result, the liquid 20 is also ejected from the ejection nozzle 26. Cobalt-supported zeolite catalyst is 3
Since it has a high NOx selective reduction function at 50 to 550 ° C., N contained in the exhaust gas that has passed through the NOx catalyst 23.
Ox is reduced to N ₂ with high efficiency. As a result, as shown in FIG. 2, the NOx reduction rate according to the exhaust gas temperature of the present embodiment is the curve A by the first NOx catalyst 13 and the second NOx catalyst 2
It is shown as a curve A + B which is a composite of the curve B according to No. 3 and FIG. As a comparative example, the broken line in FIG. 2 is a conventional copper ion exchange ZSM-
5 shows a change curve C of the NOx reduction rate with respect to the catalyst inlet temperature of the No. 5 zeolite catalyst.

In the above example, an indium-supported zeolite catalyst was used as the first NOx catalyst 13.
If, instead of, Fe, Sm, Ga, Co, Cu, etc. are supported on the zeolite catalyst, the same effect is obtained. The second
Although a cobalt-supported zeolite catalyst is shown as the NOx catalyst 23, if Cu or a combination of Cu and Co is supported on the zeolite catalyst instead of this Co, a highly efficient reduction temperature region can be widened. Further, a honeycomb-shaped monolith carrier made of alumina may be used instead of the cordierite monolith carrier.

Instead of the ceramic monolithic carrier, a metal monolithic carrier may be used as a catalyst carrier for the first NOx catalyst 13 and the second NOx catalyst 23. As the metal monolith carrier, a corrugated metal foil 32a and a flat metal foil 32b are alternately laminated as shown in FIG. 3 and then formed into a cylindrical metal monolith carrier 32, or a large number of metal monolith carriers 32 as shown in FIG. 80 to 100 m in diameter formed by bundling metal pipes 33a having a diameter of 0.5 to 2 mm
The cylindrical metal monolithic carrier 33 may be m. In this metal monolith carrier 33, the surface area of the carrier is wider than that of the carrier 32, the absolute amount of the catalyst is further increased, and the NOx catalyst reduction rate is further improved. Fe-C, which has heat resistance as a carrier metal
An r-Al-based alloy or an aluminum alloy that is light in weight is used, and the active ingredient is coated on the inner surface and outer surface of the metal foil or the metal pipe. Metal monolith carrier 32
And 33 are housed in casings 34 and 35, respectively. In this example, the outer diameter and appearance of the casing 35 are substantially the same as the outer diameter and appearance of the exhaust pipe 12.

The conditions for opening and closing the regulating valve shown in the above example are merely examples, and the present invention is not limited to the above conditions. Furthermore, in the above example, light oil was used as the hydrocarbon-based liquid as the NOx reducing agent, but the present invention is not limited to this, and other reducing agents may be used.

[0015]

As described above, according to the present invention, by providing two NOx catalysts having different compatible temperatures in series in the exhaust pipe, NOx can be reduced more efficiently in a wide temperature range. be able to. Particularly, the first NOx catalyst has a high NOx selective reduction function in the exhaust gas temperature range of 250 to 350 ° C., and the second NOx catalyst has the exhaust gas temperature of 350.
By having a high NOx selective reduction function in the range of up to 550 ° C, NOx contained in the exhaust gas can be reduced stably and with high efficiency in the temperature range of 250 to 550 ° C.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a NOx reduction device according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in the NOx reduction rate with respect to the NOx catalyst inlet temperature.

FIG. 3 is a perspective view of an essential part of the metal monolith carrier.

FIG. 4 is a perspective view of a main part of another metal monolith carrier.

[Explanation of symbols]

 10 engine 12 exhaust pipe 13,23 NOx catalyst 14,24 temperature sensor 16,26 injection nozzle 18,28 adjusting valve 19 pump (hydrocarbon-based liquid supply means) 20 hydrocarbon-based liquid 22 rotation sensor 25 load sensor 30 controller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/94 F01N 3/28 ZAB 301 CF B01D 53/36 101 A

Claims (5)

[Claims] 1. A first NOx catalyst (13) provided in an exhaust pipe (12) of an engine (10) and an exhaust pipe (12) downstream of the first NOx catalyst (13) in exhaust gas.
A second NOx catalyst (23) provided in the first NOx catalyst (13) and an inlet of the first NOx catalyst (13).
a first injection nozzle (16) capable of injecting a hydrocarbon-based liquid (20) toward the x catalyst (13), and the second NOx provided at the inlet of the second NOx catalyst (23).
x A second injection nozzle (26) capable of injecting the liquid (20) toward the catalyst (23) and the first and second adjustment valves (18) to the first and second injection nozzles (16, 26), respectively. , 28) a hydrocarbon-based liquid supply means (19) for supplying the liquid (20) via a rotation sensor (22) for detecting the rotation speed of the engine (10).
A load sensor (25) for detecting the load of the engine (10), a first temperature sensor (14) for detecting the temperature of the exhaust gas in the exhaust pipe at the inlet of the first NOx catalyst (13), and the second NOx A second temperature sensor (24) for detecting the temperature of the exhaust gas in the exhaust pipe at the inlet of the catalyst (23), the rotation sensor (22), a load sensor (25), and a first temperature sensor
(14) and the second temperature sensor (24) based on the detection output, the first adjustment valve (18) and the second adjustment valve (28) is opened and closed the liquid
A NOx reduction device for an engine, comprising: a controller (30) for adjusting the supply amount of the first injection nozzle (16) and the second injection nozzle (26) of (20). 2. The first NOx catalyst (13) has an exhaust gas temperature of 250.
Has a high NOx selective reduction function in the range of ~ 350 ° C,
The NOx reduction device for an engine according to claim 1, wherein the second NOx catalyst (23) has a high NOx selective reduction function in an exhaust gas temperature range of 350 to 550 ° C. 3. A first NOx catalyst (13) and a second NOx catalyst
The NOx reduction device for an engine according to claim 1, wherein the carrier of (23) is a ceramic monolith carrier or a metal monolith carrier. 4. The catalytically active component supported on the carrier of the first NOx catalyst (13) is one or more metal oxides selected from the group consisting of zeolite, alumina, zirconia and titania, and the metal oxides. In, Fe carried on the object,
The catalytically active component comprised of one or more metals selected from the group consisting of Sm, Ga, Co and Cu, and supported on the carrier of the second NOx catalyst (23) is zeolite, alumina, zirconia and The NOx reduction device for an engine according to claim 2, comprising one or more metal oxides selected from the group consisting of titania and Cu or Co supported on the metal oxides. 5. A metal monolithic support having a large number of diameters of 0.
The NOx reduction device for an engine according to claim 3, wherein the cylinder is formed by bundling metal pipes of 5 to 2 mm, and the active ingredient is coated on the inner surface and the outer surface of the metal pipe.