JPH04171215A - Exhaust air cleaning device for diesel engine - Google Patents

Abstract

PURPOSE:To prevent the creation of sulfate in an oxidation catalyser and reduce the discharge amount of exhaust air particles in the atmosphere by providing a SO2 trap, which carries active alumina and base metal group metal to trap SO2 components in exhaust gas, in an exhaust gas passage on the upstream side of the oxidation catalyser. CONSTITUTION:An oxidation catalyser 3 is often used to oxidize SOF mainly containing hydro-carbon in exhaust and convert into H2O and CO2. A SO2 trap 4 traps SO2 components by creating sulfide through the combination of SO2 in exhaust gas with carried base metal group metal. As the SO2 trap has no recycling operation, base metal in the trap is consumed in such a process. A greater amount of carried base metal gives a longer life of the SO2 trap. By passing exhaust gas through the SO2 trap 4 on the upstream side of the oxidation catalyser 3, SO2 components are combined with base metal group metal in the trap 4 and excluded out of exhaust gas. In this way, exhaust gas not including SO2 components is supplied to the oxidation catalyser to prevent the creation of sulfate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust gas purification device that reduces the amount of particulates contained in the exhaust gas of a diesel engine.

[Conventional technology]

As a method for reducing the amount of exhaust particulates contained in the exhaust gas of a diesel engine, a method of collecting exhaust particulates using a diesel particulate filter is conventionally known. In this type of diesel particulate filter, in order to treat a large amount of carbon particles that form exhaust black smoke, it was
As in the device described in Japanese Patent No. 9-159718, it is common to regenerate the filter by periodically igniting and burning exhaust particulates collected in the filter.

Further, as a method that does not use a diesel particulate filter, there is a method of suppressing the generation of carbon particles that form exhaust black smoke among particulates by improving the combustion characteristics of the diesel engine itself. In this case, particulate components mainly composed of hydrocarbons such as unburned fuel and lubricating oil in the exhaust gas, that is, soluble organic components (
Soluble Organic Fraction:
Since the amount of SOF (SOF) increases relatively, a method is generally used in which an oxidation catalyst is used in combination to purify SOF and the like in the exhaust gas.

[Problem to be solved by the invention]

When using an oxidation catalyst to purify SOF, etc., there is a problem in that sulfate is produced by the catalyst especially when the engine exhaust temperature becomes high, and the amount of particulates discharged into the atmosphere increases. That is, in the exhaust gas of a diesel engine, an SO□ gas component is present due to the combustion of sulfur contained in the fuel, but this S02 is easily oxidized by an oxidation catalyst in a high temperature range to generate S03. S03 exists as particles and further combines with water to produce sulfate (sulfuric acid compound) particles such as sulfuric acid mist, so treating exhaust gas with an oxidation catalyst actually results in an increase in particulates.

To solve the above problem, Japanese Patent Application Laid-Open Nos. 59-36543, 59-80330, and 62-1
No. 93648 and other publications propose a method of preventing the formation of sulfate by imparting selectivity to the catalyst itself and suppressing the oxidation of SO2.

However, when the catalyst is given selectivity as described above, the oxidizing power of the catalyst tends to decrease, so although sulfate generation can be prevented, treatments such as SOF become insufficient and the particulate reduction effect is insufficient. There is a possibility that a problem may arise in which it is not possible to obtain

The present invention solves the above problems in an exhaust purification device that processes SOF, etc. in the exhaust of a diesel engine using an oxidation catalyst, and provides an exhaust purification device that can prevent the generation of sulfate while maintaining the high oxidizing power of the catalyst. is intended to provide.

[Means to solve the problem]

According to the present invention, in a diesel engine exhaust purification device in which an oxidation catalyst for purifying hydrocarbon components in exhaust gas is provided in the exhaust gas passage, SO□ in the exhaust gas is provided in the exhaust gas passage upstream of the oxidation catalyst. There is provided an exhaust gas purification device for a diesel engine characterized by providing a 5o2 trap carrying activated alumina and a base metal for trapping components.

[For production]

By passing the exhaust gas through the 802 trap on the upstream side of the oxidation catalyst, the SO2 component is combined with the base metal of the trap and removed from the exhaust gas.

Therefore, the oxidation catalyst is supplied with exhaust gas that does not contain SO2 components, thereby preventing the generation of sulfate.

〔Example〕

The configuration of an embodiment of the present invention is shown in FIG. In the figure, 1 is a diesel engine, 2 is an exhaust pipe, and 3 is an oxidation catalyst. The oxidation catalyst 3 has a structure in which a catalyst is supported on a carrier such as a ceramic or metal monolith carrier, a foam filter, or a honeycomb filter, and the catalyst used may be platinum-based, base metal-based, or composite oxide-based. Further, 4 is an SO□ trap provided in the exhaust pipe on the upstream side of the oxidation catalyst 3.

Similarly to the oxidation catalyst 3, the trap 4 has a structure in which a base metal is supported on a carrier such as a ceramic or metal monolith carrier, a foam filter, or a honeycomb filter, and the metals used include copper, iron, nickel, etc. Particularly preferred.

The diesel engine of this example uses a type that has a swirl chamber type combustion chamber and generates relatively little black exhaust smoke.
The oxidation catalyst 3 is mainly used to oxidize S'OF, which is mainly composed of hydrocarbons in exhaust gas, and convert it into water and CO2. SO again. Trap 4 is 80% in the exhaust gas.
2 collects the S02 component by combining with the supported base metal to generate sulfide. Since SO□ traps do not regenerate, the base metals in the traps are consumed as they are used. Therefore, the life of the SO□ trap increases as the amount of base metal supported increases.

FIG. 2 shows the configuration of another embodiment of the invention.

In this embodiment, the exhaust pipe 2 is provided with a bypass passage 5 that bypasses the SO□ trap 4 and a three-way switching valve 6. The switching valve 6 includes a temperature sensing part 6a that detects the exhaust temperature upstream of the bypass passage 5 of the exhaust pipe 2 and an actuator 6b, and when the exhaust temperature is below a predetermined value, the exhaust gas is directly transferred to the oxidation catalyst 3 via the bypass passage 5. The exhaust gas is made to flow through the S02 trap 4 only when the exhaust gas temperature reaches a predetermined value or higher. This is because when the exhaust temperature is low, the activity of the oxidation catalyst is low and no sulfate is generated even if the exhaust gas containing SO□ is passed directly through the oxidation catalyst 3, so there is no need to use the SO□ trap 4. The temperature at which sulfate generation starts varies depending on the catalyst, but is approximately 250°C, and in this example, when the exhaust temperature reaches 250°C or higher, the 5o2 trap 4
Exhaust gas is allowed to flow to the side. In this way, by using the S02 trap only under the specified exhaust temperature conditions, the service life of the S02 trap can be extended, and while the exhaust temperature is low, the exhaust air can be used without passing through the SO□ trap 4. Burmese, which can be operated with little resistance.
This has the advantage of improving engine fuel efficiency.

Next, a test conducted on the particulate removal effect when using the exhaust purification device according to the present invention will be described.

[1] Traps A1 and B manufactured by the following method were used as S-port 2 traps S [12].

(1) SO2 trap A: A T-alumina coating layer was formed on the surface of a cordierite monolith carrier with a volume of 1.7β using a slurry consisting of T-alumina powder, alumina zone aluminum nitrate, and distilled water.
After drying for an hour, it was fired at 700° C. for 2 hours to obtain a T-alumina coat layer of 120 g per 11 carrier volumes.

Next, the above carrier was immersed in a copper nitrate solution whose concentration was adjusted so that 20 g of copper was supported per carrier volume 1β, the carrier was pulled up, excess droplets were blown off, and then dried at 300°C for 2 hours.
Baked for an hour.

As a result, a 5o2 trap A was obtained which supported 120 g of T-alumina layer and 20 g of copper per carrier volume 1β.

(2) SO. Trap B: A cordierite monolith carrier with a volume of 1.71 was prepared in the same manner as SO□Trap A.
) was formed with a T-alumina coating layer of 120 g per 1 p of the carrier volume, immersed in a nickel nitrate solution whose concentration was adjusted so that 20 g of nickel was supported per 1 p of the carrier volume, and then pulled up to remove excess droplets. After blowing off, it was dried and baked at 300°C for 2 hours.

This results in SO supporting 120 g of γ-alumina layer and 20 g of nickel per 11 carrier volumes. I got Trap B.

[2] Oxidation Catalyst Oxidation Catalyst C and Oxidation Catalyst R produced by the following method were used as oxidation catalysts.

(1) Oxidation catalyst C: A T-alumina layer in an amount of 120 g per 11 carrier volume was formed on a cordierite monolith carrier with a volume of 1.7 β in the same manner as 802 traps A and B.
This carrier was immersed in a dinitrodiamine platinum solution whose concentration was adjusted so that 1 g of platinum was supported per 11 carrier volumes, and then the excess droplets were blown off and calcined at 300° C. for 2 hours.

As a result, an oxidation catalyst C was obtained which supported 120 g of γ-alumina layer and 1 g of platinum per 11 carrier volumes.

(2> Oxidation catalyst D: A TiO□ layer was formed on the surface of a cordierite monolith carrier with a volume of 1.71 using a slurry consisting of TiO□ powder and TiO□ Zonope distilled water,
After drying at ℃ for 2 hours, baking at 700℃ for 2 hours to reduce the carrier volume to 1
120 g of TiO2 coating layer was obtained.

Next, the above-mentioned carrier was immersed in an ammonium metavanadate solution whose concentration was adjusted so that 20 g of V2O5 was supported per 1β of the carrier volume, and then dried and fired.

Further, this carrier was immersed in a dinitrodiamine platinum solution whose concentration was adjusted so that 1 g of platinum was supported per 1β of the carrier volume, and then dried and fired.

Correniyori N body volume 1 fl corresponding Tio□120 g
A catalyst supporting 520 g of SV2O and 1 g of platinum was obtained.

[3] Test method (1) 2nd TI on the exhaust system of a 2400 cc swirl chamber diesel engine! As shown in J, the bypass passage 5 and the three-way switching valve 6 were installed, and the above-mentioned oxidation catalyst C1 was used as the oxidation catalyst 3, and the above-mentioned S was used as the trap 4.
When O□ traps A1 and B were used, the amount of particulates was measured at two locations: the engine outlet and the oxidation catalyst outlet. In addition, the exhaust temperature of the three-way switching valve 6 is 250°C.
In the following, the exhaust gas was set to flow bypassing the SO□ trap 4.

Furthermore, as a comparative example, the oxidation catalyst 4 was used without using SO or a trap.
Measurements were made for oxidation catalysts C and D using only oxidation catalysts C and D.

At this time, the three-way switching valve 6 was locked so that the S02 trap 4 was always bypassed and the exhaust gas was directly supplied to the oxidation catalyst. The above test conditions are summarized as follows.

S02 trap Oxidation catalyst test IA C Test 2B C Comparative example 1 Not used C Comparative example 2 Not used D (2) The operating mode of the diesel engine used in the test is shown in FIG. Diesel engine speed is 2ooor
The exhaust temperature is changed by load adjustment, assuming that the pm is constant. The exhaust gas temperature is increased stepwise from 100° C. to 450° C. at 5 minute intervals as shown in the figure. Although not shown, after 30 minutes, the exhaust temperature was lowered stepwise to be symmetrical to the mode shown, and the operation was performed for a total of 1 hour.

[4] Test Results Figure 4 shows the measurement results obtained when the machine was operated in the above mode for one hour.

In Test 1.2 using the SO□ trap, it can be seen that the amount of particulates was reduced by about 50% compared to the engine outlet. Furthermore, in Comparative Example 1, the amount of particulates increased by more than twice that at the engine outlet, indicating that S03 was generated by the oxidation catalyst C. Furthermore, in Comparative Example 2, as a result of imparting selectivity to the catalyst, although SO3 was not produced, the oxidizing power of the catalyst was reduced, and the particulate reduction effect was also reduced.

〔Effect of the invention〕

The exhaust purification device of the present invention is equipped with an SO□ trap upstream of the oxidation catalyst to remove SO and components from the exhaust gas in advance, thereby preventing sulfate generation in the oxidation catalyst and emitting exhaust particulates into the atmosphere. It has the effect of reducing the amount.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a first embodiment of the exhaust gas purification device according to the present invention, FIG. 2 is a schematic diagram showing the configuration of the second embodiment of the exhaust gas purification device according to the present invention, and FIG. The figure shows the exhaust gas temperature during the test of the above exhaust gas purification device, and FIG. 4 shows the test results. l...Diesel engine, 2...Exhaust pipe, 3...
・Oxidation catalyst, 4...S02 trap, 5
...Bypass passage, 6...Three-way switching valve, 6a
... Temperature sensing part, 6b... Actuator. Time (minutes) Figure 3 1 Figure 4

Claims (1)

[Claims] 1. In a diesel engine exhaust purification device in which an oxidation catalyst for purifying hydrocarbon components in exhaust gas is provided in the exhaust gas passage, S in the exhaust gas is disposed in the exhaust gas passage upstream of the oxidation catalyst.
An exhaust gas purification device for a diesel engine, characterized in that an SO_2 trap supporting activated alumina and base metals for collecting O_2 components is provided.