Exhaust gas purification device

Abstract

To provide an exhaust gas purification device capable of more effectively suppressing a NOx emission at low temperature.SOLUTION: An exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine, comprises, in order from an upstream side of an exhaust gas flow direction in an exhaust pipe, a first selective reduction catalyst, a NOx adsorption catalyst, and a second selective reduction catalyst.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an exhaust gas purification device.

Background Art

[0002] In response to existing exhaust gas regulations, in an exhaust gas purification device, a configuration in which a DOC (Diesel Oxidation Catalyst), a DPF (Diesel Particulate Filter), and an SCR (Selective Catalytic Reduction) catalyst are arranged in order from the upstream side of the exhaust gas is widely adopted (see, for example, Patent Document 1).

[0003] Although temperature is required for the activation of the SCR catalyst used for NOx purification, in the upcoming higher-order exhaust gas regulations, it is required to suppress the NOx emission amount at low temperatures. However, in the above configuration, there is a problem that a temperature sufficient for the activation of the SCR catalyst cannot be obtained.

[0004] Therefore, a configuration in which an SCR catalyst is added upstream of the DOC (see FIG. 2 described later) has been devised for the above configuration and is partially mass-produced.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, even in a configuration in which an SCR catalyst is added upstream of the DOC, there is a problem that the SCR catalyst is not activated in an extremely low temperature range, and thus the NOx emission amount cannot be effectively suppressed.

[0007] An object of one aspect of the present disclosure is to provide an exhaust gas purification device capable of more effectively suppressing NOx emissions at low temperatures.

Means for Solving the Problems

[0008] An exhaust gas purification device according to one aspect of the present disclosure is an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine, and includes a first selective reduction type catalyst, a NOx adsorption catalyst, and a second selective reduction type catalyst in order from the upstream side in the flow direction of the exhaust gas in the exhaust pipe.

Effects of the Invention

[0009] According to the present disclosure, NOx emissions at low temperatures can be more effectively suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] First, the configuration of the exhaust gas purification device 100 according to the present embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing the configuration of the exhaust gas purification device 100.

[0013] The exhaust gas purification device 100 is, for example, mounted on a vehicle (not shown) and purifies the exhaust gas discharged from its internal combustion engine (not shown). In the present embodiment, a diesel engine is assumed as the internal combustion engine, but it is not limited thereto. Further, the exhaust gas purification device 100 may be applied not only to the internal combustion engine of a vehicle but also to, for example, the internal combustion engine of a ship or a stationary type.

[0014] The upstream side (left side in the figure) of the exhaust pipe 10 is connected to the downstream side of an exhaust manifold (not shown) connected to the internal combustion engine or the outlet side of the turbine housing (not shown) of a turbocharger. In FIG. 1, the exhaust gas flows through the exhaust pipe 10 from the left side to the right side in the figure (see the arrow in the figure) and is finally discharged to the outside of the vehicle.

[0015] In the exhaust pipe 10, a catalytic converter 20 and a catalytic converter 30 are provided in order from its upstream side. The catalytic converter may also be referred to as a "catalyst canning" or a "catalyst case".

[0016] In the catalytic converter 20, an SCR catalyst 1 and an ASC (Ammonia Slip Catalyst) 2 are provided in order from its upstream side.

[0017] In the catalytic converter 30, a NOx adsorption catalyst 3, a DPF 4, an SCR catalyst 1, and an ASC 2 are provided in order from its upstream side.

[0018] The SCR catalyst 1 adsorbs ammonia generated by the hydrolysis of aqueous urea as a reducing agent and thereby reduces NOx in the exhaust gas to nitrogen and water. The aqueous urea is injected into the catalytic converters 20 and 30 by an aqueous urea injection device (not shown) provided on the upstream side of the SCR catalyst 1. The injected aqueous urea is hydrolyzed to ammonia by the heat of the exhaust gas.

[0019] The ASC 2 oxidizes and decomposes ammonia that could not be completely consumed by the SCR catalyst 1. Thereby, it is possible to prevent ammonia from being discharged into the atmosphere.

[0020] The NOx storage catalyst 3 has the characteristic that its NOx storage capacity is large when the catalyst temperature is low, and the NOx storage capacity decreases as the catalyst temperature rises. Therefore, the NOx storage catalyst 3 adsorbs NOx in the exhaust gas in a situation where the temperature of the exhaust gas is low, and releases the adsorbed NOx as the temperature of the exhaust gas rises.

[0021] The DPF 4 collects particulate matter in the exhaust gas.

[0022] Note that the SCR catalyst 1 in the catalytic converter 20 is an example of a "first selective reduction type catalyst", and the SCR catalyst 1 in the catalytic converter 30 is an example of a "second selective reduction type catalyst". Also, the ASC 2 in the catalytic converter 20 is an example of a "first ammonia slip catalyst", and the ASC 2 in the catalytic converter 30 is an example of a "second ammonia slip catalyst". Further, the DPF 4 is an example of a "particulate collection filter".

[0023] The configuration of the exhaust gas purification device 100 of the present embodiment has been described above.

[0024] Next, the configurations 101 to 103 of the exhaust gas purification devices that are comparative examples of the exhaust gas purification device 100 of the present embodiment will be described with reference to FIGS. 2 to 4. In FIGS. 2 to 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and their detailed descriptions will be omitted below.

[0025] FIG. 2 is a schematic diagram showing the configuration of the exhaust gas purification device 101 as Comparative Example 1. The exhaust gas purification device 101 in FIG. 2 is different from the exhaust gas purification device 10 in FIG. 1 in that it includes a DOC 5 (an example of an oxidation catalyst) instead of the NOx storage catalyst 3 in the catalytic converter 30. The DOC 5 decomposes and removes hydrocarbons and carbon monoxide in the exhaust gas.

[0026] FIG. 3 is a schematic diagram showing the configuration of the exhaust gas purification device 102 as Comparative Example 2. The exhaust gas purification device 102 in FIG. 3 is different from the exhaust gas purification device 10 in FIG. 1 in that it does not include the catalytic converter 20 itself.

[0027] FIG. 4 is a schematic diagram showing the configuration of the exhaust gas purification device 103 as Comparative Example 3. The exhaust gas purification device 103 in FIG. 4 is different from the exhaust gas purification device 10 in FIG. 1 in that a NOx adsorption catalyst 3 is provided upstream of the SCR catalyst 1 in the catalyst converter 20, and a DOC 5 is provided in the catalyst converter 30 instead of the NOx adsorption catalyst 3.

[0028] The configurations of the exhaust gas purification devices 101 to 103 of Comparative Examples 1 to 3 have been described above.

[0029] The exhaust gas purification device 100 and the exhaust gas purification device 103 have a configuration in which a NOx adsorption catalyst 3 is added to the exhaust gas purification device 101.

[0030] Here, when the exhaust gas purification device 100 and the exhaust gas purification device 103 are compared, for the following reasons 1 and 2, the exhaust gas purification device 100 can suppress the NOx emission amount more effectively than the exhaust gas purification device 103.

[0031] (Reason 1) In the exhaust gas purification device 103, since the exhaust gas flowing into the NOx adsorption catalyst 3 becomes high temperature compared to the exhaust gas purification device 100, before the SCR catalyst 1 is activated, the NOx adsorption capacity decreases and the release of NOx starts.

[0032] (Reason 2) Even at low temperatures, the NOx purification amount of the SCR catalyst 1 on the upstream side (inside the catalyst converter 20) is not zero. The NOx adsorption capacity of the NOx adsorption catalyst 3 is not so large, and in the exhaust gas purification device 103, the NOx discharged from the internal combustion engine directly flows into the NOx adsorption catalyst 3, resulting in an early capacity over.

[0033] Next, the time change of the NOx emission amount of each of the exhaust gas purification devices 100 to 103 is shown in FIG. 5. In FIG. 5, it is assumed that the higher the elapsed time, the higher the temperature of the exhaust gas.

[0034] Since the exhaust gas purification device 101 does not include the NOx storage catalyst 3, it cannot suppress the NOx emission amount at low temperatures.

[0035] Since the exhaust gas purification device 102 only includes one SCR catalyst 1, it cannot suppress the NOx emission amount after the NOx storage catalyst 3 has exceeded its capacity.

[0036] Since the NOx storage catalyst 3 of the exhaust gas purification device 103 is arranged on the most upstream side, NOx emission has started before the SCR catalyst 1 is activated.

[0037] In the exhaust gas purification device 100, the NOx storage catalyst 3 and the SCR catalyst 1 complement each other, and the NOx emission amount can be reduced the most.

[0038] As described above, the exhaust gas purification device 100 of the present embodiment is an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine, and includes, in order from the upstream side in the exhaust gas flow direction in the exhaust pipe 10, an SCR catalyst 1 (first selective reduction type catalyst), a NOx storage catalyst 3, and an SCR catalyst 1 (second selective reduction type catalyst).

[0039] Due to this feature, when NOx is released in the NOx storage catalyst 3 of the exhaust gas purification device 100 of the present embodiment, the SCR catalyst 1 is activated by the temperature rise of the exhaust gas, and as a result, it is possible to reduce the NOx discharged into the atmosphere. That is, the exhaust gas purification device 100 of the present embodiment can more effectively suppress the NOx emission amount at low temperatures by appropriately arranging the two SCR catalysts 1 and the NOx storage catalyst 3.

[0040] Note that the present disclosure is not limited to the description of the above embodiment, and various modifications are possible without departing from the gist thereof.

Industrial Applicability

[0041] The exhaust gas purification device of the present disclosure is useful for the technology of purifying exhaust gas.

Explanation of Reference Numerals

[0042] 1 SCR catalyst 2 ASC 3 NOx storage catalyst 4 DPF 5 DOC 10 Exhaust pipe 20, 30 Catalytic converter 100 - 103 Exhaust gas purification device

Claims

1. An exhaust gas purification device for purifying exhaust gas discharged from an internal combustion engine, comprising, in order from the upstream side in the flow direction of the exhaust gas in the exhaust pipe, a first selective reduction catalyst, a NOx adsorption catalyst, and a second selective reduction catalyst. An exhaust gas purification device.

2. A first ammonia slip catalyst provided on the downstream side of the first selective reduction catalyst and on the upstream side of the NOx adsorption catalyst, and a second ammonia slip catalyst provided on the downstream side of the second selective reduction catalyst. The exhaust gas purification device according to claim 1.

3. Further comprising a particulate collection filter provided on the downstream side of the NOx adsorption catalyst and on the upstream side of the second selective reduction catalyst. The exhaust gas purification device according to claim 1 or 2.

Images