JP5188477B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification device that purifies harmful substances in exhaust gas.

  Exhaust gas discharged from the engine contains harmful substances such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). For this reason, an exhaust gas purification device, a diesel oxidation catalyst (DOC), and a diesel particulate filter (having a catalyst in which an active component and an additive component are supported on a carrier are disposed in an exhaust passage to convert a harmful material into a harmless material by a chemical reaction) DPF) is disposed in the exhaust passage, and an exhaust purification device that continuously collects and removes PM has been put into practical use. One example of such an exhaust purification device is described in “three-way catalyst” described in Japanese Patent Application Laid-Open No. 2009-114994 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2000-27627 (Patent Document 2). "Urea SCR (Selective Catalytic Reduction) catalyst", "Continuous regeneration type DPF" described in JP-A-2002-339733 (Patent Document 3), and the like.

JP 2009-114994 A JP 2000-27627 A JP 2002-339733 A

  By the way, in an exhaust gas purification apparatus using a chemical reaction, in order to efficiently purify harmful substances, at least an active component must be activated, and the temperature of the catalyst (catalyst temperature) is maintained above the activation temperature. There is a need. However, since the heat is radiated to the atmosphere from the peripheral wall of the exhaust passage where the catalyst is disposed, for example, when the outside air temperature is low such as in winter, the catalyst temperature does not reach the activation temperature or the catalyst temperature rises to the activation temperature. Without this, the required exhaust purification performance may not be exhibited.

  Therefore, in view of the problems of the prior art, an object of the present invention is to provide an exhaust purification device that suppresses a decrease in catalyst temperature by allowing exhaust to pass around the catalyst.

For this reason, in the present invention, the casing is inserted only in a straight line along the axial direction of the casing, so that a gap is formed between the bottomed cylindrical casing having one end opened and the inner peripheral surface and the bottom surface of the casing. The catalyst is in contact with the inner peripheral surface of the casing, the opening of the casing is closed, the exhaust introduction path for introducing exhaust gas into the gap located between the inner peripheral surface of the casing and the catalyst, and the opening side of the casing At least one basic unit that covers the end face of the catalyst and has a cap formed with exhaust exhaust passages for exhausting exhaust that has passed through the catalyst to the outside is disposed in the exhaust passage.

  According to the present invention, in the basic unit, the exhaust gas introduced into the inside from the exhaust introduction passage of the cap passes through the gap located between the inner peripheral surface of the casing and the catalyst and goes to the innermost part of the casing. It flows. The exhaust gas flowing to the innermost part of the casing is folded back at the bottom surface of the casing, and the entire amount flows into the catalyst. The exhaust gas that has passed through the catalyst is led out through the exhaust lead-out passage of the cap. Therefore, the exhaust gas passes around the catalyst, and the amount of heat released from the peripheral wall of the casing into the atmosphere is reduced, so that a so-called “heat insulation structure” is realized. And since the heat dissipation from a basic unit is suppressed, the fall of catalyst temperature can be suppressed.

Overall configuration diagram showing a first embodiment of an exhaust purification device Perspective view showing details of basic unit The perspective view which shows the connection state of a basic unit Explanatory drawing of an effect | action and effect of the exhaust gas purification apparatus which concerns on 1st Embodiment. Partial sectional view showing the main part of the second embodiment of the exhaust emission control device Partial sectional view showing the main part of the third embodiment of the exhaust emission control device Explanatory drawing of the modification of the method of inserting the catalyst with respect to the casing

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of an exhaust purification device that uses an aqueous urea solution as a precursor of a liquid reducing agent and selectively reduces and purifies NOx contained in exhaust gas from a diesel engine (hereinafter referred to as “engine”).

An exhaust pipe 14 (exhaust passage) connected to the exhaust manifold 12 of the engine 10 includes a DOC 16 that oxidizes nitrogen monoxide (NO) into nitrogen dioxide (NO ₂ ) along the exhaust flow direction, and an aqueous urea solution. An SCR catalyst 18 for selectively reducing and purifying NOx upon receipt of the generated ammonia, and an ammonia oxidation catalyst 20 for oxidizing the ammonia that has passed through the SCR catalyst 18 are arranged in this order.

As a method of disposing the DOC 16, the SCR catalyst 18 and the ammonia oxidation catalyst 20 in the exhaust pipe 14, a basic unit 22 as shown in FIG. 2 is used.
That is, the basic unit 22 includes the DOC 16, the SCR catalyst 18 or the SCR catalyst 18 inserted (stored) so that a gap is formed between the bottomed cylindrical casing 24 whose one end is open and the inner peripheral surface and the bottom surface of the casing 24. The ammonia oxidation catalyst 20 (hereinafter referred to as “catalyst 26” unless otherwise specified) and a cap 28 that closes the opening of the casing 24 are included. The cap 28 covers an exhaust introduction path 28 </ b> A for introducing exhaust into a gap located between the inner peripheral surface of the casing 24 and the catalyst 26, and an end face of the catalyst 26 located on the opening side of the casing 24. An exhaust lead-out path 28B for leading the exhaust that has passed through to the outside is formed. The exhaust introduction path 28A of the cap 28 is preferably a simple “opening” in order to facilitate the formation thereof. Further, the cross sections of the casing 24 and the catalyst 26 are not limited to the substantially circular shape shown in the figure, and may be, for example, each round rectangle.

  Here, the gaps located between the inner peripheral surface and the bottom surface of the casing 24 and the catalyst 26 function as a part of the exhaust passage. Further, considering that a plurality of basic units 22 are connected, it is desirable that the exhaust outlet of the exhaust lead-out path 28 </ b> B is located at a position corresponding to the exhaust inlet of the exhaust introduction path 28 </ b> A of the other basic unit 22. Further, if the catalyst 26 is inserted so as to contact a part of the inner peripheral surface of the casing 24 and the catalyst 26 is fixedly supported with respect to the casing 24 at this contact location, for example, the catalyst 26 is fixedly supported. A stay or the like is not necessary, and the number of parts can be reduced.

  The three basic units 22 interpolating the DOC 16, the SCR catalyst 18, and the ammonia oxidation catalyst 20 connect the exhaust lead-out path 28B of one basic unit 22 to the exhaust introduction path 28A of the other basic unit 22, As shown in FIG. 3, it becomes compact as a whole.

  In addition, a temperature sensor 30 for measuring the temperature of exhaust gas (exhaust temperature) is provided in an exhaust passage located between the DOC 16 and the SCR catalyst 18, specifically, a cap 28 of the basic unit 22 in which the DOC 16 is inserted, An injection nozzle 32 that supplies the urea aqueous solution in an atomized state is attached.

  The aqueous urea solution stored in the reducing agent tank 34 is supplied to the injection nozzle 32 via a reducing agent addition device 38 that is electronically controlled by a reducing agent addition control unit (hereinafter referred to as “DCU (Dosing Control Unit)”) 36. Is done. The output signal of the temperature sensor 30 is input to the DCU 36, and an engine control unit (hereinafter referred to as “ECU”) is connected via a CAN (Controller Area Network) or the like so that the rotational speed and load of the engine 10 can be read. ) 40 is connected. Here, as the load of the engine 10, known state quantities such as a fuel injection amount, an accelerator operation amount, a throttle opening, an intake flow rate, an intake negative pressure, a supercharging pressure, and the like can be employed. The rotational speed and load of the engine 10 may be directly detected using a known sensor.

In such an exhaust purification device, the urea aqueous solution injected and supplied from the injection nozzle 32 is hydrolyzed by the exhaust heat and the water vapor in the exhaust to produce ammonia that functions as a reducing agent. It is known that ammonia generated from the urea aqueous solution undergoes a selective reduction reaction with NOx in the exhaust gas in the SCR catalyst 18 and is converted into harmless water (H ₂ O) and nitrogen (N ₂ ). . At this time, in order to improve the NOx purification efficiency in the SCR catalyst 18, NO is oxidized to NO ₂ by the DOC 16, and the ratio of NO and NO ₂ in the exhaust is improved to be suitable for the selective reduction reaction. On the other hand, the ammonia that has passed through the SCR catalyst 18 is oxidized by the ammonia oxidation catalyst 20 disposed downstream of the SCR catalyst 18, so that the ammonia is suppressed from being released into the atmosphere as it is.

  As shown in FIG. 4, the DOC 16, the SCR catalyst 18, and the ammonia oxidation catalyst 20 are prevented from lowering the catalyst temperature when exhaust gas passes through them. That is, in the basic unit 22 in which the DOC 16 is inserted, the exhaust gas introduced from the exhaust gas introduction path 28A of the cap 28 into the basic unit 22 passes through a gap located between the casing 24 and the DOC 16, It flows to the innermost part of the casing 24. The exhaust gas that has flowed to the innermost part of the casing 24 is folded back at the bottom surface of the casing 24, and the entire amount thereof flows into the DOC 16. Exhaust gas that has passed through the DOC 16 passes through the exhaust outlet passage 28B of the cap 28 and flows into the basic unit 22 in which the SCR catalyst 18 is inserted. Then, through a process similar to that of the basic unit 22 in which the DOC 16 is inserted, exhaust gas is discharged into the atmosphere from the exhaust lead-out path 28B of the basic unit 22 in which the ammonia oxidation catalyst 20 is inserted.

  Since the exhaust gas flowing into the basic unit 22 flows through a gap located between the casing 24 and the catalyst 26, the exhaust gas passes around the catalyst 26. For this reason, the presence of exhaust gas around the catalyst 26 reduces the amount of heat released from the peripheral wall of the casing 24 into the atmosphere, thereby realizing a so-called “heat insulation structure”. And since the heat radiation from the basic unit 22 is suppressed, it is possible to suppress a decrease in the catalyst temperature. Therefore, the catalyst temperature of the catalyst 26 is difficult to decrease, and a decrease in NOx purification efficiency can be suppressed.

  The present invention is not limited to an exhaust purification device that selectively reduces and purifies NOx, but a “continuous regeneration type DPF” (see FIG. 5), in which a DOC 16 and a CSF (Catalyzed Soot Filter) 42 are arranged in series, DOC 16, The present invention can also be applied to a “DPF + urea SCR catalyst” (see FIG. 6) in which the CSF 42, the SCR catalyst 18 and the ammonia oxidation catalyst 20 are arranged in series, a “three-way catalyst” of a gasoline engine, and the like. Here, “CSF” is a DPF carrying an active ingredient and an additive ingredient.

  Further, the catalyst 26 may be inserted into the casing 24 so that a cylindrical gap is formed between the catalyst 26 and the inner peripheral surface of the casing 24 as shown in FIG. In this case, a stay or the like for fixing the catalyst 26 to the casing 24 is required. However, the gap located between the inner peripheral surface of the casing 24 and the catalyst 26 has a cylindrical shape. Variations in the exhaust flow velocity passing through the gap are reduced, and the catalyst temperature can be made uniform.

14 Exhaust pipe 16 DOC
18 SCR catalyst 20 Ammonia oxidation catalyst 22 Basic unit 24 Casing 26 Catalyst 28 Cap 28A Exhaust inlet path 28B Exhaust outlet path 42 CSF

Claims (4)

A bottomed cylindrical casing with one end open;
A catalyst that is inserted so that a gap is formed between the inner peripheral surface and the bottom surface of the casing, and that contacts the inner peripheral surface of the casing only in a straight line along the axial direction of the casing ;
The opening of the casing is closed, the exhaust introduction path for introducing exhaust into a gap located between the inner peripheral surface of the casing and the catalyst, and the end face of the catalyst located on the opening side of the casing are covered, Caps each having exhaust outlet passages for exhausting exhaust that has passed through the catalyst to the outside;
An exhaust emission control device characterized in that at least one basic unit having the above is disposed in the exhaust passage. A plurality of the basic units are provided,
The exhaust emission control device according to claim 1 , wherein the exhaust lead-out path of one basic unit is connected to the exhaust introduction path of another basic unit . The exhaust emission control device according to claim 1 or 2, wherein the exhaust introduction path includes an opening formed in the cap . 4. The exhaust lead-out path of one basic unit is formed at a position corresponding to the exhaust lead-in path of another basic unit in a state where a plurality of the basic units are arranged in parallel. The exhaust emission control device according to any one of the above.

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