JP5698002B2 - Exhaust purification equipment - Google Patents

Description

  The present invention relates to an exhaust purification device using a NOx storage reduction catalyst.

  Conventionally, in diesel engines, when the exhaust air-fuel ratio is lean, NOx in the exhaust gas is oxidized and temporarily stored in the form of nitrate, and when the oxygen concentration in the exhaust gas decreases, unburned HC, CO, etc. A NOx occlusion reduction catalyst having the property of decomposing and releasing NOx through the intervention of the catalyst to reduce and purify is provided in the middle of the exhaust pipe, and this NOx occlusion reduction catalyst is used to reduce the NOx emission concentration.

  However, in the NOx occlusion reduction catalyst, if the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded, so the oxygen concentration of the exhaust gas that periodically flows into the NOx occlusion reduction catalyst Needs to be reduced by a reducing agent such as HC to decompose and release NOx.

  For example, when used in a gasoline engine, by reducing the operating air-fuel ratio of the engine (operating the engine at a rich air-fuel ratio), the oxygen concentration in the exhaust gas is reduced and unburned HC in the exhaust gas is reduced. Although it is possible to promote the decomposition and release of NOx by increasing the reducing components such as CO, it is difficult to operate the engine at a rich air-fuel ratio when the NOx occlusion reduction catalyst is used as an exhaust purification device of a diesel engine. .

  Therefore, by adding fuel to the exhaust gas upstream of the NOx storage reduction catalyst, the added fuel is used as a reducing agent to react with oxygen on the NOx storage reduction catalyst, thereby reducing the oxygen concentration in the exhaust gas. There is a need (see, for example, Patent Document 1).

JP 2002-81111 A

However, in the exhaust gas of the diesel engine, SO ₂ gas (sulfurous acid gas) derived from sulfur contained in the light oil of the fuel is present, so this SO ₂ gas is combined with NOx on the NOx storage reduction catalyst. Similarly, it is unavoidable that it is oxidized and occluded as a sulfate, but since this sulfate is more stable than nitrate, even if fuel addition is performed to regenerate the NOx occlusion reduction catalyst, the NOx As a result of the fact that only a part of the sulfate stored in the storage reduction catalyst is released and remains, there is a problem that the recovery rate of the NOx storage site of the NOx storage reduction catalyst is reduced and the storage capacity is reduced. In reality, no practical solution has yet been established for the problem of residual sulfate.

That is, the method of desorbing sulfate from the NOx occlusion reduction catalyst itself involves increasing the catalyst bed temperature of the NOx occlusion reduction catalyst to a desulfurization temperature condition of about 600 to 700 ° C. It is already known that the NOx occlusion reduction catalyst can be desulfurized by releasing sulfate as SO ₂ gas from the SOx, but the SOx that has been stored in the NOx occlusion reduction catalyst over time during the desulfurization treatment There is a problem that a high concentration of SO ₂ gas is generated by releasing _two gases at once, and the generation of this high concentration of SO ₂ gas greatly hinders the practical use of the NOx storage reduction catalyst desulfurization treatment. It was a factor.

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust emission control device that prevents high-concentration SO ₂ gas from being generated during the desulfurization treatment of the NOx storage reduction catalyst.

The present invention provides an exhaust gas purification apparatus provided with a NOx storage reduction catalyst in the middle of an exhaust pipe so that fuel can be added to the inlet side of the NOx storage reduction catalyst. An oxidation catalyst for reacting SO ₂ gas contained in the exhaust gas with water vapor to form sulfate is disposed, and the temperature of the exhaust gas during the desulfurization treatment is set between the oxidation catalyst and the NOx storage reduction catalyst. A mist that captures the mist of the sulfate by forming a ventilating structure having a rough opening immediately after the oxidation catalyst, with a connecting pipe having a required length for reducing the SO ₂ gas to a temperature range that can be sulfated by the oxidation catalyst. A catcher is provided.

Thus, when desulfurization treatment is performed on the NOx storage reduction catalyst, if fuel is added to the inlet side of the NOx storage reduction catalyst, the added fuel reacts with oxygen on the NOx storage reduction catalyst, so that the surrounding exhaust gas As a result, the catalyst bed temperature is raised to the desulfurization temperature condition by the reaction heat, and the sulfate is released as SO ₂ gas from the NOx storage reduction catalyst.

The SO ₂ gas released from the NOx storage reduction catalyst decreases in temperature while passing through the connecting pipe, reaches the oxidation catalyst, reacts with water vapor in the exhaust gas on the oxidation catalyst, becomes sulfate mist, and is oxidized. Since it is captured and held by the mist catcher immediately after the catalyst, it is possible to prevent a situation in which a high concentration of SO ₂ gas is collected and released outside the vehicle during the desulfurization process of the NOx storage reduction catalyst.

  Furthermore, in the present invention, it is preferable that the oxidation catalyst also serves as an HC anti-slip catalyst for oxidizing HC remaining in the exhaust gas. In this case, it is not necessary to separately provide an HC anti-slip catalyst. The overall configuration can be made compact.

  Further, in the present invention, it is preferable that the mist catcher is made of a metal material capable of reacting with sulfate to form a sulfide, and in this way, the mist catcher is caught by the mist catcher and the mist catcher is formed. By reacting with the catcher, a sulfide is formed, and it is held as it is as a part of the mist catcher.

  In addition, as the mist catcher becomes more difficult to take in the sulfate mist as sulfide as the sulfidation by the mist of the sulfate progresses, the mist catcher has been sufficiently sulfidized to become a sulfide as a whole. And replace it with a new mist catcher.

Furthermore, in the present invention, it is preferable that the oxidation catalyst contains zeolite or magnesia as a catalyst raw material so that the SO ₂ gas can be adsorbed, and in this way, the oxidation treatment cannot be performed with the oxidation catalyst during the desulfurization treatment. Even if this amount of SO ₂ gas is released from the NOx occlusion reduction catalyst, part of the SO ₂ gas is temporarily adsorbed by the oxidation catalyst, and the emission of SO ₂ gas to the outside of the vehicle is suppressed.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

(I) According to the invention described in claim 1 of the present invention, the temperature of SO ₂ gas released from the NOx storage reduction catalyst during the desulfurization treatment is lowered while passing through the connecting pipe, and the exhaust gas is exhausted on the oxidation catalyst. steam and reacted by the mist of sulfate, because the mist of the sulphates can be held caught by the mist catcher immediately after the oxidation catalyst, high concentration of sO ₂ gas is generated during desulfurization of the NOx storage-reduction catalyst Can solve the problem.

  (II) According to the invention described in claim 2 of the present invention, it is not necessary to separately provide an HC slip prevention catalyst for oxidizing HC remaining in the exhaust gas. As a result, the overall configuration can be made compact, and the mountability on the vehicle can be greatly improved.

(III) According to the invention described in claim 3 of the present invention, it can be held as a sulfide immediately reacted with the mist catcher mist sulfates caught in the mist catcher, high concentration of SO ₂ gas It is possible to more reliably prevent a situation in which they are gathered and discharged outside the vehicle.

(IV) According to the invention described in claim 4 of the present invention, even if an amount of SO ₂ gas that cannot be oxidized by the oxidation catalyst during the desulfurization treatment is released from the NOx storage reduction catalyst, the SO ₂ gas it is possible to temporarily adsorbed to the oxidation catalyst part of suppressing the discharge of the outside of the sO ₂ gas, more reliably prevent the would be released to the outside of the vehicle together with high concentrations of sO ₂ gas can do.

It is the schematic which shows an example of the form which implements this invention. It is the schematic which shows another form example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In the exhaust purification apparatus of this embodiment, the exhaust pipe 4 through which the exhaust gas 3 discharged from the diesel engine 1 through the exhaust manifold 2 flows is shown. In addition, a NOx occlusion reduction catalyst 5 having a flow-through type honeycomb structure is mounted and mounted on a casing 6, and fuel 8 (light oil) in a light oil tank 7 is supplied to a gas oil pump at an inlet portion of the casing 6. A fuel addition injector 10 is provided for injecting through 9.

  In the example shown here, a catalyst-carrying particulate filter 11 (supporting an NOx occlusion reduction catalyst if necessary) is formed after the NOx occlusion reduction catalyst 5 in the casing 6 and carrying an oxidation catalyst. The particulate matter contained in the exhaust gas 3 that has passed through the NOx occlusion reduction catalyst 5 in the previous stage can be collected to further purify the exhaust gas.

Further, a casing 12 is connected to the downstream side of the casing 6 via a long connecting pipe 13, and the front stage side in the casing 12 has SO 2 contained in the exhaust gas 3 during the desulfurization process. An oxidation catalyst 14 for sulfating by reacting _two gases with water vapor is disposed.

Here, it is possible to transfer and divert the HC slip prevention catalyst that has been arranged in the final stage in the casing 6 so far to the oxidation catalyst 14, and it remains in this kind of exhaust gas 3. Even if the HC anti-slip catalyst for oxidizing HC is used as it is, it is possible to exhibit the function of reacting the SO ₂ gas contained in the exhaust gas 3 during the desulfurization treatment with water vapor to form sulfate.

However, when the oxidation catalyst 14 is newly installed, it is preferable to include zeolite or magnesia as a catalyst raw material so that SO ₂ gas can be adsorbed. By doing so, the oxidation catalyst 14 cannot be oxidized at the time of the desulfurization treatment. Even if a moderate amount of SO ₂ gas is released from the NOx occlusion reduction catalyst 5, a part of the SO ₂ gas is temporarily adsorbed on the oxidation catalyst 14 and the emission of SO ₂ gas to the outside of the vehicle is suppressed. become.

Further, the long connecting pipe 13 described above is set to such a length that the temperature of the exhaust gas 3 during the desulfurization treatment can be lowered to a temperature range in which the SO ₂ gas can be sulfated by the oxidation catalyst 14. Specifically, since the temperature of the exhaust gas 3 at the time of the desulfurization treatment is about 600 to 700 ° C., the temperature can be sufficiently reduced to about 500 ° C. or less at which the SO ₂ gas can be sulfated by the oxidation catalyst 14. However, since the 100% purification temperature of HC is 350 ° C. or higher, it is necessary to keep the length so that at least the oxidation catalyst 14 can maintain a temperature not lower than 350 ° C. during the desulfurization process.

  Further, on the rear stage side in the casing 12, an iron-based metal (metal material) is used as a mist catcher that forms a coarse ventilation structure to capture a sulfate mist described later and react with the mist to form a sulfide. A pair of mist catch plates 15 and a metal mesh filter 16 made of iron-based metal sandwiched between the mist catch plates 15 are arranged. The mist catch plate 15 and the metal mesh filter 16 are It is preferable that the entire structure including the casing can be replaced with a cartridge.

  Each mist catch plate 15 has a ventilation structure made of punched metal, and the holes between the front and rear mist catch plates 15 are arranged alternately so that the exhaust gas 3 passes straight. I can't do that.

Thus, with regard to the exhaust purification apparatus configured as described above, when performing a desulfurization treatment in which the sulfate stored in the NOx occlusion reduction catalyst 5 is released as SO ₂ gas, the NOx occlusion reduction catalyst 5 is placed on the inlet side. When the fuel 8 is added from the fuel addition injector 10, the added fuel 8 reacts with oxygen on the NOx occlusion reduction catalyst 5, thereby reducing the oxygen concentration in the surrounding exhaust gas 3 and the heat of reaction causes the catalyst bed temperature. Is raised to the desulfurization temperature condition, and the sulfate is released from the NOx occlusion reduction catalyst 5 as SO ₂ gas.

The SO ₂ gas released from the NOx occlusion reduction catalyst 5 decreases in temperature while passing through the connecting pipe 13 and reaches the oxidation catalyst 14, and reacts with the water vapor in the exhaust gas 3 on the oxidation catalyst 14. It becomes sulfate mist, is caught by the mist catch plate 15 and the metal mesh filter 16 immediately after the oxidation catalyst 14 and reacts with the mist catch plate 15 and the metal mesh filter 16 to form sulfide, and the mist catch plate 15 as it is. As a result, the high-concentration SO ₂ gas is prevented from being released to the outside of the vehicle during the desulfurization process of the NOx storage reduction catalyst 5.

  The mist catch plate 15 and the metal mesh filter 16 are difficult to take in the sulfate mist as sulfides as the sulfidation of the sulfate mist progresses. It is sufficient to replace the mist catch plate 15 and the metal mesh filter 16 with new mist catch plates when the process has sufficiently progressed to become sulfides.

Therefore, according to the above embodiment, the temperature of the SO ₂ gas released from the NOx occlusion reduction catalyst 5 during the desulfurization process is lowered while passing through the connecting pipe 13, and reacts with the water vapor in the exhaust gas 3 on the oxidation catalyst 14. The sulfate mist is captured by the mist catch plate 15 and the metal mesh filter 16 immediately after the oxidation catalyst 14, and reacted with the mist catch plate 15 and the metal mesh filter 16 to be held as sulfide. Therefore, it is possible to reliably prevent a situation in which high concentration SO ₂ gas is collected and released to the outside of the vehicle.

  Particularly in the present embodiment, the oxidation catalyst 14 also serves as an HC slip prevention catalyst for oxidizing HC remaining in the exhaust gas 3, so that it is not necessary to separately provide an HC slip prevention catalyst, and the overall configuration can be made compact. As a result, the mountability on the vehicle can be greatly improved.

In addition, if zeolite or magnesia is included in the oxidation catalyst 14 as a catalyst raw material so that SO ₂ gas can be adsorbed, an amount of SO ₂ gas that cannot be oxidized by the oxidation catalyst 14 during the desulfurization process is reduced by NOx storage reduction. Even if released from the catalyst 5, a part of the SO ₂ gas can be temporarily adsorbed on the oxidation catalyst 14 and the exhaust of the SO ₂ gas to the outside of the vehicle can be suppressed, so that a high concentration of SO ₂ gas is collected. Thus, it is possible to more reliably prevent a situation where the product is discharged outside the vehicle.

FIG. 2 shows another embodiment of the present invention. In this embodiment, the HC slip prevention catalyst 17 is left in the final stage in the casing 6 as before, but is shown here. As shown in the figure, when a configuration in which the oxidation catalyst 14, the mist catch plate 15 and the metal mesh filter 16 are connected to the downstream side of the existing configuration through the connection pipe 13 is adopted, the existing equipment is simply modified. It is possible to solve the problem that a high concentration of SO ₂ gas is generated during the desulfurization process simply by applying.

The exhaust emission control device of the present invention is not limited to the above-described embodiment. It is also possible to configure the mist catcher with only a plurality of mist catch plates and omit the metal mesh filter. In addition, an oxidation catalyst that oxidizes NO in the exhaust gas to NO ₂ and assists the storage in the NOx occlusion reduction catalyst may be additionally provided before the NOx occlusion reduction catalyst, if necessary. Of course, various changes can be made without departing from the scope of the invention.

3 exhaust gas 4 exhaust pipe 5 NOx occlusion reduction catalyst 8 fuel 10 fuel addition injector 13 communication pipe 14 oxidation catalyst 15 mist catch plate (mist catcher)
16 Metal mesh filter (mist catcher)
17 HC anti-slip catalyst

Claims (4)

In an exhaust gas purification apparatus provided with a NOx occlusion reduction catalyst in the middle of an exhaust pipe so that fuel can be added to the inlet side of the NOx occlusion reduction catalyst, in the exhaust gas at the time of desulfurization treatment downstream of the NOx occlusion reduction catalyst An oxidation catalyst for reacting the SO ₂ gas contained in the catalyst with water vapor to form a sulfate is disposed, and the temperature of the exhaust gas during the desulfurization treatment is set between the oxidation catalyst and the NOx storage reduction catalyst by the oxidation catalyst. A connecting pipe of a required length that reduces the SO ₂ gas to a temperature range that can be sulfated is interposed, and immediately after the oxidation catalyst, a mist catcher is provided that forms a coarse air vent structure and catches sulfate mist. An exhaust purification device characterized by that.   2. The exhaust emission control device according to claim 1, wherein the oxidation catalyst also serves as an HC slip prevention catalyst that oxidizes HC remaining in the exhaust gas.   The exhaust purification device according to claim 1 or 2, wherein the mist catcher is made of a metal material capable of reacting with sulfate to form a sulfide. The exhaust emission control device according to claim 1, 2, or 3, characterized in that zeolite or magnesia is contained as a catalyst raw material so that the oxidation catalyst can adsorb SO ₂ gas.

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