JP4285596B2 - Diesel exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diesel exhaust gas purification device, and more particularly to a purification device that efficiently removes particulate matter floating in exhaust gas of a diesel engine over a wide range from idle to high load. is there.
[0002]
[Prior art]
Regulations on particulate matter (PM) discharged from a diesel engine are strengthened year by year together with nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (HC), and the like. As a result, it is currently impossible to satisfy the regulation value only by improving the engine. Therefore, a technique for reducing the amount of particulate matter collected by the particulate matter filter (DPF) discharged from the engine and released into the atmosphere is being adopted.
[0003]
As conventional particulate matter trapping filters, heat resistance is required due to high temperature of exhaust gas, so monolithic honeycomb wall flow type made of ceramic and fiber type filter made of ceramic or metal fiber There are types.
[0004]
The main component of the particulate matter generally increases the soot component as the diesel engine load increases, and most of the organic matter is soluble organic matter (SOF) during idling or low load operation.
[0005]
[Problems to be solved by the invention]
By the way, when the particulate matter filter collects the particulate matter, the pressure loss increases in proportion to the amount collected. Therefore, it is necessary to regenerate the filter by removing the particulate matter captured by the filter by burning or the like.
[0006]
Various methods have been proposed for regenerating the filter by burning the particulate matter, such as an electric heater heating type, a burner heating type, and a reverse cleaning type. However, these systems have the disadvantage that fuel consumption is deteriorated and the apparatus is enlarged because it is necessary to apply energy from the outside in order to burn the particulate matter. On the other hand, there is a device called a continuous regeneration type DPF, which basically allows the collection of particulate matter and the regeneration of the filter to be carried out continuously with the thermal energy of the exhaust gas. The filter system can be simplified, and there is an advantage that control can be simplified with little deterioration in fuel consumption. Specifically, the following have been proposed.
[0007]
In the NO ₂ regeneration type DPF device shown in FIG. 1, a NO oxidation reactor 1 that oxidizes nitric oxide NO to nitrogen dioxide NO ₂ is arranged upstream of the exhaust gas flow, and a PM filter 2 is arranged downstream thereof. A thing is interposed in the middle of the exhaust gas passage 4 of the diesel engine 3. In addition, the code | symbol 5 shown in FIG. 1 is a silencer, 6 is a battery, 7 is a fuel-injection system, 8 is a fuel tank.
[0008]
The NO oxidation reactor 1 is a honeycomb structure made of a porous ceramic supporting an oxidation catalyst, and the PM filter 2 is a normal wall flow filter made of ceramic. When the high-temperature exhaust gas passes through the NO oxidation reactor 1, NO in the exhaust gas is oxidized to NO ₂ , so most of the NOx in the exhaust gas downstream of the NO oxidation reactor 1 is converted to NO ₂ . Become. Since NO ₂ has a smaller energy barrier than oxygen (O ₂ ), the temperature at which the particulate matter trapped by the PM filter 2 is burned and removed can be reduced, and the PM filter 2 can be regenerated without externally supplying energy. it can.
[0009]
The NO ₂ regeneration type DPF device shown in FIG. 2 is an improvement of the NO ₂ regeneration type DPF device shown in FIG. 1, and, as shown in FIG. 2A, an oxidation catalyst 9 is a PM comprising the wall flow type filter. It is applied to the wall surface of the filter 2, and oxidation of NO and oxidation removal of particulate matter by NO ₂ are performed at once in the PM filter 2, thereby simplifying the apparatus. In this method, since the catalyst is applied to the surface of the PM filter 2, the initial filter pressure loss tends to increase due to a residue of a component that spreads the catalyst on the filter.
[0010]
As shown in FIG. 2A, the wall flow filter is a honeycomb structure made of a porous ceramic as in the oxidation reactor, and the cells 11-1 on both sides of the wall 10 constituting the honeycomb. 11-2 have a structure in which one opening is alternately closed with ceramic material 11.
[0011]
The regenerative DPF apparatus shown in FIG. 3 is one in which a catalyst 12 that directly oxidizes particulate matter captured by the PM filter 2 with O ₂ is applied. Here, the structure of the wall flow filter will be described with reference to a partially enlarged sectional view A of FIG.
[0012]
That is, the exhaust gas G that has flowed into the cell 11-1 penetrates through the wall portion 10 and traps the particulate matter in the PM filter 2 at the wall portion 10 when flowing out from the cell 11-2 to the downstream side. It has a structure to do. Method for oxidizing particulate matter directly O ₂ Thus, by applying the catalyst 12 on the exhaust gas inlet side surface of the wall portion 10, removing the particulate matter trapped on the portion directly oxidized by O ₂ can do.
[0013]
Any of the above catalysts has an action of lowering the oxidation start temperature of the particulate matter, but in the case of a catalyst that can be supplied industrially, a temperature of about 350 ° C. is required as the exhaust gas temperature. Therefore, the collected particulate matter cannot be removed from the PM filter 2 and regenerated when the exhaust gas temperature does not reach 350.degree.
[0014]
As a result, when idling or low load operation is continued, particulate matter accumulates on the filter surface, the back pressure increases, fuel consumption deteriorates, and the engine eventually stops.
[0015]
As a proposal for solving this problem, for example, a method disclosed in Japanese Patent Laid-Open No. 7-109917 is provided with a wall flow type filter provided with an electric heater on the exhaust gas inlet side, and the collected particulate matter is collected. An oxidation catalyst for burning soluble organic components (SOF) and a supported SOF filter are provided on the downstream side of the combustion without propagating combustion, and a bypass with a switching valve is attached in parallel with the wall flow filter. When loaded, exhaust gas is directly passed to the catalytic reactor through a bypass. This method has a drawback that the exhaust gas exhausted in a large amount during high load operation flows into the SOF filter and becomes large.
[0016]
The present invention has been made paying attention to the above-mentioned problems, and both exhaust gas purification at idle and low load where the emission of flammable organic matter increases and high load where emission of particulate matter increases. An object of the present invention is to provide a diesel exhaust gas purification device capable of achieving purification.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a diesel exhaust gas purification apparatus of the present invention includes a first purifier that captures particulate matter in exhaust gas of a diesel engine by a filter and oxidizes and removes it, and the above-mentioned mainly composed of a soluble organic substance A second purifier that captures particulate matter in the exhaust gas of the engine by a filter and oxidizes and removes it is connected in parallel to the exhaust gas passage of the engine. Each part has a cross-sectional area and a filtration area sufficient to circulate a large amount of exhaust gas discharged at the time of loading, and the second purifier conforms to the amount of exhaust gas discharged at idle and low load of the diesel engine. each unit cross-sectional area and comprising a heater for heating the exhaust gas and a catalyst which has a filtration area, the passage cross-sectional of the second clarifier said first purifier the cross-sectional area of which Said second clarifier side exhaust gas flow resistance is larger than the first clarifier side exhaust gas flow resistance is made smaller than the product, wherein the idle and low load of the diesel engine, said first purifier cold exhaust While clogged with gas, the second purifier purifies the low-temperature exhaust gas heated by the heater, and the clogged first purifier is regenerated by the high-temperature exhaust gas at high load. The high-temperature exhaust gas is purified .
[0018]
The second purifier mainly needs to maintain the exhaust gas temperature at the catalyst activation temperature in order to exert the purification function during low load operation with a small amount of exhaust gas. Therefore, it is preferable that the temperature of the heater is controlled by a controller. There is no particular limitation on the heating method, but an electric heater is usually used.
[0019]
According to the said structure, many exhaust gas flows into the direction where the 1st purifier and a 2nd purifier flow easily. Therefore, during a high load operation, a large amount flows to the first purifier having a low flow resistance, but a small amount flows into the second purifier. In this case, since the second purifier is provided with a heater, the trapped particulate matter can be oxidized and removed, and there is no possibility of clogging the filter.
[0020]
On the other hand, since the amount of exhaust gas occurs during idling and low load operation, the exhaust gas naturally flows into the first purifier having a small flow resistance. However, since there is no heater in the first purifier, soluble organic substances cannot be oxidized / removed and the flow resistance gradually increases. On the other hand, the second purifier is equipped with a heater so that purification is performed.
[0021]
By the way, when switching from a low load operation to a high load operation, the flow resistance of the first purifier has increased for the above reasons, so the initial purification function cannot be fully exhibited, and the purification is performed by the second purifier. Is done. However, the purification function is restored by the inflow of high-temperature exhaust gas, and eventually the exhaust gas purification is performed mainly by the first purifier.
[0022]
The operation of the present invention described above can be efficiently generated by designing the flow resistance between the first purifier and the second purifier in a balanced manner for each target engine, and the purification function against load fluctuations can be achieved. It is possible to prevent the occurrence of engine troubles due to lowering and back pressure.
[0023]
In the present invention, a low load refers to a load state in which most of the particulate matter in the exhaust gas becomes soluble organic matter (SOF), and a high load refers to a load state in which the soot component has increased relative to the above.
[0024]
The present invention can be carried out by providing a switching valve at a branch portion that leads exhaust gas to the first purifier and the second purifier, and alternatively allowing exhaust gas to flow into one of the purifiers. In this case, the switching valve can be controlled by detecting the engine load or the like.
[0025]
The purifying means of the first purifier used in the present invention includes the filter for capturing particulate matter in the exhaust gas downstream of the exhaust gas of the reactor carrying the oxidation catalyst for nitric oxide in the exhaust gas. Or at least one means selected from a means for supporting an oxidation catalyst for nitric oxide on the surface of the filter and a means for supporting an oxidation catalyst for the particulate matter on the surface of the filter. it can.
[0026]
As the oxidation catalyst used in the present invention, a generally used oxidation catalyst can be appropriately used. However, since a soluble organic oxidation catalyst is used at a low exhaust gas temperature, it is preferable to use a platinum (Pt) -based strong oxidation catalyst. In this case, oxidation removal can be performed at a relatively low exhaust gas temperature of about 150 ° C., and consumption of exhaust gas heating energy can be reduced.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, and the diesel exhaust gas purification apparatus of the present invention will be described in detail.
[0028]
The diesel exhaust gas purification device 15 of the present embodiment shown in FIG. 4 branches the exhaust gas passage 4 of the diesel engine 3 so that one is connected to the first purifier 16 and the other is connected to the second purifier 17. It is a thing. Note that reference numeral 18 in FIG. 4 denotes an electronically controlled controller.
[0029]
In order to oxidize NO in the exhaust gas to NO ₂ , the first purifier 16 arranges the NO oxidation reactor 1 having a honeycomb structure carrying an oxidation catalyst (not shown) on the upstream side and the downstream side thereof. The PM filter 2 for collecting particulate matter is arranged on the filter surface of the wall flow filter, and the sectional area and the filtration area sufficient to distribute a large amount of exhaust gas discharged when the engine 3 is at a high load are provided. I gave it.
[0030]
The second purifier 17 is provided with a wall flow filter 18 having a soluble organic matter oxidation catalyst (not shown) supported on the filter surface in order to oxidize soluble organic matter in the exhaust gas of the engine 3. A heater 19 made of an electric heater for heating the catalyst and exhaust gas was disposed around and upstream of the catalyst. The cross-sectional area and the filtration area corresponding to the amount of exhaust gas discharged when the engine 3 is idle and when the load is low are such that the flow resistance is higher than the exhaust gas flow resistance of the first purifier 16.
[0031]
Based on input data such as an engine rotation sensor, a load state sensor (not shown), and an exhaust gas temperature detected by the temperature sensor 21, the controller 20 energizes the heater 19 and flows into the second purifier. The gas temperature is maintained at the activation temperature of the oxidation catalyst.
[0032]
Therefore, the exhaust gas flows in a distributed manner based on the flow resistance of each of the first purifier 16 and the second purifier 17. In this case, since the exhaust gas temperature becomes low during idling or low load operation, the oxidation function of the first purifier 16 is lowered and the PM filter 2 is clogged, but the second purifier 17 maintains a sufficient regeneration function. Since it is made, the purification function will not be hindered.
[0033]
In addition, when switching from low load operation to high load operation, the flow resistance of the first purifier 16 is increased due to clogging, but the purification function is maintained because the second purifier 17 has a purification capacity. can do. Meanwhile, since the high temperature exhaust gas also flows into the first purifier 16, the regeneration function of the filter is rapidly recovered. Therefore, since a large amount of exhaust gas flows, the back pressure does not increase and the engine 3 is not hindered.
[0034]
As another embodiment of the present invention, a switching valve is provided at a portion where the exhaust gas passage 4 is branched into the first purifier 16 and the second purifier 17 to control the flow of exhaust gas in accordance with the load condition of the engine 3. You can also
[0035]
Further, the first purifier 16 can be implemented not only by the means shown in FIG. 4 but also by other methods, for example, by the method for capturing and regenerating particulate matter having the configuration described with reference to FIGS.
[0036]
【The invention's effect】
As described above, the diesel exhaust gas purification apparatus of the present invention is adapted for high-load operation, the first purifier that continuously purifies particulate matter (PM) in the exhaust gas, and idle or low-load operation. Since the second purifier that continuously purifies the particulate matter (PM) in the exhaust gas is arranged in parallel in order to perform the purification, problems such as engine stall may occur. In addition, the particulate matter in the exhaust gas can be stably performed over a wide range from idle to high load operation without complicated control for regeneration of the filter function. Therefore, a highly reliable purification device can be supplied at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a conventional method for capturing and regenerating particulate matter in diesel exhaust gas.
FIG. 2 is a schematic explanatory diagram of a conventional method for capturing and regenerating particulate matter in diesel exhaust gas by a method different from that of FIG.
FIG. 3 is a schematic explanatory view of another conventional method for capturing and regenerating particulate matter in diesel exhaust gas different from FIGS. 1 and 2;
FIG. 4 is a schematic explanatory diagram of a diesel exhaust gas purification device according to an embodiment of the present invention.
[Explanation of symbols]
1 NO oxidation reactor 2 PM filter 3 Diesel engine 4 Exhaust gas passage
15 Diesel exhaust gas purification device
16 First purifier
17 Second purifier
18 Filter
19 Heater

Claims (2)

A first purifier that traps particulate matter in the exhaust gas of a diesel engine on a filter and oxidizes and removes it, and traps particulate matter in the exhaust gas of the engine consisting mainly of soluble organic matter and oxidizes it. A second purifier to be removed in parallel with the exhaust gas passage of the engine,
The first purifier has a cross-sectional area and a filtration area sufficient to circulate a large amount of exhaust gas discharged at a high load of the diesel engine,
The second purifier includes a heater that heats the exhaust gas and the catalyst and has a cross-sectional area and a filtration area that correspond to the amount of exhaust gas that is discharged when the diesel engine is idling and under a low load .
Said second clarifier side exhaust gas flow resistance is larger than the first clarifier side exhaust gas flow resistance of the cross-sectional area of the second purifier to be smaller than the passage sectional area of the first clarifier,
At the time of idling and low load of the diesel engine, the first purifier is clogged with low temperature exhaust gas, while the second purifier purifies the low temperature exhaust gas heated by the heater, A diesel exhaust gas purifier that purifies the hot exhaust gas while the clogged first purifier is regenerated by the hot exhaust gas when loaded .   Means for disposing the filter for capturing particulate matter in the exhaust gas on the downstream side of the exhaust gas of the reactor carrying the oxidation catalyst for nitric oxide in the exhaust gas; 2. The diesel exhaust according to claim 1, wherein the diesel exhaust gas is one or more means selected from a means for supporting an oxidation catalyst for nitrogen oxide on the surface of the filter and a means for supporting an oxidation catalyst for the particulate matter on the surface of the filter. Gas purification device.

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