JP2006029132A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device and its control method for promoting combustion removal of PM collected in regenerating processing of respective filters, in the exhaust emission control device having a plurality of filters arranged in parallel in an exhaust flow passage. <P>SOLUTION: This exhaust emission control device supplies and regenerates regenerative gas, by separating the regenerating filter 14 from the exhaust flow passage in regeneration, by building the particulate collecting filters 13 and 14 in the respective branch flow passages, by arranging a plurality of branch flow passages 11 and 12 in a part of the exhaust flow passage. The exhaust emission control device has a discharge reactor for activating and supplying exhaust gas as the regenerative gas by discharge. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device that purifies exhaust from an internal combustion engine or the like. In particular, the present invention relates to an exhaust emission control device that has a plurality of filters that collect and remove particulates contained in exhaust gas, and that regenerates the filters by burning the particulates collected by the filters.

  Internal combustion engines such as automobiles, especially diesel engines, contain particulates mainly composed of carbon (hereinafter referred to as “PM (Particulate Matter)”), which causes exhaust black smoke. . From the viewpoint of environmental pollution, it is desirable to collect and remove this PM. For this purpose, a ceramic filter is arranged in the exhaust passage of the diesel engine, PM is collected and removed by this filter, and the PM collected by this filter is burned intermittently to regenerate the filter. An exhaust purification device has been proposed.

  Such a conventional exhaust purification device is shown in FIG. Here, this conventional exhaust gas purification apparatus includes a plurality of branch flow paths 11 and 12 that are part of the exhaust flow path, switching valves 17 and 18 that switch these branch flow paths, and particulate collection in each branch flow path. Filters (hereinafter simply referred to as “filters”) 13 and 14, electric heaters 15 and 16 adjacent to the filters 13 and 14, respectively, and at the time of regeneration of the filter, a regeneration gas such as secondary air is supplied from a pump (not shown) by an arrow 23. And 24, the regeneration gas passages 19 and 20 are supplied to the filter.

  When regenerating the filter 14 of the exhaust gas purification apparatus of FIG. 2, the switching valves 17 and 18 are moved to the positions shown in FIG. 2 to disconnect the filter 14 from the exhaust flow path and energize the electric heater 16 adjacent to the filter 14. After heating, a regeneration gas such as secondary air is supplied from a pump (not shown) as indicated by arrows 23 and 24. Here, the regeneration gas is heated by the electric heater 16 to burn the PM collected by the filter 14, thereby regenerating the filter 14. During this time, the exhaust gas containing PM passes through the filter 13 as indicated by arrows 21 and 22 to collect and remove PM in the exhaust gas.

  When the filter 13 is regenerated, the switching valves 17 and 18 are moved to disconnect the filter 13 from the exhaust flow path, and the filter 14 collects PM in the exhaust gas while regenerating the filter 13 with regenerated gas. Remove.

  In general, the regeneration process is performed individually for each of the filters when the pressure loss before and after the filter is detected using a pressure sensor and the detected pressure loss becomes a predetermined value or more. However, if excessive PM is collected in the filter during this regeneration, the combustion temperature of the filter may increase excessively, causing melting and cracking.

  In this regard, Patent Document 1 is an exhaust purification device in which a plurality of branch channels are provided in a part of the exhaust channel, and a particulate collection filter is built in each branch channel. An exhaust gas purification device that makes the collected amount of PM uniform is provided. According to the exhaust gas purification device of Patent Document 1, overheating of each filter due to PM combustion in filter regeneration processing is prevented, and damage to the filter can be prevented.

  The exhaust emission control device disclosed in Patent Document 1 includes a collection amount detection unit that individually detects a collection amount of each filter, a maximum collection filter detection unit that detects a filter having the largest collection amount, and the most collection unit. Control valve position adjustment means that adjusts the collection amount of other filters by adjusting the control valve provided in the branch part of the exhaust flow path so that it matches the collection amount of the filter, and the collection amount of each filter is almost Reproducing operation starting means for starting the reproducing operation of the filter when equal to a predetermined reproducing reference value is reached.

Patent Document 2 discloses an exhaust emission control device that collects PM in exhaust discharged from a diesel engine with a filter, generates NO ₂ with a catalyst upstream of the filter, and oxidizes and removes PM by the NO ₂ . It is disclosed. Here, it is disclosed that combustion removal of PM is achieved from a relatively low temperature of 250 ° C. when NO ₂ is supplied to a filter that collects PM.

JP-A-5-222922 Japanese Patent No. 3012249

  In the present invention, an exhaust gas purification apparatus in which a plurality of branch channels are provided in a part of the exhaust channel, and a filter for collecting particulates is built in each branch channel, and in the regeneration process of each filter An exhaust emission control device that promotes combustion removal of collected PM is provided.

The exhaust gas purification apparatus of the present invention has a plurality of branch flow paths provided in a part of the exhaust flow path, each of the branch flow paths includes a filter for collecting particulates, and the filter that is regenerated during regeneration is connected to the exhaust flow path. An exhaust gas purification device that regenerates the filter by separating and removing the collected particulates by supplying the regeneration gas to the filter, and exhausting, particularly in a lean state (that is, an oxidizing property such as O ₂ ) It has a discharge reactor that activates at least a part of the exhaust gas in a state where there are few reducing components such as hydrocarbons relative to the components by discharge and supplies it as a regenerated gas to the regenerated filter.

According to the exhaust purification apparatus of the present invention, at least a part of the exhaust is activated by discharge to generate a strong oxidizing component such as NO ₂ and O ₃ , and this can be supplied to the filter as a regeneration gas. Even at a relatively low temperature, combustion removal of PM collected by the filter can be promoted. It is preferable that the filter can be regenerated at a relatively low temperature in order to prevent deterioration of the filter.

  In one aspect of the exhaust emission control device of the present invention, when the regeneration gas temperature in the regenerated filter is within a predetermined temperature range, particularly 250 ° C. to 450 ° C., more particularly 250 ° C. to 400 ° C., the discharge reactor is at least exhaust gas. A part is activated by discharge and supplied as a regeneration gas to the regenerated filter.

Combustion (oxidation) removal of PM by NO ₂ can be achieved from a relatively low temperature such as 250 ° C. However, when the regeneration gas temperature is relatively high, when it is 450 ° C. or higher, NO ₂ is destabilized and converted to NO, N ₂ , O _2, etc., and the oxidation removal of PM by NO ₂ is not effectively performed. Sometimes. Further, when the regeneration gas temperature is sufficiently high, PM oxidation removal is achieved by O ₂ in the regeneration gas even if NO ₂ is not present. These are shown schematically in FIG.

Therefore, according to this exhaust purification device, NO ₂ obtained by the activation of exhaust is important, and when functioning particularly effectively, the exhaust is activated by the discharge reactor to generate NO _2, and by the discharge Exhaust activation can be used effectively.

  In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings are diagrams showing an outline of an exhaust emission control device constituting the present invention, and the present invention is limited to these embodiments. Is not to be done.

  One embodiment of the exhaust emission control device of the present invention will be described with reference to FIG.

  As shown in FIG. 1, in one embodiment of the exhaust gas purification apparatus of the present invention, a plurality of branch flow paths 11 and 12 that are part of the exhaust flow path, and a butterfly valve that switches these branch flow paths are used. The regenerative gas supplied to the filter as indicated by arrows 34, 23 and 24 through the discharge reactor 31 when the filter is regenerated. It has a flow path.

  When regenerating the filter 14 of the exhaust purification apparatus of the present invention, the switching valve 17 is moved to the position shown in FIG. 1 to disconnect the filter 14 from the exhaust flow path, and the regeneration gas is supplied to the filter 14 by arrows 23 and 24. As shown, the PM trapped in the filter 14 is burned, thereby regenerating the filter 14. Here, the regeneration gas supplied to the filter 14 takes out a part of the exhaust gas from the exhaust flow path as shown by an arrow 34, supplies it to the discharge reactor 31, and generates a discharge in the exhaust gas in the discharge reactor 31 to activate the regeneration gas. To obtain. During this period, the exhaust gas containing PM passes through the filter 13 as indicated by arrows 21 and 22, and the PM in the exhaust gas is collected and removed by the filter 13.

  In this embodiment of FIG. 1, as shown by arrows 23 and 24, the regeneration gas is passed through the filter 14 in the same direction as when PM is collected, but in the opposite direction, that is, PM capture. It is also possible to regenerate the filter 14 by passing the regeneration gas through the filter 14 in the opposite direction to the collection.

  In the regeneration of the filter 14, an optional electric heater adjacent to the filter 14 can be energized and heated to heat the regeneration gas supplied to the filter 14. A high temperature of the regeneration gas supplied to the filter generally promotes combustion removal of PM collected by the filter.

In the exhaust gas purification apparatus of the present invention, when a part of the exhaust gas is subjected to a discharge treatment to obtain a regeneration gas containing NO ₂ and O ₃ , and PM is burned by this regeneration gas, the regeneration gas generally circulating through the filter is When the temperature is 250 ° C. or higher, a good oxidation removal rate of PM can be obtained. Therefore, for example, when this temperature does not reach 250 ° C., the heater disposed adjacent to the filter can be heated by energization, and the regeneration gas can be heated by this heater.

  In the use of the exhaust gas purification apparatus of the present invention, whenever the filter is regenerated, the exhaust gas can be activated by the discharge reactor and supplied to the filter as a regenerated gas. However, a regeneration gas other than the exhaust activated by the discharge reactor can be used as the regeneration gas used for regeneration of the filter. Examples of the regeneration gas other than the activated exhaust gas include air obtained from the outside air, and exhaust gas that has not been activated by the discharge reactor. When the air obtained from the outside air is used for the regeneration of the filter, the exhaust purification device of the present invention needs to further have a flow path for this air flow.

  Therefore, for example, the regeneration gas supplied to the regenerated filter can be changed based on the temperature of the regenerated filter, the temperature of the obtained exhaust gas, and the like. For example, the exhaust emission control device of the present invention detects the temperature of the regeneration gas flowing through the filter to be regenerated, and controls the exhaust to be activated by discharge and supplied as regeneration gas when the temperature is lower than a predetermined temperature. . The temperature of the regenerated gas flowing through the regenerated filter can be measured by directly attaching a temperature sensor in the filter. This temperature is obtained by attaching temperature sensors 5 and 6 for measuring the temperature of the regeneration gas flowing into the filter and / or the regeneration gas flowing out of the filter to the inflow side and / or the outflow side of the filter. It is also possible to determine the temperature of the exhaust gas in the PM trapping part based on the rotational speed of the engine, the time since engine startup, and the like.

The filter used in connection with the exhaust emission control device of the present invention may be a ceramic honeycomb made of a material such as cordierite or SiC. The filter also optionally can also support a catalyst component such as _the NO _x purification catalyst, can also be arranged _the NO _x purification catalyst in the exhaust flow downstream of the filter.

In the exhaust purifying apparatus of the present invention, in order to prevent the NO _x in the exhaust gas was used to burn off PM is released into the atmosphere, the exhaust gas exiting the filter, and purified by _the NO _x purification catalyst Can also be discharged. Further, before the exhaust gas is treated by the exhaust gas purification apparatus of the present invention, the exhaust gas can be treated in advance by a three-way catalyst.

A discharge reactor capable of activating at least a part of exhaust gas by discharge for the exhaust gas purification apparatus of the present invention activates components in the exhaust gas by discharge, particularly discharge plasma generated by the discharge, such as NO ₂ and O ₃ . Any discharge reactor capable of producing a strong oxidizing power component may be used. For example, the discharge reactor may be any discharge reactor known for applications intended for exhaust purification, in particular a discharge reactor known as an exhaust gas purification device for diesel engines, more particularly a discharge plasma reactor.

  In this discharge reactor, the applied voltage and current are controlled based on the operating state, filter temperature, engine state, exhaust air-fuel ratio (A / F ratio), gas flow rate of the discharge reactor, etc., thereby regenerating the filter. A suitable regeneration gas can be obtained.

  An example of this discharge reactor is shown in FIG. In the discharge reactor shown in FIG. 3, a cylindrical electrode 54 is disposed so as to surround the central electrode 52, and the central electrode 52 and the cylindrical electrode 54 are connected to a power source 56 and grounded. The exhaust gas activated in the discharge reactor 50 passes through the space surrounded by the cylindrical electrode 54 from the left side to the right side in FIG. In the use of this discharge reactor, a voltage is applied between the center electrode 52 and the cylindrical electrode 54 by the power source 56, thereby causing a discharge between these power sources. Here, the center electrode 52 is connected to the power source 56 and the cylindrical electrode 54 is grounded, but this can be reversed, and either can be the cathode or the anode. .

  The center electrode 52 and the cylindrical electrode 54 can be manufactured using a material that can be used as a discharge electrode by applying a voltage between them. As such a material, a conductive material or a semiconductor material can be used, but a metal material such as copper, tungsten, stainless steel, iron, aluminum, or the like is preferable. Moreover, in order to use barrier discharge, an insulating material can also be arrange | positioned on these electroconductive or semiconductive materials.

  When plasma is generated in this discharge reactor using corona discharge, the power source 56 may supply a pulsed direct current or alternating current voltage. The applied voltage is generally 1 kV to 100 kV, for example, 40 kV. A voltage of ˜60 kV can be used. The pulse period of the applied voltage can be 10 ms to 0.1 μs, particularly 0.1 to 10 μs.

It is sectional drawing which shows the exhaust gas purification apparatus of this invention. It is sectional drawing which shows the conventional exhaust gas purification apparatus. It is a perspective view of the discharge reactor which can be used for the exhaust gas purification apparatus of this invention. It is a diagram representing the PM oxidation rate by NO ₂ and O _2.

Explanation of symbols

5, 6 ... Temperature sensors 11, 12 ... Branch flow paths 13, 14 ... Filters 15, 16 ... Electric heaters 17, 18 ... Switching valves 21, 22 ... Arrows 23, 24, 34 ... showing the flow of exhaust gas containing PM Arrow 31 indicating the flow of regenerative gas ... Discharge reactor 52 ... Center electrode 54 ... Cylindrical electrode 56 ... Power source

Claims (3)

  A plurality of branch passages are provided in a part of the exhaust passage, and a filter for collecting particulates is built in each branch passage. A filter to be regenerated is separated from the exhaust passage at the time of regeneration, and the regeneration gas is supplied to the filter. An exhaust gas purification device that regenerates the filter by burning and removing the collected particulates by activating the exhaust, and at least a part of the exhaust is activated by discharge, and the regenerated gas is supplied to the regenerated filter. An exhaust purification device having a discharge reactor supplied as   The discharge reactor activates at least a part of exhaust gas by discharge when the regenerated gas temperature in the regenerated filter is within a predetermined temperature range, and supplies the regenerated filter as a regenerated gas. The exhaust emission control device described.   The exhaust emission control device according to claim 2, wherein the predetermined temperature range is 250 ° C to 450 ° C.

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