ES2545406T3 - Procedure for cleaning particulate filters - Google Patents

Abstract

Procedure for cleaning particulate filters (10) that have a catalytically active surface (18), characterized by the following steps: - allow a cleaning substance absorbable on the catalytically active surface (19) to act on the catalytically active surface, which has an evaporation or decomposition temperature greater than 100°C and less than 300°C, which is non-flammable and contains as its main component a nitrogen compound which is a precursor substance of NH3, and - heating the cleaning substance on the catalytically active surface (18) at a temperature higher than its evaporation or decomposition temperature.

Description

DESCRIPTION

Procedure for cleaning particle filters.

The invention relates to a method for cleaning particle filters having a catalytically active surface, especially exhaust gas particle filters for diesel engines.

Vehicles and work machines powered by diesel engines must be equipped with exhaust gas particle filters 5. The current standard is called EURO 5, the next level is called EURO 6 and will be introduced shortly. Despite many technical advances, there is a need for cleaning for these filters. The need for cleaning is so much greater, the more short distances are traveled. In these paths, the diesel engine does not reach the temperatures that guarantee the combustion of the exhaust gas particles, usually soot. The cleaning of the filters is generally carried out in such a way that, once disassembled from the vehicle, the filters are heated to 600 ° in an oven 10 suitable for burning soot. During this, there is often a deformation of the filter housing that hinders subsequent assembly. The ash remaining in the filter is then removed for example by blowing with compressed air. To do this, at least in the case of car filters, the filter housing must be opened to be able to orient the nozzle towards the filter surfaces. The procedure is laborious and cumbersome, all the more so that several combustion and blowing processes are frequently needed to achieve an acceptable cleaning success. fifteen

WO2008 / 131573A1 disclosed a method whereby the filter can be regenerated continuously while the vehicle is running. Since during normal engine operation, the temperature of the exhaust gases is not sufficient for thermal regeneration of the filter, an additional fuel that catalytically oxidizes into the catalytically active surface is introduced upstream of the filter.

An alternative to the thermal regeneration of the filter is the regeneration by NO2. For the realization of this procedure, for the catalytically active layer of the filter a catalyst material must be chosen with which a high NO2 production rate is achieved.

A procedure in which the filter is washed with a cleaning liquid and then dried by heating is disclosed by DE103212990A1.

EP2166203 discloses the addition by mixing of an aqueous urea solution to the hot exhaust gas. 25 Urea serves as an ammonia precursor that by selective catalytic reduction contributes to the decomposition of nitrogen oxides into nitrogen and water vapor.

The invention aims to provide a simple and economical process for cleaning exhaust filters.

This objective is achieved through a procedure with the following stages: 30

- allowing an absorbable cleaning substance to act on the catalytically active surface on the catalytically active surface, which has an evaporation or decomposition temperature greater than 100 ° C and less than 300 ° C, which is not flammable and which contains a nitrogen compound as the main component which is a precursor substance of NH3, and

- heating the cleaning substance on the catalytically active surface to a temperature higher than its evaporation or decomposition temperature.

In the process according to the invention, the cleaning substance is applied to the catalytically active surface without the filter being washed with this substance. In this way, the duration of the procedure and the consumption of material are significantly reduced. The effect of the process consists in that the cleaning substance enters into reciprocal action with the catalytically active surface, the catalytically active material being able to catalyze, if necessary, a decomposition of the cleaning substance and / or a reaction of said substance with the impurities adhered to the catalytically active surface. In any case, by adsorption of the cleaning substance on the catalytically active surface, the adhesion of the impurities to said surface is loosened. By heating, the cleaning substance is then removed from the catalytically active surface together with the impurities or decomposition products thereof. Since, for this purpose, the cleaning substance has to be heated only at a maximum of 45 300 ° C, a significant energy saving is also achieved and filter damage is avoided.

Some advantageous embodiments are indicated in the dependent claims.

The cleaning substance may be a non-electrolytic aqueous solution that is applied in liquid form on the catalytically active surface. In this context, a nitrogen compound will be called "non-electrolytic" if its dissociation constant is less than approx. 2 • 10-5, which corresponds roughly to the dissociation constant of acetic acid. However, the cleaning substance can also be a solid substance that is applied on the catalyst surface as fine grained granules or by vaporization. Preferably, the decomposition or evaporation temperature, at least for the main component of the cleaning substance, is less than 180 ° C, especially

preferably below 140 ° C.

As a cleaning substance an NH3 precursor substance is used. The cleaning substance must not be toxic or flammable. For example, carbonic acid diamide is suitable. To prepare the aqueous solution, demineralized water must be used.

To impregnate the filter with the cleaning substance, a jet application method can be used by means of a carrier gas, for example compressed air, to which the liquid solution or the granulate is added. Optionally, a spraying process can also be used without the help of a carrier gas, or the liquid is pumped through the filter or simply poured without pressure into the filter, or the filter is immersed in the liquid.

In one embodiment, the filter is disassembled from the vehicle, impregnated with the cleaning substance and then heated in an oven. During this, most of the impurities pass into the gas phase and escape from the cleaning substance 10 next to the steam or the decomposition products. Any remaining impurities will then be present only in a loose manner in the filter and can be removed without problems, for example by simply tipping the filter, by vibration, knocking, suction or blowing by means of compressed air.

In another variant of the procedure, the filter can remain mounted on the vehicle. Then, the cleaning substance is introduced into the filter, preferably in the form of an aqueous solution, at a time when the filter 15 still has a relatively high temperature after prolonged running of the vehicle's engine. While a part of the water evaporates, the catalytically active surface of the filter cools, so that the component of the cleaning substance can precipitate on it. Once the liquid supply is finished, the residual heat accumulated in the catalyst causes the active surfaces to reheat causing evaporation or decomposition of the cleaning substance. twenty

Next, an embodiment example is described in detail with the help of the drawing.

They show:

1 shows a schematic section through a filter during a first stage of the process according to the invention;

Figure 2 a drying stage for the filter; 25

Figure 3 a stage for mechanical dry cleaning of the filter; Y

Figure 4 a schematic diagram of a modified embodiment of the process.

The filter 10 shown in FIG. 1, for example a diesel exhaust filter of a tourism engine, has a metal housing 12 open at both ends, the walls of which are lined on the inner side with heat-resistant mats 14 and housing the filter body 16 of a porous ceramic material, whose surfaces 18 of 30 filter action have a catalytically active coating. After prolonged use of the filter, the surfaces 18 have adhered soot particles attached.

For cleaning, the filter 10 is disassembled from the vehicle's exhaust system and with a jet nozzle 20 a mixture of liquid and compressed air is jetted into the filter body 16, at least from one end, by example from the end located on the inlet side, or preferably from both ends. The liquid is, for example, demineralized water in which a cleaning substance is dissolved.

Since the liquid is sprayed directly into the filter body 16 with the aid of the jet nozzle 20, excessive wetting of the mats 14 can be avoided.

After the liquid has acted for some time on the soot layers in the walls and pores of the filter body 16, the filter 10 is introduced into an oven 22 (Figure 2) and dried carefully to a 40 temperature of for example 140 to 180 °. The drying temperature should be higher than the boiling point of the liquid (and the substances dissolved in it) previously introduced by jet. In this way, the liquid evaporates and escapes from the oven through the holes 24. The drying process continues until all the liquid has evaporated.

By means of this treatment, the deposit is broken down chemically / catalytically on the catalytically active surfaces in the walls of the filter body 16. The remaining residues eventually decompose into small particles that are easily released from the walls of the filter material.

As shown in Fig. 3, it is then sufficient to tip the filter 10 or tap it on a base 26 to remove dry impurities 28 from the filter.

In the example shown here, the filter 10 has a temperature sensor 30 which, during the running of the vehicle, serves to monitor the temperature of the filter. The filter is removably disposed in the wall of the housing 12. 50 Since the liquid is jetted into the filter body with the aid of the jet nozzle 20 from at least

at an open end, it is not necessary to disassemble the temperature sensor 30 during the cleaning procedure.

Optionally, instead of the liquid, a solid cleaning substance such as a granulate can also be jetted into the filter.

Figure 4 illustrates a process variant in which the filter 10 does not have to be removed from the vehicle's exhaust gas installation. 5

In FIG. 4, an engine 32 and an exhaust gas installation 34 of the vehicle are schematically represented. The exhaust gas installation 34 comprises an exhaust pipe 36 and an exhaust silencer 38 in which the filter 10 is arranged such that it is traversed by the exhaust gases of the engine 32. In a section of the exhaust pipe 36 a connection point 40 is provided between the engine 32 and the muffler 38 which optionally allows the connection of a jet group 42 or a suction group 44. In the example shown, the 10 jet group 42 is connected with a clamp 46 to the open end of the exhaust pipe 36, while the suction group 44 is connected to the connection point 40.

The cleaning of the filter 10 is carried out after the ceramic material of said filter has been heated to its operating temperature by a prolonged operation of the engine 32. A carrier gas, for example compressed air, is introduced through the jet module 42. in the exhaust pipe 36. The jet group 42 also has a supply line 48, through which the cleaning substance is dosed in liquid form, as a solution, to the compressed air stream. The atomized cleaning substance is deposited on the catalytically active surfaces of the filter. In order for the cleaning substance to penetrate homogeneously and completely into the filter, the duration of the jet process and the volume of the carrier gas are sized such that the complete filter 10 is at least briefly subjected to a pressure of at least 1 kPa ( 0.01 bar). Then, the supply of compressed air and cleaning substance 20 is terminated and the jet group 42 is released from the end of the exhaust pipe 36. The residual heat of the particulate filter 10 is so large that the catalytically active surfaces that were previously catalyzed they have cooled to less than 100 ° C by means of compressed air, the cleaning substance and - in case of using an aqueous solution - by water, they are reheated to a temperature higher than the evaporation or decomposition temperature of the cleaning substance . In this way, the impurities are released from the 25 surfaces 18 of the filter, so that they can be aspirated with the suction group 44.

In a modified embodiment, the jet group 42 is connected to the connection point 40 and the suction group 44 is connected to the end of the exhaust pipe, so that the cleaning substance enters the filter 10 from the opposite side . It is also possible to perform the procedure in several stages in which the cleaning substance enters the filter alternating from opposite sides. 30

If the impurities in the catalytically active surfaces of the filter 10 chemically decompose and evaporate in their entirety, the suction can also be dispensed with completely.

In order to avoid excessive cooling of the filter, the cleaning substance and / or compressed air can be preheated.

The embodiment shown in Figure 4 in which it is not necessary to disassemble the filter 10 is advantageous 35 especially in the case of high-power diesel engines, for example for driving ships.

Claims (9)

1. Procedure for cleaning particle filters (10) that have a catalytically active surface (18), characterized by the following steps: - allowing an absorbable cleaning substance to act on the catalytically active surface on the catalytically active surface (19), which has an evaporation or decomposition temperature of greater than 100 ° C and less than 300 ° C, which is not flammable and which contains as main component a nitrogen compound that is an NH3 precursor substance, and - heating the cleaning substance on the catalytically active surface (18) to a temperature higher than its evaporation or decomposition temperature. 2. The method according to claim 1, wherein the cleaning substance has an evaporation or decomposition temperature of less than 180 °. 3. The method according to claim 2, wherein the cleaning substance has an evaporation or decomposition temperature of less than 140 °. Method according to one of the preceding claims, in which the cleaning substance is introduced in liquid form in the filter (10). fifteen 5. The method according to claim 4, wherein the cleaning substance is dissolved in water. Method according to one of the preceding claims, in which the cleaning substance is introduced into the jet filter (10) by means of a jet group (18; 42). 7. Method according to claim 1, wherein the filter (10) is heated in an oven (22). Method according to one of claims 1 to 6, in which the cleaning substance is introduced into the filter (10) in the form of an aqueous solution, while the filter has a temperature higher than the evaporation or decomposition temperature. of the cleaning substance, the temperature of the catalytically active surface (18) being reduced temporarily below the evaporation or decomposition temperature by the introduction of the cleaning substance. 9. Method according to one of the preceding claims, wherein after the heating of the cleaning substance a mechanical dry cleaning of the filter (10) is performed.