EP0132166A1 - Regeneration of particle filters, especially for diesel engines - Google Patents

Abstract

Apparatus and process for regeneration of clogged solid particle filters, particularly for diesel engines. There is periodically injected upstream from the clogged filter an organic liquid such as CxHyOz, of the ethyl or methyl alcohol type, having a low vaporization temperature, if necessary with water added. The organic liquid, after having been preheated and cracked to give rise to a very flammable mixture consisting essentially of hydrogen and carbon monoxide, is introduced in the path of the incident exhaust gases. The regeneration apparatus comprises two prechambers, each of which contains a glow plug. The burning of the flammable mixture regenerates the clogged filter.

Description

The present invention relates to the regeneration of solid particle filters for diesel engines, gradually imposed by national laws against atmospheric pollution and intended to significantly reduce the smoke emissions of these engines.

Such filters can result from cellular ceramics such as cordierite extruded in the form of a honeycomb monolith, impregnated or not with a catalyst, of which one cell in two is closed at one of its ends; said closed ends alternate from one cell to the other contiguous cell, so that the gas to be filtered cannot flow directly through a given cell, but is, on the contrary, forced to pass through the wall.

Other types of filters are also known, using metallic fibers, covered or not with alumina, or even comprising balls, etc.

It follows from the first of the preceding arrangements that the solid particles in suspension in the gas arriving on the filter are trapped in the cells which, ultimately, clog up, causing an increasing pressure drop of the filter and thus a significant power loss of the engine.

It is therefore necessary to periodically regenerate the filter by combustion of said trapped particles, essentially consisting of carbon, in the form of a sufficient supply of thermal energy intended to initiate their combustion. However, this contribution must be able to be controlled, because, otherwise, the combustion of the solid particles can lead to a too rapid rise in the temperature of the ceramic and deteriorate its structure by local melting.

Note that the combustion of these particles begins to occur around 550 ° C in the case of a filter not impregnated with catalyst and of the order of 450 ° C in the opposite case.

Devices for regenerating such filters are already known.

In the case of catalytic filters, the injection at a given moment of a certain volume of gasol into one of the engine cylinders causes the partial cracking of this fuel into gaseous hydrocarbons which, with the excess oxygen present in the combustion gases burn on the catalytic surfaces, producing the quantity of heat necessary to initiate the combustion of the trapped particles.

For non-catalytic filters, other devices exist such as gas oil burners, the external combustion air supply of which is effected by the action of an additional pump placed near the pot.

In the various cases cited, the drawbacks are multiple: momentary and annoying disturbances in the operation of the engine, risk of formation of carbon particles resulting from incomplete cracking, or of the non-ignition of the oil burner, need to have a air pump, etc.

The object of the present invention overcomes the above drawbacks; the oxidation of trapped carbon particles occurs using a simplified device, normally not using an air injection pump, compact and integrated inside the pot containing the ceramic filter.

• - la figure 1, à une coupe longitudinale d'un filtre en céramique utilisé et antérieurement.connu ;
• - la figure 2, à un schéma de principe du dispositif de régénération du filtre, selon l'invention ;
• - les figures 3 à 8, à un détail grossi vu en coupe, du pot contenant la céramique, selon six variantes de l'invention.

In addition, the energy supply is determined by the injection of an organic liquid such as methanol, vaporizing at low temperature (close to 70 ° C), not releasing any annoying by-product during its cracking; this gives rise to a very rich combustible gas comprising a large quantity of hydrogen which is easy to ignite. The invention will now be described by way of nonlimiting example with regard to Figures 1 to 8 attached, which relate respectively:

• - Figure 1, a longitudinal section of a ceramic filter used and anteriorly known;
• - Figure 2, a block diagram of the filter regeneration device according to the invention;
• - Figures 3 to 8, in an enlarged detail seen in section, of the pot containing the ceramic, according to six variants of the invention.

The filter 1 of FIG. 1 is subjected by its left part to the incident flow of exhaust gas from the diesel engine. It can be seen that on this side, only one out of two cells is of free access, the other comprising a closure 2. The right face of this filter also has closures 3 corresponding to the opposite ends of the cells of free access on the left side of the filter. The arrows clearly show the path of the gases through the walls 5 of the cells and makes it possible to grasp the phenomenon of fouling of the filter resulting from the accumulation of carbon particles 4 on the porous walls of the cells.

This filter 1 is found in FIG. 2, included in the cylindrical part of a pot 20 crossed by the exhaust gases arriving through its upper part 21 and leaving it, purified, in its lower part 22.

In accordance with the invention, an organic liquid of the methanol type coming from a reservoir 23 is dosed, and periodically injected, into the upper zone 24 of the pot, the flow rate of this injection being optionally modulated over time, after having possibly been preheated and vaporized by passing at 25 in contact with the pot 20.

Si le filtre 1 est non catalytique, le mélange précédent s'enflamme au contact de la bougie 27 et élève la température du filtre et de ses particules de carbone 4 ; ces dernières s'oxydent en CO₂et traversent les parois 5.The vapors thus obtained are cracked in a prechamber 26 comprising a heating candle 27 of the Diesel type which can reach 800 to 1000 ° C., then injected in the direction of the filter 1, to which it provides the energy necessary for its regeneration, in the form a combustible mixture of hydrogen and carbon monoxide.

If the filter 1 is non-catalytic, the preceding mixture ignites on contact with the spark plug 27 and raises the temperature of the filter and of its carbon particles 4; the latter oxidize to CO ₂ and pass through the walls 5.

If the filter 1 has been impregnated with a catalytic phase (preferably based on platinum or palladium), the cracked gas burns only at the level of the catalytic support 1 itself and thus causes the combustion of the carbon particles . In this case, the temperature at which the soot starts to burn is significantly lower than that of the previous case and is of the order of 450 ° C.

Other organic liquids of type C H 0 can be used in accordance with the above; preferably those which have a rather low vaporization temperature will be chosen, such as ethanol, if necessary glycol, or glycerin, or a mixture of these giving a stable gas mixture. This list is not exhaustive.

• 1 mole d'éthanol + 1 mole d'eau
  
  

It is also possible to use the stable mixtures of the above liquids with water, according to the following scheme:

• 1 mole of ethanol + 1 mole of water
  
  

We will endeavor to ensure that the organic liquid used has an equal number of carbon and oxygen molecules so as to avoid the formation of free carbon during cracking, or to have a cracking atmosphere containing a high percentage. methane which can be the source of a carbon deposition, for example propanol:

The desired gas mixture is highly flammable, being essentially composed of carbon monoxide (33%) and hydrogen (66%).

The triggering of the filter regeneration operation follows the detection of clogging of the latter and can be made automatic. It results from the supply of an electrical signal which comes from the contact being established between two ceramic electrodes, originally insulating and made conductive by accumulation of carbon particles; or relates to the measurement of an overpressure in the enclosure of the pot 20 for a given speed of rotation of the motor; or results from the counting of a determined number of engine revolutions, etc.

When the regeneration threshold is reached, an opening signal arrives at the solenoid valve 28, which determines the filling of the capacity 29 corresponding to the volume of organic liquid necessary for the regeneration of the filter. Then the solenoid valve 28 is closed and the solenoid valve 30 opened, causing the organic liquid to be introduced by gravity via the pipe 31, into the prechamber 26 in which the heating plug 27 is simultaneously energized by any known means.

The organic liquid, due to the calories taken in contact with the exhaust wall at 25 and under the influence of the candle 27, is transformed after cracking, into gas with high calorific value which, when burned, determines the combustion of the particles. carbon trapped in filter 1 when the engine is idling.

The organic liquid can also be metered by means of a small turbine pump with timed electric control, then driven through a calibrated opening, or any other equivalent means.

By way of example, good results have been obtained by injecting, under the conditions of the invention, a volume of 35 cm ³ of methanol in 90 seconds, raising the temperature of the gases to approximately 650 ° C. at the inlet of the filter. and at 350 ° C at its exit. Such regeneration can be repeated with a periodicity of around 300 km.

According to the embodiment of Figure 3, there is the filter 1, located in the cylindrical part of the pot 20, at the upper end 21 from which the exhaust gases arrive.

The organic liquid arrives via the pipe 31 at the prechamber 26 containing the heating candle 27, the free end of which opens inside the upper end of the pot 20, in a burner body 32 curved towards the filter 1 and having on its opposite face, openings 33 through which an exhaust gas flow passes. The dynamic pressure of the latter ensures a good mixture of the cracking gases coming from the prechamber 26 and the oxygen contained in the exhaust gases, at the hottest end 34 of the spark plug, thereby causing their combustion. The internal diameter of the burner 32 is of the order of three times that of the end 34 of the spark plug that it surrounds.

The liquid or its vapor phase meets a vaporization zone at medium temperature (500 ° C), located around the part 35 of the spark plug 27 preceding its reduction in diameter.

The vapor of organic liquid then crosses a cracking zone at high temperature represented by the small diameter part 38 of the candle brought to approximately 1000 ° C. and the extension 36 of the front part of the prechamber 26 which surrounds it at a short distance close to 1 mm, over a length close to a third of that of the active part of the candle.

The cracked gases then arrive at a hot point formed by the end 34 of the spark plug, at the level of which they mix with the exhaust gases and ignite, thus constituting the heat supply necessary for the oxidation of the particles of carbon 4 trapped in the filter 1. The surface of the latter is located at a distance from the opening of the burner 32 close to the diameter of the filter.

The burner which must undergo relatively severe operating conditions is made of stainless steel, refractory or even ceramic.

In order to avoid overheating of the filter 1, it is possible to control the arrival of the organic liquid and / or the supply of the spark plug 27 to a thermocouple determining the stopping of the operation of the device for temperatures exceeding a given setpoint, for example 800 ° C.

According to the variants of the invention illustrated in FIGS. 4 and 5, it is noted that the organic liquid supplied by the pipe 31 arrives in a double-walled envelope 41 and respectively 51, determining the vaporization zone of the liquid and using for this purpose the calories available on the surface of the pot 20.

Note also in Figure 4 the particular shape of the free end 43 of the burner 42, further improving the diffusion of gases to the surface 37 of the filter.

The variants of FIGS. 5 and 6 indicate the possibility which exists according to the invention of placing the vaporization, cracking and mixing assembly of the gases coming from the organic liquid on an independent element 50-60, attached to the pot 20, this which allows you to change the filter 1 if necessary and to improve the distribution of calories on the surface of the latter.

According to the device of Figure 7, the vaporization of the organic liquid arriving through the pipe 31 is carried out by means of a first candle 70 brought to the temperature of 500 ° C whose tip 71 plunges into a first prechamber 72 in which s accumulates the organic liquid and opened at its upper part so as to allow the evacuation of the vapors obtained. The latter then come into contact with the second spark plug 27 brought to high temperature and disposed in the second prechamber 26 where the cracking of the gas occurs.

This arrangement allows the regeneration of the filter 1 from the start of the vehicle, and at idle, even when the surface of the pot 20 is not yet at the temperature allowing the vaporization of the liquid.

In the variant of FIG. 8, the filter 81 comprises, unlike those of the preceding representations, a catalytic phase, preferably based on a metal of the platinum or palladium type.

In this case, cracking gases do not burn directly in the burner unlike the previous examples, because they are not in contact with the additional oxygen at the hot spot 34 of the spark plug 27. In fact, note the absence openings at the top of nozzle 82.

The mixing of the cracked gases and the oxygen of the exhaust gases takes place further, at the level of the filter 81; this is where the oxidation occurs, inducing over the entire catalytic surface the increase in temperature necessary (approximately 450 ° C) for the initiation of combustion of the trapped carbon particles.

It will be noted that in this embodiment, the nozzle 82 is constituted by the extension of the front part 36 of the prechamber 26, which in this case is larger than the spark plug 27, and terminates in the upper part 21 of the pot 20.

Note also the possibility of introducing into the device of the invention additional air by means of an additional air pump, which then allows automatic regeneration, when the engine is stopped and even in the absence driver.

Claims (8)

1. Method for regenerating particulate filters, in particular for diesel engines, characterized in that an organic liquid such as C _x H _Y O _z , of the ethanol or methanol type having a temperature, is injected periodically upstream of the clogged filter of low vaporization, if necessary added with water, said organic liquid, after having been preheated and cracked so as to give rise to a highly flammable mixture essentially consisting of hydrogen and carbon monoxide, is introduced into the path of the incident exhaust gases. 2. Device for implementing the method of claim 1, characterized in that the organic liquid is introduced via the pipe (31) into a prechamber (26) of vaporization in contact with a candle (27) at level d '' a zone (35) of the latter with an average temperature of approximately 500 ° C, then crosses a cracking zone at high temperature (800 to 1000 ° C) represented by the part (38) of small diameter of the spark plug (27 ) and, after having crossed the constriction (36) of the anterior end of the prechamber (26) which surrounds it at a short distance, reaches a hot point (34) formed by the end of the spark plug and which opens out to the interior of the upper part (21) of the pot (20) in a burner body (32) curved towards the filter (1) and having on its opposite face openings (33) traversed by a flow of gas oxygenated exhaust, which mixes with the cracking gases coming from the prechamber (26), the assembly igniting at the hot spot (34) and thus constituting the heat input necessary for the oxidation of the particles (4) trapped in the filter (1). 3. Device according to claim 2, characterized in that the organic liquid arriving via the pipe (31) is preheated before its arrival in the vaporization prechamber (26) by passing through a double-walled envelope (41 ~ 51), thus recovering the calories available on the surface of the pot (20). 4. Device according to claim 2, characterized in that the end of the burner (32), directed towards the surface of the filter (1), is flared (43). 5. Device according to claim 2, characterized in that the vaporization, cracking and gas mixture assembly, coming from the organic liquid, is arranged on an independent element (50-60) attached to the pot (20). 6. Device according to claim 2, characterized in that the vaporization of the organic liquid is carried out upstream of the prechamber (26), by means of a first candle (70) whose tip (71) is housed in a first prechamber (72) where the organic liquid accumulates and which is open at its upper part so as to allow the evacuation of the vapors obtained. 7. Device for implementing the method of claim 1, characterized in that the filter (1) comprises a catalytic phase, preferably based on a metal of the platinum or palladium type, and that the front part of the prechamber (26) extends beyond the free end (34) of the spark plug (27) to the upper part (21) of the pot (20) and bends in the direction of the filter (1), thus constituting a nozzle (82) injecting only gases from the organic liquid, and having no opening allowing the exhaust gases to mix with the preceding gases, thereby preventing their ignition before they come into contact with the catalytic surface of the filter (1) on which the carbon particles (4) to be oxidized are trapped. 8. Device for implementing the method of claim 1, characterized in that an additional forced air supply is provided by means of a pump whose preferably automatic activation can be triggered when stopped of the motor.

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