WO2000063539A1

WO2000063539A1 - Method for avoiding accumulation and clogging in filters

Info

Publication number: WO2000063539A1
Application number: PCT/FR2000/000908
Authority: WO
Inventors: Olivier Touret; Gilbert Blanchard; Thierry Seguelong
Original assignee: Rhodia Chimie
Priority date: 1999-04-19
Filing date: 2000-04-10
Publication date: 2000-10-26
Also published as: FR2792219A1

Abstract

The present invention relates to a method for avoiding accumulation and clogging in filters from particles contained in a gas, wherein the gas is brought into contact with a filtering system comprising: a supply of gas (1) which is to be processed, a filtering enclosure (2), one or several filtering elements (3) consisting of a hollow part (4) defined by a filtering wall (5) and disposed inside the filtering enclosure (2), in addition to a outlet (6) for the gas after filtering has occurred. The invention is characterized in that the inlet surface of the filtering elements (3) is disposed in such a way that the particles thus retained can fall to the outer periphery of said elements as a result of the effect of gravity. The invention also concerns a filtering system for carrying out the inventive method.

Description

PROCESS FOR AVOIDING ACCUMULATION AND CLOGGING OF FILTERS BY PARTICLES

The present invention relates to a method for preventing the accumulation and clogging of filters by particles contained in a gas, and to a filtration system for implementing said method.

During the combustion of diesel fuel in internal combustion engines, in particular diesel engines and petrol engines operating in lean mixture, significant quantities of soot are produced. Attempts have already been made in various ways to extract the soot by filtration and to regenerate the filter by burning the soot. This combustion of soot can take place during the operation of the diesel engine, since these engines operate in the presence of an excess of oxygen, so that there is always sufficient oxygen in the exhaust gases for burning soot. However, the regeneration technique is extremely expensive to implement.

It is also known that under certain operating conditions, the temperature of the exhaust gases can reach a level high enough for combustion of the soot to take place before the filter is clogged. However, this technique has many drawbacks, such as a risk of thermal shock leading to a fracture or cracking of the ceramic filter, or a melting of the metal filter.

Another solution consists in bringing intimate contact with the soot of the oxidation catalysts in order to lower the ignition temperature of the soot and thus allowing controlled combustion of the soot during normal engine operation.

This latter approach, which today appears to be the most effective way to reduce soot emissions, does not solve the problem due to the accumulation of residues of the oxidation catalysts in the filter. In addition, due to the good filtration efficiency, other residues are also retained by the filters. The main residues come either from the combustion of oils such as particles of calcium or zinc compounds or from corrosion and wear and tear of the engine such as, for example, particles of compounds of nickel, chromium, iron, magnesium , lead or their mixtures.

The progressive accumulation of soot and various residues then leads to clogging of the filter and therefore to an increase in the pressure drop in the filter. This increase in pressure drop leads to overconsumption of fuel, induces inconvenience in driving the vehicle, and finally in certain cases can cause the vehicle to stop. The object of the invention is therefore to propose an effective method for avoiding the accumulation of various residues on the filter and thus preventing its clogging, and which does not have the drawbacks mentioned above.

For the sake of simplification, in the rest of the description, the term "particles" will be used to designate both the residual soot and the residues of various origins which can accumulate on the filter and clog it.

To this end, the subject of the present invention is a method for preventing the accumulation and clogging of filters by particles contained in a gas, in which the gas is brought into contact with a filtration system comprising: • a supply in gas (1) to be purified,

• a filtration chamber (2),

One or more filter elements (3) comprising a hollow part (4) delimited by a filter wall (5), and disposed (s) inside the filtration enclosure (2), and

• an evacuation (6) of the gases after filtration, characterized in that the inlet surface of the filter elements (3) is arranged so that the particles retained can fall to the external periphery of said elements, under the effect of gravity .

The method according to the invention is simple, economically viable, makes it possible to delay or even eliminate the cleaning or replacement of the filters and to significantly reduce the pressure drop in the filters.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, with reference to the appended schematic drawings given solely by way of examples illustrating a possible mode. of embodiment of the invention and in which: - Figure 1 is a partial sectional view of a filtration system for the exhaust gases of an internal combustion engine according to a particular embodiment of the invention; - Figure 2 is a partial sectional view of a filtration system for the exhaust gases of a conventional internal combustion engine according to an embodiment of the prior art.

The nature of the materials constituting the filter elements (3) should not be specified is not critical for the present invention. As such, there may be mentioned, for example, cordierite, mullite, porous metal plates, silicon carbide, alumina, zirconia, zirconia mullite. As indicated above, the filtration system includes:

• a gas supply (1) to be purified,

• a filtration chamber (2), • one or more filter elements (3) comprising a hollow part (4) delimited by a filter wall (5), and disposed (s) inside the filtration enclosure (2), and "an outlet (6 ) gases after filtration, with the inlet surface of the filter elements (3) arranged so that the particles retained can fall to the outer periphery of said elements, under the effect of gravity.

The filter elements (3) can have a honeycomb structure in hexagonal, tetragonal, square, triangular or wavy shape. The gases can enter the hollow part (4) of said elements, and pass through the filtering walls (5). The particles contained in the gases will then be retained and will fall to the external periphery of said walls, under the effect of gravity.

For better efficiency, it is preferable that the longitudinal axis (xy) corresponding to the direction of flow of the gas in the filter element, or the plane of the filter elements (3) have an angle of at most 45 °, advantageously at most 30 ° relative to the vertical. According to a particular embodiment of the invention, this angle is 0 ° relative to the vertical.

The particles can fall on the external periphery of the elements (3) at any time, but especially when the engine is stopped, when the engine speed changes (deceleration, idling, etc.), or under the effect of vibrations. of the exhaust line.

Any arrangement of the gas supply (1) which will allow the particles retained to fall to the outer periphery of said elements, under the effect of gravity, is suitable.

According to a preferred embodiment of the invention, the gas supply (1) is arranged in such a way that the arrival of the gas before the purification takes place from below, in the direction indicated by the arrow in the Figure 1.

The filtering walls (5) have pores with diameters allowing both the retention of particles and the diffusion of gases after purification, while remaining compatible with the pressure drop constraints linked to use. The filtration system may be provided with a device (7) for removing particles. Thus, after the purification of the gases, the particles which have fallen onto the external periphery of the filter elements (3) can be removed. The evacuation device can for example be an orifice, a grooved surface, a slide valve.

To extract the fallen particles, we will have to open the device (7). The extraction of the particles can be carried out in various ways, for example by a simple suction.

The exhaust device (7) is particularly advantageous because it allows the cleaning of the particle filter without the need to dismantle it. Another object of the invention is a filtration system for implementing the method as described above.

Although the filtration system having the above characteristics is more particularly suitable for internal combustion engines, in particular diesel engines and gasoline engines operating in lean mixture, it is not excluded to use it in other fields where such results are sought, such as, for example, in gasoline engines operating under stoichiometric conditions, gas turbines, generator sets, boilers.

Concrete but nonlimiting examples of the invention will now be given.

EXAMPLES

Example 1 (comparative)

This example is carried out with a filtration system conventionally used in which the longitudinal axis corresponding to the direction of flow of the gas in the filter element, or the plane of the filter elements has an angle of 90 ° with respect to the vertical.

The engine bench used for these tests is equipped ^'with an engine 1, 9 liter equipped with a direct fuel injection diesel and a recirculation device for exhaust gas recirculation (EGR) and a turbocharger.

The diesel fuel used to monitor the change over time in the loading of the particulate filter complies with European legislation (G04). In addition, this diesel fuel is added by a soot combustion additive marketed by the company

RHODIA TERRES RARES, under the reference EOLYS ™. The cerium concentration used is 50 ppm of cerium compared to diesel.

The filtration system is composed of a silicon carbide filter placed at the outlet of the exhaust manifold as shown in Figure 2. Figure 2 essentially shows the elements of the system of Figure 1, with the difference that the axis longitudinal (pz) corresponding to the direction of flow of the gas in the filter element or the plane of the filter elements (3b), has an angle of 90 ° relative to the vertical. The system of Figure 2 thus comprises:

• a gas supply (1b) to be purified,

• a filtration chamber (2b), Several filter elements (3b) comprising a hollow part (4b) delimited by a filtering wall (5b), and

• an evacuation (6b) of the gases after filtration, with the entry of the gases before purification which takes place in the direction indicated by the arrow in Figure 2.

The main characteristics of the filtration enclosure are as follows:

- dimension of the filter elements (3b) = 33 x 33 x 150 mm

- number of filter elements (3b) = 9 + (1/4) x 12 = 12

- volume of all filter elements = 1.96 liters - dimension of filter elements = 100 cpsi

- thermal resistance of the filtration system = 2200 ° C

The engine bench durability test is carried out by accumulating successive NEDC cycles including the Urban Driving Cycle (UDC) and the Extra Urban Driving Cycle (EUDC), which correspond to the cycles defined by European regulations.

During this endurance test, it is noted that the filtration and regeneration system works in a completely satisfactory manner: the soot accumulated during the UDC cycle is burned during the EUDC phase in particular after or during the deceleration phases and / or heavy load when the amount of soot reaches a level sufficient to maintain the propagation of combustion.

During this operating phase, it is observed for more than 1000 hours that the pressure drop which was initially measured at idle speed of 35.10 ² Pa does not exceed 400.10 ² to 450.10 ² Pa.

Beyond 1000 hours, it is observed that the pressure drop determined after each regeneration increases regularly.

From 1150 hours, engine operation is significantly disturbed by the pressure drop in the particle filter, which results in significant overconsumption of around 5% in diesel.

At 1200 hours, the endurance test is stopped to carry out an assessment of the particle filter. Visual examination of the filter shows that all of the filter elements (3b) of the filtration enclosure are clogged with a deposit of particles composed essentially of particles of cerium oxide and calcium sulphate and zinc sulphate. By sectioning the filtration chamber lengthwise, deposits are observed at different places in the filter elements: - a deposit at the end on the outlet side of the gas flow, deposits characterized by heaps of residues, positioned at different places in the filter elements and in particular on the inlet side of the filtration enclosure. Unambiguously, this accumulation of residues in the filter led to the prohibitive increase in pressure drop beyond 1000 hours of endurance.

A complete cleaning of the filter is then necessary to continue the tests. This cleaning is generally carried out by a dismantling and opening stage of the exhaust line.

Example 2 (according to the invention)

This example illustrates a particular embodiment of the invention.

The whole of the experimental device described in Example 1 is used with the exception of the silicon carbide particle filter, the geometric shape and location of which at the outlet of the exhaust manifold are of the "pancake" type, placed horizontally. such that the longitudinal axis (xy) corresponding to the direction of gas flow in the filter element (3), or the plane of the filter elements (3) have an angle of 0 ° to the vertical as shown in Figure 1.

The main features of the filter are:

- dimension of the filter elements (3) = 33 x 33 x 75 mm

- number of filter elements = 24 - volume of all filter elements = 1.96 liters

- dimension of the filter elements = 100 cpsi

- thermal resistance of the filtration system = 2200 ° C

The endurance test on an engine test bench is carried out as in Example 1 by accumulating successive UDC and EUDC cycles. Compared to Example 1, the following differences are observed:

the maximum initial pressure drop measured at idle is only 20 × 10 ² Pa, which is explained by the fact that the filtration height is only 75 mm instead of 150 mm in Example 1,

- regenerations are more frequent than in Example 1 and the pressure drop does not exceed 350.10 ² to 400 .10 ² Pa.

Up to 1500 hours, no significant increase in residual pressure is observed after regeneration.

From 1550 hours, it is observed that the pressure drop observed after each regeneration increases regularly. From 1550 hours, the residues accumulated in the lower part of the filtration chamber (2) are evacuated by aspirating these residues by the evacuation device (7) as shown in Figure 1. After aspiration of the residues, the device (7) is closed and the endurance test is resumed. After this cleaning operation, it is noted that the pressure drop measured at idle is substantially identical to that of a new filter; it is equal to 55.10 ² Pa.

It is important to note that in the context of the invention, at no time has the exhaust line been removed or disassembled, which has an undeniable technical and economic advantage.

The endurance test is continued for 800 hours without the pressure drop exceeding 400. 10 ² Pa.

This nonlimiting test of the invention clearly shows that, compared to conventional filtration systems, the filtration system according to the invention has, among other things, the following advantages:

- it allows to operate for a much longer time, and

- it allows a cleaning operation - very simple, inexpensive, and very fast regeneration.

Claims

1. Method for preventing the accumulation and clogging of filters by particles contained in a gas, in which the gas is brought into contact with a filtration system comprising:

• a gas supply (1) to be purified,

• a filtration chamber (2),

• one or more filter elements (3) comprising a hollow part (4) delimited by a filter wall (5) and disposed (s) inside the filtration enclosure (2), and • an outlet (6) gases after filtration, characterized in that the inlet surface of the filter elements (3) is arranged so that the retained particles can fall to the outer periphery of said elements, under the effect of gravity.

2. Method according to claim 1 characterized in that the longitudinal axis (xy) corresponding to the direction of flow of the gas in the filter element, or the plane of the filter elements (3), has an angle of at most 45 °, advantageously at most 30 ° relative to the vertical.

3. Method according to one of claims 1 or 2, characterized in that the longitudinal axis (xy) has an angle of 0 ° relative to the vertical.

4. Method according to any one of claims 1 to 3, characterized in that the gas supply (1) is arranged in such a way that the arrival of the gas before the purification is done from below.

5. Method according to any one of claimsl to 4, characterized in that the filtration system is provided with a device (7) for evacuating the particles fallen to the outer periphery of the filter elements (3).

6. Method for preventing the accumulation and clogging of filters by particles contained in a gas according to any one of claims 1 to 5, characterized in that it is suitable for internal combustion engines, in particular diesel engines and gasoline engines operating in lean mixture.

7. filtration system for implementing the method according to any one of claims 1 to 6.

8. Filtration system for particles contained in a gas comprising:

• a gas supply (1) to be purified,

• a filtration chamber (2),

One or more filter elements (3) comprising a hollow part (4) delimited by a filter wall (5) and disposed (s) inside the filtration enclosure (2), and

9. filtration system according to claim 8, characterized in that the longitudinal axis (xy) corresponding to the direction of flow of the gas in the filter element, or the plane of the filter elements (3), has an angle d '' at most 45 °, advantageously at most 30 ° relative to the vertical.

10. Filtration system according to claim 9, characterized in that the longitudinal axis (xy) has an angle equal to 0 ° relative to the vertical.

11. Filtration system according to any one of claims 8 to 10, characterized in that the gas supply (1) is arranged in such a way that the arrival of the gas before the purification is done from below.

12. Filtration system according to any one of claims 8 to 11, characterized in that the filtration system comprises a device (7) for evacuating the particles dropped on the external periphery of the filter elements (3).

13. A filtration system according to any one of claims 8 to 12, characterized in that it is used in internal combustion engines, in particular diesel engines and petrol engines operating in lean mixture.