FR2792219A1 - Method for avoid accumulation and clogging in filters of internal combustion engine has filtrating elements with inlet surface placed so that kept particles fall down at outer periphery of elements - Google Patents

Abstract

Method involves contact between gas and filtration system. Filtration system comprises supply of gas to filter (1), filtration housing (2), filtrating elements (3), and gas outlet (6). Filtrating elements have hollow part (4) delimited by filtrating wall (5) and placed inside filtration housing. Inlet surface of filtrating elements are placed so that kept particles fall down, due to gravity, at outer periphery of elements. An Independent claim is also included for the filtration system.

Description

PROCESS FOR AVOIDING ACCUMULATION AND CLOGGING

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 a system for

  filtration for the implementation of said process.

  During the combustion of diesel fuel in internal combustion engines, in particular diesel engines and petrol engines operating in lean mixture,

  significant amounts 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 filter.

  ceramic, or a fusion 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 a controlled combustion of the soot during normal walking.

of the motor.

  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

  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 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 to avoid the accumulation of various residues on the filter and thus avoid its clogging, and which does not

  not have the disadvantages mentioned above.

  For the sake of simplicity, in the rest of the description, the term "particles" will be used to designate both the residual soot and the residue of origins

  various which can accumulate on the filter and clog it.

  To this end, the present invention relates to a process 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 enclosure (2), * one or more filter elements (3) comprising a hollow part (4) delimited by a filtering wall (5), and disposed (s) at the interior of the filtration chamber (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 back to the outer 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 reduce

  significantly the pressure drop in the filters.

  The invention will be better understood and other characteristics, details and advantages

  of it will appear more clearly during the explanatory description which will

  follow, with reference to the accompanying schematic drawings given only by way of examples illustrating a possible embodiment of the invention and in which: - Figure 1 is a partial sectional view of a filtration system for d gases 'exhaust from 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 a mode of

realization 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, mullite zirconia.

  As indicated above, the filtration system comprises: C a gas supply (1) to be purified, ò 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, with the inlet surface of the filter elements (3) disposed so that the retained particles can fall on 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 outer 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 not more than 30 from 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 line

exhaust.

  Any arrangement of the gas supply (1) which will allow the particles retained to fall to the external periphery of said elements, under the effect of the

gravity, 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 Figure 1.

  The filter 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

  may for example be an orifice, a grooved surface, a slide valve.

  To extract the fallen particles, we will have to open the device (7).

  Particle extraction can be done in different ways, for example by

a simple aspiration.

  The evacuation device (7) is particularly advantageous because it allows the

  cleaning the particulate filter without having to dismantle it.

  Another object of the invention is a filtration system for the implementation

  of 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 petrol engines operating in lean mixture, it is not excluded to use it in other fields. o such results are sought, as for example in petrol engines operating under conditions

  stoichiometric, gas turbines, generator sets, boilers.

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

EXAMPLES

  Example I (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 relative to

vertically.

  The engine test bench used for these tests is equipped with a 1.9 liter engine fitted with a direct injection diesel fuel supply and a device for recirculating

  exhaust gas (EGR) and a turbocharger.

  The diesel fuel used to monitor the change over time in the loading of the particle filter complies with European legislation (G04). In addition, this diesel fuel is added by a soot combustion additive sold by the company TM RHODIA TERRES RARES, under the reference EOLYSTM. Cerium concentration

  implementation 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 (lb) 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 the filter elements = 1.96 liters - dimension of filter elements = 100 cpsi - thermal resistance of the filtration system = 2200 C. The durability test on the engine test bench is carried out by accumulating successive NEDC cycles including the Urban Driving Cycle (UDC) and the Extra Urban Driving Cycle (EUDC) ), who. 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 spread 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 35.102 Pa,

  does not exceed 400.102 to 450.102 Pa.

  Beyond 1000 hours, it is observed that the pressure drop determined after

  each regeneration increases regularly.

  From 1150 hours onwards, the operation of the engine is significantly disturbed by the pressure drop in the particle filter, which results in a

  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 chamber are clogged by 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 buildup of residue in the filter resulted in

  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 step of dismantling and opening 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 flow of the gas in the filter element (3), or the plane of the filter elements (3) have an angle of 0 by

  with respect to the vertical as shown in Figure 1.

  The main characteristics of the filter are as follows: - dimension of the filter elements (3) = 33 x 33 x 75 mm - number of filter elements = 24 - volume of all the filter elements = 1.96 liters dimension of the filter elements = 100 cpsi - thermal resistance of the filtration system = 2200 C The endurance test on the engine test bench is carried out as in Example 1 in

  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 20.102 Pa, which is explained by the fact that the filtration height is only 75 mm instead of mm in example 1, - regenerations are more frequent than in example 1 and the pressure drop

  does not exceed 350.102 to 400.102 Pa.

  Up to 1500 hours there is no significant increase in pressure

residual after regeneration.

  From 1550 hours, it is observed that the pressure drop observed after

  each regeneration increases regularly.

  From 1550 hours, we proceed to the evacuation of the accumulated residues in the lower part of the filtration enclosure (2) by proceeding with the suction of these

  residues by the discharge 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 55.102 Pa.

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

  undeniable technical and economic.

  The endurance test is continued for 800 hours without loss of

load does not exceed 400. 102 Pa.

  This nonlimiting test of the invention clearly shows that, compared with conventional filtration systems, the filtration system according to the invention has, among other things, the following advantages: - it allows operation for a much longer time, and - it makes it possible to carry out a cleaning operation - very simple regeneration, little

expensive, and very fast.

Claims (12)

  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 filtering wall (5) and disposed (s) inside the filtration chamber (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.   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 with respect to the vertical.   3. Method according to one of claims 1 or 2, characterized in that the axis   longitudinal (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 gas inlet before The purification is done from the bottom.   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 fallen particles   at 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, especially diesel engines   and gasoline engines operating in lean mixture.   7. A filtration system for particles contained in a gas comprising: At a gas supply (1) to be purified, * a filtration enclosure (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 retained particles can fall to the outer periphery of said particles   elements, under the effect of gravity.   8. filtration system according to claim 7, 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.   9. filtration system according to claim 10, characterized in that the axis   longitudinal (xy) has an angle equal to 0 with respect to the vertical.   10. filtration system according to any one of claims 7 to 9,   characterized in that the gas supply (1) is arranged in such a way that   the gas arrives before the purification is done from below.   11. Filtration system according to any one of claims 9 to 10, characterized   in that the filtration system comprises a device (7) for evacuating   particles dropped on the outer periphery of the filter elements (3).   12. Use of a filtration system according to any one of claims 7 to   11 in internal combustion engines, including diesel engines and   gasoline engines operating in lean mixture.