FR2902348A1 - MONOLITHIC POROUS BODY HAVING A BEES NUCK STRUCTURE, ESPECIALLY PARTICULATE FILTER FOR EXHAUST GASES - Google Patents

Abstract

The body has a honeycomb structure comprising a multiplicity of channels (16) delimited by porous partitions (18). A part of the channels is closed at one of inlet and evacuation faces (12, 14) for forming input channels (20), and the other part of the channels is closed at the other face for forming output channels (22). The channels comprise a transversal section in the form of polygon with three sides. The input channels are surrounded by the output channels so that no porous partition of one of the input channels is common with a porous partition of the other of the input channels.

Description

The present invention relates to a porous monolithic body with

  honeycomb structure. It relates more particularly to a monolith of a porous ceramic material used for the filtration of a gaseous stream or a liquid stream. This invention aims especially but not exclusively a porous body used as a particulate filter (catalyzed or uncatalysed), better known under the name of FAP, for the exhaust gas of an internal combustion engine, in particular of diesel type . Generally, the exhaust gases of an internal combustion engine, especially of the Diesel type, comprise pollutants, such as particles or soot which are released into the atmosphere via the exhaust line without being treated. It is well known that the rejection of such particles causes environmental and human health nuisances.

  In an attempt to remedy these nuisances, particle treatment systems are put in place on the exhaust line of certain engines 20 to trap these particles, then their combustion to ensure the regeneration of this FAP.

  Thus, as better described in the French patent application N 2 473 113, it is known to use a filter with a monolithic body made of a refractory porous material comprising a multiplicity of channels substantially parallel to each other and arranged between the two end faces of this body. The channels are placed in the direction of circulation of the exhaust gases and are separated from each other by porous partitions. These channels are alternately plugged, at the faces of the body, at one or the other of their ends so as to form inlet channels with open ends facing the gas stream and the outlet channels with These exhaust gases penetrate into the open ends of the inlet channels and, taking into account the obstacle formed by the plugs placed at the other ends, can only through the porous walls and out through the exit channels. During this crossing, the particles contained in the gas stream are retained by the partitions and the gases flowing in the outlet channels are largely free of these particles. These captured particles are then burned in situ, in particular during an increase in the temperature of the exhaust gases flowing in the filter, so as to ensure the regeneration of this filter.

  It is further mentioned in this document, as an example embodiment, that the section of the input channels is hexagonal in shape and that the section of the output channels that surround each input channel is triangular in shape. With this arrangement, the total volume of the input channels is larger than the total volume of the output channels. This makes it possible to better distribute, in the input channels, the ash resulting from the combustion of the particles. Indeed, it is advantageous to incorporate a catalytic additive, particularly in the fuel, to promote the regeneration of this type of filter by lowering in particular the temperature of the gases required for this regeneration. During the combustion of the particles, some of the components of this additive, usually metal oxides, are not burned. This unburned part remains in the inlet channels in the form of ash and accumulates there over time during successive regeneration operations. As a result, this accumulation of ash has the disadvantage of increasing the pressure losses between the inlet and outlet channels and decreasing the filtration capacity of the FAP. It is therefore necessary to change it, or to disassemble and clean it, then to go back on the exhaust line of the engine. These operations are not only long but also a significant cost.

  The present invention proposes to overcome the drawbacks mentioned above through a filter whose period of use is increased before replacement or cleaning.

  For this purpose, the present invention relates to a monolithic porous body having a honeycomb structure comprising a plurality of channels delimited by porous walls extending from one of the end faces of the body to the other of the faces of said body. body, a portion of said channels being obstructed at one of the faces to form input channels and the other portion of the channels being obstructed at the other side to form output channels, characterized in that the channels The input and output include a three-sided polygonal cross section and at least one side of the input channels is common to one side of at least two output channels.

  Preferably, the cross section may be in the shape of an equilateral triangle.

  The sum of the transverse surfaces of the inlet channels may be between 35 and 50% of the cross sectional area of the body. The sum of the transverse surfaces of the outlet channels can be between 15 and 30% of the cross sectional area of the body.

  Advantageously, each input channel may be surrounded by output channels.

  The monolithic porous body can be used as a particulate filter for exhaust gases. The monolithic porous body can also be used as a membrane for the filtration of liquid or gaseous streams. The other features and advantages of the invention will now be apparent. on reading the description which follows, given by way of illustration only and not limiting, and to which are appended: - Figure 1 which is a diagram showing a perspective view of the porous monolithic body according to the invention; FIG. 2 which illustrates a view on a larger scale of a portion S of the view of FIG. 1 and FIG. 3 which is a section along the line 33 of FIG. 2.

  In FIG. 1, the body 10 is a monolithic porous body with a honeycomb structure which is used preferentially but not exclusively as a particulate filter (FAP) for the exhaust gases of an internal combustion engine, especially of Diesel type.

  The material of this monolith can be silicon carbide, silicon nitride, cordierite, or any other refractory ceramic material.

  This body is preferably a cylindrical body, here circular, delimited by two faces of substantially parallel ends to one another, an inlet intake face 12 and a discharge face 14. Between these two faces extends a plurality of channels 16 substantially parallel to each other. These channels are separated from each other by porous partitions 18 of substantially constant thickness and form input channels 20 and output channels 22 whose configuration will be explained in the following description. Referring additionally to Figures 2 and 3, these channels are alternately plugged at one or the other of their ends to form inlet channels 20 having open ends at the inlet face. 12 and obstructed ends at the discharge face 14 by plugs 24 and outlet channels 22 with ends plugged by a plug 26 on the intake face 12 and open ends on the discharge face 14 .

  In practice, the input channels 20 are surrounded by output channels and the open ends of these input channels are placed opposite the exhaust gas stream while the plugged ends of the output channels are opposite this same gas flow. As shown in more detail in FIG. 2, the inlet and outlet channels are delimited by porous partitions 18 so as to each constitute a channel with an arrangement of these porous partitions which, in cross-section, forms a three-dimensional polygon. sides, more particularly in the form of equilateral triangle, and this along the entire length of these channels. It may be noted that the respective configuration of the channels is such that the input channels are surrounded by the output channels so that no partition of an input channel is in common with a partition of another input channel. In addition, the cross sections of the input channels 20 have a larger surface area than the sections of the output channels 22 and the total volume of the input channels is greater than the total volume of the output channels. More specifically, the volume of the input channels is between 35 and 50%, advantageously greater than 40%, of the volume of the filter and the volume of the output channels is 15 to 30%, preferably greater than 18%, of this volume. filter volume. In addition, the input channels all have identical sections and the output channels also all have identical sections. As best seen in FIG. 2, the porous partitions of each input channel 20 are walls common to at least two output channels so as to place the interior of the input channel in communication with six regularly distributed output channels. around this entrance channel.

  To arrive at such a configuration, it is considered an initial equilateral triangle cross-section (ABC) of an input channel corresponding to the periphery of this channel with a horizontal base BC and a coaxial internal equilateral triangular section A'B ' C ', with a horizontal base B'C', representing the internal volume of this channel. The three sides of this channel being formed by the porous partitions 18. For reasons of simplification of the description, it will be specifically mentioned section ABC, the latter each incorporating the internal section A'B'C '. On section ABC, it is placed a median line Y passing through the vertex A which shares the base BC in two equal parts. It is also placed a point G which is the center of gravity of the input channel and which is located on the right Y, by the equilateral triangle configuration. From these elements, the triangular pattern ABC (with its pattern A'B'C ') is reproduced identically along this line Y in such a way that the vertex Al of the new triangular outer section Al BI Cl (with its internal section A'l B'l Cil) is located on the horizontal base B'C 'of the inlet channel 20 and in the middle and that the centroid G1 is located on the right Y. This operation is repeated a number of times necessary and sufficient to obtain the desired size. This dimension may correspond, as illustrated by way of example in FIG. 1, to substantially the radius of the monolithic body. Of course, and without departing from the scope of the invention, the point A'l of the triangle A'1 B'1 C'1 can lie between the position shown in FIG. 2 and at most on the base BC so as to do not locally thin the porous wall 18. To continue the establishment of these channels, it is planned to postpone the triangle ABC with its internal volume A'B'C 'and its center of gravity G in a position parallel to that it busy. To do this, the new triangle with a vertex A2 and a base B2C2 keeps its orientation but its centroid G2 is placed on a line D. This line D extends the median passing through the point G and the point C of the triangle ABC and forms with the line Y an angle al which corresponds, in the case of an equilateral triangle, to that of the angle at the apex of this triangle of a value of 60. The point B2 of the triangle A2B2C2 and the point C of the triangle ABC are situated respectively on the internal side A'1 C'l and A'2B'2 by dividing these sides into two equal parts. In this configuration an output channel 22 is created by the cooperation of parts of partitions of triangles ABC, Al BI C1 and A2B2C2 and communicates with these three triangles through the parts of partitions. From point A2, it is placed a median line Y1 which passes through the centroid G2 of the triangle A2B2C2 and which is parallel to the line Y. From this and as has been described in relation to the line Y, the triangles are reported identically along this line Y1 to the desired size, which in the case considered will be smaller than that taken along the line Y. These operations are reproduced to the left of the line Y and symmetrically thereto, so as to place a succession of triangular channels along a line Y2 as described in relation to the line Y1 and using a line D2, an angle cil (also 60) and a line G3 center of gravity. Thanks to this arrangement, the distance X between the lines Y, Y1 and Y, Y2 is smaller than the side of the triangle, here the base BC. This makes it possible to accommodate a greater number of input channels in the same area. In the final, an input channel 20 is obtained in an equilateral triangle ABC communicating by its base BC with two output channels, its side AC with two other output channels and the last side AB with two output channels. In practice and as can be seen more clearly in FIG. 1, the body 10 is formed of six longitudinally-shaped segments 28, in the shape of a segment or quarter with a substantially triangular cross-section, assembled together by any means, such as a cement 30. Each segment thus comprises inlet and outlet channels whose number, considering the radial direction of the body, varies according to the circumferential position of these channels and more precisely varies from the central part (right Y ) towards the ends.

  By this arrangement, as shown in FIG. 3, the exhaust gas enters only the inlet channels according to the arrows F and then passes through the porous partitions (arrows F1) and then emerges through the exit channels according to the arrows. F2. During this crossing, the particles contained in the gas stream are retained on the upstream part of the partitions and the gases, which exit from the downstream part of these partitions, circulate in the outlet channels while being largely free of of these particles.

  With this configuration, the ash storage capacity resulting from the regeneration of the filter is increased and the life of such a filter is greatly increased.

  In addition, since no porous partition of an input channel is common to another input channel, almost the entire surface of the input channels is common with the output channels which limits the loss of load compared to a filter of the state of the prior art. This is mainly due to the fact that all the surfaces of the input channels are filtering. Furthermore, considering a filter as described in the French patent application N 2 473 113 and with the same cross-sectional area value, the filtration surface constituted by the parts of the partitions common between the inlet channels and the channels output is vastly larger.

  The present invention is not limited to the example described above but encompasses all variants or all equivalents. In particular, the body may be formed of a single circular element or a multiplicity of polygonal elements assembled to each other by a bonding cement. In addition, this body can be used both as a particulate filter, catalysed or uncatalysed, to treat pollutants (particles, CO, NOx and HC) contained in the exhaust gas of an internal combustion engine that as a membrane for separation, such as the separation of gaseous bodies, such as the separation of hydrogen from a gaseous stream.

Claims (7)

  Monolithic porous body having a honeycomb structure comprising a multiplicity of channels (16) delimited by porous walls (18) extending from one (12) of the end faces of the body to the other ( 14) faces of said body, a portion of said channels being obstructed at one side to form input channels (20) and the other portion of the channels being obstructed at the other side to form output channels (22), characterized in that the input (20) and output (22) channels comprise a three-sided polygonal cross-section and that at least one of the sides of the input channels (20) is common to one side of at least two output channels (22).   2) Porous monolithic body according to claim 1, characterized in that the cross section is in the shape of an equilateral triangle.   3) porous monolithic body according to claim 1 or 2, characterized in that the sum of the transverse surfaces of the inlet channels is between 35 and 50% of the cross-sectional area of the body. 20   4) Porous monolithic body according to one of the preceding claims, characterized in that the sum of the transverse surfaces of the outlet channels 22 is between 15 and 30% of the cross-sectional area of the body. 25   5) monolithic porous body according to one of the preceding claims, characterized in that each input channel (20) is surrounded by output channels (22).   6) Use of the porous monolithic body according to one of the preceding claims as particulate filter for exhaust gases.   7) Use of the porous monolithic body according to one of claims 1 to 5 as a membrane for the filtration of liquid or gaseous currents.