Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
  • G01N15/082—Investigating permeability by forcing a fluid through a sample
  • G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
  • B01D65/10—Testing of membranes or membrane apparatus; Detecting or repairing leaks
  • B01D65/102—Detection of leaks in membranes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
  • G01N2015/0846—Investigating permeability, pore-volume, or surface area of porous materials by use of radiation, e.g. transmitted or reflected light

Definitions

• the invention relates to the field of honeycomb structural particle filters used in an exhaust line of an engine for the removal of soot, typically produced by the combustion of a diesel fuel in a combustion engine. internal combustion. More particularly, the invention relates to a method or method for detecting and characterizing internal defects of the filter such as porous, absent or additional plugs, cracks and generally any fault likely to cause a decrease in performance even an inactivation of said filter.
• Filtration structures for soot contained in the exhaust gas of an internal combustion engine are well known in the prior art.
• a typical filter most often has a honeycomb structure, one of its faces allowing the admission of the exhaust gases to be filtered and the other side the evacuation of the filtered exhaust gases.
• the structure comprises, between the intake and discharge faces, a set of adjacent channels or ducts of axes parallel to each other separated by porous filtration walls, which ducts are closed at one or the other of their ends for delimiting input chambers s 'opening according to the inlet face and outlet chambers s' opening according to the discharge face.
• the peripheral part of the structure is advantageously surrounded by a cement, called coating cement in the following description.
• the channels are alternately closed in an order such that the exhaust gases during the crossing of the nest body of bees, are forced to cross the side walls of the inlet channels to join the outlet channels.
• the filter bodies are porous ceramic material, for example cordierite or silicon carbide.
• the particulate filter is subjected to a succession of filtration phases (accumulation of soot) and regeneration (removal of soot).
• filtration phases the soot particles emitted by the engine are retained and are deposited inside the filter.
• regeneration phases the soot particles are burned inside the filter, in order to restore its filtration properties.
• the porous structure is then subjected to intense thermal and mechanical stresses, which can cause micro-cracking likely over time to cause a severe loss of filtration capacity of the unit, or even its complete deactivation. This phenomenon is particularly observed on monolithic filters of large diameter.
• a typical succession of the main steps in a conventional production process includes, among others, the extrusion of an SiC-based paste or cordierite into monolithic elements of the honeycomb type, the plugging of certain ends of the conduits, the baking, possibly machining, the application of a coating cement and seal between said elements followed by their assembly, the solidification of said cement generally by a suitable heat treatment.
• a typical succession of such steps is for example described in the patent applications WO 2004/065088 or EP 1 142 619.
• these steps are as many sources of potential defects in the internal structure of the filter eg discontinuity (s) of the walls within a honeycomb element or joints between elements, imperfect plugging of ducts, crack (s) of walls or joints, missing plug (s), porous or additional, uneven distribution (s) of wall thicknesses or joints, imperfect sealing of coating cement.
• the detection and preferably the characterization of these defects are thus essential because these can significantly affect the efficiency and the integrity of the filter, as soon as it is put into service or after a few successive cycles of regeneration, during which the filter is subjected to strong constraints thermomechanical.
• a known method is based on pressure drop measurements between the two faces of the structure. However, this measure does not allow sufficient discrimination because it is too strongly related to the intrinsic variation of the porosity and the thickness of the walls.
• Patent Application FR 2 840 405 describes a non-destructive method for detecting defects in a particle filter by the use of ultrasound. It is indicated that the measurement of the ultrasound travel time and / or power and amplitude variations of the ultrasonic signal during the passage through the porous mass is representative of the intrinsic defects of the structure.
• One of the objects of the present invention is to provide a method for non-destructively characterizing a particle filter as previously described.
• the present invention relates to a non-destructive, simple, economical and sufficiently discriminating method for characterizing and distinguishing, for example during a production process, honeycomb structures without internal defects structures with internal defects to make them unacceptable for use as a particulate filter.
• the present invention relates to a non-destructive method for detecting the internal defects of a filter, possibly catalytic, in particular used for the treatment of a gas charged with soot particles, said filter comprising a honeycomb filter element or a plurality of honeycomb filter elements, the one or more elements comprising a set of adjacent ducts or channels with mutually parallel axes separated by porous walls, which ducts are closed by means of plugs at one or the other of their ends to define inlet chambers s 'opening on a gas inlet face and outlet chambers s' opening on a gas evacuation face, in such a way that the gas passes through the porous walls, said method being characterized in that it determines the presence or absence of said defects by measuring the propagation of a flow of ga z such as air through the filter element (s).
• the term "flow propagation” means the variation of the flow of a gas passing through the structure via its porous walls.
• Said defects may be of the type: discontinuity of the walls within a honeycomb element or joints between elements, imperfect plugging of the ducts, cracks in the walls or joints, missing, porous or additional plug, non-homogeneous distribution of thicknesses of walls or joints, imperfect sealing of the coating cement.
• the presence or absence of said defects is determined with respect to a reference value corresponding to a filter having no internal defects.
• the propagation of the gas flow through the filter is evaluated by analyzing the emission spectrum of an infrared radiation at the filter outlet, in particular by thermographic analysis. infrared.
• the propagation of the gas flow through the filter is evaluated by at least one measurement of the gas velocity at the outlet of said filter.
• a set of measurements of the speed of the gases is carried out so as to obtain a profile of the said speeds at the output of the filter.
• the presence or absence of said defects can be determined by comparison between the different values of the velocity of the gases obtained on the filter.
• the pitch of the measurement is advantageously equal to or less than the width of a duct.
• the porous walls of the filter may be preloaded with a soot concentration of at least 1 gram per liter.
• the present invention relates to a device for implementing the method described above, comprising in particular means for impelling a gas such as air into the filter, means for controlling the flow of air introduced into the filter, means for regulating the flow rate and / or the pressure of the air introduced into the filter, means for measuring, at the outlet of the filter, the propagation of a flow of gas such as air through the filter element or elements.
• the measuring means are, for example, means for measuring the speed of the gases, for example chosen from propeller anemometers, hot wires, pitot tubes, hot-ball systems, hot-film systems PIV type (velocimetry image particles), LDA (laser doppler anemometry) type systems measuring the doppler effect related to air velocity.
• the control means may comprise a butterfly valve associated with a precision valve.
• the measuring means can also be systems in which the propagation of the gas flow is evaluated by analyzing the emission spectrum of an infrared radiation at the filter outlet, in particular the infrared thermography analysis systems.
• the method or device described above finds particular application in the control of manufacturing processes of particulate filters, the control of particle filter recycling processes, studies for the design, characterization or development of new filters with particles, in particular as regards the selection of new or improved materials that can be used in said filters, endurance control studies of filters.
• FIG. 1 of an example embodiment of a device according to the invention for implementing the present method.
• the device has been designed with the primary purpose of visualizing the defects of the filter developing in a radial direction.
• the experiments conducted by the applicant have shown that other types of defects, present in the structure in a longitudinal direction, have an effect on the signal detected according to the present method and its associated device and can therefore also be characterized.
• a gas typically air
• the velocity profile of the gases is measured and analyzed at the outlet of the latter.
• the measurements are carried out at a rate and ideally at constant pressure, at the inlet (upstream) of the particulate filter, in the direction of propagation of the gas.
• the device is composed of a tubular member 1 on which are arranged in succession:
• an air filter 2 This filter is optional and its function is to prevent the accumulation in the system of the dust present in the ambient air.
• This valve makes it possible to roughly regulate the flow rate and the pressure at the inlet of the particle filter 4.
• this valve 3 may be advantageous to couple this valve 3 with a valve of This valve 5 is for example of the guillotine type and allows to work with a flow of air whose temperature is substantially constant.
• the contribution of this valve 5 advantageously allows a precision on the flow rate of less than 1 m 3 / h (cubic meter per hour) as well as a facilitated regulation of the pressure near and upstream of the particle filter 4, in the direction of air movement.
• the blower makes it possible to drive the air into the filter 4.
• the rate of blown air depends in general on the type of defect that is to be characterized.
• the flow rate of air blown by the blower can typically vary between 10 and 700 m 3 / h, preferably between 200 and 400 m 3 / h.
• the flow of air blown by the blower varies between 10 and 700 m 3 / h, preferably between 10 and 100 m 3 / h.
• the flow meter allows verification and control of the air flow during handling. 5 °) a length of tube 8 fitted between the blower 6 and the divergent 9:
• the length of the tube 8 between the fan and the divergent is advantageously greater than about 50 times the diameter of the tube.
• Such a configuration makes it possible in particular to obtain a substantially constant speed of the gas flow lines at the outlet of the tube 8, that is to say a stabilized flow of gas at the inlet of the diverging portion.
• the apex angle of the divergent is preferably less than 7 °, for example 6 °. Such a configuration allows in particular a homogeneity of the gas stream lines arriving at the input of the particle filter.
• the inlet of the filter and the outlet of the divergent are directly joined.
• the envelope 10 of the filter (called “canning" in the loom) had a length greater than that of the filter 4, so that there is a space between the outlet 11 of the divergent 9 and the inlet 12 of the filter 4.
• the function of the pressure sensor is to check and control the absolute and / or relative pressure in the portion of the divergent immediately upstream of the particulate filter, in the direction of progression of the air. 8 °) optionally a temperature sensor 14, near the inlet of the filter 12.
• the measuring system can be selected according to the invention from any known system in the field of fluid mechanics for measuring the velocity of a gas flow. Without this being considered restrictive, it is possible, for example, according to the invention to use one or more mobile propeller anemometers sweeping the downstream surface of the particle filter at the outlet of the present device, a series or battery of fixed anemometers.
• one or more hot son or a set of hot son the speed of the gas being measured according to the heat loss of the son or son
• one or more tubes pitot hot-ball systems, hot-film systems, PIV-type systems, laser-doppler-anemometry (LDA) systems measuring Doppler effect related to air velocity.
• LDA laser-doppler-anemometry
• the presence or absence of defects is determined by measuring the propagation of the gas flow through the structure. For example and as previously described in relation with FIG. 1, this measurement is associated with a study of the gas velocity at the output of the structure.
• any other means for carrying out the said known measure for this purpose can be used according to the invention.
• the variations obtained being related to the conditions of passage of gas through said filter, a spectrum is obtained characteristic of the presence or absence of defects (s).
• the distance between the rear face 16 of the filter and the air measuring system 15 is in general a compromise between the dimensions generated by the dimensions of the measurement system itself and the power of the air flow at the outlet of the air. filtered.
• the distance filter / measuring system is between 0 and a few centimeters, preferably between 0 and 2 cm.
• control method according to the invention of a particulate filter can be carried out according to different modes, in particular according to the type of defect sought.
• a first mode it is sought to visualize defects of the type broken cap, porous, additional or non-filtering wall.
• the filter is directly placed in the measuring device as just described, without prior charge.
• the air flow rate is in general between 200 and 400 m 3 / h.
• the analysis may be comparative, for example with respect to a reference value corresponding to a filter that does not have this type of defect.
• the experiments carried out by the applicant have indeed shown that the gas velocity values obtained at the filter outlet were particularly reproducible if the flow rate and ideally the gas pressure at the inlet of the filter were substantially identical for the two filters (reference filter and filter to be analyzed). It is preferable according to the invention to work at constant pressure for a better characterization of the filter.
• the analysis can also be carried out by comparison between the different values of the speeds obtained, a substantial difference with respect to a measured average speed indicating the presence of the defect sought.
• a local relative difference of at least 5%, preferably at least 10% relative to the average speed of the gases measured at the output of the filter may be sufficient to detect, characterize and locate an internal defect.
• relative difference it is understood, in the sense of the present description, the absolute value of the difference in speed relative to the speed observed on the reference filter of the same format, multiplied by 100.
• the filter is placed in the measuring device previously described after a prior step in which it has been loaded in soot or preferably in a powdery material model less harmful than soot but whose characteristics (granulometry, grain shape etc.) are close.
• the air flow can be between 20 and 40 m 3 / h.
• the analysis can be compared with a known reference, under the same conditions of air flow and preferably pressure, measured immediately at the inlet of the filter, in the direction of propagation of the gas.
• the analysis can also be performed by comparing the speeds obtained on the filter analyzed, for example with respect to an observed average speed.
• a local relative difference of at least 10%, preferably at least 20% relative to the average speed of the gases measured at the output of the filter makes it possible to detect, characterize and locate an internal defect of the crack type, under the conditions of the measure.
• the invention is not limited to these embodiments.
• the filter used in the following examples combines in a filter block several monolithic elements in honeycomb.
• the extruded elements are made of silicon carbide (SiC). After firing, they are machined and then bonded to each other by bonding with a SiC silicon carbide cement, the structure thus obtained being then coated with a coating cement, according to well-known techniques.
• the manufacture of such filtering structures is in particular described in patent applications EP 816 065, EP 1 142 619, EP 1 455 923 or WO 2004/090294.
• the device used is of the type described in relation with FIG. 1.
• the divergent has an apex angle of 6 °.
• the gas velocity measuring system consists of a propeller anemometer of the brand Schiltknecht, marketed by the company RBI Instrumentations, mounted on two cylinders arranged in a cross, which thus allow its mobility along two axes of displacement X and Y .
• the system moves stepwise on a first line in the X direction, the pitch being set at 1.8 mm.
• the pitch is chosen equal to the width of a channel, so as to obtain optimal discrimination.
• the relative difference between the reference value thus determined and the speed value obtained when the measurement is made at the level of the defective plugs is again significant (12.5%) although the air flows are important and allows the determination, characterization and even localization of the additional plugs.
• the positions of the defects found by measuring the gas velocities correspond to the exact positions of the additional plugs intentionally added.
• the air pressure at the filter inlet is substantially greater than that of the first two examples and the measured gas output rates much lower.
• the results obtained under these conditions show that, for equivalent flow and air pressure conditions at the inlet of the filter, the speeds measured at each step by the anemometer between the reference filter and the parts of the flawless filter are substantially identical (1.9 m / s) with a small absolute variation (0.1 m / s).
• the device and the method according to the invention can make it possible to quickly evaluate a particulate filter at the end of its production.
• the device can be installed on the margins of the production line, the analysis of a portion of the filters produced allowing the validation of a whole batch of production.
• a device according to the invention may be placed at the output of the production line and all the product filters controlled at the end of the line, to meet product quality objectives.
• the invention is also applicable to the search for defects on the filter after recycling thereof, providing in this a less expensive and more precise technique than that described in patent FR 2 840 405.
• the method and the device according to the invention apply not only to the control of the manufacturing or recycling processes of the filters as previously described but also
• the present invention is applicable for the detection of defects present both in particle filters simple, ie ensuring only a function of filtering soot, than in catalytic filters, associating the soot filtration function with a conversion activity of the nitrogen oxide type, sulfur or carbon monoxide.
• Such catalytic filters are, for example, obtained by impregnating the initial structure in a solution comprising the catalyst or a precursor of the catalyst.

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Dispersion Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)
• Sampling And Sample Adjustment (AREA)
• Filtering Materials (AREA)
• Processes For Solid Components From Exhaust (AREA)

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• 2005
  • 2005-06-29 FR FR0551817A patent/FR2887984B1/fr not_active Expired - Fee Related
• 2006
  • 2006-06-27 EP EP06778975A patent/EP1896825A2/fr not_active Withdrawn
  • 2006-06-27 EA EA200800164A patent/EA200800164A1/ru unknown
  • 2006-06-27 US US11/994,130 patent/US20090120062A1/en not_active Abandoned
  • 2006-06-27 BR BRPI0613572A patent/BRPI0613572A2/pt not_active IP Right Cessation
  • 2006-06-27 WO PCT/FR2006/050631 patent/WO2007003839A2/fr active Application Filing
  • 2006-06-27 JP JP2008518937A patent/JP2009500600A/ja active Pending
  • 2006-06-27 CA CA002613710A patent/CA2613710A1/fr not_active Abandoned
  • 2006-06-27 AU AU2006264719A patent/AU2006264719A1/en not_active Abandoned

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