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WO2008138146A1 - Filtre segmenté contre les matières en suspension pour flux d'échappement de moteur - Google Patents

Filtre segmenté contre les matières en suspension pour flux d'échappement de moteur Download PDF

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Publication number
WO2008138146A1
WO2008138146A1 PCT/CA2008/000945 CA2008000945W WO2008138146A1 WO 2008138146 A1 WO2008138146 A1 WO 2008138146A1 CA 2008000945 W CA2008000945 W CA 2008000945W WO 2008138146 A1 WO2008138146 A1 WO 2008138146A1
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WO
WIPO (PCT)
Prior art keywords
segments
filter
segment
regeneration
stream
Prior art date
Application number
PCT/CA2008/000945
Other languages
English (en)
Inventor
Xuantian Li
Paul Sebright Towgood
Campbell R. Mcconnell
Erik Paul Johannes
Original Assignee
Nxtgen Emission Controls Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nxtgen Emission Controls Inc. filed Critical Nxtgen Emission Controls Inc.
Publication of WO2008138146A1 publication Critical patent/WO2008138146A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2425—Honeycomb filters characterized by parameters related to the physical properties of the honeycomb structure material
    • B01D46/2429—Honeycomb filters characterized by parameters related to the physical properties of the honeycomb structure material of the honeycomb walls or cells
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2425—Honeycomb filters characterized by parameters related to the physical properties of the honeycomb structure material
    • B01D46/24491—Porosity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/2455—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure of the whole honeycomb or segments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/247—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure of the cells
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/2474—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure of the walls along the length of the honeycomb
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/2478—Structures comprising honeycomb segments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/2482—Thickness, height, width, length or diameter
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
    • B01D46/2403—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies characterised by the physical shape or structure of the filtering element
    • B01D46/2418—Honeycomb filters
    • B01D46/2451—Honeycomb filters characterized by the geometrical structure, shape, pattern or configuration or parameters related to the geometry of the structure
    • B01D46/2484—Cell density, area or aspect ratio
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/022—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F01N3/025—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust
    • F01N3/0253—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust adding fuel to exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/60—Discontinuous, uneven properties of filter material, e.g. different material thickness along the longitudinal direction; Higher filter capacity upstream than downstream in same housing

Definitions

  • the present invention relates to engine exhaust stream particulate filters and, more particularly, to diesel engine exhaust stream particulate filters.
  • a diesel particulate filter (sometimes abbreviated herein as a "DPF") is a device designed to remove diesel particulate matter or soot from the exhaust gas stream of a diesel engine.
  • Diesel engines during combustion of the fuel/air mixture, produce a variety of particles, generically classified as diesel particulate matter, due to incomplete combustion.
  • the composition of the particles varies widely depending upon engine type, age and the emissions specification that the engine was designed to meet.
  • diesel engine emissions were not regulated until 1987 when the first California Heavy Truck rule was introduced capping particulate emissions at 0.60 g/BHP hour. Since then, progressively stricter standards have been introduced for diesel engine particulate emissions. While particulate emissions from diesel engines were first regulated in the United States, similar regulations have also been adopted by the European Union, most Asian countries, and the rest of North and South America.
  • a DPF cleans an exhaust gas stream by forcing the gas stream to flow through the filter.
  • Diesel particulate filter technologies on the market. Each is designed around similar requirements:
  • Filters generally require more maintenance than catalytic converters. Particulates trapped by the filter will eventually clog the pores. This increases the pressure drop across the filter which, when it reaches or exceeds a critical value, is capable of reducing the efficiency of the engine. Regular filter maintenance or regeneration therefore becomes necessary.
  • Regeneration is the process of removing accumulated particulates from a filter. This is done either passively or actively by intentionally increasing the temperature of the trapped particulates.
  • On-board active filter management can employ a variety of strategies, for example:
  • a computer monitors one or more sensors that measure back-pressure and/or temperature and, based on pre-programmed set points, makes decisions on when to activate and end the regeneration cycle. Running the regeneration cycle too often, although keeping the back-pressure in the exhaust system low will use extra fuel. Not regenerating the DPF sufficiently frequently can increase the risk of engine damage, can reduce engine eff ⁇ ciency due to high back pressure, and can result in excessive regeneration temperatures and possible DPF failure.
  • diesel particulate matter combusts when temperatures around 600 0 C and above are attained.
  • the start of combustion causes a further increase in temperature.
  • the combustion of particulate matter can raise the temperature of the DPF above a threshold temperature that can cause damage to the DPF.
  • spark- ignited engines which typically have less than 0.5% oxygen in the exhaust gas stream upstream from the emission control device(s)
  • many diesel engines typically have 8% to 18% oxygen in the exhaust stream pre-filter. While the amount of available oxygen makes fast regeneration of a filter possible, it can also contribute to runaway regeneration problems.
  • the particulate filter can be divided into segments which can be regenerated at different times by the selective introduction of a fuel into the particular segment(s) being regenerated, while the engine exhaust stream continues to flow though all segments of the filter including those that are being regenerated.
  • Regenerating a segment or portion of the filter at a given time compared to the entire filter, reduces the required mass flow rate of the fuel used for regeneration. If, for example, syngas is used as the fuel, this approach can offer the advantage of reducing the size and cost of a syngas generator required by the system.
  • a DPF is segmented into equal segments of the substantially same dimensions and structure, when all segments are equally loaded with soot the flow rate of exhaust gas passing through each of the segments will be about the same. For example, if the DPF is segmented into four quadrants then about 25% of the exhaust gas flow will pass through each segment when all segments are equally loaded with soot.
  • the heat value ratio of the engine exhaust stream to the fuel stream introduced into each individual segment during regeneration is maintained substantially consistent among segments. This offers the advantages of reducing the risk of thermal damage to the filter during regeneration (by decreasing the variation in the maximum regeneration temperatures reached in each segment), increased regeneration consistency between the segments, and reduced fuel consumption.
  • the filter comprises a plurality of filter segments that have differing physical properties or structural characteristics such that the engine exhaust stream to fuel stream ratio is maintained substantially consistent among segments during their regeneration.
  • the segments can be designed and constructed so that if they were each supplied with a gas stream under the same conditions, the mass flow of that gas stream through each of them would be different.
  • filters are described herein as "unequally segmented filters”.
  • the mass flow rate of the fuel stream or syngas stream introduced to each individual segment can be varied to enable a substantially consistent heat value ratio of the streams introduced into each segment during regeneration.
  • an engine exhaust stream particulate filter comprises at least two filter segments wherein the segments are structured so that if they were each supplied with a gas stream under identical conditions, the gas stream mass flow through each of the segments would be different.
  • the segments can differ from each other in at least one structural characteristic selected from the group consisting of cross-sectional area, longitudinal filter length, filter porosity and filter cell density.
  • the segments differ from each other in at least one structural characteristic such that the engine exhaust stream mass flow rate through each segment during their regeneration is approximately equal.
  • the filter segments can be housed in a common enclosure.
  • the method comprises:
  • the engine exhaust stream mass flow rate through each segment is different so that the heat value ratio is maintained substantially consistent among segments during their regeneration.
  • the segments can be structured as described above, so that if they were supplied with a gas stream under identical conditions, the gas stream mass flow through each one of the plurality segments would be different.
  • the heat value ratio is maintained substantially consistent among segments during their regeneration by varying the mass flow rate of the hydrogen- containing gas stream that is introduced to regenerate each segment.
  • the mass flow rate of the hydrogen-containing gas stream that is introduced to regenerate each segment can depend upon its position in a regeneration sequence
  • the hydrogen-containing gas stream can be introduced into the plurality of segments sequentially in a regeneration sequence.
  • the duration of regeneration of each segment can be substantially the same.
  • the above-described methods can be employed in a non- continuous regeneration cycle or in a continuous regeneration cycle in which the hydrogen-containing gas stream is being introduced into at least one filter segment at a given time, so that at least one filter segment is undergoing regeneration during operation of the particulate filter.
  • the system comprises:
  • a particulate filter connected to receive an exhaust gas stream from the engine via an exhaust stream conduit, the particulate filter comprising a plurality of filter segments with different structural characteristics from one another, wherein during operation of the particulate filter the exhaust gas stream is directed through the segments in parallel;
  • a controller configured to selectively direct the syngas stream to each of the segments in sequence to regenerate the segment.
  • the filter segments are structured so that if they were each supplied with a gas stream under identical conditions, the gas stream mass flow through each of the segments would be different.
  • FIG. 1 is a photographic image showing an end view of a diesel particulate filter with one of four equal segments regenerated.
  • FIG. 2a is a simplified end view of a diesel particulate filter divided into four equal segments.
  • FIG. 2b is a simplified end view of a diesel particulate filter divided into four unequal segments.
  • FIG. 3 is a table that summarizes the exhaust gas flow splits, temperature and pressure drop history at various phases in a regeneration cycle of a four-segment, equally divided diesel particulate filter.
  • FIG. 4 is a plot of exhaust gas flow splits over a DPF regeneration test cycle, at the various phases in the regeneration cycle that is tabulated in FIG. 3.
  • FIG. 5 is a plot of exhaust gas outlet temperatures from the various segments of a diesel particulate filter at the various phases in the regeneration cycle that is tabulated in FIG. 3.
  • FIG. 6 is a table that summarizes the exhaust gas flow splits, temperature and pressure drop history at various phases in a regeneration cycle of a four-segment, unequally divided diesel particulate filter.
  • FIG. 7 is a plot of exhaust gas outlet temperatures from the various segments of a diesel particulate filter at the various phases in the regeneration cycle that is tabulated in FIG. 6.
  • FIG. 8 illustrates a schematic view of a combustion engine system comprising a segmented diesel particulate filter.
  • a diesel particulate filter can be segmented into at least two segments, for example, by providing a baffle on the upstream side of the filter monolith, or by having separate filter segments housed in a common enclosure or not.
  • This enables the introduction of a fuel, for example, a syngas stream, selectively into different portions or segments of the filter and the regeneration of each segment separately or independently from another.
  • a fuel for example, a syngas stream
  • filter regeneration of the segments can be conducted sequentially and in a continuous cycle.
  • the segments can be regenerated in sequence, one after the other, and then the DPF can be operated for a period without any segments being regenerated, with the regeneration sequence repeated only when regeneration is required.
  • the engine exhaust stream flows through all segments of the DPF, whether the segment is being regenerated or not. As each segment is regenerated, the mass flow of the engine exhaust stream through the segment being regenerated tends to change as a result of the removal of particulate matter. This in turn can alter the heat value ratio of the engine exhaust stream to the fuel stream during the regeneration of subsequent segments.
  • FIG. 1 is a photographic image showing an end view of a diesel particulate filter with one of four equal segments regenerated.
  • the segments regenerated later in the sequence will receive more fuel relative to engine exhaust (that is, an increased heat value ratio), with the potential to over-heat and thermally damage the segment.
  • the present approach reduces the variation in the heat value ratio of the streams flowing through the various segments during regeneration, by factoring into the filter design and/or regeneration technique the change in the engine exhaust stream flow rate through the segments that occurs as they are regenerated or cleaned.
  • a diesel particulate filter is divided into at least two segments having different cross-sectional areas.
  • FIG. 2a (prior art) is a simplified end view of a diesel particulate filter that has a substantially circular or round cross-sectional profile, and that is divided into four equal segments, A, B, C and D.
  • FIG. 2b is a simplified end view of an improved diesel particulate filter divided into four unequal segments with differing cross-sectional areas where the smallest segment AA would be regenerated first, followed in sequence by the progressively larger segments BB, CC and then DD.
  • the appropriate relative cross-sectional area of the segments will be dependent upon the operating parameters of the DPF and/or the engine exhaust gas after-treatment system, including the regeneration control strategy and sequence.
  • the segments are preferably sized so that there is a substantially consistent heat value ratio during regeneration, if the rate of fuel flow supplied for regeneration is consistent among segments (for example, so that the ratio is consistent at the start of regeneration of each segment, or on average over the regeneration of each segment).
  • Unequal segmentation of the diesel particulate filter can reduce the variation in the heat value ratio, and thus the variation in temperature of the regeneration process, among individual segments as they are regenerated. It can also substantially reduce the overall fuel consumption associated with filter regeneration. For example, if the first segment AA was at approximately 65° compared to an equally segmented filter segment at 90°, the mass flow rate of the engine exhaust stream flowing through the first segment would be 65/90 or approximately 72% of the amount it would be in an equally segmented filter segment. Therefore, the required flow rate of the fuel stream or syngas stream would be about 72% of the amount required for an equally segmented filter, in order to maintain a similar heat value ratio. In the foregoing example the overall fuel saving would be about 28%.
  • FIG. 3 summarizes modeled data from a DPF regeneration test cycle of a four segment, equally divided DPF (of the type illustrated in FIG. 2a), at various phases of a test cycle.
  • the test starts off with a clean DPF (phase 1) which then becomes loaded with soot (phase 2).
  • phase 1 a clean DPF
  • phase 2 soot
  • FIG. 4 illustrates the mass flow rate of the engine exhaust gas stream (EG) through the four DPF segments during the various phases of the test cycle that are tabulated in FIG. 3, as well as the overall pressure drop across the DPF at the various phases. This data is included in FIG. 3.
  • FIG. 3 illustrates the mass flow rate of the engine exhaust gas stream (EG) through the four DPF segments during the various phases of the test cycle that are tabulated in FIG. 3, as well as the overall pressure drop across the DPF at the various phases. This data is included in FIG. 3.
  • FIG. 3 illustrates the mass flow rate of the engine exhaust gas stream (EG) through the four DPF segments during the various phases of
  • FIG. 4 shows that, as would be expected, the overall pressure drop decreases as each segment is regenerated.
  • the EG flow is split about equally among the four segments (as at phase 1, 2, 3 and 10 where approximately 25% of the EG flow passes through each segment).
  • a larger proportion (about 45%) of the EG passes through the cleaned segment with only about 18% passing through each of the three loaded segments (see phase 4 data points).
  • the proportion of EG passing through the remaining loaded segment(s) drops even further to about 12%.
  • FIG. 5 illustrates the temperatures of the various segments during the various phases of the test cycle that are tabulated in FIG.
  • the outlet temperature for the segment being regenerated gets hotter for each of the four segments. This is because the ratio of fuel (syngas) to EG is lowest in the first segment to be regenerated but increases with regeneration of each of the remaining three segments, because proportionately less of the EG is passing through the remaining loaded segments, but the supply of fuel (syngas) is the same.
  • FIGS. 6 and 7 illustrates how an unequally divided DPF (of the type illustrated in FIG. 2b) can be used to reduce the variation in outlet temperature from the segments as they are regenerated in sequence.
  • FIG. 6 summarizes data modeled for a similar DPF regeneration test cycle of a four segment, unequally divided DPF. The test starts off with a clean DPF (phase 1) which then becomes loaded with soot (phase 2). The EG mass flow rate through the four DPF segments during the various phases of the test cycle is shown in FIG. 6, as well as the overall pressure drop across the DPF at the various phases.
  • the EG flow is split unequally among the four segments (approximately 19%, 22% 27% and 32% at phases 1, 2 and 10).
  • a larger proportion of the EG (about 33%) passes through that first segment (see phase 4 data points).
  • the proportion of EG passing through a segment during regeneration of that segment is consistently about 14% for all four segments (see phases 3, 5, 7 and 9).
  • FIG. 6 shows that, as would be expected, the overall pressure drop decreases as each segment is regenerated.
  • Temperature data is also provided for the various phases as and after each of the four segments is regenerated in sequence by supplying syngas at about the same flow rate.
  • the outlet temperature for the segment being regenerated is substantially the same for each of the four segments as they are regenerated. This is because the ratio of fuel to EG is substantially the same for each of the four segments during regeneration because of the variation in cross-sectional area of the segments.
  • filter segments can be different from one another, besides or in addition to their cross-sectional area.
  • the mass flow of the engine exhaust stream can be made more consistent among the different segments during regeneration by having segments with differing filter cell density, differing filter porosity and/or differing longitudinal filter lengths or volumes.
  • Ceramic wall-flow monoliths used for DPFs can be manufactured by extruding a large unitary section or by cementing or bonding together multiple smaller sections or "bricks" to form one complete larger section.
  • the DPF in FIG. 1 is constructed of multiple bricks; the joints between the bricks are visible in FIG. 1. If the DPF is constructed of smaller bricks rather than being one complete extrusion, preferably the divisions between the segments do not coincide with the area or joints where individual bricks are joined to form the DPF, or at least care is taken to reduce the degree of overlap. This reduces the thermal gradient and thermal stress across the adhesive or cement that joins the individual bricks of a DPF together.
  • the heat value ratio during the regeneration of an individual segment can be held substantially consistent among segments by controlling and varying the mass flow rate of the fuel stream introduced to each individual segment.
  • the mass flow rate of the fuel stream can be adjusted depending on the mass flow rate of the engine exhaust stream flowing through an individual segment during regeneration to maintain the desired heat value ratio.
  • This technique can reduce the overall fuel consumption associated with filter regeneration, but can cause a fluctuating demand for fuel (for example, syngas) for regeneration purposes, and requires a more complex control system.
  • the technique can be used with an equally segmented particulate filter to reduce the variation in the heat value ratio, and thus the variation in temperature of the regeneration process, among individual segments as they are regenerated. It can also be used with unequally segmented particulate filters of the types described herein, to provide further non-passive control of the heat value ratio.
  • the present segmented filter designs and regeneration techniques can provide some or all of the following advantages over those used in conventional DPFs: [0061] (A) Reduced potential of thermal damage to the filter substrate and catalyst during regeneration.
  • the segments can be regenerated by various methods, for example, conducted sequentially until all segments have been regenerated, conducted in a specific order, conducted in a continuous cycle, conducted in a non-continuous cycle, and/or conducted only when regeneration is of the filter required.
  • the regeneration process can be controlled through an open-loop control method and/or a closed loop control method employing sensors and/or pre-determined regeneration algorithms.
  • FIG. 8 illustrates a schematic view of a combustion engine system 100 comprising an exhaust after-treatment subsystem 101.
  • Engine 110 produces an engine exhaust stream which travels through conduit 111, through an optional turbo-compressor 112, and through conduit 113 to DPF assembly 120 where the engine exhaust stream is filtered by a filter 121 to reduce the level of regulated particulate emissions therein.
  • the filtered engine exhaust stream is then released to the atmosphere via an exhaust conduit 114.
  • Conduit 113 and exhaust conduit 114 can comprise additional exhaust after-treatment devices, not shown in FIG. 8.
  • An optional sensor can be employed to monitor the temperature of the engine exhaust stream and can be located near the engine outlet, for example, sensor 133.
  • An optional pressure sensor 131 monitors the pressure of the engine exhaust stream upstream of filter 121 and can be located along conduits 111 or 113.
  • An optional pressure sensor 132 monitors the pressure of the engine exhaust stream downstream of filter 121 and can be located along conduits 114 or other optional conduits located downstream of filter 121 (not shown in FIG. 8).
  • a pair of pressure sensors 131 and/or 132 can be located within DPF assembly 120 upstream and downstream of filter 121.
  • a differential pressure sensor (not shown in FIG. 8) can be employed to monitor the pressure of the exhaust stream upstream and downstream of filter 121.
  • an optional sensor can be employed to monitor the temperature of the engine exhaust stream near the DPF outlet, for example, sensor 134, or at other locations along conduits 113 or 114 or within DPF assembly 120.
  • a controller 130 receives signals from optional pressure sensors 131 and 132, and optional temperature sensors 133 and 134.
  • control strategies that can be used to initiate and terminate regeneration of filter 121. These strategies are applicable to unsegmented filters, and equally- divided segmented filters or unequally divided segmented filters of the type described herein.
  • controller 130 initiates a regeneration process for filter 121 based on employing one of equations (1), (2), (3) or (4).
  • P 1 pressure of engine exhaust stream upstream of the DPF filter
  • P 2 pressure of engine exhaust stream downstream of the DPF filter
  • P 3 predetermined first pressure value, which represents a pressure differential between the inlet and outlet of a clean DPF (without trapped particulates or a regenerated DPF) during the present operating condition of the engine. This value can be pre-programmed or stored in a lookup table, or calculated (as a function of the mass flow of exhaust stream or mass flow of the inlet air steam of the engine, temperature of exhaust stream at the inlet to DPF, cross-sectional area of DPF, and a constant).
  • T 1 temperature of engine exhaust stream at, for example: engine outlet, DPF outlet, or other position along engine exhaust stream conduits
  • controller 130 initiates a regeneration process for filter 121 based on employing one of equations (5), (6), (7) or (8).
  • Pi - P 2 can be employed in place of Pi.
  • controller 130 initiates a regeneration process for filter 121 based on employing one of equations (9), (10), (11) and (12).
  • m 2 mass flow of engine intake air stream.
  • equations (1) through (12) the parameters that are actually monitored and associated signals sent to the controller can be indicative of another parameter, for example, in equation (9) a pressure sensor can be employed to monitor the engine exhaust stream in order to indicate the mass flow rate of the engine exhaust stream.
  • controller 130 initiates a regeneration process for filter 121 based on employing at least one of equations (1) through (12) and at least one of equations (13) (14).
  • controller 130 terminates a regeneration process for filter 121 based on at least one of equations (15), (16), (17) or (18).
  • T 2 temperature of engine exhaust stream at, for example: DPF outlet, or other position along engine exhaust stream conduit downstream of DPF outlet
  • y 3 predetermined third temperature value, which can be the same as y 2 or different.
  • DPF assembly 120 is divided into equally or unequally divided segments which enables the regeneration of at least one segment or portion of filter 121 at a given time.
  • DPF assembly 120 comprises a baffle 122 which is a means to divide and channel the flow of the syngas stream through a segment within filter 121, while allowing the engine exhaust stream to flow though all segments of filter 121 including those that are being regenerated.
  • DPF assembly 120 comprises a baffle downstream (not shown in FIG. 8) of filter 121 in order to divide and channel the engine exhaust stream as it exits a segment within filter 121. This allows the engine exhaust stream exiting each individual segment to be monitored. For example, the temperature of the engine exhaust stream exiting each segment can be monitored and regeneration of individual segments can be triggered depending on the monitored value for that segment.
  • syngas generator assembly 140 can be operated essentially continuously when engine system 100 is in operation.
  • a fuel and oxidant reactant supply and control system (not shown in FIG. 8) supplies the necessary reactants to syngas generator assembly 140.
  • the syngas stream produced by syngas generator assembly 140 flows through conduit 141 to valve 142 where it is diverted to flow selectively through at least one of conduits 143, 144, 145 or 146 and the respective segments within DPF assembly 120.
  • syngas can be directed to DPF assembly 120 via a single conduit and the selective flow of syngas to the different segment accomplished by flow diverters or other devices within DPF assembly 120.
  • Valve 142 is controlled by controller 130.
  • Various algorithms can be used for controlling regeneration of a segmented DPF.
  • the algorithm can include factors such as:
  • This can be, for example, individual segment or overall DPF assembly;
  • control system employed for regeneration This can be, for example, closed-loop or open-loop systems or some combination; and [0087] (e) the operating parameter(s) to be monitored for the regeneration control system. This can be, for example, duration of regeneration or temperature of exhaust gas stream for DPF assembly or filter or an individual segment thereof; or pressure drop across the filter or DPF assembly.
  • Table 1 illustrates examples of various regimes that can be used to control the regeneration of an equally or unequally segmented DPF assembly. One or more of these regimes can be used.
  • Controller 130 employing at least one programmed control regime and/or signals received from various sensors, determines when to terminate the regeneration process for the particular segment(s) of filter 121 and sends a signal to valve 142.
  • the controller that controls regeneration of the filter can be dedicated for that purpose or can be part of another controller, for example, an overall engine control module.
  • exhaust after-treatment sub-system 101 can optionally comprise one or more additional exhaust after-treatment devices which at least periodically utilize a syngas stream (for example, for regeneration and/or heating),
  • the controller can determine where the syngas is to be directed, and may need to assign different priorities to the various devices and their requirements or demands for syngas.
  • the syngas stream can be preferably directed by the controller in order of priority for:
  • syngas generator assembly 140 can from time to time require a regeneration process which would be a higher priority over the above stated processes.
  • the fuel employed to regenerate the DPF can be another fuel (other than syngas) for example diesel, gasoline, natural gas, propane, ethanol, methanol or kerosene can be used.
  • the engine can be a lean burn combustion engine fueled by suitable fuels, for example, diesel, fuel oil, kerosene, natural gas, propane, liquefied petroleum gas (LPG), methanol, ethanol or gasoline.
  • suitable fuels for example, diesel, fuel oil, kerosene, natural gas, propane, liquefied petroleum gas (LPG), methanol, ethanol or gasoline.
  • the engine system can comprise additional devices which utilize a syngas stream for example, a lean NOx trap, selective catalytic reactor (SCR), diesel oxidation catalyst (DOC) and or a fuel cell.
  • a diverter valve can be used to selectively direct the flow of syngas stream to such additional devices.

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  • Physics & Mathematics (AREA)
  • Geometry (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Processes For Solid Components From Exhaust (AREA)
  • Filtering Of Dispersed Particles In Gases (AREA)

Abstract

Le filtre selon l'invention est raccordé fluidiquement à une sortie de flux d'échappement d'un moteur diesel et disposé en aval de celle-ci. Le filtre présente une pluralité de segments de filtre qui ont des propriétés physiques ou des caractéristiques structurelles différentes de telle sorte que le rapport du flux d'échappement du moteur au flux de carburant soit maintenu sensiblement consistant parmi les segments pendant leur régénération. L'invention concerne aussi une méthode de régénération d'un filtre segmenté, ladite méthode comprenant le maintien du rapport du flux d'échappement du moteur au flux de carburant à un niveau sensiblement consistant parmi les segments pendant leur régénération.
PCT/CA2008/000945 2007-05-15 2008-05-15 Filtre segmenté contre les matières en suspension pour flux d'échappement de moteur WO2008138146A1 (fr)

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EP2662551A1 (fr) * 2012-05-07 2013-11-13 Electro-Motive Diesel, Inc. Système d'échappement comportant de multiples doseurs

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