WO2016175697A1 - Système de traitement de gaz d'échappement - Google Patents

Système de traitement de gaz d'échappement Download PDF

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Publication number
WO2016175697A1
WO2016175697A1 PCT/SE2016/050350 SE2016050350W WO2016175697A1 WO 2016175697 A1 WO2016175697 A1 WO 2016175697A1 SE 2016050350 W SE2016050350 W SE 2016050350W WO 2016175697 A1 WO2016175697 A1 WO 2016175697A1
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WO
WIPO (PCT)
Prior art keywords
exhaust gas
partial flow
zone
flow
treatment system
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PCT/SE2016/050350
Other languages
English (en)
Inventor
David Raymand
Daniel Hjortborg
Original Assignee
Scania Cv Ab
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 Scania Cv Ab filed Critical Scania Cv Ab
Priority to KR1020177032685A priority Critical patent/KR20170136610A/ko
Priority to EP16786851.2A priority patent/EP3289197A4/fr
Publication of WO2016175697A1 publication Critical patent/WO2016175697A1/fr

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Classifications

    • 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
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • 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
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • 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
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/011—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more purifying devices arranged in parallel
    • 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
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/103—Oxidation catalysts for HC and CO only
    • 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
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/106—Auxiliary oxidation catalysts
    • 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
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/14—Nitrogen oxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present disclosure relates in general to an exhaust gas treatment system comprising an oxidation catalyst and a selective catalytic reduction catalyst.
  • the exhaust gas treatment system may for example be an exhaust gas treatment for a vehicle, especially a heavy vehicle such as a bus or a truck.
  • the present disclosure also relates to a method for providing a desired ratio between N0 2 and NO in an exhaust gas flow intended to pass through a selective catalytic reduction catalyst for reduction of NO x .
  • a combustion engine combusts a fuel and air mixture in order to generate a driving moment for powering for example a heavy vehicle, such as a bus or truck.
  • the combustion process generates exhaust gases, which exit the engine and are transferred to an exhaust gas treatment system.
  • the exhaust gases from the combustion engine comprise nitrogen containing gases (NO x ), carbon dioxide (C0 2 ), carbon monoxide (CO), hydrocarbon (HC), and particles.
  • NO x is a commonly used generic term to describe the nitrogen containing gases, which primarily comprises nitrogen monoxide (NO) and nitrogen dioxide (N0 2 ).
  • the exhaust gas treatment system often comprises a diesel oxygen catalyst (DOC) adapted to primarily oxidise hydrocarbons, but also carbon monoxide and nitrogen monoxide. Furthermore, the exhaust gas treatment system often comprises a selective catalytic reduction (SCR) catalyst in which a reduction agent and NO x are converted into nitrogen and water, thereby reducing the amount of NO x released to the surrounding atmosphere.
  • the reduction agent used is usually a urea-containing aqueous solution, such as AdBlue, and is introduced into the system upstream of the SCR.
  • the exhaust gas treatment system may typically further include one or more particulate filters, for example, a diesel particulate filter (DPF) and/or a catalysed soot filter (CSF), in order to trap and oxidise for example soot particles.
  • particulate filters for example, a diesel particulate filter (DPF) and/or a catalysed soot filter (CSF)
  • DPF diesel particulate filter
  • CSF catalysed soot filter
  • Additional types of catalysts may also be provided in the exhaust gas treatment system, for example an ammonium slip catalyst (ASC).
  • ASC ammonium slip catalyst
  • the catalysts of the exhaust gas treatment system cooperates in order to clean the exhaust gases from emissions in terms of hydrocarbons (HC), particulate matter (PM), carbon monoxide (CO), NO x and ammonium (NH 3 ).
  • HC hydrocarbons
  • PM particulate matter
  • CO carbon monoxide
  • NO x NO x
  • NH 3 ammonium
  • a major challenge in order to optimise an exhaust gas treatment system is to make the DOC and DPF cooperate in an optimal manner with the SCR catalyst.
  • the performance of the SCR catalyst is highly dependent on the composition of the exhaust gas entering the SCR. It is well know that the highest conversion rate of NO x in the SCR catalyst is achieved in case the exhaust gas comprises a ratio of N0 2 to NO of 50:50.
  • the exhaust gases leaving the engine comprises mainly NO (usually about 90 %), but a part of the NO is oxidised to N0 2 when the exhaust gas passes the DOC and the DPF.
  • NO usually about 90 %
  • many systems seek to optimise the oxidation of NO in the DOC and/or DPF to achieve the desired 50:50 ratio of N0 2 and NO in the exhaust gas when it enters the SCR.
  • the catalytic substance normally used in DOC and DPF i.e. platinum, has the activity for oxidising CO, HC and NO.
  • the DOC and the DPF should oxidise all of the CO and the HC, but only about 50 % of the NO.
  • N0 2 and NO is the ratio, which gives the highest conversion rate in the SCR
  • the SCR catalyst is a V 2 0 5 -based catalyst
  • even a small excess of N0 2 may have a detrimental effect on the performance of the SCR and thereby result in considerably lower reduction degree of NO x .
  • the oxidation capacity of NO in an oxidation catalyst is strongly dependent on both the mass flow of the exhaust gas and the temperature, and to a lower degree of the NO x concentration.
  • the capability of oxidising NO increases with increasing temperature for temperatures below approximately 300°C. Above said temperature, the capability of oxidising NO decreases because the conversion is limited of the thermodynamic equilibrium between NO and N0 2 . Exactly where the breaking point between increasing and decreasing NO/N0 2 ratio is depends on the DOC and DPF activities.
  • the ability to oxidise NO also depends on the exhaust gas mass flow as disclosed above.
  • the capability of oxidising NO decreases with increasing mass flow of the exhaust gas.
  • the temperature of the exhaust gases and the mass flow varies greatly between different operation points, whereby it is difficult to find an activity which is suitable both in case of high mass flow and low temperature as well as in case of low mass flow and medium temperature.
  • the problem of achieving the optimal composition of the exhaust gas for the SCR is especially pronounced at low temperatures of the exhaust gas.
  • An oxidation catalyst which is capable of oxidising enough NO to N0 2 at low temperatures, such as about 200 to 250°C, would likely produce too much N0 2 at a medium exhaust gas temperature, such as about 350°C.
  • the NO x -sensor used to determine the composition of the exhaust gas in order to determine the correct amount of reducing agent to be introduced for the reduction in the SCR catalyst is generally calibrated against "normal" N0 2 /NO x ratios.
  • the deviation from a 50 % N0 2 / NO x ratio is amplified by the SCR-catalysts' affinity for removing NO x in a 1:1 NO:N0 2 ratio, e.g. if 90% of the NO x is removed in the SCR from a 55% N0 2 /NO x mixture, the remaining fraction of N0 2 after the SCR is likely to have increased towards 100% N0 2 /NO x .
  • US 6,846,464 B2 discloses a method of reducing NO x in exhaust gases of an internal combustion engine.
  • the exhaust gases from the engine are converted to roughly 50:50 mixture of NO and N0 2 while simultaneously oxidising hydrocarbons which may interfere with the reduction of NO x by urea.
  • the method disclosed comprises selective oxidation of the exhaust gases of an engine in which the NO and hydrocarbons in a first portion of the exhaust gases are oxidised separately from the remaining second portion of the exhaust gases. In the second portion of the exhaust gases, only hydrocarbons are oxidised while NO is left essentially unreacted. This is achieved by the first and the second exhaust stream each separately allowed to pass through a different catalytic chamber.
  • the first and second portions of the exhaust cases are then recombined in order to achieve the desired ratio of NO to N0 2 and passed through an SCR catalyst.
  • the solution disclosed has however certain limitations. Firstly, it is optimised against a 50:50 ratio between NO and N0 2 , which may not be optimal for a NOx-sensor as, discussed above.
  • the NO x -sensor is generally calibrated against intended ratios of NO and N0 2 and therefore even a very small change of the ratio between NO and N0 2 to the SCR catalyst will have a large impact on registered amount of NO x in the sensor.
  • US 2010/0107610 Al discloses an exhaust system for an internal combustion engine, the system comprising two oxidation catalysts disposed upstream of a SCR catalyst.
  • the two oxidation catalysts are configured for different activities and/or different temperature ranges.
  • the exhaust gas flow through the two oxidation catalysts is adjusted by means of an actuator, more specifically a flap.
  • the proposed system however has the disadvantage of the need for a movable part in the form of the flap inside the system in order to adjust the flows.
  • DE 10 2013 204 405 Al discloses an oxidation catalyst having different coating compositions in different segments in order to provide different catalytic activities between the segments.
  • a covering device rotatable around a central axis of the catalyst, the flow of exhaust gas is directed to the segment(s) intended for the specific operating condition such as to achieve the desired conversion degree.
  • This solution also suffers from the disadvantage of the need of a movable part. Furthermore, it has the disadvantage of not being able to use the whole catalytic surface available during operation, thereby providing an unnecessarily bulky catalyst which also contributes to increased weight of the system.
  • the object of the present disclosure is to be able to achieve an optimised ratio of N0 2 and NO in an exhaust gas adapted to pass a selective catalytic reduction (SCR) catalyst for conversion of NO x , which is optimised for a large range of operating conditions as regards to temperature and mass flow of the exhaust gas.
  • SCR selective catalytic reduction
  • the object is achieved by means of an exhaust gas treatment system and a method for providing a desired ratio between N0 2 and NO in an exhaust gas flow intended to pass through an SCR catalyst of an exhaust gas treatment system in accordance with the appended independent claims.
  • the present invention is based on the fact that the exhaust gas flow is divided into at least two separate partial flows which are essentially parallel to each other (as opposed to arranged in sequence).
  • the two partial flows are both subjected to oxidising conditions wherein hydrocarbons, as well as preferably CO, are oxidised to a degree as high as possible, preferably essentially fully oxidised.
  • NO in the first partial flow is only oxidised to a low degree, i.e. 5-30 % of the total content of NO in the first partial flow, whereas the NO in the second partial flow is oxidised to a high degree of at least 70 %.
  • the two partial flows are then recombined, before passing the SCR, such that the resulting exhaust gas flow constitutes a mixture of the two partial flows, thereby achieving the desired ratio of N0 2 to NO in the exhaust gas entering the SCR catalyst.
  • This is achieved without the need for any mechanical movable parts inside the exhaust gas treatment system for diverting the exhaust gas flow into separate partial flows.
  • the mass ratio between the two partial flows is adapted to be the same for any operating condition of the engine, i.e. any
  • composition/concentration, temperature and mass flow of the exhaust gas and hence for any operating condition of the exhaust gas treatment system.
  • the system and the method can be controlled by selecting the appropriate activities of the first and the second zones as well as the mass flow ratio between the two parallel partial flows such that a desired ratio of N0 2 to NO in the recombined exhaust gas is achieved before entry into the SCR catalyst. This can be achieved while avoiding the risk for arriving at a N0 2 :NO ratio above a predetermined threshold value, such as 50:50.
  • the exhaust gas treatment system comprises an inlet for introduction of a flow of exhaust gas into the system, such as a flow of exhaust gas from a combustion engine.
  • the flow of exhaust gas after entry into the system through the inlet, is divided into at least a first partial flow and at least a second partial flow, the second partial flow being essentially parallel to said first partial flow.
  • the system is configured such that a mass ratio between the first partial flow and the second partial flow is essentially constant for all operating conditions of the system, i.e. for any mass flow, any composition or concentration, and any temperature of the exhaust gas entering the system through the inlet.
  • the system is further configured such that the first partial flow passes a first zone having a catalytic activity adapted for oxidising 5 to 30 %, preferably 8-25%, of NO in the first partial flow.
  • the system is further configured such that the second partial flow passes a second zone having a catalytic activity adapted for oxidising at least 70 %, preferably at least 75%, of NO in the second partial flow.
  • the first and the second zones both have a catalytic activity adapted for oxidising hydrocarbons, preferably at least 70 % of the hydrocarbons in the respective partial flows.
  • the system is further configured such that the first partial flow and the second partial flow, after oxidation of NO, are recombined into a single exhaust gas flow before the exhaust gas passes through the SCR.
  • the first partial flow may suitably constitute at least 30 % of the exhaust gas mass flow entering the exhaust gas flow treatment system, preferably 35-65 % of the exhaust gas mass flow entering the exhaust gas treatment system.
  • the exhaust gas treatment system comprises a first oxidation catalyst comprising the first zone and a second oxidation catalyst comprising the second zone.
  • the exhaust gas treatment system comprises an oxidation catalyst comprising said first zone and said second zone.
  • an oxidation catalyst may comprise a plurality of said first zone and a plurality of said second zone.
  • the zones may suitably be arranged parallel to each other and alternatively with respect to each other.
  • the SCR of the exhaust gas treatment system may suitably be a V 2 0 5 -based catalyst for reasons of economy, robustness and control strategy.
  • the first zone may suitably comprise a metal oxide based catalytic substance for reasons of cost efficiency.
  • a catalytic substance of the first zone may further comprise a platinum group metal (e.g. Pt or Pd).
  • the second zone may comprise a metal oxide based catalytic substance.
  • Such a catalytic substance of the second zone may preferably further comprise a platinum group metal (e.g. Pt or Pd).
  • the metal of the metal oxide based catalytic substance (of any of the first and second zones) may for example be Cu, Mn, Fe, Co, or Ni.
  • the metal of the metal oxide based catalytic substance can be rare earth metal(s).
  • the exhaust gas treatment system may further comprise stationary means for creating and/or increasing turbulence in the recombined exhaust gas flow upstream of the SCR.
  • the method for providing a desired ratio between N0 2 and NO x in an exhaust gas flow intended to pass through an SCR catalyst of an exhaust gas treatment system according to the present invention comprises dividing the exhaust gas flow, upstream of the SCR, into a first partial flow and a second partial flow, the second partial flow being essentially parallel to the first partial flow.
  • the mass ratio between the first partial flow and the second partial flow is essentially constant for all operating conditions of the exhaust gas treatment system.
  • the method further comprises oxidising the first partial flow such that 5 to 30 %, preferably 8-25%, of the NO in the first partial flow is oxidised to N0 2 , and oxidising the second partial flow such that at least 70 %, preferably at least 75%, of the NO in the second partial flow is oxidised to N0 2 .
  • the first partial flow is combined with the second partial flow in order to achieve a recombined exhaust gas flow having the desired ratio between N0 2 and NO x .
  • the desired ratio between N0 2 and NO x may suitably be 20 % ⁇ N0 2 /NO x ⁇ 50%, preferably the desired ratio between N0 2 and NO x is 30 % ⁇ N0 2 /NO x ⁇ 45%.
  • the method may suitably also comprise oxidising hydrocarbons both in the first partial flow and in the second partial flow, thereby reducing the problems associated with hydrocarbons in the SCR.
  • the present disclosure further relates to a diesel oxidation catalyst comprising a first zone extending from an inlet of the oxidation catalyst to an outlet of the oxidation catalyst, the first zone having a catalytic activity capable of oxidising 5 to 30 % of NO in a gas flow passing trough said first zone, and a second zone arranged parallel to said first zone, the second zone having a catalytic activity capable of oxidising at least 70 % of NO in a gas flow passing through said second zone, the catalytic activity of the first zone and the catalytic activity of the second zone both capable of oxidising hydrocarbons.
  • the diesel oxidation catalyst is suitable for use in the method as disclosed above as well as in the exhaust gas treatment system disclosed above.
  • the present invention also relates to a vehicle comprising the exhaust gas treatment system as disclosed above.
  • FIG. 1 schematically illustrates a side view of a vehicle comprising an internal combustion engine and an exhaust gas treatment system.
  • Fig. 2 schematically illustrates an exhaust gas treatment system.
  • Fig. 3 schematically illustrate N0 2 /NO x ratio vs. temperature of exhaust gas after oxidation of NO using different oxidation catalysts.
  • Fig. 4 schematically illustrates an exhaust gas treatment system according to one exemplifying embodiment comprising two parallel oxidation catalysts.
  • Fig. 5a schematically illustrates a cross sectional view of an oxidation catalyst comprising zones having different catalytic activities according to an exemplifying embodiment.
  • Fig. 5b schematically illustrates a cross sectional view of an oxidation catalyst comprising zones having different catalytic activities according to another exemplifying embodiment.
  • an exhaust gas flow is divided into a first partial flow and a second partial flow, wherein the second partial flow is essentially parallel to the first partial flow.
  • parallel partial flows are intended to mean partial flows, which are simultaneous and continuously present.
  • the partial flows are divided out of a single exhaust gas flow, at a single common point in the system, and recombined at a common point in the system.
  • parallel partial flows does not necessarily mean that the geometrical flow directions of the partial flows are necessarily parallel (unless otherwise explicitly given) as the parallel partial flows can have different geometrical flow directions inside the exhaust gas treatment system.
  • the exhaust gas treatment system comprises an inlet for introduction of a flow of exhaust gas into the system, such as a flow of exhaust gas from a combustion engine.
  • the flow of exhaust gas after entry into the system through the inlet, is divided (at a common diving point) into at least a first partial flow and at least a second partial flow, the second partial flow being essentially parallel to said first partial flow.
  • the system is configured such that a mass ratio between the first partial flow and the second partial flow is essentially constant for all operating conditions of the system, i.e. for any mass flow, any composition and any temperature of the exhaust gas entering the system through the inlet.
  • the system is further configured such that the first partial flow passes a first zone having a catalytic activity adapted for oxidising 5 to 30 % of NO in the first partial flow.
  • the system is further configured such that the second partial flow passes a second zone having a catalytic activity adapted for oxidising at least 70 % of NO in the second partial flow.
  • the first and the second zones both have a catalytic activity adapted for oxidising hydrocarbons, preferably at least 70 % of the hydrocarbons in the respective partial flows.
  • the system is further configured such that the first partial flow and the second partial flow, after oxidation of NO in the respective partial flows, are recombined into a single exhaust gas flow before the exhaust gas passes through the SCR.
  • the constant mass flow ratio of the first partial flow and second partial flow for all operating conditions of the exhaust gas treatment system may be achieved by selecting the appropriate dimensions and shapes of the tubes or conduits of the respective partial flows in case of a plurality of oxidation catalysts, or the cross sectional sizes of the respective zones when present in a single oxidation catalyst.
  • the exhaust gas treatment according to the present invention does not need any movable parts in order to divert or control the mass flow ratio between the first and the second partial flows. Thereby, a more robust system is achieved and the need for maintenance measures minimised.
  • the catalytic activity of the first zone is adapted for oxidising 5 to 30 % of NO in the first partial flow at least in a temperature range of 200 to 500 °C.
  • the catalytic activity of the second zone is preferably adapted for oxidising at least 70 % of NO in the second partial flow at least in the temperature interval of 250 to 300 °C, preferably in the temperature interval of 225 to 325 °C.
  • Figure 1 depicts a vehicle 1, here in the form of a truck, in a schematic side view.
  • the vehicle may however be any other motor driven vehicle, for example a bus or a passenger car.
  • the vehicle comprises a combustion engine 2, which powers the vehicle's tractive wheels 3 via a gearbox (not shown), and a propeller shaft (not shown).
  • the engine is provided with an exhaust gas treatment system 4.
  • the engine is powered by fuel supplied to it via a fuel system, which comprises a fuel tank 5.
  • a fuel system which comprises a fuel tank 5.
  • the system and the method according to the invention are well suited to exhaust gas treatment systems other than for land borne motor vehicles, such as watercraft or stationary systems.
  • the watercraft may be of any suitable type, such as motor boats, ships, ferries or vessels.
  • Examples of stationary systems may be industrial engines or engine-powered industrial robots, power plants or the like.
  • FIG. 2 schematically illustrates one exemplifying exhaust gas treatment system 4 comprising a diesel oxidation catalyst (DOC) 6 and a selective catalytic reduction (SCR) catalyst 7 arranged downstream of the DOC in the flow direction of the exhaust gas through the exhaust gas treatment system.
  • the exhaust gas treatment system 4 may further include one or more additional catalysts as well as one or more particulate filters as previously known.
  • a particulate filter may be arranged between the DOC and the SCR
  • a particulate filter may be arranged downstream of the SCR
  • an ammonium slip catalyst (ASC) may be arranged downstream of the SCR.
  • ASC ammonium slip catalyst
  • the highest conversion rate in the SCR is achieved in the case of a 50:50 ratio of N0 2 and NO in the exhaust gas entering the SCR.
  • the desired ratio of N0 2 in the exhaust gas is achieved by the oxidation of NO to N0 2 in the catalyst(s) provided upstream of the SCR.
  • the catalytic activity of the oxidation catalyst(s) may be selected in order to achieve the desired oxidation of NO.
  • the capability of oxidation is dependent on the temperature of the exhaust gas as well as the mass flow as previously explained.
  • Figure 3 schematically illustrates one example of the temperature dependence of the capability of two different commercially available oxidation catalysts to oxidize NO to N0 2 .
  • Line 10 illustrates the thermodynamic equilibrium of N0 2 /NO x , and thus sets the upper limit for the oxidation of NO to N0 2 .
  • Line 11 represents a catalyst having the ability to oxidize NO to a high degree even at low temperatures, such as about 250°C, whereas line 12 represents a catalyst, which is also capable of oxidizing NO but to a much lower degree compared to the first catalyst illustrated by line 11. It is clear from Figure 3 that neither of the oxidation catalysts provides a desirable degree of oxidation for all temperature ranges to which a conventional gas exhaust treatment system may be subjected during operation thereof. While Figure 3 only illustrates the temperature dependence on the oxidation capacity, the dependence of mass flow has a similar dependence on the oxidation capacity as previously discussed.
  • the exhaust gas flow is divided into a first partial flow and a second partial flow.
  • This may according to one aspect of the invention be achieved as shown in Figure 4 illustrating a first oxidation catalyst 6a and a second catalyst 6b arranged essentially parallel to the first oxidation catalyst.
  • the first oxidation catalyst 6a comprises the first zone and the second oxidation catalyst 6b comprises the second zone.
  • the recombined exhaust gas flow will (for a preselected mass ratio between the first partial flow and the second partial flow) comprise an amount of N0 2 as illustrated by line 13 in Figure 13.
  • the oxidation catalysts need not have their respective central axis (also coinciding with the flow direction through the catalysts) being parallel.
  • the catalyst may thus be arranged in any convenient manner depending on factors such as space, for example inside a common housing of the exhaust gas treatment system, and/or the other catalysts of the exhaust gas treatment system.
  • Figure 4 illustrates an example comprising two parallel oxidation catalysts
  • the first partial flow and the second partial flow need not necessarily pass separate oxidation catalysts but may alternatively both pass through a single oxidation catalyst.
  • the oxidation catalyst comprising a first zone and a second zone arranged parallel to the first zone in the flow direction through the catalyst.
  • the first zone has a different catalytic activity than that of the second zone. This may for example be accomplished by providing the respective zones with different coatings having the intended catalytic activities for the respective zones.
  • a first wash coat may be applied/deposited to a first zone whereas the other zone is masked during such application/deposition step, thereafter the first zone is masked and another wash coat is applied/deposited to the second zone.
  • Masking may for example be made by a suitable wax or the like which is melted and removed in a subsequent processing step of the oxidation catalyst.
  • it is not necessary to mask the entire surface of a zone when a desired wash coat is applied to the other zone. It is sufficient that just the openings of the respective zone is masked such that the wash coat intended for the other zone cannot flow into the cells or channels of the first zone.
  • Fig. 5a illustrates a cross sectional view of an exemplifying single oxidation catalyst 6.
  • the oxidation catalyst comprises a plurality of cells or channels 8 through which the exhaust gas flows.
  • the cells or channels 8 are arranged in a honeycomb pattern and extend through the oxidation catalyst from the inlet to the outlet.
  • the cells or channels may also be arranged in other cross sectional patterns as known in the art.
  • the oxidation catalyst 6 comprises two first zones 61 having a first catalytic activity and two second zones 62 having a second catalytic activity.
  • the first and second zones are arranged as circle sectors as seen in the cross sectional view of the oxidation catalyst 6.
  • the catalyst may comprise only one first zone and one second zone. It is also plausible that the oxidation catalyst comprises more than two of the respective zones without departing from the scope of the present invention.
  • the first zones 61 and the second zones 62 are arranged in an alternating manner in the cross section of the oxidation catalyst.
  • Each of the zones preferably extends from the inlet end of the oxidation catalyst to the outlet end of the catalyst, the inlet and outlet ends defined by the flow direction of exhaust gas through the oxidation catalyst.
  • the cross sectional surface of the first zones 61 and the second zones 62 have essentially the same size.
  • the mass ration between the first partial flow and the second partial flow will necessarily be 50:50 (supposing that the channels have the same cross sectional opening size).
  • the respective cross sectional size of the zones may be selected accordingly.
  • Fig. 5b illustrates a cross sectional view of an alternative exemplifying single oxidation catalyst 6 comprising a plurality of first zones 61 having a first catalytic activity and a plurality of second zones 62 having a second catalytic activity.
  • the first and second zones are arranged in a chess-like pattern with regard to the cross sectional view of the oxidation catalyst 6.
  • Each zone preferably extends from the inlet end of the oxidation catalyst to the outlet end of the oxidation catalyst, the inlet and outlet ends defined by the flow direction trough the catalyst.
  • first and second zones 61, 62 when arranged in a single oxidation catalyst, should be essentially parallel to each other with respect to the flow direction of exhaust gas through the oxidation catalyst.
  • the first and the second partial flows after having passed the respective first and second zones, are mixed into a single flow of exhaust gas before the exhaust gas flows into the SCR catalyst.
  • the recombined exhaust gas flow will constitute a mixture of the first partial flow and the second partial flow. It is desired to achieve as homogenous mixture of the recombined exhaust gas as possible to ensure an appropriate reading in a NO x -sensor as well as ensure the appropriate conversion in the subsequent SCR.
  • stationary means adapted to create and/or increase turbulence of the gas flow.
  • Such stationary turbulence increasing means may suitably be arranged in a conduit at, or close to, the point in the system where the two partial flows are recombined.
  • Examples of such turbulence increasing means may for example be one or more radially extending rods or partitions, or a circumferential radially extending flange or the like. It is also plausible to create or increase the turbulence in the respective partial flows before they are recombined such as to facilitate mixing when they are recombined. This may suitably also be accomplished by stationary means in a similar manner as described above. By creating turbulence in the gas flow upstream of the SCR, the partial flows are better mixed.
  • increasing the number of first zones and second zones in a single catalyst may also increase the mixing of the first partial flow and the second partial flow.
  • the catalytic activities of the first and the second zones is that one of the zones (the second zone) has a catalytic activity above a certain level (with no other limitation on its activity for NO-oxidation), while the other zone (the first zone) has a small catalytic activity with regard to NO-oxidation.
  • the determination of the upper and lower threshold limits for the respective catalytic activities can be done with respect to cost and performance demands.
  • the system and method according to the present invention retain the possibility to maximize the activity of one of the zones to increase the durability of the system, without compromising SCR- performance.
  • the ability to specify the activity of the one of the zones (the zone which is passed by the second partial flow) without any upper limit may be critical when using non-PGM catalysts, since these may, or may not, require this to achieve adequate durability.
  • To maximize activity is not possible for a conventional single-catalyst system (having one single catalytic activity) for the reasons as previously discussed.
  • the first and the second zone should both have as high catalytic activity as possible with regard to oxidation of hydrocarbons as well as carbon monoxide.
  • the development of oxidation catalyst during recent years have resulted in catalysts fulfilling both the requirements with regard to oxidation of HC and CO, as well as the respective capabilities with regard to oxidation of NO.
  • Such oxidation catalysts are now commercially available and will therefore not be further discussed in the present disclosure.
  • the exhaust gas treatment system as disclosed above can be used for a method for providing a desired pre-determined ratio between N0 2 and NO x in an exhaust gas flow intended to pass through a selective catalytic reduction catalyst.
  • the method comprises, upstream of the SCR, dividing an exhaust gas flow (intended to pass the SCR) flow into a first partial flow and a second partial flow, the second partial flow being essentially parallel to the first partial flow.
  • the method is further configured to provide a mass ratio between the first partial flow and the second partial flow, which is essentially constant for all operating conditions, such as temperature, mass flow and composition or concentration of the exhaust gas.
  • the method further comprises oxidising the first partial flow such that 5 to 30 % of the NO in the first partial flow is oxidised to N0 2 , and oxidising the second partial flow such that at least 70 % of the NO in the second partial flow is oxidised to N0 2 .
  • the method comprises combining and mixing the first partial flow with the second partial flow in order to achieve a recombined exhaust gas flow having the desired ratio between N0 2 and NO x .
  • the pre-determined desired ratio is adapted for achieving a desired conversion rate while avoiding the problems associated with the NO x -sensor as previously disclosed. More specifically, desired ratio between N0 2 and NO x may suitably be 20 % ⁇ N0 2 /NO x ⁇ 50%. Preferably, the desired ratio between N0 2 and NO x is 30 % ⁇ N0 2 /NO x ⁇ 45%. As disclosed above, the exhaust gas treatment system and the method ensures that a high ratio of N0 2 /NO x is achieved irrespective of the temperature and mass flow while at the same time avoiding the risk of temporarily exceeding an upper threshold value which could risk incorrect reading of the NO x by the NO x -sensor.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

L'invention concerne un système de traitement de gaz d'échappement (4) comprenant un catalyseur de réduction catalytique sélective (7), et un procédé pour obtenir un rapport souhaité entre le NO2 et le NOxdans les gaz d'échappement devant passer par un catalyseur de réduction catalytique sélective (7). Le flux de gaz d'échappement dans le système est divisé en deux flux partiels, le NO étant oxydé jusqu'à un faible degré dans le premier flux partiel et jusqu'à un degré élevé dans le second flux partiel. Le système de traitement de gaz d'échappement (4) et le procédé de l'invention assurent un taux de conversion élevé dans le catalyseur SCR pour une large gamme de paramètres de fonctionnement en termes de température et de débit massique.
PCT/SE2016/050350 2015-04-29 2016-04-21 Système de traitement de gaz d'échappement WO2016175697A1 (fr)

Priority Applications (2)

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KR1020177032685A KR20170136610A (ko) 2015-04-29 2016-04-21 배기가스 처리 시스템
EP16786851.2A EP3289197A4 (fr) 2015-04-29 2016-04-21 Système de traitement de gaz d'échappement

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SE1550513-4 2015-04-29
SE1550513A SE541476C2 (en) 2015-04-29 2015-04-29 Exhaust gas treatment system

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WO2016175697A1 true WO2016175697A1 (fr) 2016-11-03

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KR (1) KR20170136610A (fr)
DE (1) DE202016008865U1 (fr)
SE (1) SE541476C2 (fr)
WO (1) WO2016175697A1 (fr)

Citations (5)

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US20050129601A1 (en) * 2003-11-04 2005-06-16 Engelhard Corporation Emissions treatment system with NSR and SCR catalysts
EP1589199A1 (fr) * 2004-04-19 2005-10-26 Peugeot Citroen Automobiles S.A. Dispositif de purification de gaz d'échappement
WO2009017597A1 (fr) * 2007-07-31 2009-02-05 Caterpillar Inc. Système de traitement d'échappement avec régulation de no2
US20100154392A1 (en) * 2008-12-18 2010-06-24 Caterpillar Inc. Adjusting nitrogen oxide ratios in exhaust gas
WO2013042080A1 (fr) * 2011-09-23 2013-03-28 Basf Se Catalyseur d'oxydation diesel à structure en couches, contenant une composition d'oxyde de cérium comme matériau de support de palladium pour conversion de gaz hc et co améliorée

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US6846464B2 (en) * 2002-11-20 2005-01-25 Ford Global Technologies, Llc Bimodal catalyst-urea SCR system for enhanced NOx conversion and durability
DE112007000322B4 (de) 2006-03-02 2019-04-18 Avl List Gmbh Abgassystem für eine Brennkraftmaschine
US7810316B2 (en) * 2006-12-29 2010-10-12 Cummins Filtration Ip, Inc Apparatus, system, and method for exhaust aftertreatment efficiency enhancement
DE102013204405A1 (de) 2013-03-13 2014-09-18 Mtu Friedrichshafen Gmbh System zur Abgasnachbehandlung für eine Brennkraftmaschine, Verfahren zur Beeinflussung einer Abgas-Zusammensetzung und Brennkraftmaschine

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US20050129601A1 (en) * 2003-11-04 2005-06-16 Engelhard Corporation Emissions treatment system with NSR and SCR catalysts
EP1589199A1 (fr) * 2004-04-19 2005-10-26 Peugeot Citroen Automobiles S.A. Dispositif de purification de gaz d'échappement
WO2009017597A1 (fr) * 2007-07-31 2009-02-05 Caterpillar Inc. Système de traitement d'échappement avec régulation de no2
US20100154392A1 (en) * 2008-12-18 2010-06-24 Caterpillar Inc. Adjusting nitrogen oxide ratios in exhaust gas
WO2013042080A1 (fr) * 2011-09-23 2013-03-28 Basf Se Catalyseur d'oxydation diesel à structure en couches, contenant une composition d'oxyde de cérium comme matériau de support de palladium pour conversion de gaz hc et co améliorée

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SE1550513A1 (en) 2016-10-30
DE202016008865U1 (de) 2020-03-13
SE541476C2 (en) 2019-10-15
EP3289197A4 (fr) 2018-09-19
KR20170136610A (ko) 2017-12-11
EP3289197A1 (fr) 2018-03-07

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