US20110030343A1 - Scr reductant deposit removal - Google Patents
Scr reductant deposit removal Download PDFInfo
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- US20110030343A1 US20110030343A1 US12/536,891 US53689109A US2011030343A1 US 20110030343 A1 US20110030343 A1 US 20110030343A1 US 53689109 A US53689109 A US 53689109A US 2011030343 A1 US2011030343 A1 US 2011030343A1
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- Prior art keywords
- scr
- heat source
- reductant
- engine
- exhaust aftertreatment
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- 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]
- F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
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- 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
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1622—Catalyst reducing agent absorption capacity or consumption amount
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- 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 to engine exhaust aftertreatment systems, and more particularly to exhaust aftertreatment systems employing reductants for NOx reduction technologies.
- a selective catalytic reduction (SCR) system may be included in an exhaust treatment or aftertreatment system for a power system to remove or reduce nitrous oxide (NOx or NO) emissions coming from the exhaust of an engine.
- SCR systems use reductants, such as urea. These reductants may form deposits in the exhaust system, creating backpressure, reducing efficiency, and potentially corroding components and inhibiting injection of the reductant.
- PCT Patent Application Publication WO 2005/073528 discloses a heater around the outside of the exhaust conduit to remove solute deposited on the exhaust conduit.
- the '528 publn may not address deposits in other areas of the SCR system and may not be the most efficient solution.
- the present disclosure provides an engine exhaust aftertreatment system including a selective catalytic reduction (SCR) system.
- SCR system includes a reductant injection system configured to introduce a reductant into a exhaust stream of a engine, a SCR catalyst configured to reduce NOx in the presence of a reductant, and a SCR monitoring system configured to determine temperatures associated with the SCR system.
- the SCR system also includes a heat source configured to raise the temperature of the exhaust stream and a controller configured to operate the heat source to reach temperatures in the SCR system of at least about 400 degrees Celsius.
- a method for removing deposits from a selective catalytic reduction (SCR) system.
- the method includes determining temperatures associated with the SCR system, activating a heat source to increase exhaust stream temperatures to reach temperatures in the SCR system of at least about 400 degrees Celsius, and controlling the heat source 20 based on temperatures in the SCR system.
- SCR selective catalytic reduction
- a selective catalytic reduction (SCR) system including an injector, SCR catalyst, and an injector heater.
- the injector introduces a reductant into the exhaust stream of the engine.
- the injector heater is associated with the injector to prevent or remove deposits.
- FIG. 1 is a diagrammatic view of a power system including an engine and an aftertreatment system.
- FIG. 2 is a cross-sectional view of a exhaust conduit from FIG. 1 , showing a reductant deposit upstream from a mixer.
- FIG. 3 is a cross-sectional view of a exhaust conduit from FIG. 1 , showing a reductant deposit upstream in the exhaust conduit.
- FIG. 4 is a cross-sectional view of a SCR canister from FIG. 1 , showing a reductant deposit on a face of a SCR catalyst.
- a power system 10 includes an engine 12 and an aftertreatment system 14 to treat an exhaust stream 16 produced by the engine 12 .
- the engine 12 may include other features not shown, such as controllers, fuel systems, air systems, cooling systems, peripheries, drivetrain components, turbochargers, exhaust gas recirculation systems, etc.
- the engine 12 may be any type of engine (internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, and in any configuration (“V,” in-line, radial, etc.).
- the engine 12 may be used to power any machine or other device, including on-highway trucks or vehicles, off-highway trucks or machines, earth moving equipment, generators, aerospace applications, locomotive applications, marine applications, pumps, stationary equipment, or other engine powered applications.
- the aftertreatment system 14 includes an exhaust conduit 18 , a heat source 20 , a Selective Catalytic Reduction (SCR) system 22 , and a control system 24 .
- the aftertreatment system 14 may also include a diesel oxidation catalyst (DOC) 26 , a diesel particulate filter (DPF) 28 , and a clean up catalyst 29 or other exhaust treatment devices upstream, downstream, or within the SCR system 22 .
- DOC diesel oxidation catalyst
- DPF diesel particulate filter
- the DOC 26 oxidizes NOx into Nitrogen dioxide (NO2).
- NO2 Nitrogen dioxide
- the DPF 28 collects particulate matter or soot.
- the DOC 26 and DPF 28 may be in the same canister, as shown, or separate.
- the heat source 20 may embody a burner 30 including a combustion head 32 and a housing 33 .
- the housing 33 may contain a flame 35 generated by the combustion head 32 .
- the housing 33 may also route the exhaust stream 16 to be heated by the burner 30 .
- the burner 30 may receive a supply of fuel and may also include an ignition source and air supply to generate the flame 35 .
- the heat source 20 may not employ a fuel-fired burner 30 .
- the heat source 20 may embody an electric heating element, microwave device, or other heat source.
- the heat source 20 may also embody operating the engine 12 under conditions to generate elevated exhaust stream 16 temperatures.
- the SCR system 22 may include a reductant system 34 , mixer 36 , diffuser 38 , SCR canister 40 , and SCR catalyst 42 .
- the SCR system 22 may also include one or more changes of direction or bends 43 in the exhaust conduit 18 .
- the reductant system 34 may include a reductant source 44 , pump 46 , valve 48 , and injector 50 .
- Reductant 52 is drawn from the reductant source 44 via the pump 46 and delivery to the injector 50 is controlled via the valve 48 .
- the reductant 52 comes from a nozzle or injector tip 54 of the injector 50 to form a reductant spray 56 or is otherwise introduced into the exhaust stream 16 or SCR catalyst 42 .
- Components of the reductant system 34 may be cooled or insulated to prevent overheating of the reductant 52 .
- the mixer 36 may be added to aid mixing of the reductant 52 with the exhaust stream 16 .
- the diffuser 38 may be added to aid in distributing the exhaust stream 16 evenly into the SCR catalyst 42 .
- the diffuser 38 may be disposed in the SCR canister upstream of the SCR catalyst 42 and may include a plurality of diffuser openings 55 that the exhaust stream 16 exits from.
- the SCR catalyst 42 includes a catalyst material disposed on a substrate.
- the catalyst is configured to reduce an amount of NOx in the exhaust stream 16 by using the reductant 52 .
- the substrate may consist of cordierite, silicon carbide, other ceramic, or metal.
- the substrate may include a plurality of through going channels 57 .
- the channels 57 may form a honeycomb structure.
- a face 58 of the SCR catalyst 42 is exposed to the oncoming exhaust stream 16 .
- urea is the most common source of reductant 52 .
- Urea reductant 52 decomposes into ammonia (NH3) and is then adsorbed or stored in the SCR catalyst 42 .
- the length of the SCR system 22 between the injector tip 54 and SCR catalyst 42 may be sufficiently long to achieve the mixing of reductant 52 into the exhaust stream 16 and provide the dwell time for the urea reductant 52 to convert into NH3.
- urea reductant 52 may only occur above an injection threshold temperature, which may be about 180 degrees Celsius. Below about 180 degrees Celsius sulfates are formed from the urea reductant 52 that may deactivate the SCR catalyst 42 .
- the NH3 is consumed in the SCR Catalyst 42 through a reduction of NOx into Nitrogen gas (N2).
- Desorption of NH3 from the SCR catalyst 42 also occurs at temperatures in excess of about 200 degrees Celsius and continues to accelerate as temperatures increase. Some NH3 oxidation also occurs above about 500 degrees Celsius. However, the rates of NH3 desorption and oxidation do not exceed the rate of adsorption and NOX reduction, making the dosing of Urea still effective for emission reductions.
- the clean-up catalyst 29 may embody an ammonia oxidation catalyst (AMOX) and may be included downstream of the SCR system 22 .
- the clean-up catalyst 29 and SCR catalyst 42 may be in the same canister, as shown, or separate.
- the clean-up catalyst 29 is configured to capture, store, oxidize, reduce, and/or convert NH3 that may slip past or breakthrough the SCR catalyst 42 .
- the clean-up catalyst 29 may also be configured to capture, store, oxidize, reduce, and/or convert other constituents present.
- Control system 24 includes a controller 60 , engine connection 62 , heat source connection 64 , DPF sensor system 66 , reductant system connection 68 , and SCR monitoring system 70 .
- the engine connection 62 receives data from the engine 12 and machine and may provide control signals to the engine 12 .
- the heat source connection 64 activates the heat source 20 when ordered by the controller 60 .
- the DPF sensor system 66 may include upstream sensors 72 and a soot sensor 74 .
- the upstream sensors 72 may include temperature and or pressure sensors.
- the soot sensor 74 provides an indication of soot levels in the DPF 28 and may be based on pressure differential or attenuated radio frequencies (RF) or another sensor system.
- RF radio frequencies
- the reductant system connection 68 activates the reductant system 34 when ordered by the controller 60 .
- the SCR monitoring system 70 determines a temperature associated with the SCR system 22 .
- the SCR monitoring system 70 may include upstream sensors 76 , inside sensors 78 , and downstream sensors 80 .
- the SCR monitoring system 70 may also determine the temperature of the SCR system 22 directly from these sensors or may calculate or predict the temperature based on temperatures sensed elsewhere in the power system 10 , operating or ambient conditions, or any combination thereof.
- the upstream sensors 76 , inside sensors 78 , and downstream sensors 80 may also include any of NOx, NH3, temperature, signal frequency, and pressure sensors and may include more than one.
- One or more of the upstream sensors 76 , inside sensors 78 , and downstream sensors 80 may not be needed.
- the upstream sensors 76 are located in the exhaust stream 16 upstream of the reductant system 34 .
- the inside sensors 78 are located in the exhaust stream 16 downstream of the reductant system 34 and upstream of the SCR catalyst 42 .
- the downstream sensors 80 are located in the exhaust stream 16 downstream of the SCR catalyst 42 . The location of the sensors may be changed or moved with appropriate compensations made to any measurements.
- An unintended consequence of urea reductant 52 injections may be the formation of deposits 82 . While the reductant system 34 may or may not be air-assisted, deposits more readily develop in airless reductant systems 34 . Airless reductant systems 34 tend to produce reductant sprays 56 with larger droplet sizes than air-assisted reductant systems 34 . The larger droplet size in the reductant spray 56 may cause deposit 82 formations.
- the deposits 82 may form as settlements 83 on an inside wall 84 of the exhaust conduit 18 .
- the settlements 83 may form in areas where the reductant spray 56 impinges or settles.
- the deposits 82 may form opposite the injector 50 before the mixer 36 , as seen in FIG. 2 , or on the far wall of a bend 43 as seen in FIG. 3 .
- the deposits 82 may also form on or in other components of the exhaust system, such as the injector 50 , mixer 36 , diffuser 38 , or face 58 of the SCR catalyst 42 .
- the deposits 82 may also break away as flakes 86 . As seen in FIG. 4 , these flakes 86 may land or be blown onto the face 58 of the SCR catalyst 42 . The flakes 86 may also come to rest in other locations, such as in the mixer 36 , in the exhaust conduit 18 , in the diffuser 38 , the diffuser openings 55 , or in the canister 40 .
- the deposits 82 may form under a number of different conditions and through a number of different mechanisms. Deposits 82 may form when the urea reductant 52 is not quickly decomposed into NH3 and thick layers of urea reductant 52 collect. These layers may build as more and more urea reductant 52 is sprayed or collected, which may have a cooling effect that prevents decomposition into NH3. As a result, the urea reductant 52 sublimates into crystals or otherwise transforms into a solid composition to form the deposit 82 .
- This composition may consist of biuret (NH2CONHCONH2) or cyanuric acid ((NHCO)3) or another composition depending on temperatures and other conditions.
- deposits 82 may have negative impacts on the operation of the power system 10 .
- the deposits 82 may block flow of the exhaust stream 16 , causing higher back-pressure and reducing engine 12 and aftertreatment system 14 performance and efficiency.
- the deposits 82 may also disrupt the flow and mixing of the urea reductant 52 into the exhaust stream 16 , thereby reducing the decomposition into NH3 and reducing NOx reduction efficiency.
- the deposits 82 may also block the injector tip 54 or disrupt the reductant spray 56 .
- the formation of the deposits 82 also consumes urea reductant 52 , making control of injection harder and potentially reducing NOx reduction efficiency.
- the deposits 82 may also corrode components of the aftertreatment system 14 materials and degrade the structural and thermal properties of the SCR catalyst 42 .
- the deposits 82 may also block channels 57 of the SCR catalyst 42 , again reducing NOx reduction efficiency.
- the heat source 20 is upstream of the SCR system 22 for heating the exhaust stream 16 .
- the heat source 20 is able to decompose or remove any deposits 82 present in the SCR system 22 .
- the heat source 20 may also be upstream of the DPF 28 for the regeneration or soot removal of the DPF 28 .
- the deposits 82 have been found to decompose into ammonia and carbon dioxide (CO2) at SCR system 22 temperatures in excess of about 400 degrees Celsius.
- the SCR system 22 temperatures may be the temperature of the exhaust stream 16 entering the SCR system 22 as measured by the upstream sensors 76 . Tests have shown that deposits 82 are removed in the SCR system 22 when exposed to about 450 degree Celsius for between about 15 and 30 minutes or about 650 degrees Celsius for between about 5 and 10 minutes.
- Heating the outside of the exhaust conduit 18 and not significantly heating the exhaust stream 16 would not be effective in removing the deposits 82 that may be inside the exhaust conduit 18 , such as those on the face 58 of the SCR catalyst 42 , in the mixer 36 , or in the diffuser 38 .
- Heating the outside of the exhaust conduit 18 may also require a large and complex heating system to apply heat to all the needed areas of the aftertreatment system 14 as compared to a single heat source 20 that heats the exhaust stream 16 .
- a robust heat source 20 such as a burner 30 , may be needed to reach the temperatures needed for decomposition in the SCR system, especially if the heat source 20 is upstream of the DPF 28 or otherwise far away from the SCR system 22 and given the length and number or mass of components in the SCR system 22 .
- Controller 60 receives data from SCR monitoring system 70 and controls the operation of the heat source 20 .
- the controller 60 orders the heat source 20 to activate, temperatures associated with the SCR monitoring system 70 are reported to the controller 60 from the SCR monitoring system 70 .
- the controller 60 calculates or determines whether a sufficient temperature has been reached in the SCR system 22 for a sufficient amount of time to decompose any deposits 82 that may be present. If not, the controller 60 will order the heat source 20 to provide more heat for longer.
- the controller 60 may control the heat source 20 for deposit 82 removal in conjunction with regeneration or soot removal of the DPF 28 . Removal of deposits 82 in the SCR system 22 may also be needed at times when additional heat is not needed for regeneration of the DPF 28 . Under certain engine 12 operating conditions passive regeneration of the DPF 28 may occur or the amount of soot produced may be reduced, extending the time between active DPF 28 regenerations that require activation of the heat source 20 . During these periods, however, deposits 82 may continue to form in the SCR system 22 , requiring activation of the heat source 20 for deposit 82 removal even when not needed for DPF 28 regeneration.
- the controller 60 may be configured to activate the heat source 20 for deposit 82 removal under a number of different conditions.
- the activation of the heat source 20 may be based on a time period during which deposits 82 are known to normally accumulate to a limit threshold.
- the activation of the heat source 20 may also be a function of several parameters. Those parameters may include time, engine 12 operating conditions, reductant 52 dosing rates, or SCR system 22 temperatures.
- the controller 60 may include a map or algorithm or combination thereof to calculate or predict a time based on those parameters when deposits 82 will be expected to accumulate beyond the threshold limit and the heat source 20 will need to be activated to remove the deposits 82 .
- the controller 60 may also use the SCR monitoring system 70 to measure that deposits 82 have formed beyond the threshold limit and the heat source 20 will need to be activated to remove the deposits 82 .
- This measurement from the SCR monitoring system 70 may be changes in back pressure, changes in a signal frequency attenuation, changes in NOx reduction efficiency, changes in ammonia conversion, or changes in temperature distributions.
- the controller 60 may also slow, stop, or inhibit the injection of reductant 52 when activating the heat source 20 to remove deposits 82 .
- the injection of the reductant 52 may have a cooling effect on the deposits 82 , preventing their decomposition, which is a function of temperature. Accordingly, inhibiting the injection of reductant 52 when activating the heat source 20 may aid in the removal of deposits 82 .
- the inhibiting of reductant 52 injection may represent short delays between injection events or may last a longer period of time while the heat source 20 is activated.
- the heat source 20 may be configured to operate during periods of engine 12 idle.
- the urea reductant 52 is injected when the SCR system 22 temperature is above the injection threshold temperature, which may be about 180 degrees Celsius.
- the injection threshold temperature which may be about 180 degrees Celsius.
- the exhaust stream 16 temperature in the SCR system 22 may fall under this injection threshold temperature.
- the exhaust stream 16 temperature in the SCR system 22 may still exceed this injection threshold temperature and urea reductant 52 injection may ordinarily be occurring.
- the heat source 20 may be configured to also operate at high engine 12 speeds and load or other non-idle engine 12 conditions. At these higher engine 12 speeds and loads, SCR system 22 temperatures will also probably be above the injection threshold temperature and urea reductant 52 injection may ordinarily be occurring.
- the controller 60 may slow, stop, suspend, or inhibit the injection of urea reductant 52 .
- the injection of urea reductant 52 may be at least partially suspended because lower amounts of reductant 52 are needed as low levels of NOx are probably being produced from engine 12 .
- the inhibiting of reductant 52 injection may not be possible or may only represent short delays between injection events because of the higher levels of NOx probably being produced.
- the controller 60 controls the injection of urea reductant 52 based on a predicted amount of NH3 stored in the SCR catalyst 42 .
- desorption of NH3 from the SCR catalyst 42 occurs at temperatures in excess of about 200 degrees Celsius and continues to accelerate as temperatures increase. Therefore, because of the temperatures reached, the SCR catalyst 42 will have nearly zero NH3 remaining after the heat source 20 is activated to remove the deposits 82 .
- the controller may accordingly be configured to reset the predicted amount of NH3 stored in the SCR catalyst 42 to zero in conjunction with the activation of the heat source 20 .
- the SCR system 22 temperature may be below the injection threshold temperature. If the heat source 20 is activated during these times, the time period following the deactivation of the heat source 20 may be used as an opportunity to inject reductant 52 before the temperature falls below the injection threshold temperature again. This may provide the ability to inject reductant 52 when not otherwise possible, such as during periods of extended idle or other low temperature conditions. This injection may help store NH3 in the SCR catalyst 42 and provide better response during transient engine 12 conditions following an extended engine 12 idle.
- the heat source 20 may be activated solely for this purpose of reductant 52 injections or in conjuncture with deposit 82 removal, DPF 28 regeneration, or another purpose.
- the method includes sensing or determining a temperature associated with the SCR system 22 , activating a heat source 20 to increase exhaust stream 16 temperatures to reach temperatures in the SCR system 22 , as discussed above, and controlling the heat source 20 based on temperatures in the SCR system, as determined by the SCR monitoring system 70 .
- the method may also include at least partially inhibiting an introduction of the reductant 52 and may include assigning a value of about zero for an amount of reductant 52 stored in the SCR catalyst 42 for control of the reductant system 34 .
- the injector 50 may also include an injector heater 90 to prevent formation of or remove deposits 82 from inside or on the injector 50 .
- the injector heater 90 may be located in, around, or proximate to the injector tip 54 or otherwise located to apply heat to the injector 50 .
- the injector heater 90 may consist of an electric resistance-heating coil connected to a power source.
- the injector heater 90 may also consist of another heat source.
- the injector heater 90 may be connected to the controller 60 or otherwise controlled to activate periodically or when predetermined conditions are met.
- the injector heater 90 may prevent the formation of deposits 82 in the injector 50 by being activated or otherwise applying heat to the injector 50 and injector tip 54 after an injection. This heat will cause any water or other liquid contained in reductant 52 remaining in the injector 50 to boil and steam. This steam will drive the reductant 52 from critical components in the injector 50 or injector tip 54 , such as a check valve. Because the reductant 52 is no longer present, deposits 82 will not form.
- the injector heater 90 may also be used to remove urea deposits 82 that may form around or inside the injector 50 .
- the injector heater 90 may be capable of heating the injector 50 or injector tip 54 to the temperatures mentioned above for deposit 82 removal (between about 400 and 650 degrees Celsius and higher).
- the use of the injector heater 90 may also eliminate a need to cool the injector or other components of the reductant system 34 because deposits 82 are prevented or removed.
- the use of the injector heater 90 may or may not be included in the same embodiment as the use of the heat source 20 .
Abstract
An engine exhaust aftertreatment system including a selective catalytic reduction (SCR) system. The SCR system includes a reductant injection system configured to introduce a reductant into a exhaust stream of a engine, a SCR catalysts configured to reduce NOx in the presence of a reductant, and a SCR monitoring system configured to determine temperatures associated with the SCR system. The SCR system also includes a heat source configured to raise the temperature of the exhaust stream and a controller configured to operate the heat source to reach exhaust stream temperatures in the SCR system of at least about 400 degrees Celsius based on the temperature associated with the SCR system.
Description
- The present disclosure relates to engine exhaust aftertreatment systems, and more particularly to exhaust aftertreatment systems employing reductants for NOx reduction technologies.
- A selective catalytic reduction (SCR) system may be included in an exhaust treatment or aftertreatment system for a power system to remove or reduce nitrous oxide (NOx or NO) emissions coming from the exhaust of an engine. SCR systems use reductants, such as urea. These reductants may form deposits in the exhaust system, creating backpressure, reducing efficiency, and potentially corroding components and inhibiting injection of the reductant.
- PCT Patent Application Publication WO 2005/073528 (the '528 publn) discloses a heater around the outside of the exhaust conduit to remove solute deposited on the exhaust conduit. The '528 publn, however, may not address deposits in other areas of the SCR system and may not be the most efficient solution.
- In one aspect, the present disclosure provides an engine exhaust aftertreatment system including a selective catalytic reduction (SCR) system. The SCR system includes a reductant injection system configured to introduce a reductant into a exhaust stream of a engine, a SCR catalyst configured to reduce NOx in the presence of a reductant, and a SCR monitoring system configured to determine temperatures associated with the SCR system. The SCR system also includes a heat source configured to raise the temperature of the exhaust stream and a controller configured to operate the heat source to reach temperatures in the SCR system of at least about 400 degrees Celsius.
- In another aspect a method is provided for removing deposits from a selective catalytic reduction (SCR) system. The method includes determining temperatures associated with the SCR system, activating a heat source to increase exhaust stream temperatures to reach temperatures in the SCR system of at least about 400 degrees Celsius, and controlling the
heat source 20 based on temperatures in the SCR system. - In yet another aspect, a selective catalytic reduction (SCR) system is provided including an injector, SCR catalyst, and an injector heater. The injector introduces a reductant into the exhaust stream of the engine. The injector heater is associated with the injector to prevent or remove deposits.
- Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
-
FIG. 1 is a diagrammatic view of a power system including an engine and an aftertreatment system. -
FIG. 2 is a cross-sectional view of a exhaust conduit fromFIG. 1 , showing a reductant deposit upstream from a mixer. -
FIG. 3 is a cross-sectional view of a exhaust conduit fromFIG. 1 , showing a reductant deposit upstream in the exhaust conduit. -
FIG. 4 is a cross-sectional view of a SCR canister fromFIG. 1 , showing a reductant deposit on a face of a SCR catalyst. - As seen in
FIG. 1 , apower system 10 includes anengine 12 and anaftertreatment system 14 to treat anexhaust stream 16 produced by theengine 12. Theengine 12 may include other features not shown, such as controllers, fuel systems, air systems, cooling systems, peripheries, drivetrain components, turbochargers, exhaust gas recirculation systems, etc. Theengine 12 may be any type of engine (internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, and in any configuration (“V,” in-line, radial, etc.). Theengine 12 may be used to power any machine or other device, including on-highway trucks or vehicles, off-highway trucks or machines, earth moving equipment, generators, aerospace applications, locomotive applications, marine applications, pumps, stationary equipment, or other engine powered applications. - The
aftertreatment system 14 includes anexhaust conduit 18, aheat source 20, a Selective Catalytic Reduction (SCR)system 22, and acontrol system 24. Theaftertreatment system 14 may also include a diesel oxidation catalyst (DOC) 26, a diesel particulate filter (DPF) 28, and a clean upcatalyst 29 or other exhaust treatment devices upstream, downstream, or within theSCR system 22. - The
exhaust stream 16 exits theengine 12, passes by or through theheat source 20, passes through theDOC 26,DPF 28, then passes through theSCR system 22, and then passes through the clean upcatalyst 29 via theexhaust conduit 18. During operation, theDOC 26 oxidizes NOx into Nitrogen dioxide (NO2). TheDPF 28 collects particulate matter or soot. TheDOC 26 and DPF 28 may be in the same canister, as shown, or separate. - The
heat source 20 may embody aburner 30 including acombustion head 32 and ahousing 33. Thehousing 33 may contain aflame 35 generated by thecombustion head 32. Thehousing 33 may also route theexhaust stream 16 to be heated by theburner 30. Theburner 30 may receive a supply of fuel and may also include an ignition source and air supply to generate theflame 35. In alternative embodiments theheat source 20 may not employ a fuel-firedburner 30. Theheat source 20 may embody an electric heating element, microwave device, or other heat source. Theheat source 20 may also embody operating theengine 12 under conditions to generateelevated exhaust stream 16 temperatures. - The
SCR system 22 may include areductant system 34,mixer 36,diffuser 38,SCR canister 40, andSCR catalyst 42. TheSCR system 22 may also include one or more changes of direction orbends 43 in theexhaust conduit 18. - The
reductant system 34 may include areductant source 44,pump 46,valve 48, andinjector 50.Reductant 52 is drawn from thereductant source 44 via thepump 46 and delivery to theinjector 50 is controlled via thevalve 48. Thereductant 52 comes from a nozzle orinjector tip 54 of theinjector 50 to form areductant spray 56 or is otherwise introduced into theexhaust stream 16 orSCR catalyst 42. Components of thereductant system 34 may be cooled or insulated to prevent overheating of thereductant 52. - The
mixer 36 may be added to aid mixing of thereductant 52 with theexhaust stream 16. Thediffuser 38 may be added to aid in distributing theexhaust stream 16 evenly into theSCR catalyst 42. Thediffuser 38 may be disposed in the SCR canister upstream of theSCR catalyst 42 and may include a plurality ofdiffuser openings 55 that theexhaust stream 16 exits from. - The
SCR catalyst 42 includes a catalyst material disposed on a substrate. The catalyst is configured to reduce an amount of NOx in theexhaust stream 16 by using thereductant 52. The substrate may consist of cordierite, silicon carbide, other ceramic, or metal. The substrate may include a plurality of through goingchannels 57. Thechannels 57 may form a honeycomb structure. Aface 58 of the SCRcatalyst 42 is exposed to theoncoming exhaust stream 16. - While
other reductants 52 are possible, urea is the most common source of reductant 52. Urea reductant 52 decomposes into ammonia (NH3) and is then adsorbed or stored in theSCR catalyst 42. The length of theSCR system 22 between theinjector tip 54 andSCR catalyst 42 may be sufficiently long to achieve the mixing ofreductant 52 into theexhaust stream 16 and provide the dwell time for the urea reductant 52 to convert into NH3. - The dosing of urea reductant 52 may only occur above an injection threshold temperature, which may be about 180 degrees Celsius. Below about 180 degrees Celsius sulfates are formed from the urea reductant 52 that may deactivate the
SCR catalyst 42. - The NH3 is consumed in the
SCR Catalyst 42 through a reduction of NOx into Nitrogen gas (N2). Desorption of NH3 from theSCR catalyst 42 also occurs at temperatures in excess of about 200 degrees Celsius and continues to accelerate as temperatures increase. Some NH3 oxidation also occurs above about 500 degrees Celsius. However, the rates of NH3 desorption and oxidation do not exceed the rate of adsorption and NOX reduction, making the dosing of Urea still effective for emission reductions. - The clean-up
catalyst 29 may embody an ammonia oxidation catalyst (AMOX) and may be included downstream of theSCR system 22. The clean-upcatalyst 29 andSCR catalyst 42 may be in the same canister, as shown, or separate. The clean-upcatalyst 29 is configured to capture, store, oxidize, reduce, and/or convert NH3 that may slip past or breakthrough theSCR catalyst 42. The clean-upcatalyst 29 may also be configured to capture, store, oxidize, reduce, and/or convert other constituents present. -
Control system 24 includes acontroller 60,engine connection 62,heat source connection 64,DPF sensor system 66,reductant system connection 68, andSCR monitoring system 70. Theengine connection 62 receives data from theengine 12 and machine and may provide control signals to theengine 12. Theheat source connection 64 activates theheat source 20 when ordered by thecontroller 60. - The
DPF sensor system 66 may includeupstream sensors 72 and asoot sensor 74. Theupstream sensors 72 may include temperature and or pressure sensors. Thesoot sensor 74 provides an indication of soot levels in theDPF 28 and may be based on pressure differential or attenuated radio frequencies (RF) or another sensor system. - The
reductant system connection 68 activates thereductant system 34 when ordered by thecontroller 60. TheSCR monitoring system 70 determines a temperature associated with theSCR system 22. TheSCR monitoring system 70 may includeupstream sensors 76, insidesensors 78, anddownstream sensors 80. TheSCR monitoring system 70 may also determine the temperature of theSCR system 22 directly from these sensors or may calculate or predict the temperature based on temperatures sensed elsewhere in thepower system 10, operating or ambient conditions, or any combination thereof. Theupstream sensors 76, insidesensors 78, anddownstream sensors 80 may also include any of NOx, NH3, temperature, signal frequency, and pressure sensors and may include more than one. One or more of theupstream sensors 76, insidesensors 78, anddownstream sensors 80 may not be needed. - The
upstream sensors 76 are located in theexhaust stream 16 upstream of thereductant system 34. Theinside sensors 78 are located in theexhaust stream 16 downstream of thereductant system 34 and upstream of theSCR catalyst 42. Thedownstream sensors 80 are located in theexhaust stream 16 downstream of theSCR catalyst 42. The location of the sensors may be changed or moved with appropriate compensations made to any measurements. - An unintended consequence of
urea reductant 52 injections may be the formation ofdeposits 82. While thereductant system 34 may or may not be air-assisted, deposits more readily develop inairless reductant systems 34.Airless reductant systems 34 tend to producereductant sprays 56 with larger droplet sizes than air-assistedreductant systems 34. The larger droplet size in thereductant spray 56 may causedeposit 82 formations. - As seen in
FIGS. 2 and 3 , thedeposits 82 may form assettlements 83 on aninside wall 84 of theexhaust conduit 18. Thesettlements 83 may form in areas where thereductant spray 56 impinges or settles. For example, thedeposits 82 may form opposite theinjector 50 before themixer 36, as seen inFIG. 2 , or on the far wall of abend 43 as seen inFIG. 3 . Thedeposits 82 may also form on or in other components of the exhaust system, such as theinjector 50,mixer 36,diffuser 38, or face 58 of theSCR catalyst 42. - The
deposits 82 may also break away asflakes 86. As seen inFIG. 4 , theseflakes 86 may land or be blown onto theface 58 of theSCR catalyst 42. Theflakes 86 may also come to rest in other locations, such as in themixer 36, in theexhaust conduit 18, in thediffuser 38, thediffuser openings 55, or in thecanister 40. - The
deposits 82 may form under a number of different conditions and through a number of different mechanisms.Deposits 82 may form when theurea reductant 52 is not quickly decomposed into NH3 and thick layers ofurea reductant 52 collect. These layers may build as more andmore urea reductant 52 is sprayed or collected, which may have a cooling effect that prevents decomposition into NH3. As a result, theurea reductant 52 sublimates into crystals or otherwise transforms into a solid composition to form thedeposit 82. This composition may consist of biuret (NH2CONHCONH2) or cyanuric acid ((NHCO)3) or another composition depending on temperatures and other conditions. - These
deposits 82 may have negative impacts on the operation of thepower system 10. Thedeposits 82 may block flow of theexhaust stream 16, causing higher back-pressure and reducingengine 12 andaftertreatment system 14 performance and efficiency. Thedeposits 82 may also disrupt the flow and mixing of theurea reductant 52 into theexhaust stream 16, thereby reducing the decomposition into NH3 and reducing NOx reduction efficiency. Thedeposits 82 may also block theinjector tip 54 or disrupt thereductant spray 56. The formation of thedeposits 82 also consumesurea reductant 52, making control of injection harder and potentially reducing NOx reduction efficiency. Thedeposits 82 may also corrode components of theaftertreatment system 14 materials and degrade the structural and thermal properties of theSCR catalyst 42. Thedeposits 82 may also blockchannels 57 of theSCR catalyst 42, again reducing NOx reduction efficiency. - The
heat source 20 is upstream of theSCR system 22 for heating theexhaust stream 16. By heating theexhaust stream 16, theheat source 20 is able to decompose or remove anydeposits 82 present in theSCR system 22. Theheat source 20 may also be upstream of theDPF 28 for the regeneration or soot removal of theDPF 28. - The
deposits 82 have been found to decompose into ammonia and carbon dioxide (CO2) atSCR system 22 temperatures in excess of about 400 degrees Celsius. TheSCR system 22 temperatures may be the temperature of theexhaust stream 16 entering theSCR system 22 as measured by theupstream sensors 76. Tests have shown thatdeposits 82 are removed in theSCR system 22 when exposed to about 450 degree Celsius for between about 15 and 30 minutes or about 650 degrees Celsius for between about 5 and 10 minutes. - Only heating the outside of the
exhaust conduit 18 and not significantly heating theexhaust stream 16 would not be effective in removing thedeposits 82 that may be inside theexhaust conduit 18, such as those on theface 58 of theSCR catalyst 42, in themixer 36, or in thediffuser 38. Heating the outside of theexhaust conduit 18 may also require a large and complex heating system to apply heat to all the needed areas of theaftertreatment system 14 as compared to asingle heat source 20 that heats theexhaust stream 16. Arobust heat source 20, such as aburner 30, may be needed to reach the temperatures needed for decomposition in the SCR system, especially if theheat source 20 is upstream of theDPF 28 or otherwise far away from theSCR system 22 and given the length and number or mass of components in theSCR system 22. -
Controller 60 receives data fromSCR monitoring system 70 and controls the operation of theheat source 20. When thecontroller 60 orders theheat source 20 to activate, temperatures associated with theSCR monitoring system 70 are reported to thecontroller 60 from theSCR monitoring system 70. Thecontroller 60 calculates or determines whether a sufficient temperature has been reached in theSCR system 22 for a sufficient amount of time to decompose anydeposits 82 that may be present. If not, thecontroller 60 will order theheat source 20 to provide more heat for longer. - The
controller 60 may control theheat source 20 fordeposit 82 removal in conjunction with regeneration or soot removal of theDPF 28. Removal ofdeposits 82 in theSCR system 22 may also be needed at times when additional heat is not needed for regeneration of theDPF 28. Undercertain engine 12 operating conditions passive regeneration of theDPF 28 may occur or the amount of soot produced may be reduced, extending the time betweenactive DPF 28 regenerations that require activation of theheat source 20. During these periods, however,deposits 82 may continue to form in theSCR system 22, requiring activation of theheat source 20 fordeposit 82 removal even when not needed forDPF 28 regeneration. - The
controller 60 may be configured to activate theheat source 20 fordeposit 82 removal under a number of different conditions. The activation of theheat source 20 may be based on a time period during whichdeposits 82 are known to normally accumulate to a limit threshold. The activation of theheat source 20 may also be a function of several parameters. Those parameters may include time,engine 12 operating conditions,reductant 52 dosing rates, orSCR system 22 temperatures. Thecontroller 60 may include a map or algorithm or combination thereof to calculate or predict a time based on those parameters whendeposits 82 will be expected to accumulate beyond the threshold limit and theheat source 20 will need to be activated to remove thedeposits 82. - The
controller 60 may also use theSCR monitoring system 70 to measure thatdeposits 82 have formed beyond the threshold limit and theheat source 20 will need to be activated to remove thedeposits 82. This measurement from theSCR monitoring system 70 may be changes in back pressure, changes in a signal frequency attenuation, changes in NOx reduction efficiency, changes in ammonia conversion, or changes in temperature distributions. - The
controller 60 may also slow, stop, or inhibit the injection ofreductant 52 when activating theheat source 20 to removedeposits 82. The injection of thereductant 52 may have a cooling effect on thedeposits 82, preventing their decomposition, which is a function of temperature. Accordingly, inhibiting the injection ofreductant 52 when activating theheat source 20 may aid in the removal ofdeposits 82. The inhibiting ofreductant 52 injection may represent short delays between injection events or may last a longer period of time while theheat source 20 is activated. - The
heat source 20 may be configured to operate during periods ofengine 12 idle. As explained before, theurea reductant 52 is injected when theSCR system 22 temperature is above the injection threshold temperature, which may be about 180 degrees Celsius. During periods ofextended engine 12 idle, theexhaust stream 16 temperature in theSCR system 22 may fall under this injection threshold temperature. During shorter periods ofengine 12 idle theexhaust stream 16 temperature in theSCR system 22 may still exceed this injection threshold temperature andurea reductant 52 injection may ordinarily be occurring. - In other embodiments, the
heat source 20 may be configured to also operate athigh engine 12 speeds and load or othernon-idle engine 12 conditions. At thesehigher engine 12 speeds and loads,SCR system 22 temperatures will also probably be above the injection threshold temperature andurea reductant 52 injection may ordinarily be occurring. - However, as mentioned above, if the
heat source 20 is activated to removedeposits 82, thecontroller 60 may slow, stop, suspend, or inhibit the injection ofurea reductant 52. Especially duringengine 12 idle conditions, the injection ofurea reductant 52 may be at least partially suspended because lower amounts ofreductant 52 are needed as low levels of NOx are probably being produced fromengine 12. Duringnon-idle engine 12 conditions, the inhibiting ofreductant 52 injection may not be possible or may only represent short delays between injection events because of the higher levels of NOx probably being produced. - The
controller 60 controls the injection ofurea reductant 52 based on a predicted amount of NH3 stored in theSCR catalyst 42. As mentioned above, desorption of NH3 from theSCR catalyst 42 occurs at temperatures in excess of about 200 degrees Celsius and continues to accelerate as temperatures increase. Therefore, because of the temperatures reached, theSCR catalyst 42 will have nearly zero NH3 remaining after theheat source 20 is activated to remove thedeposits 82. The controller may accordingly be configured to reset the predicted amount of NH3 stored in theSCR catalyst 42 to zero in conjunction with the activation of theheat source 20. - During extended periods of idle, the
SCR system 22 temperature may be below the injection threshold temperature. If theheat source 20 is activated during these times, the time period following the deactivation of theheat source 20 may be used as an opportunity to injectreductant 52 before the temperature falls below the injection threshold temperature again. This may provide the ability to injectreductant 52 when not otherwise possible, such as during periods of extended idle or other low temperature conditions. This injection may help store NH3 in theSCR catalyst 42 and provide better response duringtransient engine 12 conditions following anextended engine 12 idle. Theheat source 20 may be activated solely for this purpose ofreductant 52 injections or in conjuncture withdeposit 82 removal,DPF 28 regeneration, or another purpose. - As described above a method for removing deposits from a selective catalytic reduction (SCR) system has been disclosed. The method includes sensing or determining a temperature associated with the
SCR system 22, activating aheat source 20 to increaseexhaust stream 16 temperatures to reach temperatures in theSCR system 22, as discussed above, and controlling theheat source 20 based on temperatures in the SCR system, as determined by theSCR monitoring system 70. The method may also include at least partially inhibiting an introduction of thereductant 52 and may include assigning a value of about zero for an amount ofreductant 52 stored in theSCR catalyst 42 for control of thereductant system 34. - The
injector 50 may also include aninjector heater 90 to prevent formation of or removedeposits 82 from inside or on theinjector 50. Theinjector heater 90 may be located in, around, or proximate to theinjector tip 54 or otherwise located to apply heat to theinjector 50. Theinjector heater 90 may consist of an electric resistance-heating coil connected to a power source. Theinjector heater 90 may also consist of another heat source. Theinjector heater 90 may be connected to thecontroller 60 or otherwise controlled to activate periodically or when predetermined conditions are met. - The
injector heater 90 may prevent the formation ofdeposits 82 in theinjector 50 by being activated or otherwise applying heat to theinjector 50 andinjector tip 54 after an injection. This heat will cause any water or other liquid contained inreductant 52 remaining in theinjector 50 to boil and steam. This steam will drive thereductant 52 from critical components in theinjector 50 orinjector tip 54, such as a check valve. Because thereductant 52 is no longer present,deposits 82 will not form. - The
injector heater 90 may also be used to removeurea deposits 82 that may form around or inside theinjector 50. Theinjector heater 90 may be capable of heating theinjector 50 orinjector tip 54 to the temperatures mentioned above fordeposit 82 removal (between about 400 and 650 degrees Celsius and higher). - The use of the
injector heater 90 may also eliminate a need to cool the injector or other components of thereductant system 34 becausedeposits 82 are prevented or removed. The use of theinjector heater 90 may or may not be included in the same embodiment as the use of theheat source 20. - Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and variations can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
Claims (20)
1. An engine exhaust aftertreatment system comprising:
a selective catalytic reduction (SCR) system including:
a reductant injection system for introducing a reductant into a exhaust stream of a engine;
a SCR catalyst configured to reduce NOx in the presence of the reductant; and
a SCR monitoring system;
a heat source configured to increase the temperature of the exhaust stream; and
a controller operating the heat source to reach a temperature associated with the SCR system of at least about 400 degrees Celsius as determined by the SCR monitoring system.
2. The engine exhaust aftertreatment system of claim 1 wherein the controller operates the heat source to reach a temperature associated with the SCR system of at least about 450 degrees Celsius as determined by the SCR monitoring system.
3. The engine exhaust aftertreatment system of claim 1 wherein the controller operates the heat source to reach a temperature associated with the SCR system of at least about 450 degrees Celsius for at least about 15 minutes as determined by the SCR monitoring system.
4. The engine exhaust aftertreatment system of claim 1 wherein the controller operates the heat source to reach a temperature associated with the SCR system of at least about 650 degrees Celsius as determined by the SCR monitoring system.
5. The engine exhaust aftertreatment system of claim 1 wherein the controller operates the heat source to reach a temperature associated with the SCR system of at least about 650 degrees Celsius for at least about 5 minutes as determined by the SCR monitoring system.
6. The engine exhaust aftertreatment system of claim 1 wherein the heat source is a burner.
7. The engine exhaust aftertreatment system of claim 1 further including a diesel particulate filter upstream of the SCR system in the exhaust stream, wherein the heat source is upstream of the diesel particulate filter in the exhaust stream.
8. The engine exhaust aftertreatment system of claim 7 wherein the operation of the heat source by the controller coincides with a regeneration of the diesel particulate filter.
9. The engine exhaust aftertreatment system of claim 1 wherein the controller activates the operation of the heat source based on parameters measured by the SCR monitoring system.
10. The engine exhaust aftertreatment system of claim 1 wherein the controller activates the operation of the heat source based on an elapsed period of time.
11. The engine exhaust aftertreatment system of claim 1 wherein during the operation of the heat source, the controller at least partially suspends the introduction of the reductant by the reductant injection system.
12. The engine exhaust aftertreatment system of claim 1 wherein following the operation of the heat source, the controller assigns a value of about zero for an amount of reductant stored in the SCR catalyst for control of the reductant injection system.
13. The engine exhaust aftertreatment system of claim 1 wherein following the operation of the heat source and during an engine idle condition, the controller orders the introduction of reductant by the reductant injection system.
14. A method for removing deposits from a selective catalytic reduction (SCR) system comprising:
determining temperatures associated with the SCR system;
activating a heat source to increase exhaust stream temperatures to reach temperatures in the SCR system of at least about 400 degrees Celsius; and
controlling the heat source based on temperatures in the SCR system.
15. The method of claim 14 wherein the heat source is activated to reach temperatures in the SCR system of at least about 450 degrees for at least about 15 minutes.
16. The method of claim 14 wherein the heat source is activated to reach temperatures in the SCR system of at least about 650 degrees.
17. The method of claim 14 wherein the heat source is activated to reach temperatures in the SCR system of at least about 650 degrees for at least about 5 minutes.
18. The method of claim 14 further including at least partially suspending an introduction of a reductant in the SCR system.
19. The method of claim 14 further including assigning a value of about zero for an amount of reductant stored in a SCR catalyst for control of a reductant injection system in the SCR system.
20. A selective catalytic reduction (SCR) system comprising:
an injector configured to introduce a reductant into a exhaust stream of a engine;
a SCR catalyst configured to reduce NOx in the presence of the reductant; and
an injector heater associated with the injector and configured to prevent or remove deposits.
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US12/536,891 US20110030343A1 (en) | 2009-08-06 | 2009-08-06 | Scr reductant deposit removal |
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US12/536,891 US20110030343A1 (en) | 2009-08-06 | 2009-08-06 | Scr reductant deposit removal |
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