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Selective catalytic reduction

January 19, 2023

Selective catalytic reduction (SCR) is a means of converting nitrogen oxides, also referred to as NO
x with the aid of a catalyst into diatomic nitrogen (N
2), and water (H
2O). A reductant, typically anhydrous ammonia (NH
3), aqueous ammonia (NH
4OH), or a urea (CO(NH
2)
2) solution, is added to a stream of flue or exhaust gas and is reacted onto a catalyst. As the reaction drives toward completion, nitrogen (N
2), and carbon dioxide (CO
2), in the case of urea use, are produced.

Selective catalytic reduction of NO
x using ammonia as the reducing agent was patented in the United States by the Engelhard Corporation in 1957. Development of SCR technology continued in Japan and the US in the early 1960s with research focusing on less expensive and more durable catalyst agents. The first large-scale SCR was installed by the IHI Corporation in 1978.[1]

Commercial selective catalytic reduction systems are typically found on large utility boilers, industrial boilers, and municipal solid waste boilers and have been shown to reduce NO
x by 70-95%.[1] More recent applications include diesel engines, such as those found on large ships, diesel locomotives, gas turbines, and even automobiles.

SCR systems are now the preferred method for meeting Tier 4 Final and EURO 6 diesel emissions standards for heavy trucks, and also for cars and light commercial vehicles. As a result, emissions of NOx, particulates, and hydrocarbons have been reduced by as much as 95% when compared with pre-emissions engines.[2]

Chemistry

The NO
x reduction reaction takes place as the gases pass through the catalyst chamber. Before entering the catalyst chamber ammonia, or other reductant (such as urea), is injected and mixed with the gases. The chemical equation for a stoichiometric reaction using either anhydrous or aqueous ammonia for a selective catalytic reduction process is:

 
 
 

With several secondary reactions:

 
 
 
 
 

With urea, the reactions are:

 
 

As with ammonia, several secondary reactions also occur in the presence of sulfur:

 
 

The ideal reaction has an optimal temperature range between 630 and 720 K (357 and 447 °C), but can operate as low as 500 K (227 °C) with longer residence times. The minimum effective temperature depends on the various fuels, gas constituents, and catalyst geometry. Other possible reductants include cyanuric acid and ammonium sulfate.[3]

Catalysts

SCR catalysts are made from various porous ceramic materials used as a support, such as titanium oxide, and active catalytic components are usually either oxides of base metals (such as vanadium, molybdenum and tungsten), zeolites, or various precious metals. Another catalyst based on activated carbon was also developed which is applicable for the removal of NOx at low temperatures.[4] Each catalyst component has advantages and disadvantages.

Base metal catalysts, such as vanadium and tungsten, lack high thermal durability, but are less expensive and operate very well at the temperature ranges most commonly applied in industrial and utility boiler applications. Thermal durability is particularly important for automotive SCR applications that incorporate the use of a diesel particulate filter with forced regeneration. They also have a high catalysing potential to oxidize SO
2 into SO
3, which can be extremely damaging due to its acidic properties.[5]

Zeolite catalysts have the potential to operate at substantially higher temperature than base metal catalysts; they can withstand prolonged operation at temperatures of 900 K (627 °C) and transient conditions of up to 1120 K (847 °C). Zeolites also have a lower potential for SO
2 oxidation and thus decrease the related corrosion risks.[5]

Iron- and copper-exchanged zeolite urea SCRs have been developed with approximately equal performance to that of vanadium-urea SCRs if the fraction of the NO
2 is 20% to 50% of the total NO
x.[6] The two most common catalyst geometries used today are honeycomb catalysts and plate catalysts. The honeycomb form usually consists of an extruded ceramic applied homogeneously throughout the carrier or coated on the substrate. Like the various types of catalysts, their configuration also has advantages and disadvantages. Plate-type catalysts have lower pressure drops and are less susceptible to plugging and fouling than the honeycomb types, but are much larger and more expensive. Honeycomb configurations are smaller than plate types, but have higher pressure drops and plug much more easily. A third type is corrugated, comprising only about 10% of the market in power plant applications.[1]

Reductants

Several nitrogen-bearing reductants are currently used in SCR applications including anhydrous ammonia, aqueous ammonia or dissolved urea. All those three reductants are widely available in large quantities.

Anhydrous ammonia can be stored as a liquid at approximately 10 bar in steel tanks. It is classified as an inhalation hazard, but it can be safely stored and handled if well-developed codes and standards are followed. Its advantage is that it needs no further conversion to operate within a SCR and is typically favoured by large industrial SCR operators. Aqueous ammonia must be first vaporized in order to be used, but it is substantially safer to store and transport than anhydrous ammonia. Urea is the safest to store, but requires conversion to ammonia through thermal decomposition. [7] At the end of the process, the purified exhaust gasses are sent to the boiler or condenser or other equipment, or discharged into the atmosphere.[8][1]

Limitations

Many catalysts are given a finite service life due to known amounts of contaminants in the untreated gas.

Most catalysts on the market have porous structures and a geometries optimized for increasing their specific surface area (a clay planting pot is a good example of what SCR catalyst feels like). This porosity is what gives the catalyst the high surface area needed for reduction of NOx. However, the pores are easily plugged by fine particulates, such as soot, ammonium sulfate, ammonium bisulfate (ABS), and silica compounds. Ultrasonic horns and soot blowers can remove most of these contaminants while the unit is online. The unit can also be cleaned during a turnaround or by raising the exhaust temperature.

Of more concern to SCR performance are poisons, which will block the catalyst's active sites and render it ineffective at NO
x reduction, and in severe cases this can result in the ammonia or urea being oxidized and a subsequent increase in NO
x emissions. These poisons are alkali metals, alkaline earth metals, halogens, phosphorus, arsenic, antimony, chromium, heavy metals (copper, cadmium, mercury, thallium, and lead), and many heavy metal compounds (e.g. oxides and halides).

Most SCRs require tuning to properly perform. Part of tuning involves ensuring a proper distribution of ammonia in the gas stream and uniform gas velocity through the catalyst. Without tuning, SCRs can exhibit inefficient NOx reduction along with excessive ammonia slip due to not utilizing the catalyst surface area effectively. Another facet of tuning involves determining the proper ammonia flow for all process conditions. Ammonia flow is in general controlled based on NOx measurements taken from the gas stream or preexisting performance curves from an engine manufacturer (in the case of gas turbines and reciprocating engines). Typically, all future operating conditions must be known beforehand to properly design and tune an SCR system.

Ammonia slip is an industry term for ammonia passing through the SCR unreacted. This occurs when ammonia is injected in excess, temperatures are too low for ammonia to react, or the catalyst has been poisoned.

Temperature is SCR's largest limitation. Engines all have a period during start-up where exhaust temperatures are too low, and the catalyst must be pre-heated for the desired NOx reduction to occur when an engine is first started, especially in cold climates.

Power plants

In power stations, the same basic technology is employed for removal of NO
x from the flue gas of boilers used in power generation and industry. In general, the SCR unit is located between the furnace economizer and the air heater, and the ammonia is injected into the catalyst chamber through an ammonia injection grid. As in other SCR applications, the temperature of operation is critical. Ammonia slip (unreacted ammonia) is also an issue with SCR technology used in power plants.

Other issues that must be considered in using SCR for NO
x control in power plants are the formation of ammonium sulfate and ammonium bisulfate due to the sulfur content of the fuel as well as the undesirable catalyst-caused formation of SO
3 from the SO
2 and O
2 in the flue gas.

A further operational difficulty in coal-fired boilers is the binding of the catalyst by fly ash from the fuel combustion. This requires the usage of sootblowers, ultrasonic horns, and careful design of the ductwork and catalyst materials to avoid plugging by the fly ash. SCR catalysts have a typical operational lifetime of about 16,000 – 40,000 hours (1.8 – 4.5 years) in coal-fired power plants, depending on the flue gas composition, and up to 80,000 hours (9 years) in cleaner gas-fired power plants.

Poisons, sulfur compounds, and fly ash can all be removed by installing scrubbers before the SCR system to increase the life of the catalyst, though in most power plants and marine engines, scrubbers are installed after the system to maximize the SCR system's effectiveness.

Automobiles

History

SCR was applied to trucks by Nissan Diesel Corporation, and the first practical product "Nissan Diesel Quon" was introduced in 2004 in Japan.[9]

In 2007, the United States Environmental Protection Agency (EPA) enacted requirements to significantly reduce harmful exhaust emissions. To achieve this standard, Cummins and other diesel engine manufacturers developed an aftertreatment system that includes the use of a diesel particulate filter (DPF). As the DPF does not function with low-sulfur diesel fuel, diesel engines that conform to 2007 EPA emissions standards require ultra-low sulfur diesel fuel (ULSD) to prevent damage to the DPF. After a brief transition period, ULSD fuel became common at fuel pumps in the United States and Canada. The 2007 EPA regulations were meant to be an interim solution to allow manufacturers time to prepare for the more stringent 2010 EPA regulations, which reduced NOx levels even further.[10]

2010 EPA regulations

 
Hino truck and its Standardized SCR Unit which combines SCR with Diesel Particulate Active Reduction (DPR). DPR is a diesel particulate filtration system with regeneration process that uses late fuel injection to control exhaust temperature to burn off soot.[11][12]

Diesel engines manufactured after January 1, 2010 are required to meet lowered NOx standards for the US market.

All of the heavy-duty engine (Class 7-8 trucks) manufacturers except for Navistar International and Caterpillar continuing to manufacture engines after this date have chosen to use SCR. This includes Detroit Diesel (DD13, DD15, and DD16 models), Cummins (ISX, ISL9, and ISB6.7), Paccar, and Volvo/Mack. These engines require the periodic addition of diesel exhaust fluid (DEF, a urea solution) to enable the process. DEF is available in bottles and jugs from most truck stops, and a more recent development is bulk DEF dispensers near diesel fuel pumps. Caterpillar and Navistar had initially chosen to use enhanced exhaust gas recirculation (EEGR) to comply with the Environmental Protection Agency (EPA) standards, but in July 2012 Navistar announced it would be pursuing SCR technology for its engines, except on the MaxxForce 15 which was to be discontinued. Caterpillar ultimately withdrew from the on-highway engine market prior to implementation of these requirements.[13]

BMW,[14][15] Daimler AG (as BlueTEC), and Volkswagen have used SCR technology in some of their passenger diesel cars.

See also

References

  1. ^ a b c d Steam: Its Generation and Uses. Babcock & Wilcox.
  2. ^ Denton, Tom (2021). Advanced Automotive Fault Diagnosis: Automotive Technology: Vehicle Maintenance and Repair. Routledge. pp. 49–50. ISBN 9781000178388.
  3. ^ "Environmental Effects of Nitrogen Oxides". Electric Power Research Institute, 1989
  4. ^ . Archived from the original on 2015-12-08. Retrieved 2015-11-27. CarboTech AC GmbH
  5. ^ a b DOE presentation
  6. ^ Gieshoff, J; M. Pfeifer; A. Schafer-Sindlinger; P. Spurk; G. Garr; T. Leprince (March 2001). "Advanced Urea Scr Catalysts for Automotive Applications" (PDF). Society of Automotive Engineers. SAE Technical Paper Series. 1. doi:10.4271/2001-01-0514. Retrieved 2009-05-18.
  7. ^ Kuternowski, Filip; Staszak, Maciej; Staszak, Katarzyna (July 2020). "Modeling of Urea Decomposition in Selective Catalytic Reduction (SCR) for Systems of Diesel Exhaust Gases Aftertreatment by Finite Volume Method". Catalysts. 10 (7): 749. doi:10.3390/catal10070749.
  8. ^ Emigreen; Nox Reduction; SCR technology:
  9. ^ "尿素CSRシステム（FLENDS）" [CSR System "FLENDS"]. Society of Automotive Engineers of Japan (in Japanese). Retrieved 28 November 2021.
  10. ^ Mark Quasius (1 May 2013). "2010 EPA Emissions Standards And Diesel Exhaust Fluid". FamilyRVing. Retrieved 3 December 2021.
  11. ^ "Hino Standardized SCR Unit". Hino Motors. Archived from the original on 5 August 2014. Retrieved 30 July 2014.
  12. ^ "The DPR Future" (PDF). Hino Motors. Retrieved 30 July 2014.
  13. ^ "Caterpillar exits on-highway engine business". Today's Trucking. Jun 13, 2008. Retrieved 29 December 2017.
  14. ^ (PDF). Archived from the original (PDF) on 2017-01-08. Retrieved 2017-01-15.
  15. ^ . Archived from the original on 2017-01-04. Retrieved 2017-01-15.

January 19, 2023
selective, catalytic, reduction, means, converting, nitrogen, oxides, also, referred, with, catalyst, into, diatomic, nitrogen, water, reductant, typically, anhydrous, ammonia, aqueous, ammonia, urea, solution, added, stream, flue, exhaust, reacted, onto, cata. Selective catalytic reduction SCR is a means of converting nitrogen oxides also referred to as NOx with the aid of a catalyst into diatomic nitrogen N2 and water H2 O A reductant typically anhydrous ammonia NH3 aqueous ammonia NH4 OH or a urea CO NH2 2 solution is added to a stream of flue or exhaust gas and is reacted onto a catalyst As the reaction drives toward completion nitrogen N2 and carbon dioxide CO2 in the case of urea use are produced Selective catalytic reduction of NOx using ammonia as the reducing agent was patented in the United States by the Engelhard Corporation in 1957 Development of SCR technology continued in Japan and the US in the early 1960s with research focusing on less expensive and more durable catalyst agents The first large scale SCR was installed by the IHI Corporation in 1978 1 Commercial selective catalytic reduction systems are typically found on large utility boilers industrial boilers and municipal solid waste boilers and have been shown to reduce NOx by 70 95 1 More recent applications include diesel engines such as those found on large ships diesel locomotives gas turbines and even automobiles SCR systems are now the preferred method for meeting Tier 4 Final and EURO 6 diesel emissions standards for heavy trucks and also for cars and light commercial vehicles As a result emissions of NOx particulates and hydrocarbons have been reduced by as much as 95 when compared with pre emissions engines 2 Contents 1 Chemistry 2 Catalysts 3 Reductants 4 Limitations 5 Power plants 6 Automobiles 6 1 History 6 2 2010 EPA regulations 7 See also 8 ReferencesChemistry EditThe NOx reduction reaction takes place as the gases pass through the catalyst chamber Before entering the catalyst chamber ammonia or other reductant such as urea is injected and mixed with the gases The chemical equation for a stoichiometric reaction using either anhydrous or aqueous ammonia for a selective catalytic reduction process is 2 NO 2 NH 3 1 2 O 2 2 N 2 3 H 2 O displaystyle ce 2 NO 2 NH3 1 2 O2 gt 2 N2 3 H2O NO 2 2 NH 3 1 2 O 2 3 2 N 2 3 H 2 O displaystyle ce NO2 2 NH3 1 2 O2 gt 3 2 N2 3 H2O NO NO 2 2 NH 3 2 N 2 3 H 2 O displaystyle ce NO NO2 2 NH3 gt 2 N2 3 H2O With several secondary reactions 1 8 S 8 O 2 SO 2 displaystyle ce 1 8 S8 O2 gt SO2 SO 2 1 2 O 2 SO 3 displaystyle ce SO2 1 2 O2 gt SO3 SO 3 H 2 O H 2 SO 4 displaystyle ce SO3 H2O gt H2SO4 2 NH 3 H 2 SO 4 NH 4 2 SO 4 displaystyle ce 2 NH3 H2SO4 gt NH4 2SO4 NH 3 H 2 SO 4 NH 4 HSO 4 displaystyle ce NH3 H2SO4 gt NH4HSO4 With urea the reactions are 3 NO CO NH 2 2 5 2 N 2 2 H 2 O CO 2 displaystyle ce 3 NO CO NH2 2 gt 5 2 N2 2 H2O CO2 3 NO 2 2 CO NH 2 2 7 2 N 2 4 H 2 O 2 CO 2 displaystyle ce 3 NO2 2 CO NH2 2 gt 7 2 N2 4 H2O 2 CO2 As with ammonia several secondary reactions also occur in the presence of sulfur CO NH 2 2 H 2 SO 4 H 2 O NH 4 2 SO 4 CO 2 displaystyle ce CO NH2 2 H2SO4 H2O gt NH4 2SO4 CO2 CO NH 2 2 2 H 2 SO 4 H 2 O 2 NH 4 HSO 4 CO 2 displaystyle ce CO NH2 2 2 H2SO4 H2O gt 2 NH4HSO4 CO2 The ideal reaction has an optimal temperature range between 630 and 720 K 357 and 447 C but can operate as low as 500 K 227 C with longer residence times The minimum effective temperature depends on the various fuels gas constituents and catalyst geometry Other possible reductants include cyanuric acid and ammonium sulfate 3 Catalysts EditSCR catalysts are made from various porous ceramic materials used as a support such as titanium oxide and active catalytic components are usually either oxides of base metals such as vanadium molybdenum and tungsten zeolites or various precious metals Another catalyst based on activated carbon was also developed which is applicable for the removal of NOx at low temperatures 4 Each catalyst component has advantages and disadvantages Base metal catalysts such as vanadium and tungsten lack high thermal durability but are less expensive and operate very well at the temperature ranges most commonly applied in industrial and utility boiler applications Thermal durability is particularly important for automotive SCR applications that incorporate the use of a diesel particulate filter with forced regeneration They also have a high catalysing potential to oxidize SO2 into SO3 which can be extremely damaging due to its acidic properties 5 Zeolite catalysts have the potential to operate at substantially higher temperature than base metal catalysts they can withstand prolonged operation at temperatures of 900 K 627 C and transient conditions of up to 1120 K 847 C Zeolites also have a lower potential for SO2 oxidation and thus decrease the related corrosion risks 5 Iron and copper exchanged zeolite urea SCRs have been developed with approximately equal performance to that of vanadium urea SCRs if the fraction of the NO2 is 20 to 50 of the total NOx 6 The two most common catalyst geometries used today are honeycomb catalysts and plate catalysts The honeycomb form usually consists of an extruded ceramic applied homogeneously throughout the carrier or coated on the substrate Like the various types of catalysts their configuration also has advantages and disadvantages Plate type catalysts have lower pressure drops and are less susceptible to plugging and fouling than the honeycomb types but are much larger and more expensive Honeycomb configurations are smaller than plate types but have higher pressure drops and plug much more easily A third type is corrugated comprising only about 10 of the market in power plant applications 1 Reductants EditSeveral nitrogen bearing reductants are currently used in SCR applications including anhydrous ammonia aqueous ammonia or dissolved urea All those three reductants are widely available in large quantities Anhydrous ammonia can be stored as a liquid at approximately 10 bar in steel tanks It is classified as an inhalation hazard but it can be safely stored and handled if well developed codes and standards are followed Its advantage is that it needs no further conversion to operate within a SCR and is typically favoured by large industrial SCR operators Aqueous ammonia must be first vaporized in order to be used but it is substantially safer to store and transport than anhydrous ammonia Urea is the safest to store but requires conversion to ammonia through thermal decomposition 7 At the end of the process the purified exhaust gasses are sent to the boiler or condenser or other equipment or discharged into the atmosphere 8 1 Limitations EditMany catalysts are given a finite service life due to known amounts of contaminants in the untreated gas Most catalysts on the market have porous structures and a geometries optimized for increasing their specific surface area a clay planting pot is a good example of what SCR catalyst feels like This porosity is what gives the catalyst the high surface area needed for reduction of NOx However the pores are easily plugged by fine particulates such as soot ammonium sulfate ammonium bisulfate ABS and silica compounds Ultrasonic horns and soot blowers can remove most of these contaminants while the unit is online The unit can also be cleaned during a turnaround or by raising the exhaust temperature Of more concern to SCR performance are poisons which will block the catalyst s active sites and render it ineffective at NOx reduction and in severe cases this can result in the ammonia or urea being oxidized and a subsequent increase in NOx emissions These poisons are alkali metals alkaline earth metals halogens phosphorus arsenic antimony chromium heavy metals copper cadmium mercury thallium and lead and many heavy metal compounds e g oxides and halides Most SCRs require tuning to properly perform Part of tuning involves ensuring a proper distribution of ammonia in the gas stream and uniform gas velocity through the catalyst Without tuning SCRs can exhibit inefficient NOx reduction along with excessive ammonia slip due to not utilizing the catalyst surface area effectively Another facet of tuning involves determining the proper ammonia flow for all process conditions Ammonia flow is in general controlled based on NOx measurements taken from the gas stream or preexisting performance curves from an engine manufacturer in the case of gas turbines and reciprocating engines Typically all future operating conditions must be known beforehand to properly design and tune an SCR system Ammonia slip is an industry term for ammonia passing through the SCR unreacted This occurs when ammonia is injected in excess temperatures are too low for ammonia to react or the catalyst has been poisoned Temperature is SCR s largest limitation Engines all have a period during start up where exhaust temperatures are too low and the catalyst must be pre heated for the desired NOx reduction to occur when an engine is first started especially in cold climates Power plants EditIn power stations the same basic technology is employed for removal of NOx from the flue gas of boilers used in power generation and industry In general the SCR unit is located between the furnace economizer and the air heater and the ammonia is injected into the catalyst chamber through an ammonia injection grid As in other SCR applications the temperature of operation is critical Ammonia slip unreacted ammonia is also an issue with SCR technology used in power plants Other issues that must be considered in using SCR for NOx control in power plants are the formation of ammonium sulfate and ammonium bisulfate due to the sulfur content of the fuel as well as the undesirable catalyst caused formation of SO3 from the SO2 and O2 in the flue gas A further operational difficulty in coal fired boilers is the binding of the catalyst by fly ash from the fuel combustion This requires the usage of sootblowers ultrasonic horns and careful design of the ductwork and catalyst materials to avoid plugging by the fly ash SCR catalysts have a typical operational lifetime of about 16 000 40 000 hours 1 8 4 5 years in coal fired power plants depending on the flue gas composition and up to 80 000 hours 9 years in cleaner gas fired power plants Poisons sulfur compounds and fly ash can all be removed by installing scrubbers before the SCR system to increase the life of the catalyst though in most power plants and marine engines scrubbers are installed after the system to maximize the SCR system s effectiveness Automobiles EditHistory Edit SCR was applied to trucks by Nissan Diesel Corporation and the first practical product Nissan Diesel Quon was introduced in 2004 in Japan 9 In 2007 the United States Environmental Protection Agency EPA enacted requirements to significantly reduce harmful exhaust emissions To achieve this standard Cummins and other diesel engine manufacturers developed an aftertreatment system that includes the use of a diesel particulate filter DPF As the DPF does not function with low sulfur diesel fuel diesel engines that conform to 2007 EPA emissions standards require ultra low sulfur diesel fuel ULSD to prevent damage to the DPF After a brief transition period ULSD fuel became common at fuel pumps in the United States and Canada The 2007 EPA regulations were meant to be an interim solution to allow manufacturers time to prepare for the more stringent 2010 EPA regulations which reduced NOx levels even further 10 2010 EPA regulations Edit Hino truck and its Standardized SCR Unit which combines SCR with Diesel Particulate Active Reduction DPR DPR is a diesel particulate filtration system with regeneration process that uses late fuel injection to control exhaust temperature to burn off soot 11 12 Diesel engines manufactured after January 1 2010 are required to meet lowered NOx standards for the US market All of the heavy duty engine Class 7 8 trucks manufacturers except for Navistar International and Caterpillar continuing to manufacture engines after this date have chosen to use SCR This includes Detroit Diesel DD13 DD15 and DD16 models Cummins ISX ISL9 and ISB6 7 Paccar and Volvo Mack These engines require the periodic addition of diesel exhaust fluid DEF a urea solution to enable the process DEF is available in bottles and jugs from most truck stops and a more recent development is bulk DEF dispensers near diesel fuel pumps Caterpillar and Navistar had initially chosen to use enhanced exhaust gas recirculation EEGR to comply with the Environmental Protection Agency EPA standards but in July 2012 Navistar announced it would be pursuing SCR technology for its engines except on the MaxxForce 15 which was to be discontinued Caterpillar ultimately withdrew from the on highway engine market prior to implementation of these requirements 13 BMW 14 15 Daimler AG as BlueTEC and Volkswagen have used SCR technology in some of their passenger diesel cars See also EditAcid rain Catalytic converter which also catalyzes NOx conversion but does not use urea or ammonia Diesel exhaust fluid DEF or AdBlue Exhaust gas recirculation versus selective catalytic reduction Environmental engineering Selective non catalytic reduction SNCR NOx adsorber LNT Vehicle emissions controlReferences Edit a b c d Steam Its Generation and Uses Babcock amp Wilcox Denton Tom 2021 Advanced Automotive Fault Diagnosis Automotive Technology Vehicle Maintenance and Repair Routledge pp 49 50 ISBN 9781000178388 Environmental Effects of Nitrogen Oxides Electric Power Research Institute 1989 CarbonCatalysts CarboTech AC GMBH Archived from the original on 2015 12 08 Retrieved 2015 11 27 CarboTech AC GmbH a b DOE presentation Gieshoff J M Pfeifer A Schafer Sindlinger P Spurk G Garr T Leprince March 2001 Advanced Urea Scr Catalysts for Automotive Applications PDF Society of Automotive Engineers SAE Technical Paper Series 1 doi 10 4271 2001 01 0514 Retrieved 2009 05 18 Kuternowski Filip Staszak Maciej Staszak Katarzyna July 2020 Modeling of Urea Decomposition in Selective Catalytic Reduction SCR for Systems of Diesel Exhaust Gases Aftertreatment by Finite Volume Method Catalysts 10 7 749 doi 10 3390 catal10070749 Emigreen Nox Reduction SCR technology 尿素CSRシステム FLENDS CSR System FLENDS Society of Automotive Engineers of Japan in Japanese Retrieved 28 November 2021 Mark Quasius 1 May 2013 2010 EPA Emissions Standards And Diesel Exhaust Fluid FamilyRVing Retrieved 3 December 2021 Hino Standardized SCR Unit Hino Motors Archived from the original on 5 August 2014 Retrieved 30 July 2014 The DPR Future PDF Hino Motors Retrieved 30 July 2014 Caterpillar exits on highway engine business Today s Trucking Jun 13 2008 Retrieved 29 December 2017 BMW BluePerformance AdBlue PDF Archived from the original PDF on 2017 01 08 Retrieved 2017 01 15 BMW maintenance AdBlue Archived from the original on 2017 01 04 Retrieved 2017 01 15 Retrieved from https en wikipedia org w index php title Selective catalytic reduction amp oldid 1134138050, wikipedia, wiki, book, books, library,

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