Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9431—Processes characterised by a specific device
• • 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]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/206—Ammonium compounds
  • B01D2251/2067—Urea
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
• • 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
  • F01N2610/00—Adding substances to exhaust gases
  • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
• • 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
  • F01N2610/00—Adding substances to exhaust gases
  • F01N2610/06—Adding substances to exhaust gases the substance being in the gaseous form
• • 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 invention relates to a treatment system by selective catalytic reduction of nitrogen oxides, said SCR system, in which it is done to limit the release of ammonia into the atmosphere.
• One of the most common forms of storage is storage in the form of pure liquid urea or in solution.
• the principle of the SCR technology is to inject the urea solution upstream of the SCR catalyst.
• the exhaust there is first evaporation of the water contained in the solution, then decomposition of urea ammonia.
• urea in the form of an aqueous solution has the characteristic of being relatively unstable, since, depending on the temperature, the decomposition reaction can take place in the urea reservoir, especially if the temperature becomes too high. .
• the urea decomposes to ammonia in the tank, and this ammonia created evaporates in the air of the tank.
• Ammonia is a toxic and odorous gas, its evaporation in the air represents a significant drawback, especially in the case where a vehicle is exposed to high temperatures, creating a significant release of ammonia.
• the invention therefore aims to remedy, at least in part, this disadvantage by limiting the release of ammonia in the atmosphere close to the vehicle.
• the invention relates to a selective catalytic reduction nitrogen oxide treatment system, called SCR system, intended to be installed in the engine exhaust line of a vehicle, the treatment consisting in chemically reducing, a catalyst, called SCR catalyst, the nitrogen oxides by injecting ammonia in the form of liquid urea, pure or in solution, this liquid urea being stored in a specific reservoir intended to be installed in the vehicle, and the system comprising a return tube connecting an outlet of the tank to the exhaust line of the engine, so as to direct the ammonia vapors, emitted during a decomposition of the urea in the tank, to the exhaust line of the engine, upstream of the SCR catalyst.
• SCR system selective catalytic reduction nitrogen oxide treatment system
• the treatment consisting in chemically reducing, a catalyst, called SCR catalyst, the nitrogen oxides by injecting ammonia in the form of liquid urea, pure or in solution, this liquid urea being stored in a specific reservoir intended to be installed in the vehicle, and the system comprising a
• the return pipe comprises a non-return valve to allow only gaseous transfers from the urea tank to the exhaust line of the engine.
• the check valve is such that the gas transfer from the urea tank to the engine exhaust line via the valve is allowed only when the gas pressure is above a predetermined value, for example 50 millibars.
• valve opening does not require the action of any device other than the valve itself; thus, the degassing can be performed when the vehicle is stopped.
• the system After having been degassed, ie expelled from the urea tank by the valve, the ammonia is transferred into the exhaust line.
• the system comprises means for this transferred ammonia to be trapped in a closed zone upstream of the SCR catalyst, and thus directed towards this catalyst.
• the system comprises means that, when the transfer of ammonia to the engine exhaust line takes place during a running phase of the vehicle, the ammonia is immediately used for the reduction of nitrogen oxides. in the catalyst.
• ammonia degassing being passive, it can take place during a stopping phase of the vehicle, ie a phase where no nitrogen oxide is released.
• the ammonia directed into the SCR catalyst can not be used to reduce nitrogen oxides.
• One solution to solve this is to store the ammonia, to store it and use it to reduce nitrogen oxides at the next start of the vehicle.
• the system comprises means that, when the ammonia transfer takes place during a stopping phase of the vehicle, the ammonia is stored in the SCR catalyst, for example by means of zeolites contained in the SCR catalyst, for later use for the reduction of nitrogen oxides.
• Zeolites are crystallized microporous alumino-silicates of the general formula (AlO 2 M, nSiO 2 ), where M is most often an alkali or alkaline earth metal and n> 1.
• M is most often an alkali or alkaline earth metal and n> 1.
• There are more than one hundred species of zeolites which differ by the value of n and the crystallographic structure.
• the presence of cations in the micropores generates electric fields of the order of 10 10 Vm 1 , which makes these bodies powerful polar adsorbents.
• the invention also relates to a motor vehicle comprising a system according to the invention described above.
• FIG. 1 represents an oxide treatment system nitrogen according to the invention
• FIG. 2 shows the evolution of the urea concentration of an aqueous solution of urea, for different temperatures
• FIG. 3 shows the ammonia storage capacity of an SCR catalyst incorporating zeolites in its composition as a function of temperature.
• FIG. 1 shows a system for treating nitrogen oxides present in the exhaust line 10 of a vehicle engine, in particular of diesel type. These nitrogen oxides are directed to a specific catalyst SCR 12, in which a chemical reduction is carried out. In order for this reduction to take place, it is necessary to add ammonia to the nitrogen oxides, for example contained in liquid urea 14.
• This liquid urea is generally stored in a specific tank 16 installed in the vehicle. This tank 16 is connected, via a supply duct 18, to a specific injector 19, for injecting urea 14 into the exhaust line 14 of the engine.
• the curves 20 and 22 represent the evolution over time of the concentration of urea in water, when a solution of urea is exposed to temperatures of 60 ° C. and 70 ° C., respectively. , which appear high for ambient temperatures, are however easily attainable in a vehicle engine exposed to direct sunlight for several hours.
• the concentration of urea in the water gradually decreases over the days; thus, after 5 days at 70 ° C., the concentration has already increased from 6 moles per liter initially to 5 moles per liter; after 10 days at 60 ° C., the concentration is only 5.50 mol per liter, for the same initial concentration of 6 mol per liter.
• the decomposed urea 14 is converted into ammonia which evaporates in the air of the tank 16. Since ammonia is a poisonous and odorous gas, it can be inconvenient to leave the tank in the open air.
• a return tube 11 for transferring ammonia in gaseous form to the exhaust line 10 of the engine.
• a non-return valve 13 is provided in the return tube 11.
• This value can be, depending on the type of valve used, of the order of 50 millibars or 100 millibars.
• ammonia molecules transferred into the exhaust line 10, are then trapped in a closed zone located between the oxidation catalyst 15 and the catalyst SCR 12.
• the ammonia is therefore naturally directed towards the catalyst 12. If the vehicle is operating at this moment, this means that nitrogen oxides are present in the exhaust line 10, and the ammonia is then consumed directly in the reactor. catalyst 12, for the reduction of these nitrogen oxides.
• Catalyst 12 contains zeolites, having the capacity to store ammonia. This storage capacity is shown in Figure 3.
• the curve 30 represents the evolution of the storage capacity, expressed in grams of ammonia NH3 per liter, depending on the temperature.
• the storage capacity is greater than 0.6 grams per liter.
• the ammonia arriving in the catalyst when the vehicle is not in operation can be stored, for later use for the chemical reduction of nitrogen oxides, especially during a next start of the vehicle.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Combustion & Propulsion (AREA)
• Biomedical Technology (AREA)
• Environmental & Geological Engineering (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Toxicology (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Exhaust Gas After Treatment (AREA)
• Exhaust Gas Treatment By Means Of Catalyst (AREA)

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• 2006
  • 2006-10-13 FR FR0654254A patent/FR2907027B1/fr not_active Expired - Fee Related
• 2007
  • 2007-10-03 EP EP07858506A patent/EP2074292A2/de not_active Withdrawn
  • 2007-10-03 WO PCT/FR2007/052075 patent/WO2008043937A2/fr active Application Filing

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