Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion
• • 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
  • B01D53/9495—Controlling the catalytic process
• • 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
• • 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
  • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
  • F01N3/2066—Selective catalytic reduction [SCR]
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
  • F01N2570/18—Ammonia
• • 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
• • 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

• This invention concerns combatting air pollution from the exhaust gas of a lean burn engine.
• it concerns apparatus for, and a method of, reducing the content of nitrogen oxides (NOx) in such gas.
• NOx nitrogen oxides
• Lean burn engines (which have an air-fuel ratio greater than 14.7, generally in the range 19-50) exhibit higher fuel economy and lower hydrocarbon emissions than do stoichiometrically operated engines and are increasing in number. Emissions from diesel engines are now being regulated by legislation, and whilst it is not too difficult to meet regulations on hydrocarbon or CO emissions, it is difficult to meet regulations on NOx emissions. Since exhaust gas from lean burn engines such as diesel engines is high in oxygen content throughout the engine cycle, it is more difficult to reduce NOx to nitrogen than in the case of stoichiometrically operated engines. The difficulty is compounded by the lower gas temperature. Various approaches are being considered to reduce NOx under the oxidising conditions.
• NH 3 SCR technology to the control of NOx emission from lean burn vehicles, however, requires a suitable NH 3 supply strategy, especially at low temperature, for various reasons.
• the engine-out NOx varies with temperature, so the amount of NH 3 supplied must be well controlled as a function of the temperature to maintain the appropriate stoichiometry for the reaction; an insufficient supply of NH 3 results in inadequate NOx reduction, whilst an excess may cause NH 3 to slip past the catalyst.
• the catalyst can selectively oxidise that excess NH 3 to N 2 , at low temperature, the unreacted NH 3 will be emitted as such.
• the present invention provides an improved apparatus and method for reducing the content of NOx.
• the invention provides apparatus for reducing the content of nitrogen oxides (NOx) in the exhaust gas of a lean burn engine, which apparatus comprises: (a) exhaust apparatus through which the exhaust gas flows;
• the invention provides also a method of reducing the content of nitrogen oxides (NOx) in the exhaust gas of a lean bum engine, which method comprises passing the exhaust gas over a selective catalytic reduction catalyst which catalyses the reduction of the NOx by ammonia to nitrogen and which adsorbs and desorbs ammonia during the engine cycle, ammonia being supplied intermittently to the catalyst during the engine cycle, the catalyst adsorbing ammonia during its supply and the ammonia which has been adsorbed reacting with the NOx when the ammonia is not supplied.
• a selective catalytic reduction catalyst which catalyses the reduction of the NOx by ammonia to nitrogen and which adsorbs and desorbs ammonia during the engine cycle, ammonia being supplied intermittently to the catalyst during the engine cycle, the catalyst adsorbing ammonia during its supply and the ammonia which has been adsorbed reacting with the NOx when the ammonia is not supplied.
• ammonia can be adsorbed on a SCR catalyst and thereafter used in the NOx reduction when ammonia is not being supplied. It is an advantage to be able to achieve the NOx reduction while supplying the ammonia intermittently. In particular, the ammonia supply can be halted and yet NOx reduction occur when the temperature of the catalyst is low and supply would have the problems referred to above.
• the stored ammonia can be used as reductant for NOx over the same catalyst without the presence of gas phase NH 3 .
• the ammonia can be supplied without the exhaust gas so that the catalyst adsorbs the ammonia and then the exhaust gas passed over the catalyst for the NOx reduction to occur Preferably, however, the exhaust gas is passed continuously over the catalyst.
• the invention uses adsorption and desorption characteristics of the required catalyst.
• a higher amount of NH 3 will be adsorbed, and hence be available for subsequent reaction, if adsorption is at a lower temperature than temperatures at which the catalyst adsorbs less NH 3 .
• NH 3 is adsorbed at a temperature at which a large amount is adsorbed; the temperature is preferably below that of maximum desorption. The temperature, however, is preferably above that at which any significant formation of ammonium salts occurs.
• Figure 2 shows the desorption profile from zeolite ZSM5 (non-metallised) of NH 3 which had been pre-adsorbed at 100° C.
• NH 3 stored on the ZSM5 catalyst at 250 °C can effectively be used to reduce NOx at a temperature as low as 150°C under exhaust conditions simulating those of a light duty diesel car.
• Figure 3 shows the NH 3 uptake of ZSM5 catalyst (non-metallised) from a gas mixture containing 4.5% C0 2 , 12% O 2 , 4.5% H 2 O, 200ppm CO, 1 OOppm C 3 H 6 , 20ppm SO 2 and 200ppm NH 3 with the balance N 2 at 250°C
• Figure 4 shows the subsequent reaction of that adsorbed NH 3 with NOx at 150°C.
• the means to make the supply of ammonia intermittent during the engine cycle in the present apparatus can be a switch which switches the ammonia supply on and off dependent on the level of NOx conversion occurring over the SCR catalyst.
• the means to make the supply of ammonia intermittent comprises a switch to switch on the means to supply the ammonia when the temperature of the catalyst rises above a set level (i) during the engine cycle, and to switch off the means to supply the ammonia when the temperature of the catalyst falls below a set level (ii).
• the set level (i) is preferably in the range 250-400°C, especially in the range 250-350°C.
• the set level (ii) is preferably in the range 200-250°C.
• the ammonia can be supplied for instance 1-30 times per minute.
• the present invention can be employed to provide a method of promoting the conversion of NOx under oxidising conditions in an exhaust fitted with a means of injecting NH 3 and a catalyst which adsorbs NH 3 during parts of the engine cycle in which the exhaust gas is sufficiently warmed for the hydrolysis of NH 3 precursor and injection of ammonia and ammonia is adsorbed by the catalyst for use as reductant for NOx during parts of the engine cycle in which the exhaust gas is cooler, without the need for the continuous injection of NH 3 into the exhaust gas.
• the catalyst is preferably carried out on a support substrate, in particular a honeycomb monolith of the flow-through type.
• the monolith can be metal or ceramic.
• the substrate can be conventional.
• Figure 3 shows the NH concentration in a full simulated exhaust gas mixture containing 4.5% CO 2 , 12% O 2 , 4.5% H 2 O, 200ppm CO, 1 OOppm C 3 H 6 , 20ppm SO 2 and 200ppm NH 3 with the balance N 2 after passage over ZSM5 at 250°C against time, and hence shows the NH 3 uptake by the zeolite;
• Figure 6 shows the corresponding effect to that shown in Figure 5 of successive cycles of the NH 3 pre-adsorption followed by subjection to the simulated exhaust gas
• Figure 7 corresponds to Figure 5 but with the simulated exhaust gas containing also hydrocarbon
• Figure 10 corresponds to Figure 9 but with the simulated exhaust gas containing also hydrocarbon;
• Figure 11 corresponds to Figure 10 but with the simulated exhaust gas containing also
• Figure 12 shows NOx concentration and temperature against time during part of an engine cycle
• Figure 13 corresponds to Figure 12 but shows the effect of intermittent supply ' of NH 3 ;
• Figure 14 shows the NOx concentration remaining in simulated exhaust gas after passage over Cu/ZSM5 with and without pre-adsorption of NH 3 against temperature
• Figure 15 shows the NOx concentration remaining in simulated exhaust gas which is that used in relation to Figure 14 but containing also hydrocarbon, H 2 O and SO 2 , after passage over Cu/ZSM5 with pre-adsorption of NH 3 against temperature.
• Figures 1-4 are discussed further hereinbefore, and Figures 5-15 hereinafter.
• Figure 10 shows the effect of adding C 3 H 6 on the reaction 10 of pre-adsorbed NH 3 with NOx
• Figure 11 demonstrates the effect with addition of H 2 0 and SO 2 .
• exhaust gas temperature varies during an engine cycle and for a significant fraction of that time the temperature can be low.
• the adsorbed NH 3 can subsequently be utilised in reducing NOx at both low and high temperature.
• exhaust gas containing CO 2 (14%), O 2 (12%), H 2 O (10%), CO (200ppm), C 3 H 6 (200ppm), SO 2 (20ppm) and N0 2 (200ppm) was cycled between 150°C and 350°C with a dwell of approximately 5 minutes at 250°C during the cooling-down part of the cycle.
• the NH 3 injection was switched on when the temperature was at 350° C and switched off when the temperature fell to 250°C.
• Figure 12 shows the outlet NOx concentration and the temperature against time without any NH 3 injection
• Figure 13 shows the effect of the cycling with the intermittent injection of NH 3 .
• the ordinate scale gives the degrees C for the temperature graph and the parts per million (ppm) for the NOx graph.
• This Example shows the effect of pre-adsorbing NH 3 at 250°C on the conversion of NOx over a Cu-impregnated ZSM5 (containing 5% copper by weight) in a simple gas mixture containing NOx, CO, CO 2 and O 2 during a light-off test from room temperature to 400°C.
• the gas stream containing NO (200ppm). CO (200ppm), O 2 (12%), CO 2 (14%) with the balance N 2 at a flow rate of 2 litres per minute was first passed over the Cu/ZSM5 (0.4g) from room temperature to 400°C at a heating rate of 50°C per minute and the NOx at the outlet measured.
• Cu/ZSM5 at 250°C from a gas mixture containing NO, H 2 0, C0 2 , CO, C 3 H 6 , S0 2 and O 2 and the reduction of NOx by the adsorbed NH 3 during a light-off test.

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

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Cited By (21)

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• 1998
  • 1998-04-28 GB GBGB9808876.8A patent/GB9808876D0/en not_active Ceased
• 1999
  • 1999-04-20 WO PCT/GB1999/001205 patent/WO1999055446A1/en not_active Ceased
  • 1999-04-20 PL PL99343689A patent/PL343689A1/xx unknown
  • 1999-04-20 JP JP2000545633A patent/JP4357742B2/ja not_active Expired - Lifetime
  • 1999-04-20 CN CNB998077976A patent/CN1201854C/zh not_active Expired - Fee Related
  • 1999-04-20 DE DE69918435T patent/DE69918435T2/de not_active Expired - Lifetime
  • 1999-04-20 US US09/674,349 patent/US6713030B1/en not_active Expired - Lifetime
  • 1999-04-20 CA CA002329994A patent/CA2329994C/en not_active Expired - Fee Related
  • 1999-04-20 KR KR1020007012033A patent/KR100604131B1/ko not_active Expired - Fee Related
  • 1999-04-20 EP EP99918121A patent/EP1083979B1/en not_active Expired - Lifetime
  • 1999-04-20 AU AU36164/99A patent/AU741813B2/en not_active Ceased
  • 1999-04-27 TW TW088106730A patent/TW469163B/zh not_active IP Right Cessation

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