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
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/90—Injecting reactants
• • 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
  • B01D2251/2062—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
  • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
  • F01N2240/16—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an electric heater, i.e. a resistance heater
• • 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
  • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
  • F01N2240/25—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an ammonia generator
• • 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
  • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
  • F01N2240/40—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a hydrolysis catalyst
• • 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
• • 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
  • F01N2610/10—Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
• • 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
  • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
  • F01N2610/1453—Sprayers or atomisers; Arrangement thereof in the exhaust apparatus
• • 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

• HCCI homogeneous charge compression combustion
• NH 3 Whilst it is possible to store NH 3 in liquid form on board a vehicle, this is deemed undesirable for safety and other reasons.
• the approach that is being adopted is to carry on vehicles an NH 3 precursor, and particularly an aqueous solution of urea ((NH 2 ) 2 CO), and to inject this solution directly into hot exhaust gas, so the (NH 2 ) 2 CO is decomposed in the presence of water vapour, releasing NH 3 and carbon dioxide (CO 2 ), a "hydrolysis catalyst" placed upstream of the SCR catalyst and downstream of the injection point may help this process; or to generate NH 3 "off-line” by pyrolysing solid (NH 2 ) 2 CO or some other precursor such as solid "ammonium carabamate".
• WO 2004/079171 discloses an apparatus for introducing ammonia into the exhaust pipe of a diesel internal combustion engine for the purposes of selectively reducing NO x on a selective catalytic reduction (SCR) catalyst.
• the apparatus comprises a number of spaced hollow fins that extend laterally into the exhaust pipe and that are filled with sintered material that defines a network of passageways extending within each fin from a lower end to an upper outlet end.
• JP 2004-270609 discloses a device for raising the efficiency of hydrolytic decomposition of urea in aqueous solution in an exhaust system of an internal combustion engine comprising a SCR catalyst comprising an inner tube on an upstream side of the catalyst disposed within an exhaust pipe and an injector for injecting the urea solution into the tube interior.
• JP 2004-108185 discloses an exhaust emission control device for a diesel engine comprising an ammonia generating device including a urea hydrolysis catalyst to generate ammonia gas from urea solution using the exhaust heat of the diesel engine, a pump to supply of urea solution to the ammonia generating device, and an ammonia gas tank to store ammonia gas generated in the ammonia generating device.
• an ammonia generating device including a urea hydrolysis catalyst to generate ammonia gas from urea solution using the exhaust heat of the diesel engine, a pump to supply of urea solution to the ammonia generating device, and an ammonia gas tank to store ammonia gas generated in the ammonia generating device.
• US patent no. 6,361,754 discloses an exhaust system for a lean burn engine comprising a urea solution holding tank, a pump for pumping the urea solution into a pressurised coiled line disposed within an exhaust pipe that carries the exhaust gas to atmosphere, an additional heater, a surge vessel and a valve for controlling the passage of ammonia to a nozzle, which is also disposed within the exhaust pipe.
• the urea is hydro lysed as the coiled line is heated by the exhaust gas. If necessary, an additional heater can be used.
• the nozzle can be a simple low-pressure nozzle or a high-pressure injector.
• US patent no. 6,399,034 discloses a device adapted to introduce ammonia into the exhaust gas flow of an exhaust gas system before it reaches a SCR catalyst.
• the device includes a heatable pressure-tight converter, an ammonia store and a control unit with control signals processing engine operating characteristics and determining therefrom the NO x output for controlling a timed valve for injection of an ammonia dose.
• Our WO 99/55446 discloses a method of reducing the content of nitrogen oxides in the exhaust gas of a lean burn engine, comprising passing the exhaust gas over a SCR catalyst which catalyses the reduction of the NO x by ammonia to nitrogen and which adsorbs and desorbs ammonia during the engine cycle and adsorbing ammonia intermittently on the catalyst during the engine cycle.
• the adsorbed ammonia is available to reduce cold start NO x .
• the invention provides a reactor for converting an aqueous ammonia precursor to a product comprising ammonia for supplying ammonia to a selective catalytic reduction catalyst disposed in an exhaust system of a lean burn internal combustion (IC) engine or gas turbine, which reactor comprising an electrically heated element and at least one conduit for conveying the aqueous ammonia precursor from an inlet end to an outlet end thereof, the arrangement being such that aqueous ammonia precursor carried in the conduit is brought into relatively close thermal contact with the electrically heated element, whereby the aqueous ammonia precursor is rapidly heated and converted to a product containing ammonia which is ejected from the outlet end in gaseous form.
• IC internal combustion
• the conduit twists around the electrically heated element, thereby promoting the relatively close thermal contact between the aqueous ammonia precursor and the electrically heated element.
• the aqueous ammonia precursor can contain such additives as are commonly used in the field, e.g. for automotive applications. Such a product is known as "AdBlue”.
• the electrically heated element is such that it is capable of very rapidly, i.e. "flash", heating the aqueous urea solution to a high temperature e.g. 400-500 0 C prior to ejecting the products from the outlet end of the conduit.
• the invention provides a number of very useful advantages. Firstly, it injects the reductant as ammonia per se. Problems have been reported with injector nozzles becoming blocked with ammonium cyanate crystals or biuret when aqueous urea solution per se is injected into an exhaust gas. The invention also avoids the problem of such crystals forming in the SCR catalyst substrate monolith, thus avoiding any back pressure problems and reduction in SCR catalyst activity. Secondly, because a relatively small quantity of aqueous ammonia precursor is heated at any one time, the power demand from the electrically heated element required to produce the ammonia-containing product is relatively low.
• the aqueous ammonia precursor is heated independently of the engine it is possible to inject ammonia into an exhaust gas independent of the temperature of an exhaust gas flowing in the exhaust system.
• This is an advantage over prior art cited above that rely on the temperature of the exhaust gas to convert urea disposed in a reactor in the exhaust gas flow.
• the SCR catalyst e.g. an Fe/beta zeolite catalyst
• ammonia prior to turning over the engine (provided that it may contact the catalyst directly, in the absence of flowing exhaust gas to convey it to the catalyst once the engine is turned over).
• NO x emitted at "cold start” can combine with the adsorbed ammonia to form e.g.
• the conduit is a tube of relatively small bore.
• the tube can be made from a relatively thermally conductive material such as a metal, e.g. stainless steel.
• the conduit may have an internal cross-sectional dimension, e.g. diameter, of from 0.1 -5mm, such as 0.5 to 3.0mm. Where a plurality of conduits are used, the plurality may consist of a range of different internal cross-sectional dimensions.
• the electrically heated element is a glow plug from a diesel engine.
• US 5,240,688 discloses the use of enzymes such as urease as a catalyst for the hydrolysis of (NH 2 ) 2 CO for use in a NO x reduction system.
• the enzyme can be added per se or added to an inert carrier particle.
• the process disclosed in US 5,240,688 requires the (NH 2 ) 2 CO solution to be heated to 310 0 F (approximately
• WO 99/65858 discloses the use of a substance to lower the hydrolysis reaction temperature of (NH 2 ) 2 CO such that the NH 3 produced may be used in a NO x reduction system.
• (NH 2 ) 2 CO is fed to a reactor heatable to from 20 to
• the hydrolysate is then fed into the exhaust gas stream.
• DE 44 25 420 Al also discloses the use of urease as a catalyst for hydrolysing (NH 2 ) 2 CO for use in a NO x reduction system, and suggests maintaining the reactor at a low temperature (from 40 to 65°C) and feeding the ammonia produced directly into the exhaust gas.
• urease as a catalyst for hydrolysing (NH 2 ) 2 CO for use in a NO x reduction system
• the systems described in WO 99/65858 and DE 44 25 420 Al would both suffer from disadvantages when the ammonia they produce is fed into low temperature exhaust gas, as typically found on passenger cars.
• the exhaust gas temperature is low sufficient heat is not available to completely vaporise the aqueous ammonia solution in the short time necessary before reaching the SCR catalyst that leads to maldistribution OfNH 3 across the SCR catalyst and significantly lowers NO x reduction efficiency.
• the invention provides an exhaust system for treating exhaust gas containing nitrogen oxides from a lean burn IC engine or a gas turbine, which system comprising an exhaust pipe for conveying an exhaust gas from the engine to atmosphere, a SCR catalyst disposed in the flow path of the exhaust pipe, a first reactor according to the invention and a source of aqueous ammonia precursor.
• the exhaust pipe comprises a spur in which is disposed the first reactor.
• the reactor includes a shield to prevent it from being impinged upon directly by exhaust gas components such as particulate matter.
• the aqueous ammonia precursor for use in the present invention can be selected from the group consisting of urea ((NH 2 ) 2 CO), ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate, ammonium carbamate and aqueous ammonia per se.
• urea (NH 2 ) 2 CO)
• ammonium carbonate ammonium carbamate
• ammonium hydrogen carbonate ammonium carbamate
• ammonium carbamate aqueous ammonia per se.
• the exhaust system comprises a first container for the aqueous urea solution and means for supplying the aqueous urea solution to a second reactor comprising a natural or synthetic urease-based catalyst for hydrolysing the aqueous urea to NH 3 and CO 2 at temperatures below 95°C and a conduit for conveying the urea hydro lysate containing NH 3 to the first reactor for injecting the hydro lysate into an exhaust line for carrying the exhaust gas upstream of a selective catalytic reduction (SCR) catalyst.
• a second container is disposed in the conduit between the second reactor and the first reactor for receiving the aqueous urea hydrolysate.
• the exhaust system may include means, when in use, for controlling the supply of aqueous ammonia precursor to the conduit, e.g. using an electrically operable valve such as a solenoid valve, and operation of the electrically heated element to provide ammonia in response to a demand signal from a suitable NO x sensor disposed in the exhaust gas flow.
• Such means can include a suitably preprogrammed computer chip and processor or it can be integrated with a vehicle's electronic control unit (ECU).
• ECU electronice control unit
• a suitable closed loop feedback system using sensors with cross sensitivity for both NO x and ammonia can also be used to control the supply of ammonia to reduce or prevent emission of ammonia to atmosphere.
• the invention provides an automotive vehicle comprising a lean burn IC engine, such as a diesel engine or a lean burn gasoline engine, and an exhaust system according to the invention.
• a lean burn IC engine such as a diesel engine or a lean burn gasoline engine
• the vehicle can be a passenger vehicle or heavy-duty diesel vehicle.
• Figure 1 is a Computer Aided Design (CAD) drawing of a reactor according to the present invention
• Figure 3 is a photograph showing a second working embodiment of a reactor according to the present invention.
• Figure 1 shows a CAD drawing of a reactor according to the present invention, wherein aqueous ammonia precursor is conveyed to the reactor via a 3 mm OD stainless steel pipe.
• the aqueous ammonia precursor is passed through a metal block to a coaxial chamber surrounding a glow plug.
• a photograph of the reactor is shown in Figure 2.
• the electric heating element is maintained at a temperature of about 500°C by supplying it with a current of 20 amps at 12.5 volts. Liquid entering the coaxial chamber reactor is instantly gasified to produce a strongly alkaline mist.
• FIG. 5 shows an exhaust system according to the invention referred to generally by the numeral 10 comprising a diesel engine 12, an exhaust pipe 14 for conveying a flowing exhaust gas to atmosphere 15.
• a ceramic monolith substrate 16 coated with a SCR catalyst, such as Fe/beta zeolite is disposed in the flow path of the exhaust gas. Upstream of substrate monolith 16 is spur 18 arranged at an acute angle, e.g. 45°, to the exhaust pipe and exhaust gas flow from the engine.
• a reactor 20 as shown in Figures 3 and 4 disposed in a tube 21 set back from the join with the exhaust pipe 14 by about 10-20 mm.
• the embodiment shown in Figure 6 includes an electronic controller (50) powered by for example a 12 volt DC electricity supply (51) having a number of input signals (52) and output voltages (53) which are actuated so the unit functions correctly under all possible operating conditions, or not function when conditions are not appropriate for it to operate.
• an electronic controller 50
• a 12 volt DC electricity supply (51) having a number of input signals (52) and output voltages (53) which are actuated so the unit functions correctly under all possible operating conditions, or not function when conditions are not appropriate for it to operate.
• Urea solution for example 32% by weight, is stored in a reservoir tank (01) that is prevented from freezing in cold weather, as sensed by a thermocouple (TCl), by applying a voltage to an immersion heater (03). Should the amount of solution in the tank (01) be less than a predetermined level as determined by a level sensor (Ll), the operator, e.g. driver, is alerted via the electronic controller unit. If the urea solution level in the tank falls below a certain minimum level, the unit does not operate.
• TCl thermocouple
• Ll level sensor
• the residence time in the hydrolysis reactor is sufficient for complete hydrolysis of the urea to take place so effectively no urea is passed via the solenoid control valve (33) to the reactor 31 according to Figure 1 into the exhaust gas system upstream of an iron exchanged zeolite SCR catalyst coated on to a cordierite monolithic substrate having 400 cell/square inch (40).
• a laboratory demonstration unit of hydrolysis reactor was assembled with reference to Figure 6 using components suitable for a light duty diesel vehicle application.
• the stainless steel hydrolysis unit (09) had dimensions of 38 x 120 mm packed with immobilised Jack
• Bean urease (Fluka) prepared by vacuum impregnation of porous ceramic pieces (4 mm x 5 mm).
• the unit had a stainless steel tube (6 mm diameter x 1 m) welded to its outside surface through which water was passed at 40°C recycled from a thermostatted Grant FH16-D heated recirculating pump.
• the fresh urea solution entering the hydrolysis unit had a neutral pH (6.9) and that exiting the unit had a pH of 9.5.

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

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• 2007
  • 2007-03-01 WO PCT/GB2007/050093 patent/WO2007099372A1/en active Application Filing
  • 2007-03-01 EP EP07712976A patent/EP1989411A1/de not_active Withdrawn

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