Method and apparatus for producing ammonia (NH3)

• US 6,928,807 B2
• Filed: 02/14/2003
• Issued: 08/16/2005
• Est. Priority Date: 02/14/2002
• Status: Expired due to Term

• Current Assignee: MAN Truck & Bus AG (Volkswagen AG)
• Original Assignee: MAN Nutzfahrzeuge AG (Volkswagen AG)
• Inventors: Käfer, Sebastian, Jacob, Eberhard, Müller, Werner, Herr, Andreas, Lacroix, Andreas
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, DIEM T
• Application Number:
  US10/369,348
• Publication Number:
  US 20040040288A1
• Time in Patent Office: 914 Days
• Field of Search: 602/74, 602/86, 602/95, 603/01
• US Class Current: 60/286
• CPC Class Codes: B01D 53/8631 Processes characterised by a specific device
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: C01C 1/02 Preparation, purification or separation of ammonia
• CPC Class Codes: C01C 1/086 from urea
• CPC Class Codes: F01N 2240/25 an ammonia generator
• CPC Class Codes: F01N 2240/40 a hydrolysis catalyst
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/06 the substance being in the gaseous form
• CPC Class Codes: F01N 2610/10 the substance being heated, e.g. by heating tank or supply line of the added substance
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F17C 11/00 Use of gas-solvents or gas-sorbents in vessels absorbing compositions for acetylene C10L3/04; absorbing compositions for hydrogen C01B3/0005
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02E 20/14 Combined heat and power generation [CHP]
• CPC Class Codes: Y02P 20/129 Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A method is provided for producing ammonia (NH₃) and introducing the produced ammonia (NH₃) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitrogen oxides contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner. The method comprises feeding dry urea from a supply container in a controlled amount to reactor and subjecting the dry urea in the reactor to a sufficiently rapid thermal treatment such that a gas mixture comprising the reaction products of ammonia (NH₃) and isocyanic acid (HCNO) is created. Also, the method comprises immediately catalytically treating the thus produced gas mixture in the presence of water such that the isocyanic acid (HCNO) resulting from the rapid thermal treatment is converted, via quantitative hydrolysis treatment, into ammonia (NH₃) and carbon dioxide (CO₂).

Claims

1. An apparatus for producing ammonia (NH₃) and introducing the produced ammonia (NH₃) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitric oxide contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the apparatus comprising:

a storage container in which urea in dry form in the form of powder, granulate, or micro-prills is stored;

a reactor for the production of ammonia (NH₃) and having a heated reaction chamber which is partitioned into a thermal treatment zone and a hydrolysis treatment zone, and the reaction chamber of the reactor being disposed for the treatment therein of an exhaust gas stream from the combustion exhaust gases of a selected one of an internal combustion engine, a gas turbine, and a burner;

a device for feed of the urea, preferably in controlled or measured amounts, from the supply container into the reaction chamber of the reactor;

an electrical heating element in the thermal treatment zone of the reaction chamber of the reactor;

a device for controlling the temperature of the heating element in a manner such that the urea introduced into the reaction chamber is spontaneously de-composeable, via flash hydrolysis, into ammonia (NH₃) and isocyanic acid (HCNO);

a device for introducing water in at least one form of completely liquid water and a water-containing gas-into the reaction chamber of the reactor, the device for introducing water includes a feed conduit and an electrically controllable blocking valve in the feed conduit and moveable between open and closed positions and, preferably, movable as well into flow through amount-controlling intermediate positions, the movement of the blocking valve into its respective positions being controllable by the device for controlling the temperature of the heating element; and

a hydrolysis catalyzer in the hydrolysis treatment zone of the reaction chamber of the reactor for converting, in the presence of water, the isocyanic acid (HCNO), which is produced from the flash hydrolysis of the urea in addition to ammonia (NH₃), into ammonia (NH₃) and carbon dioxide (CO₂), wherein the apparatus is operable to produce ammonia (NH₃) for use thereof as a reducing means in the selective catalytic reduction of the nitrogen oxides contained in exhaust gas of an internal combustion engine, a gas turbine, or a burner of a stationary facility such as a block heating facility or an emergency electrical current facility or a mobile facility such as a motor vehicle, a commercial vehicle, a locomotive, a ship, a boat, or an aircraft, the reactor being disposed adjacent at least one of the exhaust generating facility and the exhaust gas conduits thereof and further comprising a pre-catalyzer (an oxikat) which, in addition to its function of oxidizing carbon monoxide and hydrocarbons in the exhaust gas, also has the function of significantly raising the portion of NO₂ in the exhaust gas, from the pre-catalyzer being located upstream of one of an SCR catalyzer and several SCR catalyzers, built into a muffler and disposed for exhaust gas flow therethrough in a parallel manner, and a feed conduit extending from the reactor, in which the reaction products ammonia (NH₃) and carbon dioxide (CO₂) are collected, to an exhaust gas conduit of the exhaust gas generating facility, the feed conduit leading the products of reaction to the exhaust gas conduit and introducing such products thereinto substantially immediately after their production at a location downstream of the pre-catalyzer in the neighborhood of the exhaust gas conduit so that the entire remaining extent between the introduction location and the entrance into the respective one of the SCR catalyzer and the several SCR catalyzers can be exploited for homogenization of the reduction means ammonia (NH₃) in the exhaust gas stream.

2. An apparatus according to claim 1, and further comprising an electronic control device operable to control the respective components participating in the ammonia (NH₃) production process so as to ensure the delivery of an appropriate dosage of ammonia (NH₃) introduced into the exhaust gas conduit.

3. A method for producing ammonia (NH₃) and introducing the produced ammonia (NH₃) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitrogen oxides contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the method comprising:

feeding dry urea from a supply container in a controlled amount to a reactor;

disposing the dry urea in the reactor in contact with a heated metal surface to thereby effect flash pyrolysis resulting in the spontaneous separation of the dry urea into a gas mixture comprising the reaction products of ammonia (NH₃) and isocyanic acid (HCNO); and

substantially immediately after the flash pyrolysis, catalytically treating the thus produced gas mixture in the presence of water via a quantitative hydrolysis treatment such that the isocyanic acid (HCNO) resulting from the flash pyrolysis is converted into ammonia (NH₃) and carbon dioxide (CO₂), whereby the water required for the quantitative hydrolysis treatment is comprised solely of a water-containing gas, and completely liquid water condensed from such water-containing gas, flowing in an exhaust gas partial stream that is branched, via an exhaust gas branch conduit, from the main exhaust gas stream resulting from the combustion process, the exhaust gas partial stream and the dry urea being fed in a quantitatively controlled amount into the reactor such that the quantity of water in the exhaust gas partial stream is appropriate for substantially complete conversion of the isocyanic acid (HCNO) resulting from the flash pyrolysis into ammonia (NH₃) and carbon dioxide (CO₂) with the quantity of the exhaust gas stream which is fed into the reactor being adjustably set as a function of the exhaust gas temperature such that the temperature for conversion is not exceeded; and

conducting the ammonia (NH₃) and carbon dioxide (CO₂) generated by the catalytic hydrolysis treatment of the isocyanic acid (HCNO) into the exhaust gas stream at a location upstream of an SCR catalyzer, whereby ammonia (NH₃) in the SCR catalyzer system is reinforced as the reduction means for the reduction of NO_x.

4. A method according to claim 3, wherein the urea is stored in the supply container in at least one of a granulate, powder, and prill form, and the step of feeding dry urea from a supply container in a controlled amount to reactor includes feeding dry urea by means of a dosing device with the assistance of an air transport stream into the reactor.

5. A method according to claim 3, wherein disposing the urea into contact with a heated metal surface to thereby effect flash pyrolysis includes disposing the urea into contact with a heated metal surface having a catalytic coating so as to produce a spontaneous conversion of the urea into a gas phase, whereby the catalytic coating of the metal surface lowers the decomposition temperature of the urea.

6. A method according to claim 5, wherein disposing the urea into contact with a heated metal surface includes disposing the urea into contact with a heated metal surface having a temperature in the range between 200°

C. and 450°

C. such that the urea is substantially completely converted by the flash pyrolysis into a gas phase such that substantially no solid urea remnants are present.

7. A method according to claim 3, wherein the method is performed in a space adjacent an internal combustion engine, a gas turbine, or a burner, in that an exhaust gas partial stream is branched from the main exhaust gas stream resulting from the combustion process and fed in a controlled amount in the reactor, the water portion of the fed-in exhaust gas partial stream being available both for the catalytic hydrolysis of ammonia (NH₃) as well as, in addition to the catalytic hydrolysis of ammonia (NH₃), the hydrolysis treatment of the isocyanic acid (HCNO) to generate ammonia (NH₃) and carbon dioxide (CO₂) therefrom, whereby the gas mixture produced thereby is transported away from the reactor and is injected into an exhaust gas conduit which guides the main exhaust gas flow, at a location of the exhaust gas conduit upstream of an SCR catalyzer, whereby the ammonia (NH₃) thus provided to the SCR catalyzer system reinforces the reduction of NO_x.

8. A method for producing ammonia (NH₃) and introducing the produced ammonia (NH₃) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitrogen oxides contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the method comprising:

feeding dry urea from a supply container in a controlled amount to a reactor;

disposing the dry urea in the reactor in contact with a heated metal surface to thereby effect flash pyrolysis resulting in the spontaneous separation of the dry urea into a gas mixture comprising the reaction products of ammonia (NH₃) and isocyanic acid (HCNO); and

substantially immediately after the flash pyrolysis, catalytically treating the thus produced gas mixture in the presence of water via a quantitative hydrolysis treatment such that the isocyanic acid (HCNO) resulting from the flash pyrolysis is converted into ammonia (NH₃) and carbon dioxide (CO₂), whereby the water required for the quantitative hydrolysis treatment is comprised in an exhaust gas partial stream that is branched, via an exhaust gas branch conduit, from the main exhaust gas stream resulting from the combustion process, the exhaust gas partial stream and the dry urea being fed in a quantitatively controlled amount into the reactor such that the quantity of water in the exhaust gas partial stream is appropriate for substantially complete conversion of the isocyanic acid (HCNO) resulting from the flash pyrolysis into ammonia (NH₃) and carbon dioxide (CO₂), wherein the quantity of water (H₂O) comprised in the exhaust gas partial stream that is required for the quantitative hydrolysis treatment of the isocyanic acid (HCNO) is controlled as a function of the exhaust gas treatment such that, in the event that the exhaust gas temperature is greater than the decomposition temperature of the dry urea, the exhaust gas partial stream flowed to the reactor for contact with the heated metal surface therein has a relatively larger mass flow than the exhaust gas partial stream has in the event that the exhaust gas temperature in less than the decomposition temperature of the dry urea, whereby the exhaust gas partial stream having the relatively larger mass flow correspondingly reduces the electricity needed to heat the heated metal surface; and

conducting the ammonia (NH₃) and the carbon dioxide (CO₂) generated by the catalytic hydrolysis treatment of the isocyanic acid (HCNO) into the exhaust gas stream at a location upstream of an SCR catalyzer, whereby ammonia (NH₃) in the SCR catalyzer system is reinforced as the reduction means for the reduction of NO_x.

9. An apparatus for producing ammonia (NH₃) and introducing the produced ammonia (NH₃) into an exhaust gas stream as a reduction means for selectively catalytically reducing nitric oxide contained in the exhaust gas stream, which is an exhaust stream generated by the combustion process of a motor, a gas turbine, or a burner, the apparatus comprising:

a storage container in which urea in dry form in the form of powder, granulate, or micro-prills is stored;

a reactor for the production of ammonia (NH₃) and having a heated reaction chamber which is partitioned into a thermal treatment zone and a hydrolysis treatment zone, and the reaction chamber of the reactor being disposed for the treatment therein of an exhaust gas stream from the combustion exhaust gases of a selected one of an internal combustion engine, a gas turbine and a burner;

a device for feed of the urea, preferably in controlled or measured amounts, from the supply container into the reaction chamber of the reactor;

an electrical heating element in the thermal treatment zone of the reaction chamber of the reactor;

a device for controlling the temperature of the heating element in a manner such that the urea introduced into the reaction chamber is spontaneously de-composeable, via flash hydrolysis, into ammonia (NH₃) and isocyanic acid (HCNO);

a device for introducing water derived solely from a water-containing gas flowing the exhaust gas stream into the reaction chamber of the reactor, the device for introducing water includes a feed conduit and an electrically controllable blocking valve in the feed conduit and moveable between open and closed positions and, preferably, moveable as well into flow through amount-controlling intermediate positions, the movement of the blocking valve into its respective positions being controllable by the device for controlling the temperature of the heating element; and

a hydrolysis catalyzer in the hydrolysis treatment zone of the reaction chamber of the reactor for converting, in the presence of water, the isocyanic acid (HCNO), which is produced from the flash hydrolysis of the urea in addition to ammonia (NH₃), into ammonia (NH₃) and carbon dioxide (CO₂).

10. An apparatus according to claim 9, wherein the hydrolysis catalyzer built into the reaction chamber is dimensioned such that a quantitative conversion of the isocyanic acid (HCNO) into ammonia (NH₃) and carbon dioxide (CO₂) can be effected.

11. An apparatus according to claim 9, wherein the supply container for reserve supply of the urea is sealed against the influences of moisture and high temperatures so that the urea in the supply container neither melts nor, by reason of its hygroscopic properties, adheres to itself.

12. An apparatus according to claim 9, and further comprising a dosing device disposed at a selected one of a location on the supply container and a location adjacent to the supply container, the dosing device being operable to feed the urea via a feed conduit into the reaction chamber of the reactor.

13. An apparatus according to claim 12, wherein the dosing device is disposed at a spacing from the reactor, with its heated reaction chamber, so as to be substantially thermally decoupled from the reactor such that a melting of the urea in the dosing device and in attendant blockage for adhering together of the urea is substantially avoided.

14. An apparatus according to claim 13, wherein the thermal decoupling of the dosing device is supported by an air transport stream, which is preferably produced by an electrically-driven pump or is drawn from another pressurized air source, and the air transport stream is fed to the dosing device and serves, as well, primarily as the transport medium for the urea to be fed into the reaction chamber.

15. An apparatus according to claim 12, and further comprising an electro-magnetically controllable blocking valve disposed in the feed conduit by which the feed along the feed conduit can be blocked during predetermined operational conditions and, thereby, prevent penetration of water into the reactor via the dosing device.

16. An apparatus according to claim 15, and further comprising a pump for producing a transport air stream conducted to the feed conduit for supporting the transport therein of the dry urea and wherein the feed performance of the dosing device and the operation of the pump as well as the activation and de-activation of the blocking valve is controlled via an electric control device.

17. An apparatus according to claim 9, wherein the device for introducing water includes a feed conduit disposed between a donor source having a supply of water and a conduit having exhaust gas therein and an electrically controllable blocking valve movable between open and closed positions and, preferably, movable as well into flow through amount-controlling intermediate positions, the movement of the blocking valve into its respective positions being controllable by an electrical control device.

18. An apparatus according to claim 9, wherein the heating element disposed in the reaction chamber in the reactor for producing the thermal treatment zone is configured as a selected one of a spiral-shaped winding body, a plate-shaped heating body, and a ribbed-shaped heating body.

19. An apparatus according to claim 18, wherein the electrically-heatable surface of the heating element is provided with a catalytic coating operable to reduce the decomposition temperature of the urea and has a heat capacity such that the heat withdrawn from the heating element via the spontaneous vaporization of the maximum urea amount does not cause the heating element temperature to sink below a threshold which would otherwise lead to an incomplete vaporization of urea with the thereto attendant solid remnants.

20. An apparatus according to claim 9, and further comprising a temperature sensor for sensing at least one of the temperature produced in the reaction chamber and the temperature of the heating element, which temperature is monitored by an electronic control device for controlling the temperature of an electronically-heatable heating surface of the heating element in the reaction chamber to be in a range between 200°

C. and 450°

C. such that, during the spontaneous conversion of the urea into a gas phase, no remnants of the urea remain.

21. An apparatus according to claim 9, wherein the electrically-heatable surface of the heating element in the reaction chamber of the reactor is positioned immediately before the rear surface of the hydrolysis catalyzer.

22. An apparatus according to claim 9, wherein the electrically-heatable surface of the heating element in the reaction chamber of the reactor is integrated in a space-compatible manner in the hydrolysis catalyzer.