Multi-stage system for selective catalytic reduction

• US 7,485,272 B2
• Filed: 11/30/2005
• Issued: 02/03/2009
• Est. Priority Date: 11/30/2005
• Status: Expired due to Fees

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Driscoll, James Joshua, Milam, David M.
• Primary Examiner(s): Vanoy; Timothy C
• Application Number:
  US11/290,730
• Publication Number:
  US 20070122317A1
• Time in Patent Office: 1,161 Days
• Field of Search: 423/213.2, 423/213.7, 423/239.1, 423/DIG.5, 422/105, 422/108, 422/111, 422/170, 422/171, 422/172, 422/177, 422/180, 602/74, 602/82, 602/99, 603/01
• US Class Current: 423/213.2
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9409 Nitrogen oxides
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9477 with catalysts positioned on separate bricks, e.g. exhaust systems
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/0093 the purifying devices are of the same type
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 13/107 More than one exhaust manifold or exhaust collector
• CPC Class Codes: F01N 2240/25 an ammonia generator
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 3/04 using liquids
• CPC Class Codes: F01N 3/05 by means of air, e.g. by mixing exhaust with air silencers working by addition of air to exhaust F01N1/14; arrangements for the supply of additional air for the thermal or catalytic conversion of noxious components of exhaust F01N3/30 ; in tailpipes F01N13/082
• CPC Class Codes: F01N 3/2053 By-passing catalytic reactors, e.g. to prevent overheating
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/2073 with means for generating a reducing substance from the exhaust gases
• CPC Class Codes: F02B 37/00 Engines characterised by provision of pumps driven at least for part of the time by exhaust
• 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: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y10S 423/05 Automatic, including computer, control

Abstract

A first aspect of the present disclosure includes a method of controlling nitric oxides emissions. The method may include producing an exhaust gas stream containing NOx and supplying the exhaust gas stream to an exhaust passage. The method may further comprise supplying ammonia to the exhaust passage at a location upstream of a first selective catalytic reduction catalyst, wherein the amount of ammonia supplied at the first location is less than about 90% of the effective amount of ammonia needed for reduction of all NOx at the first location. Further, ammonia may be supplied to the exhaust passage at a second location downstream of the first selective catalytic reduction catalyst and upstream of a second selective catalytic reduction catalyst.

Claims

1. A method of controlling nitric oxides emissions, comprising:

producing an exhaust gas stream containing NOx;

supplying the exhaust gas stream to an exhaust passage;

producing a second exhaust gas stream containing NOx by combustion of a fuel within at least one engine cylinder and converting at least a portion of the NOx in the second exhaust gas stream into ammonia to produce an ammonia-containing exhaust gas stream;

supplying the ammonia-containing exhaust gas stream to the exhaust passage at a location upstream of a first selective catalytic reduction catalyst, wherein the amount of ammonia supplied at the first location is less than about 90% of the effective amount of ammonia needed for reduction of all NOx at the first location; and

supplying urea to the exhaust passage at a second location downstream of the first selective catalytic reduction catalyst and upstream of a second selective catalytic reduction catalyst.

2. The method of claim 1, wherein the amount of urea supplied at the second location is less than about 90% of the effective amount of urea needed for reduction of all NOx at the second location.

3. The method of claim 1, wherein the amount of ammonia supplied at the first location is less than about 80% of the effective amount of ammonia needed for reduction of all NOx at the first location.

4. The method of claim 3, wherein the amount of urea supplied at the second location is less than about 80% of the effective amount of urea needed for reduction of all NOx at the second location.

5. The method of claim 1, wherein the amount of ammonia supplied at the first location is less than about 70% of the effective amount of ammonia needed for reduction of all NOx at the first location.

6. The method of claim 1, wherein the effective amount of ammonia is the stoichiometric amount of ammonia for complete reduction of NOx.

7. The method of claim 1, further including supplying ammonia to the exhaust passage at a third location downstream of the second selective catalytic reduction catalyst and upstream of a third selective catalytic reduction catalyst.

8. A selective catalytic reduction system, comprising:

an exhaust passage;

a first selective catalytic reduction catalyst in fluid communication with the exhaust passage;

a second selective catalytic reduction catalyst disposed downstream of the first selective catalytic reduction catalyst and in fluid communication with the exhaust passage;

an ammonia production system including at least one cylinder of an engine configured to produce a NOx-containing exhaust gas stream and at least one catalyst configured to convert at least a portion of the NOx in the NOx-containing exhaust gas stream into ammonia, the ammonia production system being configured to supply ammonia to the exhaust passage at a first location upstream of the first selective catalytic reduction catalyst such that the amount of ammonia supplied at the first location is less than about 90% of the effective amount of ammonia needed for reduction of all NOx in the exhaust passage; and

a urea supply system configured to supply urea at a second location upstream of the second selective catalytic reduction catalyst and downstream of the first selective catalytic reduction catalyst.

9. The system of claim 8, wherein the ammonia production system further includes an ammonia producing catalyst configured to convert at least a portion of the NOx in the NOx-containing exhaust gas stream into ammonia.

10. The system of claim 9, further including at least one oxidation catalyst upstream of the ammonia producing catalyst.

11. The system of claim 9, further including an exhaust gas cooling system upstream of the ammonia producing catalyst.

12. The system of claim 8, further including a third selective catalytic reduction catalyst disposed downstream of the second selective catalytic reduction catalyst.

13. The system of claim 8, wherein the ammonia production system is configured to supply ammonia to the exhaust passage at a position upstream of the first selective catalytic reduction catalyst such that the amount of ammonia supplied at is less than about 80% of the effective amount of ammonia needed for reduction of all NOx in the exhaust passage.

14. The system of claim 8, further including at least one mixing system configured to mix the ammonia and an exhaust gas stream flowing through the exhaust passage.

15. The system of claim 8, wherein the effective amount of ammonia is the stoichiometric amount of ammonia for complete reduction of NOx.

16. A NOx-emissions control system, comprising:

an engine configured to produce a NOx-containing exhaust gas stream;

an exhaust passage configured to receive the NOx-containing exhaust gas stream;

a first selective catalytic reduction catalyst in fluid communication with the exhaust passage;

a second selective catalytic reduction catalyst disposed downstream of the first selective catalytic reduction catalyst and in fluid communication with the exhaust passage;

an ammonia production system including at least one cylinder of an engine configured to produce a NOx-containing exhaust gas stream, the ammonia production system being configured to supply ammonia to the exhaust passage at a first location upstream of the first selective catalytic reduction catalyst;

a liquid injector configured to supply a liquid that can be at least partially converted to ammonia at a second location upstream of the second selective catalytic reduction catalyst and downstream of the first selective catalytic reduction catalyst; and

a control unit configured to monitor the amount of NOx produced by the engine and the amount of ammonia supplied by the ammonia production system and to control the amount of ammonia supplied at the first location and the amount of NOx at the first location.

17. The system of claim 16, wherein the control unit is configured to control the amount of ammonia supplied at the first location and the amount of NOx at the first location such that the amount of ammonia is less than about 90% of the effective amount of ammonia needed for reduction of all NOx at the first location.