Urea pyrolysis chamber and process for reducing lean-burn engine NOx emissions by selective catalytic reduction

• US 6,203,770 B1
• Filed: 08/20/1999
• Issued: 03/20/2001
• Est. Priority Date: 05/12/1997
• Status: Expired due to Term

• Current Assignee: Clean Diesel Technologies, Inc.
• Original Assignee: Clean Diesel Technologies, Inc.
• Inventors: Tarabulski, Theodore J., Valentine, James M., Hofmann, John E., Peter-Hoblyn, Jeremy D., Balles, Eric N.
• Primary Examiner(s): Beck, Shrive
• Assistant Examiner(s): NECKEL, ALEXA DOROSHENK
• Application Number:
  US09/378,350
• Time in Patent Office: 578 Days
• Field of Search: 423/212, 423/235, 423/239.1, 422/168, 422/173, 422/176, 422/177, 422/180, 422/198, 422/211, 422/234
• US Class Current: 423/212
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• 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 2610/1453 Sprayers or atomisers; Arrangement thereof in the exhaust apparatus
• CPC Class Codes: F01N 2610/1473 Overflow or return means for the substances, e.g. conduits or valves for the return path
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: Y02C 20/10 of nitrous oxide (N2O)
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

Urea is pyrolyzed in a chamber designed to facilitate gasification of the urea by pyrolysis with conversion of urea to ammonia and isocyanic acid (HNCO) with water vapor and carbon dioxide. The product gases are introduced into exhaust gases from a lean-burn engine, preferably upstream of a turbocharger. The exhaust gases are then contacted with an SCR catalyst.

Claims

1. An apparatus for reducing the emissions of No_x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage leading to a SCR reactor effective for selective catalytic No_x reduction, comprising:

a pyrolysis chamber for pyrolizing urea fed as an aqueous solution including heated internal surfaces and having openings therein to permit discharge of gases generated by pyrolysis of urea and vaporization of water;

means for passing the gases generated by pyrolysis into the exhaust passage containing exhaust gases;

means for passing the exhaust gases containing the gases generated by pyrolysis to a SCR reactor;

spray means capable of spraying the urea solution into the pyrolysis chamber; and

said spray means comprising an injector nozzle having associated lines for feeding the solution to the nozzle and returning solution not discharged from the nozzle.

2. An apparatus according to claim 1, which further comprises:

a heat exchanger to transfer heat from the exhaust gases to the pyrolysis chamber.

3. An apparatus according to claim 1, which further comprises:

an auxiliary heater to heat the pyrolysis chamber.