Reducing NO.sub.x emissions from an engine by temperature-controlled urea injection for selective catalytic reduction

• US 5,976,475 A
• Filed: 04/02/1997
• Issued: 11/02/1999
• Est. Priority Date: 04/02/1997
• Status: Expired due to Term

• Current Assignee: TABULA (ASSIGNMENT FOR THE BENEFIT OF CREDITORS), LLC
• Original Assignee: Clean Diesel Technologies, Inc.
• Inventors: Tarabulski, Theodore J., Hofmann, John E., Peter-Hoblyn, Jeremy D., Balles, Eric N.
• Primary Examiner(s): DUNN, THOMAS G
• Application Number:
  US08/831,209
• Time in Patent Office: 944 Days
• Field of Search: 423/235, 423/239.1, 423/212, 422/168, 239/124, 239/125, 239/128
• US Class Current: 423/212
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2240/02 a heat exchanger
• CPC Class Codes: F01N 2240/16 an electric heater, i.e. a resistance heater
• CPC Class Codes: F01N 2260/022 using air
• CPC Class Codes: F01N 2260/024 using a liquid
• CPC Class Codes: F01N 2430/00 Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
• CPC Class Codes: F01N 2550/00 Monitoring or diagnosing the deterioration of exhaust systems
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 2610/14 Arrangements for the supply of substances, e.g. conduits
• 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 2900/1811 Temperature
• CPC Class Codes: F01N 2900/1814 Tank level
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/36 Arrangements for supply of additional fuel
• CPC Class Codes: F01N 9/00 : Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• 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: Y02T 10/40 : Engine management systems

Abstract

A safe, reliable SCR system for reducing NO_x emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. Overheating and hydrolysis of the solution are prevented by maintaining the temperature of the urea solution sufficiently low that it is not permitted sufficient time at elevated temperature to hydrolyze the urea to such an extent that solids precipitate. In a preferred embodiment, an injector system similar to those used for fuel injection provides a constant feed to injectors and a return line. The feed and injection can be controlled to provide sufficient urea for NO_x reduction and sufficient cooling capacity for the feed and injection system to avoid hydrolysis and deposits of hydrolysis products.

Claims

1. A method for reducing the emissions of NO_x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NO_x to a reactor effective for selective catalytic NO_x reduction, comprising:

feeding an aqueous urea solution from a storage vessel through a line to an injector;

returning urea solution from the injector to the storage vessel, the rates of feed and return being sufficient to supply urea as needed to the exhaust gases for NO_x reduction and maintain the temperature of the urea solution sufficiently low that it is not permitted sufficient time to hydrolyze the urea to such an extent that solids precipitate prior to injection of the urea solution into the exhaust gases;

injecting urea solution into the exhaust gases at an exhaust gas temperature sufficient for SCR; and

passing the exhaust gas through an SCR reactor.

2. A method according to claim 1 wherein the urea solution contains at least about 25% by weight urea.

3. A method according to claim 1 wherein the temperature of the exhaust gases is within the range of from about 180 to about 650°

C.

4. A method according to claim 1 wherein the urea solution prior to injection is maintained at a temperature below about 140°

C.

5. A method according to claim 1 wherein the urea solution is injected into the exhaust gases at a pressure of at least about 30 psi.

6. A method according to claim 1 wherein the urea solution prior to injection is heated in whole or in part by an auxiliary heating means.

7. A method according to claim 1 wherein the urea solution prior to injection is heated in whole or in part by heat transfer from the exhaust.

8. A method according to claim 1 wherein the urea solution is introduced into the exhaust between exhaust valves of the engine and a turbocharger exhaust turbine.

9. A method according to claim 1 wherein the urea is introduced into the exhaust in close-coupled relation with the SCR catalyst.

10. A method according to claim 1 wherein introduction of the urea solution into the exhaust is controlled by a controller integrated with an engine management system.