Reducing NO.sub.x emissions from an engine by selective catalytic reduction utilizing solid reagents

• US 5,809,775 A
• Filed: 04/02/1997
• Issued: 09/22/1998
• Est. Priority Date: 04/02/1997
• Status: Expired due to Term

• Current Assignee: Clean Diesel Technologies, Inc.
• Original Assignee: Clean Diesel Technologies, Inc.
• Inventors: Tarabulski, Theodore J., Valentine, James M., Peter-Hoblyn, Jeremy D.
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/831,210
• Time in Patent Office: 538 Days
• Field of Search: 60/274, 60/286, 60/303, 423/212, 423/213.7, 423/235, 423/239.1
• US Class Current: 60/274
• CPC Class Codes: B01D 2251/2062 Ammonia
• 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 2240/20 a flow director or deflector
• CPC Class Codes: F01N 2240/25 an ammonia generator
• CPC Class Codes: F01N 2560/06 the means being a temperature sensor
• 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 2610/146 Control thereof, e.g. control of injectors or injection valves
• CPC Class Codes: F01N 2900/1811 Temperature
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

Urea or other solid NO_x -reducing reagent is employed in a selective catalytic reduction process on emissions from diesel and lean-burn gasoline engines. The solid reagent is fed to a gas generator that produces a reactant gas by heating. In one embodiment the reactant gas is maintained at elevated temperatures to prevent condensation products from forming. The reactant gas contains ammonia and is fed to the exhaust on an as-needed basis.

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 leading to an SCR reactor effective for selective catalytic NO_x reduction, comprising:

supplying solid NO_x -reducing reagent capable of generating ammonia-containing reactant gas upon heating, into a vessel having an outlet;

heating the solid NO_x -reducing reagent in the vessel at a temperature above the pyrolysis temperature for the reagent, to produce a reactant gas containing ammonia;

introducing the reactant gas into the exhaust gas at an exhaust gas temperature effective for selective catalytic reduction; and

passing the exhaust gas containing the reactant gas through an SCR reactor.

2. 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.

3. A method according to claim 1 wherein the solid NO_x -reducing reagent comprises a member selected from the group consisting of include ammelide, ammeline, ammonium cyanate, biuret, cyanuric acid, isocyanic acid, melamine, tricyanourea, urea, and mixtures of any number of these;

and is heated to a temperature of at least about 300°

C.

4. A method according to claim 3 wherein the reactant gas is maintained at elevated temperature until introduced into the exhaust gas.

5. A method according to claim 3 wherein the solid NO_x -reducing reagent is heated to a temperature of at least about 400°

C.

6. A method according to claim 1 wherein the solid NO_x -reducing reagent is maintained under a pressure of at least about 50 psi during heating.

7. A method according to claim 1 wherein the solid NO_x -reducing reagent is heated at least in part with heat from the exhaust.

8. A method according to claim 1 wherein the solid NO_x -reducing reagent is heated at least in part with heat from an auxiliary heater.

9. A method according to claim 1 wherein the solid NO_x -reducing reagent comprises a member selected from the group consisting of ammonium carbonate;

ammonium bicarbonate;

ammonium carbamate;

ammonium salts of inorganic acids, including sulfuric acid and phosphoric acid;

ammonium salts of organic acids, including formic and acetic acid; and

mixture of two or more of these; and

is heated to a temperature of from about 40°

to about 150°

C.

10. A method according to claim 1 or 9 wherein the temperature of the reactant gas is not maintained after it is formed by pyrolysis.

11. A method according to claim 1 or 9 wherein the reactant is introduced into the exhaust between exhaust valves of the engine and a turbocharger exhaust turbine.

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

13. 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 an SCR reactor effective for selective catalytic NO_x reduction, comprising:

means for supplying solid NO_x -reducing reagent to a vessel having an outlet;

means for heating the solid NO_x -reducing reagent in the vessel at a temperature above the pyrolysis temperature for the reagent, to produce a reactant gas containing ammonia;

means for introducing the reactant gas into the exhaust gas at an exhaust gas temperature effective for selective catalytic reduction; and

means for passing the exhaust gas containing the reactant gas through an SCR reactor.

14. An apparatus according to claim 13, further including:

means for maintaining the solid NO_x -reducing reagent under pressure while it is being supplied to the vessel; and

means for maintaining the reactant gas under pressure in the vessel.

15. An apparat us according to claim 13, further including:

means to sense the temperature with the exhaust gas;

means to generate a signal representative of the sensed temperature;

means to sense the pressure of reactant gas;

means to generate a signal representative of the sensed pressure; and

means to compare the generated signals to referenced values and generate a control signal for controlling solid NO_x -reducing reagent feed to the means for heating the solid NO_x -reducing reagent and the feed of reactant gas to the exhaust gases.

16. An apparatus according to claim 13, further including:

means to feed the solid reagent under pressure.