Reducing no emissions from an engine by on-demand generation of ammonia for selective catalytic reduction

• US 6,361,754 B1
• Filed: 03/27/1997
• Issued: 03/26/2002
• Est. Priority Date: 03/27/1997
• Status: Expired due to Term

• Current Assignee: Clean Diesel Technologies, Inc.
• Original Assignee: Clean Diesel Technologies, Inc.
• Inventors: Hofmann, John E., Balles, Eric N., Peter-Hoblyn, Jeremy D.
• Primary Examiner(s): Griffin, Steven P.
• Assistant Examiner(s): MEDINA SANABRIA, MARIBEL
• Application Number:
  US08/826,165
• Time in Patent Office: 1,825 Days
• Field of Search: 602/74, 602/77, 602/80, 602/86, 602/82, 602/95, 602/99, 603/01, 423/235, 423/239.1, 423/212, 423/213.2, 423/213.5, 423/169, 423/171, 423/177, 423/189
• US Class Current: 423/213.2
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 2255/102 Platinum group metals
• CPC Class Codes: B01D 2255/20707 Titanium
• CPC Class Codes: B01D 2255/20723 Vanadium
• CPC Class Codes: B01D 2255/2073 Manganese
• CPC Class Codes: B01D 2255/20738 Iron
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/20776 Tungsten
• CPC Class Codes: B01D 2255/50 Zeolites
• CPC Class Codes: B01D 2255/702 Carbon
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9409 Nitrogen oxides
• 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 2610/10 the substance being heated, e.g. by heating tank or supply line of the added substance
• CPC Class Codes: F01N 2610/14 Arrangements for the supply of substances, e.g. conduits
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A safe, reliable SCR system for reducing NO_x emissions from an internal combustion engine hydrolyzes urea or like reagent under sufficient pressure to assure generation of ammonia, without production of solids that could foul injectors or catalysts. The heat for hydrolysis can be provided by the exhaust or an auxiliary means.

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 an aqueous urea solution at a preset pressure of at least about 50 psi into a vessel having an inlet and an outlet;

heating the urea solution in the vessel at a temperature above the hydrolysis temperature for the urea solution to produce an ammonia-containing gas;

responsive to control signals related to engine load and temperature measured within the exhaust gas passage, introducing the ammonia-containing gas from said vessel into the exhaust passage wherein exhaust from said engine is measured to have an exhaust gas temperature effective for selective catalytic reduction; and

passing the exhaust gas containing ammonia through an SCR reactor.

2. A method according to claim 1 wherein the urea solution contains from from about 25 to about 50% urea.

3. A method according to claim 1 wherein the temperature of the exhaust gases is within the range of from about 200 to about 650°

C.

4. A method according to claim 1 wherein the urea solution is heated to a temperature of at least about 140°

C.

5. A method according to claim 1 wherein the urea solution is maintained under a pressure of at least about 100 psi during heating.

6. A method according to claim 1 wherein the urea solution is heated in part by the exhaust and in part by an auxiliary heating means.

7. A method according to claim 1 wherein the urea solution is heated by transfer of heat from the exhaust as the sole source of heat.

8. A method according to claim 1 wherein the urea solution is heated by an auxiliary heating means as the sole source of heat.

9. A method according to claim 1 wherein the ammonia-containing gas is introduced into the exhaust between exhaust valves of the engine and a turbocharger exhaust turbine.

10. A method according to claim 1 wherein the ammonia-containing gas is introduced into the exhaust in close-coupled relation with the SCR catalyst.

11. A method according to claim 1 wherein introduction of the ammonia-containing gas into the exhaust is controlled by a controller integrated with an engine management system.

12. 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 an aqueous urea solution at a preset pressure of from about 50 to 600 psi into a vessel having an inlet and an outlet;

means for heating the urea solution in the vessel at a temperature above the hydrolysis temperature for the urea solution to produce ammonia;

means for controlling introduction of ammonia from the vessel;

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

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

13. An apparatus according to claim 12, 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 ammonia 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 urea feed to the means for heating the urea and the feed of ammonia to the exhaust gases.