Exhaust treatment system with an oxidation device for NO2 control

• US 20090035194A1
• Filed: 07/31/2007
• Published: 02/05/2009
• Est. Priority Date: 07/31/2007
• Status: Abandoned Application

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Chavannavar, Praveen Shivshankar, Hardy, William Lyle, Robel, Wade J., Schroeder, Eric Lee
• Application Number:
  US11/882,326
• Publication Number:
  US 20090035194A1
• Time in Patent Office: Days
• US Class Current: 422/177
• 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 2510/0682 having a discontinuous, uneven or partially overlapping coating of catalytic material, e.g. higher amount of material upstream than downstream or vice versa
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• 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 3/0231 using special exhaust apparatus upstream of the filter for producing nitrogen dioxide, e.g. for continuous filter regeneration systems [CRT]
• CPC Class Codes: F01N 3/025 using fuel burner or by adding fuel to exhaust
• CPC Class Codes: F01N 3/027 using electric or magnetic heating means
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/106 Auxiliary oxidation catalysts
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• 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

An exhaust treatment system includes an oxidation device having a plurality of channels through which a flow of exhaust flows. A first portion of the channels of the oxidation device are coated with catalytic material for converting NO to NO₂ and a second portion of the channels are uncoated with the catalytic material. The exhaust treatment system also includes a selective catalytic reduction device disposed downstream from the oxidation device. The selective catalytic reduction device is configured to receive the flow of exhaust passing through the oxidation device.

Claims

1. An exhaust treatment system comprising:

an oxidation device having a plurality of channels through which a flow of exhaust flows, a first portion of the channels being coated with catalytic material for converting NO to NO₂, a second portion of the channels being uncoated with the catalytic material; and

a selective catalytic reduction device disposed downstream from the oxidation device, the selective catalytic reduction device being configured to receive the flow of exhaust passing through the oxidation device.

2. The exhaust treatment system of claim 1, wherein a percentage of the channels of the oxidation device that are coated with the catalytic material is based on a target NO:

NO₂ ratio in the flow of exhaust supplied to the selective catalytic reduction device.

3. The exhaust treatment system of claim 2, wherein the target NO:

NO₂ ratio in the flow of exhaust supplied to the selective catalytic reduction device is approximately 50;

50.

4. The exhaust treatment system of claim 2, wherein the percentage of channels coated in the oxidation device is determined when operating at a predetermined operating condition when the target NO:

NO₂ ratio is achieved, the predetermined operating condition including at least one of a predetermined mass flow and a predetermined temperature.

5. The exhaust treatment system of claim 1, wherein the first portion of the channels of the oxidation device that are coated with the catalytic material constitute approximately 75% of the channels of oxidation device.

6. The exhaust treatment system of claim 1, further including a particulate filter downstream from the oxidation device.

7. The exhaust treatment system of claim 1, wherein the selective catalytic reduction device is a downstream selective catalytic reduction device, and the exhaust treatment system further includes:

an upstream selective catalytic reduction device disposed upstream from the oxidation device; and

an upstream injector disposed upstream from the upstream selective catalytic reduction device, the upstream injector configured to inject reductant into the flow of exhaust.

8. The exhaust treatment system of claim 7, wherein the oxidation device is a downstream oxidation device, and the exhaust treatment system further includes:

an upstream oxidation device disposed upstream from the upstream selective catalytic reduction device, the upstream oxidation device having a plurality of channels through which the flow of exhaust flows, and a percentage less than 100% of the channels of the upstream oxidation catalyst are coated with the catalytic material.

9. The exhaust treatment system of claim 8, further including:

a sensor for sensing a characteristic of the flow of exhaust upstream from the downstream selective catalytic reduction device and downstream from the upstream selective catalytic reduction device; and

a controller connected to the sensor, the controller being configured to receive the sensed characteristic and control an injection of reductant by the upstream injector based on the sensed characteristic.

10. The exhaust treatment system of claim 9, wherein the characteristic is a NO:

NO₂ ratio.

11. The exhaust treatment system of claim 8, wherein the percentage of coated channels in the downstream oxidation device is greater than 50%, and the percentage of coated channels in the upstream oxidation device is less than 50%.

12. The exhaust treatment system of claim 1, further including a first passageway configured to direct a portion of the flow of exhaust around the oxidation device, the oxidation device being disposed in a second passageway.

13. The exhaust treatment system of claim 12, further including:

a first particulate filter disposed in the first passageway; and

a second particulate filter disposed in the second passageway.

14. The exhaust treatment system of claim 13, wherein at least one of the particulate filters is coated with the catalytic material for converting NO to NO₂.

15. The exhaust treatment system of claim 13, wherein at least one of the particulate filters is a flow through type filter.

16. The exhaust treatment system of claim 12, wherein the oxidation device is a second oxidation device, and the exhaust treatment system further includes a first oxidation device in the first passageway, the first oxidation device having a plurality of channels through which the flow of exhaust flows, a percentage less than 100% of the channels of the first oxidation device being coated with the catalytic material.

17. The exhaust treatment system of claim 16, wherein:

the selective catalytic reduction device is a downstream selective catalytic reduction device disposed downstream from the first and second passageways; and

the exhaust treatment system further includes;

a first selective catalytic reduction device in the first passageway downstream from the first oxidation device; and

a second selective catalytic reduction device in the second passageway downstream from the second oxidation device.

18. The exhaust treatment system of claim 17, wherein the percentage of channels coated with the catalytic material in the first oxidation device is greater than 50%, and the percentage of channels coated with the catalytic material in the second oxidation device is less than 50%.

19. The exhaust treatment system of claim 17, further including:

a first particulate filter in the first passageway downstream from the first selective catalytic reduction device; and

a second particulate filter in the second passageway downstream from the second selective catalytic reduction device.

20. The exhaust treatment system of claim 1, wherein the catalytic material is platinum.

21. A method for treating a flow of exhaust comprising:

generating the flow of exhaust;

passing the flow of exhaust through a plurality of channels of a downstream oxidation device, a first portion of the channels being coated with catalytic material for converting NO to NO₂, a second portion of the channels being uncoated with the catalytic material; and

directing the combined flow of exhaust to a downstream selective catalytic reduction device disposed downstream from the downstream oxidation device.

22. The method of claim 21, further including:

passing the flow of exhaust through a plurality of channels of an upstream oxidation device disposed upstream from the downstream oxidation device, a first portion of the channels of the upstream oxidation device being coated with the catalytic material, a second portion of the channels of the channels of the upstream oxidation device being uncoated with the catalytic material;

injecting reductant with an upstream injector disposed downstream from the upstream oxidation device and upstream from the downstream oxidation device; and

passing the flow of exhaust through an upstream selective catalytic reduction device disposed upstream from the downstream oxidation device and downstream from the upstream injector.

23. The method of claim 22, further including:

sensing a characteristic of the flow of exhaust; and

controlling the injection of reductant by the upstream injector based on the sensed characteristic.

24. The method of claim 23, wherein the sensed characteristic is a sensed NO:

NO₂ ratio in the flow of exhaust.

25. The method of claim 24, wherein the injection of reductant by the upstream injector is controlled based on a target NO:

NO₂ ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device.

26. The method of claim 25, wherein the target NO:

NO₂ ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device is approximately 50;

50.

27. An exhaust treatment system comprising:

an upstream oxidation device having a plurality of channels through which a flow of exhaust flows, a first portion of the channels being coated with catalytic material for converting NO to NO₂, a second portion of the channels being uncoated with the catalytic material;

an upstream injector configured to inject reductant into the flow of exhaust upstream from the upstream selective catalytic reduction device;

an upstream selective catalytic reduction device disposed downstream from the upstream injector, the upstream selective catalytic reduction device being configured to receive the flow of exhaust;

a downstream oxidation device disposed downstream from the upstream selective catalytic reduction device, the downstream oxidation device having a plurality of channels through which the flow of exhaust flows, a first portion of the channels of the downstream oxidation device being coated with the catalytic material, a second portion of the channels of the downstream oxidation device being uncoated with the catalytic material; and

a downstream selective catalytic reduction device disposed downstream from the downstream oxidation device, the downstream selective catalytic reduction device being configured to receive the flow of exhaust.

28. The exhaust treatment system of claim 27, further including:

a sensor configured to sense a characteristic of the flow of exhaust; and

a controller connected to the sensor, the controller being configured to receive the sensed characteristic and control an injection of reductant by the upstream injector based on the sensed characteristic.

29. The exhaust treatment system of claim 28, wherein the sensed characteristic is a sensed NO:

NO₂ ratio in the flow of exhaust.

30. The exhaust treatment system of claim 29, wherein the controller controls the injection of reductant based on a target NO:

NO₂ ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device.

31. The exhaust treatment system of claim 30, wherein the target NO:

NO₂ ratio in the flow of exhaust supplied to the downstream selective catalytic reduction device is approximately 50;

50.