U.S. patent application number 12/936151 was filed with the patent office on 2011-01-27 for system and method for treating diesel exhaust gases.
This patent application is currently assigned to MACK TRUCKS, INC. Invention is credited to Jeffrey A. Brooks.
Application Number | 20110016848 12/936151 |
Document ID | / |
Family ID | 41135869 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110016848 |
Kind Code |
A1 |
Brooks; Jeffrey A. |
January 27, 2011 |
SYSTEM AND METHOD FOR TREATING DIESEL EXHAUST GASES
Abstract
A system for treating diesel exhaust gases includes an engine
for producing a diesel exhaust stream, a diesel particulate filter
downstream of the engine and adapted to remove particulates from
the exhaust stream, a heater upstream of the filter adapted to
deliver energy in sufficient amounts to the exhaust stream to cause
active regeneration of the filter, and a diesel oxidation catalyst
upstream of the heater adapted to cause passive regeneration of the
filter when the exhaust stream is above a light-off temperature of
the diesel oxidation catalyst. A NOx reduction catalyst can be
provided downstream of the heater. Methods for treating diesel
exhaust gases are also disclosed.
Inventors: |
Brooks; Jeffrey A.;
(Greencastle, PA) |
Correspondence
Address: |
WRB-IP LLP
801 N. Pitt Street, Suite 123
ALEXANDRIA
VA
22314
US
|
Assignee: |
MACK TRUCKS, INC
Greensboro
NC
|
Family ID: |
41135869 |
Appl. No.: |
12/936151 |
Filed: |
April 2, 2008 |
PCT Filed: |
April 2, 2008 |
PCT NO: |
PCT/US08/59127 |
371 Date: |
October 1, 2010 |
Current U.S.
Class: |
60/274 ; 60/286;
60/295; 60/301 |
Current CPC
Class: |
F01N 3/025 20130101;
F01N 2250/14 20130101; F01N 3/103 20130101; F01N 3/027 20130101;
F01N 3/0231 20130101; F01N 3/2066 20130101; Y02T 10/26 20130101;
F01N 9/002 20130101; Y02T 10/12 20130101; Y02T 10/40 20130101; Y02T
10/47 20130101; F01N 2240/14 20130101; F01N 3/035 20130101; F01N
3/2006 20130101; F01N 13/009 20140601; F01N 2240/16 20130101; F01N
2250/06 20130101; F01N 2610/02 20130101; F01N 2610/03 20130101;
F01N 3/0842 20130101; Y02T 10/24 20130101; F01N 2560/06 20130101;
F01N 3/2033 20130101; F01N 3/0814 20130101; F01N 2250/02 20130101;
F01N 2250/12 20130101; F01N 2250/04 20130101; F01N 2900/1404
20130101; F01N 3/0807 20130101 |
Class at
Publication: |
60/274 ; 60/295;
60/301; 60/286 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/023 20060101 F01N003/023; F01N 3/10 20060101
F01N003/10; F01N 9/00 20060101 F01N009/00 |
Claims
1. A system for treating diesel exhaust gases, comprising: an
engine for producing a diesel exhaust stream; a diesel particulate
filter downstream of the engine and adapted to remove particulates
from the exhaust stream; a heater upstream of the filter adapted to
deliver energy in sufficient amounts to the exhaust stream to cause
active regeneration of the filter; and a diesel oxidation catalyst
upstream of the heater adapted to cause passive regeneration of the
filter when the exhaust stream is above a light-off temperature of
the diesel oxidation catalyst.
2. The system as set forth in claim 1, comprising a NOx reduction
catalyst downstream of the heater.
3. The system as set forth in claim 2, wherein the NOx reduction
catalyst includes a catalyst downstream of the DPF.
4. The system as set forth in claim 2, wherein the heater is
adapted to elevate the exhaust stream temperature to a temperature
in an optimal range for NOx reduction by the catalyst.
5. The system as set forth in claim 2, comprising a controller for
controlling operation of the heater and a temperature sensor for
sensing a temperature in the exhaust stream and sending a signal
corresponding to the temperature in the exhaust stream to the
controller, the controller controlling the heater in response to
the temperature signal.
6. The system as set forth in claim 1, comprising an oxidation
catalyst coating on the filter.
7. A system for treating diesel exhaust gases, comprising: an
engine for producing a diesel exhaust stream; a diesel particulate
filter downstream of the engine and adapted to remove particulates
from the exhaust stream; a heater upstream of the filter adapted to
deliver energy to the exhaust stream; and a NOx reduction catalyst
downstream of the heater.
8. The system as set forth in claim 7, comprising an oxidation
catalyst coating on the filter.
9. The system as set forth in claim 7, wherein the NOx reduction
catalyst includes a catalyst downstream of the DPF.
10. The system as set forth in claim 7, wherein the heater is
adapted to elevate the exhaust stream temperature to a temperature
in an optimal range for NOx reduction by the NOx reduction
catalyst.
11. The system as set forth in claim 10, wherein the heater is
adapted to elevate the exhaust stream temperature to a temperature
sufficient to cause active regeneration of the filter.
12. The system as set forth in claim 11, comprising a controller
for controlling operation of the heater and a temperature sensor
for sensing a temperature in the exhaust stream and sending a
signal corresponding to the temperature in the exhaust stream to
the controller, the controller controlling the heater in response
to the temperature signal.
13. The system as set forth in claim 10, comprising a controller
for controlling operation of the heater and a temperature sensor
for sensing a temperature in the exhaust stream and sending a
signal corresponding to the temperature in the exhaust stream to
the controller, the controller controlling the heater in response
to the temperature signal.
14. The system as set forth in claim 7, comprising a diesel
oxidation catalyst upstream of the heater adapted to cause passive
regeneration of the filter when the exhaust stream is above a
light-off temperature of the diesel oxidation catalyst.
15. A method for treating diesel exhaust gases, comprising:
producing a diesel exhaust stream with a diesel engine; removing
particulates from the exhaust stream with a diesel particulate
filter downstream of the engine; periodically delivering energy
from a heater to the exhaust stream upstream of the filter in
sufficient amounts to cause active regeneration of the filter; and
periodically heating a diesel oxidation catalyst upstream of the
heater to a light-off temperature of the diesel oxidation catalyst
to cause passive regeneration of the filter.
16. The method as set forth in claim 15, comprising causing NOx
reduction with a NOx reduction catalyst downstream of the
heater.
17. The method as set forth in claim 15, comprising sensing a
temperature in the exhaust stream and sending a signal
corresponding to the temperature in the exhaust stream to a
controller for controlling operation of the heater, and controlling
the heater in response to the temperature signal.
18. A method for treating diesel exhaust gases, comprising:
producing a diesel exhaust stream with a diesel engine; removing
particulates from the exhaust stream with a diesel particulate
filter downstream of the engine; causing NOx reduction in the
exhaust stream with a NOx reduction catalyst; and delivering energy
from a heater upstream of the NOx reduction catalyst sufficient to
raise a temperature of the NOx reduction catalyst to a temperature
in an optimal range for NOx reduction by the NOx reduction
catalyst.
19. The method as set forth in claim 18, comprising delivering
energy from the heater sufficient to elevate the temperature of the
exhaust stream to a temperature sufficient to cause active
regeneration of the filter.
20. The method as set forth in claim 18, comprising sensing a
temperature in the exhaust stream and sending a signal
corresponding to the temperature in the exhaust stream to a
controller for controlling operation of the heater, and controlling
the heater in response to the temperature signal.
Description
BACKGROUND AND SUMMARY
[0001] The present invention relates, generally, to systems and
methods for treating diesel exhaust gases and, more particularly,
to systems and methods for treating non-stationary diesel exhaust
gases.
[0002] Diesel engines tend to have low emissions of gas phase
hydrocarbons and carbon monoxide, however, they tend to have
relatively high emissions of nitrogen oxides (NOx) and
particulates. As standards for NOx and particulate emissions become
more stringent, it is increasingly important to devise strategies
for reducing these emissions.
[0003] In diesel engines, a DPF can be used downstream of the
engine to filter particulates from the engine exhaust. If too much
soot collects in the DPF, the soot can burn in an uncontrolled
manner and may crack or melt the DPF. This phenomenon is sometimes
referred to as a "runaway" or uncontrolled regeneration. Other
problems can result from excessive soot accumulation in the DPF as
well, such as an increase in engine backpressure, which can have an
adverse effect on engine operation and affect fuel consumption.
[0004] To avoid aforementioned problems such as runaway
regenerations, the DPF is periodically cleaned by burning off the
soot, through a so-called active regeneration operation in a
controlled manner that does not ordinarily do serious damage the
DPF. Carbon in the filter reacts with NO.sub.2 in the exhaust gas
stream by the reactions NO.sub.2+C->NO+CO and
2NO.sub.2+2C->N.sub.2+CO.sub.2. To achieve the desirable
reaction, 2NO.sub.2+2C->N.sub.2+CO.sub.2, the carbon soot
particles typically require temperatures in excess of
500-550.degree. C. Those temperatures are much higher than typical
diesel exhaust temperatures.
[0005] A solution to this problem is to install a heater, such as a
burner or electrical coils, upstream of the DPF to raise the
exhaust stream temperature to a temperature suitable for
regeneration, a technique typically referred to as "active"
regeneration. Active regeneration results in some efficiency losses
and thermal stress on the filter, and it is desirable to limit its
use. Also, care must be taken to ensure that "runaway"
regeneration, essentially uncontrolled combustion, does not occur
and cause damage to the filter.
[0006] An alternative to active regeneration is so-called passive
regeneration. The reaction between the accumulated particles and
oxygen in the exhaust stream (usually in the form of O.sub.2 and
NO.sub.2) ordinarily naturally results in some of the particles
oxidizing. However, at ordinary exhaust temperatures, passive
regeneration generally occurs too slowly to remove accumulated
particles. To provide sufficient passive regeneration to keep the
DPF operating efficiently, a catalyst can be used. The catalyst can
be a so-called diesel oxidation catalyst (DOC) that can be provided
upstream of or on the DPF and causes NO in the exhaust stream to
convert to NO.sub.2, thereby facilitating passive regeneration when
the NO.sub.2 reacts with the particles in the DPF.
[0007] To reduce NOx emissions, NOx catalysts such as selective
catalytic reduction catalysts (SCR) or lean NOx catalysts (LNC) can
be provided in the exhaust stream. SCR catalysts are presently most
common and can be very efficient at reducing NOx emissions to
N.sub.2 using NH.sub.3 over a catalyst such as zeolite or V/Ti.
However, these catalysts typically operate most efficiently at
relatively high temperatures, such as >300.degree. C., which is
often above the exhaust temperature for a diesel engine used in a
vehicle application.
[0008] It is desirable to provide a system and method for treating
diesel exhaust gases that can efficiently remove particulate matter
and reduce NOx emissions.
[0009] According to an aspect of the present invention, a system
for treating diesel exhaust gases comprises an engine for producing
a diesel exhaust stream, a diesel particulate filter downstream of
the engine and adapted to remove particulates from the exhaust
stream, a heater upstream of the filter adapted to deliver energy
in sufficient amounts to the exhaust stream to cause active
regeneration of the filter, and a diesel oxidation catalyst
upstream of the heater adapted to cause passive regeneration of the
filter when the exhaust stream is above a light-off temperature of
the diesel oxidation catalyst.
[0010] According to another aspect of the invention, a system for
treating diesel exhaust gases comprises an engine for producing a
diesel exhaust stream, a diesel particulate filter downstream of
the engine and adapted to remove particulates from the exhaust
stream, a heater upstream of the filter adapted to deliver energy
to the exhaust stream, and a NOx reduction catalyst downstream of
the heater.
[0011] According to yet another aspect of the invention, a method
for treating diesel exhaust gases comprises producing a diesel
exhaust stream with a diesel engine, removing particulates from the
exhaust stream with a diesel particulate filter downstream of the
engine, periodically delivering energy from a heater to the exhaust
stream upstream of the filter in sufficient amounts to cause active
regeneration of the filter, and periodically heating a diesel
oxidation catalyst upstream of the heater to a light-off
temperature of the diesel oxidation catalyst to cause passive
regeneration of the filter.
[0012] According to still another aspect of the invention, a method
for treating diesel exhaust gases comprises producing a diesel
exhaust stream with a diesel engine, removing particulates from the
exhaust stream with a diesel particulate filter downstream of the
engine, causing NOx reduction in the exhaust stream with a NOx
reduction catalyst, and delivering energy from a heater upstream of
the NOx reduction catalyst sufficient to raise a temperature of the
NOx reduction catalyst to a temperature in an optimal range for NOx
reduction by the NOx reduction catalyst.
BRIEF DESCRIPTION OF THE DRAWING
[0013] The features and advantages of the present invention are
well understood by reading the following detailed description in
conjunction with the drawing in which like numerals indicate
similar elements and in which:
[0014] FIG. 1 is a schematic view of a system for treating diesel
exhaust gases according to an aspect of the present invention;
and
[0015] FIG. 2 is a schematic view of a system for treating diesel
exhaust gases according to another aspect of the present
invention.
DETAILED DESCRIPTION
[0016] A system for treating diesel exhaust gases according to an
aspect of the present invention is seen in FIG. 1. The system 21
includes an engine 23 for producing a diesel exhaust stream. A
diesel particulate filter (DPF) 25 is disposed in an exhaust line
27 downstream of the engine and is adapted to remove particulates
from the exhaust stream. A heater 29 is disposed upstream of the
DPF 25 and is adapted to deliver energy in sufficient amounts to
the exhaust stream to cause active regeneration of the DPF. The
heater 29 can be of any suitable type, such as a burner, electrical
coils, or a diesel oxidation catalyst.
[0017] A diesel oxidation catalyst (DOC) 31 is disposed upstream of
the heater 29 and is adapted to cause passive regeneration of the
DPF when the exhaust stream is above a light-off temperature of the
DOC. If the heater 29 includes a diesel oxidation catalyst, the DOC
31 is a different diesel oxidation catalyst. A diesel oxidation
catalyst forming part or all of the heater 29 will be of a type
adapted to raise temperatures upstream of the DPF 25 to
temperatures sufficient to cause active regeneration. The DOC 31
will typically be of a type that is adapted to cause NO in the
exhaust stream to form NO.sub.2, usually at ordinary diesel exhaust
temperatures.
[0018] In the system 21 according to this aspect, regeneration of
the DPF 25 can occur through passive regeneration when exhaust
stream temperatures are above the light-off temperature of the DOC
31 and, when exhaust stream temperatures are too low to permit for
adequate passive regeneration, the heater 29 can be operated to
cause active regeneration. It is ordinarily desirable to increase
exhaust stream temperatures to about 650.degree. C. upstream of the
DPF 25 for active regeneration, however, an oxidation catalyst can
be provided on the DPF, in which case temperature of the exhaust
stream can be lower, such as around 600-625.degree. C.
[0019] A NOx reduction catalyst 33 (shown in phantom) can be
provided downstream of the heater 29. The NOx reduction catalyst 33
will ordinarily be provided downstream of the DPF 25. The heater 29
can be adapted to elevate the exhaust stream temperature to a
temperature in an optimal range for NOx reduction by the catalyst,
such as a temperature greater than 300.degree. C. When an oxidation
catalyst is provided on the DPF 25, it can be of a type designed to
produce a desired ratio of the NO/NO.sub.2 (usually about 1:1) for
a fast, low temperature NOx reduction across the NOx reduction
catalyst. Providing an oxidation catalyst on the DPF 25 can lower
the temperature required for active regeneration of the DPF, and
can condition the exhaust gas going into the NOx reduction catalyst
33. In addition, the oxidation catalyst on the DPF 25 can be
formulated to increase passive regeneration activity in the DPF
when the catalyst light-off temperature is met, regardless whether
there is DOC upstream of the heater.
[0020] A controller 35, such as a suitable computer, can be
provided for controlling operation of the heater 29. A temperature
sensor 37 can be provided for sensing a temperature in the exhaust
stream. The temperature sensor 37 can send a signal corresponding
to the temperature in the exhaust stream to the controller 35, and
the controller can control the heater in response to the
temperature signal. For example, if the temperature sensor 37 sends
a signal to the controller 35 corresponding to a temperature below
the light-off temperature of the DOC, and the controller determines
that the temperature has been below the light-off temperature for a
sufficient period of time (not necessarily a continuous length of
time) such that, according to models for the particular system
which may consider other factors such as backpressure, it is
expected that regeneration of the DPF 25 is required, the
controller can initiate control the heater 29 to deliver energy
sufficient to cause active regeneration of the DPF.
[0021] A signal to the controller 35 from the temperature sensor 37
can also be used to cause the controller to control the heater 29
to deliver only enough energy to elevate the exhaust stream
temperature to an optimal temperature range for NOx reduction. The
controller 35 may also receive a signal from a NOx sensor 39 that
can provide a signal to the controller to cause the controller to
control the heater 29 to deliver sufficient heat to the exhaust
stream to reduce the NOx level. The controller 35 can control the
heater 29 in response to a variety of signals and inputs, including
one or both of temperature and NOx levels from the temperature
sensor 38 and the NOx sensor 39. There can, of course, be multiple
temperature sensors, multiple NOx sensors, and multiple other
sensors throughout the system 21 and the heater 29 can be
controlled to optimize catalyst performance or regeneration as
required.
[0022] In a method for treating diesel exhaust gases according to
an aspect of the invention, a diesel exhaust stream is produced and
particulates are removed from the exhaust stream with a diesel
particulate DPF 25 downstream of the engine 23. A heater 29
periodically delivers energy to the exhaust stream upstream of the
DPF 25 in sufficient amounts to cause active regeneration of the
DPF. A DOC 31 upstream of the heater 29 is periodically heated to a
light-off temperature of the DOC to cause passive regeneration of
the DPF. The DOC 31 can be heated to the light-off temperature by
any suitable means, such as by increasing the load on the engine 23
so that the engine exhaust stream is hotter, or heating the exhaust
stream with another heater (not shown). A NOx reduction catalyst 33
can be provided to remove NOx from the exhaust stream downstream of
the heater 29.
[0023] A temperature in the exhaust stream can be sensed by the
temperature sensor 37 which can send a signal corresponding to the
temperature in the exhaust stream to the controller 35 for
controlling operation of the heater 29. The heater 29 can be
controlled by the controller 35 in response to the temperature
signal for tuning the temperature of the exhaust stream to achieve
optimal DPF 25 regeneration temperatures (whether for a catalyzed
or uncatalyzed DPF) and/or optimal temperatures for NOx reduction
by the particular NOx reduction catalyst 33.
[0024] FIG. 2 shows a system 121 for treating diesel exhaust gases
according to another aspect of the present invention. The system
121 includes an engine 123 for producing a diesel exhaust stream, a
DPF 125 in an exhaust line 127 downstream of the engine and adapted
to remove particulates from the exhaust stream, a heater upstream
129 of the DPF adapted to deliver energy to the exhaust stream, and
a NOx reduction catalyst 133 downstream of the heater.
[0025] The system 121 can be arranged to tune the amount of energy
delivered to the exhaust stream by the heater 129 to achieve
optimal performance of the NOx reduction catalyst 133. In addition
to being able to deliver sufficient energy to the exhaust stream to
optimize performance of the NOx reduction catalyst, the heater 129
can be arranged to tune the amount of energy delivered to the
exhaust stream by the heater to cause active regeneration of the
DPF 125, usually about 650.degree. C. upstream of the DPF for an
uncatalyzed DPF and about 600-626.degree. C. for a catalyzed DPF
having a diesel oxidation catalyst coating.
[0026] A DOC 131 (shown in phantom) can be provided upstream of the
heater 129. The DOC 131 can be adapted to cause passive
regeneration of the DPF 125 when the exhaust stream is above a
light-off temperature of the DOC.
[0027] A controller 135 can be provided for controlling operation
of the heater 129. A temperature sensor 137 can be provided for
sensing a temperature in the exhaust stream and sending a signal
corresponding to the temperature in the exhaust stream to the
controller 135. The controller 135 can control the heater 129 in
response to the temperature signal to achieve optimal performance
of the NOx reduction catalyst and/or to cause active regeneration
of the DPF. Other sensors, such as a NOx sensor 139, can be
provided to provide input to the controller 135 for determining
when operation of the heater 129 should be initiated, usually based
upon modeling for the particular system involved.
[0028] In a method for treating diesel exhaust gases according to
an aspect of the present invention, a diesel exhaust stream is
produced by an engine 123. Particulates are removed from the
exhaust stream with the diesel particulate DPF 125 downstream of
the engine 123. The NOx reduction catalyst 133 reduces NOx
emissions in the exhaust stream. Energy can be delivered to the
exhaust stream from a heater 129 upstream of the NOx reduction
catalyst 133 sufficient to raise a temperature of the NOx reduction
catalyst to a temperature in an optimal range for NOx reduction by
the NOx reduction catalyst. Energy can also/instead be delivered to
the exhaust stream from the heater 129 in sufficient amounts to
elevate the temperature of the exhaust stream to a temperature
sufficient to cause active regeneration of the DPF 125. A
controller 135 can control operation of the heater 129 to tune
delivery of energy to the exhaust gas stream to obtain optimal
temperatures for NOx reduction and/or to reach temperatures for
active regeneration of the DPF 125.
[0029] In the present application, the use of terms such as
"including" is open-ended and is intended to have the same meaning
as terms such as "comprising" and not preclude the presence of
other structure, material, or acts. Similarly, though the use of
terms such as "can" or "may" is intended to be open-ended and to
reflect that structure, material, or acts are not necessary, the
failure to use such terms is not intended to reflect that
structure, material, or acts are essential. To the extent that
structure, material, or acts are presently considered to be
essential, they are identified as such.
[0030] While this invention has been illustrated and described in
accordance with a preferred embodiment, it is recognized that
variations and changes may be made therein without departing from
the invention as set forth in the claims.
* * * * *