U.S. patent application number 10/397051 was filed with the patent office on 2003-10-02 for integrated non-thermal plasma reactor-diesel particulate filter.
Invention is credited to Bonadies, Joseph V., Goulette, David Alexander.
Application Number | 20030182930 10/397051 |
Document ID | / |
Family ID | 28457235 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030182930 |
Kind Code |
A1 |
Goulette, David Alexander ;
et al. |
October 2, 2003 |
Integrated non-thermal plasma reactor-diesel particulate filter
Abstract
An integrated non-thermal plasma reactor-diesel particulate
filter exhaust treatment apparatus 10 comprises a wall flow-type
substrate 12 including a plurality of alternating high voltage 20
and ground electrode layers 22 and filter layers 24 disposed
between said high voltage 20 and ground electrode layers 22.
Channels 34 extending through the electrode layers 20, 22 are
plugged to prevent exhaust flow. A portion of the exhaust channels
18 extending through the filter layers 23 are plugged 26 such that
each channel 18 is plugged only at one end 14 or 16. During
operation, a plasma is generated in the filter layers 24. An
exhaust stream 28 is passed through the filter channels 18 and
nitrogen oxides in the exhaust stream 28 are converted in the
plasma primarily to NO.sub.2 while particulate matter in the
exhaust stream 28 is captured in the porous channel walls 19. The
filter 24 is continuously regenerated by NO.sub.2 formed in the
plasma. NO byproduct from the filter regeneration is converted back
into NO.sub.2 via plasma.
Inventors: |
Goulette, David Alexander;
(Marine City, MI) ; Bonadies, Joseph V.;
(Clarkston, MI) |
Correspondence
Address: |
VINCENT A. CICHOSZ
DELPHI TECHNOLOGIES, INC.
Legal Staff, Mail Code: 480-410-202
P.O. Box 5052
Troy
MI
48007-5052
US
|
Family ID: |
28457235 |
Appl. No.: |
10/397051 |
Filed: |
March 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60368403 |
Mar 28, 2002 |
|
|
|
Current U.S.
Class: |
60/275 ; 60/295;
60/297; 60/311 |
Current CPC
Class: |
F01N 3/0231 20130101;
F01N 2240/28 20130101 |
Class at
Publication: |
60/275 ; 60/297;
60/295; 60/311 |
International
Class: |
F01N 003/00; F01N
003/02 |
Claims
1. An integrated non-thermal plasma reactor-diesel particulate
filter exhaust treatment apparatus 10 comprising: a wall flow-type
substrate 12 having an exhaust inlet 14, an exhaust outlet 16, and
a plurality of parallel exhaust channels 18 extending through said
substrate 12; said substrate 12 having a plurality of layers
arranged in an alternating fashion comprising a high voltage
electrode layer 20; a ground electrode layer 22; and a filter layer
24 disposed between said high voltage electrode layer 20 and said
ground electrode layer 22; electrode layer channels 30 extending
through said high voltage electrode layers 20 and said ground
electrode layers 22 being plugged to prevent exhaust flow therein;
and a portion of said parallel channels 18 at exhaust inlet end 14
and exhaust outlet 16 being plugged 26 in an arrangement wherein
each channel 18 is plugged only at one end; wherein during
operation of said apparatus 10, a plasma is generated in said
filter layers 24 and an exhaust stream 28 to be treated enters at
said inlet 14, flows through said filter channels 18 and through
porous channel walls 19, and exits at said outlet 16 as a treated
exhaust stream 50; nitrogen oxides in said exhaust stream 28 being
converted in said plasma primarily to NO.sub.2; particulate matter
in said exhaust stream 28 being captured in said porous channel
walls 19; said filter layers 24 being continuously regenerated by
said plasma and by said NO.sub.2 formed in said plasma; and NO
byproduct from said filter generation being converted back into
NO.sub.2 via plasma at said outlet ends 16 of said exhaust channels
18.
2. The apparatus 10 of claim 1, wherein said wall flow substrate 12
is made of cordierite.
3. The apparatus 10 of claim 1, wherein alternating channels 26 in
said filter layers 24 are plugged to provide a checkered-type
pattern of plugged channels 26 and unplugged exhaust channels
18.
4. The apparatus 10 of claim 1, wherein said exhaust stream 28 to
be treated comprises an exhaust stream from a coal fired furnace,
an oil fired furnace, a reciprocating internal combustion engine, a
gasoline spark ignition engine, a diesel engine, or a gas turbine
engine.
5. The apparatus 10 of claim 1, wherein said exhaust stream to be
treated 28 comprises a diesel engine exhaust stream.
6. The apparatus of claim 1, comprising: high voltage electrode
layers 66 and said ground electrode layers 68 comprising dielectric
barrier electrode layers 62 to provide an integrated non-thermal
plasma reactor-diesel particulate filter exhaust treatment
apparatus 60.
7. A combustion exhaust treatment system 44 comprising: the
integrated non-thermal plasma reactor-diesel particulate filter
exhaust treatment apparatus 10 of claim 1, said apparatus 10 being
in fluid communication with an exhaust outlet 48 of a combustion
device 46; a short pulse power source 42 connected to said
integrated nonthermal plasma reactor-diesel particulate filter
apparatus 10 and a catalytic converter 52 having a catalyst for
reducing nitrogen oxides in an exhaust stream, said catalytic
converter 52 having an inlet 54 connected to said integrated
non-thermal plasma reactor-diesel particulate filter apparatus 10
for receiving a plasma and particulate treated exhaust stream 50
and an outlet 56 for emitting a catalyst treated exhaust stream
58.
8. A combustion exhaust treatment system 70 comprising: the
integrated non-thermal plasma reactor-diesel particulate filter
exhaust treatment apparatus 10 of claim 1, having high voltage
electrode layers 66 and ground electrode layers 68 comprising
dielectric barrier electrode layers 62 to provide an integrated
non-thermal plasma reactor-diesel particulate filter exhaust
treatment apparatus 60, said apparatus 60 being in fluid
communication with an exhaust outlet 48 of a combustion device 46;
an alternating current power source 72 connected to said integrated
non-thermal plasma reactor-diesel particulate filter apparatus 60;
and a catalytic converter 52 having a catalyst for reducing
nitrogen oxides in an exhaust stream, said catalytic converter 52
having an inlet 54 connected to said integrated non-thermal plasma
reactor-diesel particulate filter apparatus 60 for receiving a
plasma and particulate treated exhaust stream 50 and an outlet 56
for emitting a catalyst treated exhaust stream 58.
9. A method for treating particulate matter and nitrogen oxides in
a combustion exhaust stream 28 comprising: passing a combustion
exhaust stream 28 through an integrated non-thermal plasma
reactor-diesel particulate filter exhaust treatment apparatus 10
comprising: a wall flow-type substrate 12 having an exhaust inlet
14, an exhaust outlet 16, and a plurality of parallel exhaust
channels 18 extending through said substrate 12; said substrate 12
having a plurality of layers arranged in an alternating fashion
comprising a high voltage electrode layer 20; a ground electrode
layer 22; and a filter layer 24 disposed between said high voltage
electrode layer 20 and said ground electrode 22; electrode layer
channels 34 extending through said high voltage electrode layers 20
and said ground electrode layers 22 being plugged to prevent
exhaust flow therein; and a portion of said exhaust channels 18 at
said exhaust inlet 14 and said exhaust outlet 16 being plugged in
an arrangement wherein each exhaust channel 18 is plugged only at
one end; generating a plasma in said filter layers 24 of said
apparatus 10 wherein said exhaust stream 28 to be treated enters at
said inlet 14, flows through said exhaust channels 18 and through
porous channels walls 19, and exits at said outlet 16 as a plasma
and particulate treated exhaust stream 50; whereby nitrogen oxides
in said exhaust stream 28 are converted in said plasma primarily to
NO.sub.2; particulate matter in said exhaust stream 28 is captured
in said porous channel walls 19; and said filter layers 24 are
continuously regenerated by said plasma and by said NO.sub.2 formed
in said plasma; and NO byproduct from said filter generation are
converted back into NO.sub.2 via plasma primarily at said outlet
ends 16 of said exhaust channels 18.
10. The method of claim 9, wherein said wall flow substrate 12 is
made of cordierite.
11. The method of claim 9, wherein alternating exhaust channels 18
in said filter layers 24 are plugged to provide a checkered-type
pattern of plugged channels 26 and unplugged exhaust channels
18.
12. The method of claim 9, wherein said exhaust stream 28 to be
treated comprises an exhaust stream from a coal fired furnace, an
oil fired furnace, a reciprocating internal combustion engine, a
gasoline spark ignition engine, a diesel engine, or a gas turbine
engine.
13. The method of claim 9, wherein said exhaust stream to be
treated 28 comprises a diesel engine exhaust stream.
14. The method of claim 9, further comprising: further treating
said plasma and particulate treated exhaust stream 50 in a
catalytic converter 52 having a catalyst for reducing nitrogen
oxides in an exhaust stream; said catalytic converter 52 having an
inlet 54 connected to said integrated non-thermal plasma
reactor-diesel particulate filter apparatus 10 for receiving said
plasma and particulate treated exhaust stream 50 and an outlet 56
for emitting a catalyst treated exhaust stream 56.
15. The method of claim 9, wherein said integrated nonthermal
plasma reactor-diesel particulate filter exhaust treatment
apparatus 10 comprising is powered by a short pulse power supply
42.
16. The method of claim 9, wherein said high voltage electrode
layers 66 and said ground electrode layers 65 comprise dielectric
barrier electrode layers 62 providing an integrated non-thermal
plasma reactor-diesel particulate filter 60.
17. The method of claim 9, wherein said high voltage electrode
layers 66 and said ground electrode layers 65 comprise dielectric
barrier electrode layers 62 providing an integrated non-thermal
plasma reactor-diesel particulate filter 60; and wherein said
integrated non-thermal plasma reactor-diesel particulate filter
exhaust treatment apparatus 60 is powered by an alternating current
power supply 72.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application No. 60/368,403 (Attorney Docket No. DP-305558), of
David A. Goulette, et al., filed Mar. 28, 2002, entitled "Non
Thermal Plasma Reactor/DPF," which is hereby incorporated by
reference herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to combustion
exhaust treatment and more particularly relates to an integral
non-thermal plasma reactor-diesel particulate filter apparatus.
BACKGROUND OF THE INVENTION
[0003] Certain compounds in the exhaust stream of a combustion
process, such as the exhaust stream from an internal combustion
engine, are undesirable in that they are thought to produce adverse
health effects and must be controlled in order to meet government
emissions regulations. Among the regulated compounds are
hydrocarbons, soot particulates, and nitrogen oxide compounds
(NOx). There are a wide variety of combustion processes producing
these emissions, for instance, coal-or oil-fired furnaces,
reciprocating internal combustion engines (including gasoline spark
ignition and diesel engines), gas turbine engines, and so on. In
each of these combustion processes, control measures to prevent or
diminish atmospheric emissions of these emissions are needed.
[0004] Industry has devoted considerable effort to reducing
regulated emissions from the exhaust streams of combustion
processes. In particular, it is now usual in the automotive
industry to place a catalytic converter in the exhaust system of
gasoline spark ignition engines to remove undesirable emissions
from the exhaust by chemical treatment. Typically, a "three-way"
catalyst system of platinum, palladium, and rhodium metals
dispersed on an oxide support is used to oxidize carbon monoxide
and hydrocarbons to water and carbon dioxide and to reduce nitrogen
oxides to nitrogen. The catalyst system is applied to a ceramic
substrate such as beads, pellets, or a monolith. When used, beads
are usually porous, ceramic spheres having the catalyst metals
impregnated in an outer shell. The beads or pellets are of a
suitable size and number in the catalytic converter in order to
place an aggregate surface area in contact with the exhaust stream
that is sufficient to treat the compounds of interest. When a
monolith is used, it is usually a cordierite honeycomb monolith and
may be pre-coated with gamma-alumina and other specialty oxide
materials to provide a durable, high surface area support phase for
catalyst deposition. The honeycomb shape, used with the parallel
channels running in the direction of the flow of the exhaust
stream, both increases the surface area exposed to the exhaust
stream and allows the exhaust stream to pass through the catalytic
converter without creating undue back pressure that would interfere
with operation of the engine.
[0005] When a spark ignition engine is operating under
stoichiometric conditions or nearly stoichiometric conditions with
respect to the fuel-air ratio (just enough oxygen to completely
combust the fuel, or perhaps up to 0.3% excess oxygen), a
"three-way" catalyst has proven satisfactory for reducing
emissions. Unburned fuel (hydrocarbons) and carbon monoxide are
oxidized consuming relatively small amount of oxygen, while oxides
of nitrogen (NOx) are simultaneously reduced. However, it is
desirable to operate the engine at times under lean burn
conditions, with excess air, in order to improve fuel economy.
Under lean burn conditions, conventional catalytic devices are not
effective for reducing the NOx in the oxygen-rich exhaust
stream.
[0006] A diesel engine has substantially lower fuel consumption
than a spark ignition engine, particularly at light loads. The
exhaust stream from a diesel engine also has substantial oxygen
content, from perhaps about 2-18% oxygen, and, in addition,
contains a significant amount of particulate emissions. The
particulate emissions, or soot, are thought to be primarily
carbonaceous particles and volatile organic compounds (VOC). While
diesel combustion process developments have been made that
successfully decrease the total mass of particulates emitted, these
modifications may have actually increased the numbers of smaller
nanoparticles which are a particular health concern as they can
travel deep into the lungs.
[0007] In spite of efforts over the last decade to develop an
effective catalyst for reducing NOx to nitrogen under oxidizing
conditions in a spark ignition gasoline engine and in a diesel
engine, the need for improved conversion effectiveness has remained
unsatisfied. Moreover, there is a continuing need for improved
effectiveness in treating emissions from any combustion process,
particularly for simultaneously treating the nitrogen oxides and
soot particulate emissions from diesel engines. Several techniques
have been proposed to modify the exhaust chemistry enabling the use
of existing catalyst technology. However, these techniques can add
considerable cost and complexity to the vehicle.
[0008] One technique that has been successfully applied in large
stationary applications comprises injecting urea into the exhaust
stream ahead of the catalytic converter where it quickly decomposes
to ammonia. The ammonia reacts with NO and N0.sub.2 in the exhaust
stream on the catalytic converter surface to form N.sub.2 and
H.sub.2O. Some of the challenges presented when using this
technology include: (1) storing the aqueous urea solution onboard
and preventing it from freezing under cold ambient temperature
conditions; (2) correctly metering the urea solution into the
exhaust (too much urea can result in ammonia emissions, too little
urea can cause high NOx emissions); and (3) replenishing the
urea--this requires establishing a supply network to distribute
urea and customer acceptance of the expense and inconvenience in
maintaining an adequate urea supply onboard the vehicle.
[0009] Another approach comprises adding a NOx adsorbent to the
catalyst washcoat to adsorb NOx emissions from the exhaust stream
during lean conditions. The adsorbed NOx must be periodically
purged by shifting the air/fuel ratio from lean to slightly rich
causing the adsorbent to release the adsorbed NOx which is reduced
to nitrogen by the catalyst in the now rich exhaust stream. This
technique presents significant control problems as the air and fuel
rates must be simultaneously modified by the engine control system
to effect the air-fuel ratio change without altering the engine
load. The heterogeneous combustion diesel engine has an even more
challenging additional problem of generating extremely heavy
amounts of particulate emissions at air-fuel ratios near
stoichiometric or rich conditions.
[0010] Particulate filters have been shown to be an effective means
for controlling diesel particulate emissions. Wall flow particulate
filters have been developed over the past twenty years and can be
greater than 90% efficient in trapping particulate matter including
nanoparticles. Such filters comprise endplugged honeycomb
structures and are known as "wall flow" filters because the flow
paths resulting from alternate channel plugging require the fluid
being treated to flow through the porous ceramic cell walls prior
to exiting the filter. The honeycomb structures have a portion of
the cells plugged to allow better flow through the porous walls. A
portion of the cells at the inlet end and outlet end (or face) are
plugged in an arrangement wherein each cell is plugged only at one
end. The preferred arrangement is to have every other cell on a
given face plugged as in a checkered patter. The honeycomb
structures may be made of any suitable material, such as ceramic,
glass-ceramic, or metal. Especially preferred are ceramic
materials, such as those that yield cordierite, mullite, or
mixtures thereof on firing. The honeycomb structures are typically
circular or square in cross-section. However, other shapes such as
oval and rectangular may be suitable as dictated by the particular
exhaust system.
[0011] The principle disadvantage with particulate filters is the
need to periodically regenerate the filter to remove the trapped
particulate matter. Regeneration removes particulate matter from
the filter by oxidizing the carbon and volatile organic compounds
(VOCs) to carbon dioxide and water. This oxidation occurs
spontaneously at temperatures above about 600.degree. C. Diesel
exhaust temperatures are typically not hot enough to initiate
spontaneous regeneration, particularly in light load operating
conditions where exhaust temperatures may seldom exceed 200.degree.
C. Thus, a regeneration technique which is initiated at much lower
temperatures and is controlled to limit the particulate filter
temperature increase is required.
[0012] During particulate oxidation in the diesel particulate
filter, some of the NO.sub.2 created in an upstream non-thermal
plasma reactor is converted back to NO. However, in order to get
the most benefit from an NO.sub.2 catalyst, the exhaust feedstream
must be mostly NO.sub.2.
[0013] There is a continuing need for improved effectiveness in
treating emissions from any combustion process, particularly for
treating nitrogen oxide and soot emissions from diesel engines.
SUMMARY OF THE INVENTION
[0014] A first embodiment of the present integrated non-thermal
plasma reactor-diesel particulate filter exhaust treatment
apparatus is suitable for use with a short pulse power supply and
comprises:
[0015] a wall flow-type substrate having an exhaust inlet, an
exhaust outlet, and a plurality of parallel channels extending
through the substrate;
[0016] the substrate having a plurality of layers arranged in an
alternating fashion comprising a high voltage electrode layer; a
ground electrode layer; and a filter layer disposed between the
high voltage electrode layer and the ground electrode;
[0017] channels extending through the high voltage electrode layers
and the ground electrode layers being plugged to prevent exhaust
flow therein; and
[0018] channels extending through the filter layers serving as
exhaust flow channels, a portion of the channels at the exhaust
inlet ends and exhaust outlet ends being plugged in an arrangement
wherein each channel is plugged only at one end;
[0019] wherein during operation of the apparatus, a plasma is
generated in the filter layers and an exhaust stream to be treated
enters at the exhaust inlet, flows through the filter channels and
through the porous filter channel walls, and exits at the outlet as
a treated exhaust stream;
[0020] whereby nitrogen oxides in the exhaust stream are converted
in the plasma primarily to NO.sub.2; particulate matter in the
exhaust stream is captured in the porous channel walls; the filter
is continuously regenerated by the plasma and the NO.sub.2 formed
in the plasma; and NO byproduct from the filter regeneration is
converted back into NO.sub.2 via plasma at the outlet ends of the
exhaust channels.
[0021] A second embodiment of the present invention provides an
apparatus suitable for use with a traditional high voltage
alternating current power supply. The second embodiment of the
present integrated non-thermal plasma reactor-diesel particulate
filter exhaust treatment apparatus comprises:
[0022] a wall flow-type substrate having an exhaust inlet, an
exhaust outlet, and a plurality of parallel channels extending
through the substrate;
[0023] the substrate having a plurality of layers arranged in an
alternating fashion comprising a high voltage electrode layer; a
ground electrode layer; and a filter layer disposed between the
high voltage electrode layer and the ground electrode;
[0024] wherein said high voltage electrode layers and said ground
electrode layers comprise dielectric barrier electrode layers;
[0025] channels extending through the high voltage electrode layers
and the ground electrode layers being plugged to prevent exhaust
flow therein; and
[0026] channels extending through the filter layers serving as
exhaust flow channels, a portion of the channels at the exhaust
inlet ends and exhaust outlet ends being plugged in an arrangement
wherein each channel is plugged only at one end;
[0027] wherein during operation of the apparatus, a plasma is
generated in the filter layers and an exhaust stream to be treated
enters at the exhaust inlet, flows through the filter channels and
through the porous filter channel walls, and exits at the outlet as
a treated exhaust stream;
[0028] whereby nitrogen oxides in the exhaust stream are converted
in the plasma primarily to NO.sub.2; particulate matter in the
exhaust stream is captured in the porous channel walls; the filter
is continuously regenerated by the plasma and the NO.sub.2 formed
in the plasma; and NO byproduct from the filter regeneration is
converted back into NO.sub.2 via plasma at the outlet ends of the
exhaust channels.
[0029] A combustion exhaust treatment system comprising the
integrated non-thermal plasma reactor-diesel particulate filter
exhaust treatment apparatus includes the apparatus disposed in
fluid communication with an exhaust outlet of a combustion
device;
[0030] a high voltage power source connected to the integrated
nonthermal plasma reactor-diesel particulate filter apparatus;
and
[0031] a catalytic converter having a catalyst for reducing
nitrogen oxides in an exhaust stream, the catalytic converter
having an inlet connected to the integrated non-thermal plasma
reactor-diesel particulate filter apparatus for receiving a plasma
and particulate treated exhaust stream and an outlet for emitting a
catalyst treated exhaust stream.
[0032] A method for treating particulate matter and nitrogen oxides
in a combustion exhaust stream comprises:
[0033] passing a combustion exhaust stream through an integrated
nonthermal plasma reactor-diesel particulate filter exhaust
treatment apparatus including a wall flow-type substrate having an
exhaust inlet, an exhaust outlet, and a plurality of parallel
channels extending through the substrate;
[0034] the substrate having a plurality of layers arranged in an
alternating fashion comprising a high voltage electrode layer; a
ground electrode layer; and a filter layer disposed between the
high voltage electrode layer and the ground electrode,
[0035] channels extending through the high voltage electrode layers
and the ground electrode layers being plugged to prevent exhaust
flow therein; and
[0036] a portion of the channels at the exhaust inlet end and
exhaust outlet end being plugged in an arrangement wherein each
channel is plugged only at one end;
[0037] generating a plasma in the filter layers wherein the exhaust
stream to be treated enters at the inlet face, flows through the
filter channels and through the porous channels walls, and exits at
the outlet face as a plasma and particulate treated exhaust
stream;
[0038] whereby nitrogen oxides in the exhaust stream are converted
in plasma primarily to NO.sub.2; particulate matter in the exhaust
stream is captured in the porous channel walls; the filter layers
are continuously regenerated by the plasma and the NO.sub.2 formed
in the plasma; and NO byproduct from the filter regeneration is
converted back into NO.sub.2 via plasma primarily at the outlet
ends of the exhaust channels.
[0039] The present invention combines three major mechanisms for
diesel particulate filter cleaning and NOx reduction. First, NO
present in a diesel exhaust stream is converted to NO.sub.2 inside
the diesel particulate filter inlet channels. The converted
NO.sub.2 then reacts with trapped soot to clean the diesel
particulate filter. Second, the trapped soot is also contained
inside the plasma generated in the filter layers which also acts to
keep the diesel particulate filter clean by direct carbon removal.
Third, the exit channels of the diesel particulate filter are in
plasma which converts any NO made from the diesel particulate
filter regeneration back into NO.sub.2 for reduction by an NO.sub.2
catalyst.
[0040] The present invention provides the advantage of integration
of two significant exhaust treatment functions into one. The
present integrated non-thermal plasma reactor-diesel particulate
filter apparatus provides the advantage of generating appropriate
levels of NO.sub.2 for providing reliable filter regeneration at a
"low" temperature (below about 250.degree. C.). In addition, the
non-thermal plasma function of the integrated apparatus generates
other species which may also contribute to the oxidation of soot at
low temperatures. The invention eliminates the problem of NO back
reactions in the diesel particulate filter which reduces deNOx
catalyst functioning. Further, the present system is advantageously
less complex and requires fewer components than previously known
systems.
[0041] These and other features and advantages of the invention
will be more fully understood from the following description of
certain specific embodiments of the invention taken together with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Referring now to the drawings, which are meant to be
exemplary, not limiting, and wherein like elements are numbered
alike in the several Figures:
[0043] FIG. 1 shows an integrated non-thermal plasma reactor-diesel
particulate filter exhaust treatment apparatus in accordance with
the present invention.
[0044] FIG. 2 is a top sectional view taken along the line 2-2 in
FIG. 1 of a filter layer of the apparatus of FIG. 1.
[0045] FIG. 3 is a top sectional view taken along the line 3-3 of
an electrode layer of the apparatus of FIG. 1.
[0046] FIG. 4 is a schematic diagram showing the apparatus of FIG.
1 in an engine exhaust system.
[0047] FIG. 5 shows a front inlet sectional view of an integrated
non-thermal plasma reactor-diesel particulate filter exhaust
treatment apparatus in accordance with an alternate embodiment of
the present invention.
[0048] FIG. 6 is a schematic diagram showing the apparatus of FIG.
5 in an engine exhaust system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0049] Turning now to FIG. 1, an integrated non-thermal plasma
reactor-diesel particulate filter exhaust treatment apparatus
(integrated NTP-DPF apparatus) 10 includes a wall flow type diesel
particulate filter substrate 12 having an exhaust inlet face 14, an
exhaust outlet face 16, and a plurality of parallel channels 18
extending through the substrate 12 from the exhaust inlet 14 to the
exhaust outlet 16. The term "wall flow type diesel particulate
filter substrate" or "wall flow substrate" as used herein is meant
to refer to an endplugged honeycomb structure of the type known in
the art as "wall flow" filters since the flow paths resulting from
alternate channel plugging require the fluid being treated to flow
through the porous (typically ceramic) cell walls prior to exiting
the filter The wall flow substrate 12 may be made of any suitable
nonconductive porous material such as glass-ceramic or alumina.
Especially suited are porous ceramic materials, such as those that
yield cordierite, mullite or a mixture of these on firing. In a
most preferred embodiment, the wall flow substrate 12 comprises
cordierite.
[0050] The wall flow substrate 12 is divided into a plurality of
three types of rows or layers arranged in an alternating fashion
comprising a high voltage electrode layer 20; a ground electrode
layer 22; and a filter layer 24 disposed between the high voltage
electrode layer 20 and the ground electrode layer 22.
[0051] A portion of the channels 18 at the exhaust inlet face 14
and exhaust outlet face 16 are plugged in an arrangement wherein
each channel is plugged only at one face. The unplugged channels 18
function as exhaust channels. In a preferred embodiment, blocked
channels 26 in the filter rows 24 are plugged in an alternating,
checkered type pattern. The filter rows 24 function as a wall flow
diesel particulate filter.
[0052] FIG. 2 provides a top sectional view taken along the line
2-2 in FIG. 1 of the wall flow substrate 12 showing a filter row 24
and exhaust flow through the exhaust channels 18. As illustrated in
FIG. 2, an exhaust stream 28 to be treated (arrows indicating
exhaust flow) enters the filter rows 24 through the inlet face 14.
The present apparatus may be advantageously employed to treat an
exhaust stream from combustion devices such as, but not limited to,
coal fired furnaces, oil fired furnaces, reciprocating internal
combustion engines, gasoline spark ignition engines, diesel
engines, or gas turbine engines. While the present invention may be
advantageously employed to treat combustion exhaust streams
generally, it is particularly suited for treating a diesel engine
exhaust stream typically comprising particulates, HC, N.sub.2, NOx
(NO, NO.sub.2), O.sub.2, H.sub.2O, CO, and CO.sub.2. The exhaust
gas 28 flows through the substrate channels 1 and channel walls 19
and exits the outlet channels 16 leaving the particulate stuck in
the porous channel walls 19.
[0053] The channels 30 of the high voltage electrode rows 20 and
ground electrode rows 22 are coated with a suitable metal conductor
(not shown). A via 32 is drilled through each high voltage 20 and
ground electrode 22 to form an electrical path to connect each cell
as shown in FIG. 3. The channels 30 of each high voltage 20 and
ground electrode 22 are then blocked 34 to prevent gas flow through
the electrode channels. The channels 30 can be plugged with ceramic
cement or similar material. The plug does not have to extend
throughout the electrode channel 30 as long as both ends are
plugged up to the electrode. In this way, particulates are trapped
in adjacent flow channels 18 and the gases passing through the wall
are forced into a plasma region and treated therein before exiting
the device.
[0054] Bus bars 36 are used on the sides 38, 40 of the substrate 12
to connect the high voltage electrodes 20 and ground electrodes 22
using adequate isolation to prevent the formation of plasma forming
in undesirable areas.
[0055] The integrated NTP-DPF apparatus 10 is connected to a high
voltage power source by suitable electrical connections (not shown)
that would be apparent to one of ordinary skill in the art. In a
preferred embodiment, the power source comprises a short pulse
power supply 42 that is applied to effect plasma formation between
the high voltage electrode layers 20 and ground electrode layers 22
without the use of a dielectric material. When power is applied,
the exhaust channels 18 extending through the filter layers 24 are
in plasma. The exhaust stream 28 enters the channels 18 at the
inlet face 14 and NOx present in the exhaust stream 28 is converted
to NO.sub.2. This NO.sub.2then reacts with the particulate to form
CO, CO.sub.2, and NO, thus cleaning the diesel particulate filter
by continuous regeneration. With the entire filter section in
plasma, the particulate trapped in the porous channel walls is also
removed directly.
[0056] FIG. 4 shows in block schematic form an embodiment of the
present invention comprising an exhaust treatment system 44
including integrated NTP-DPF apparatus 10 connected to short pulse
power supply 42. The system 44 includes a diesel engine 46 that
generates a combustion exhaust stream 28 which includes NOx,
N.sub.2, particulate matter, HC, O.sub.2, H.sub.2O, CO, and
CO.sub.2. Diesel engine exhaust outlet 48 is connected to the inlet
14 of the integrated NTP-DPF apparatus 10 for receiving the
combustion exhaust stream 28. During operation, the exhaust stream
28 is treated in the plasma generated in the filter layers 24
primarily to convert nitrogen oxides (NOx) to NO.sub.2. The exhaust
stream 28 flows through the filter channels 18 and through the
porous channel walls 19 from the inlet 14 to exit at the outlet end
16. Particulate matter in the exhaust stream 28 is captured in the
porous channel walls. The filter layers 24 are regenerated by the
direct action of cleaning the particulate on the walls with the
plasma and by the NO.sub.2 formed in the plasma. Since the outlet
portion 16 of the exhaust channels are also in plasma, any NO
byproduct from the filter regeneration function is then converted
via plasma at the outlet face 16 back into NO.sub.2 for reduction
by the NO.sub.2 catalyst which follows. The plasma and particulate
treated exhaust stream 50 passes from the outlet 16 of the
integrated NTP-DPF apparatus 10 to a catalytic converter 52 having
a catalyst for further treating the plasma treated exhaust stream
50, particularly for reducing nitrogen oxides in the plasma treated
exhaust stream 50. The catalytic converter 52 has an inlet 54 for
receiving the plasma treated stream 50 and an outlet 56 for
emitting the catalyst treated exhaust stream 58.
[0057] Turning now to FIGS. 5 and 6, an alternate embodiment of the
present integrated non-thermal plasma reactor-diesel particulate
filter exhaust treatment apparatus (integrated NTP-DPF apparatus)
60 suitable for use with a traditional alternating current type
high voltage power supply is shown. The apparatus 60 employs
alternating dielectric barrier layers 62 and alternating layers of
a wall flow type diesel particulate filter substrate 12. The
dielectric barrier material may include materials such as, but not
limited to, dense cordierite, alumina, titania, mullite, plastic,
and other high dielectric constant materials, or combinations
thereof.
[0058] As in the first embodiment, the diesel particulate filter
substrate 12 includes an exhaust inlet face 14, an exhaust outlet
face 16, and a plurality of parallel channels 18 extending through
the substrate 12 from the exhaust inlet 14 to the exhaust outlet
16, The diesel particulate filter substrate layers 12 are arranged
in alternating fashion with a plurality of dielectric barrier
electrode 64 layers 62 comprising high voltage electrode layers 66
and ground electrode layers 68.
[0059] Again, a portion of the channels 18 at the exhaust inlet
face 14 and exhaust outlet face 16 are plugged in an arrangement
wherein each channel is plugged only at one face. The unplugged
channels 18 function as exhaust channels. In a preferred
embodiment, blocked channels 26 in the filter rows 24 are plugged
to provide an alternating, checkered type pattern. The filter rows
24 function as a wall flow diesel particulate filter.
[0060] In FIG. 6, the apparatus 60 is shown in an exhaust treatment
system 70. The integrated NTP-DPF apparatus 60 is connected to a
traditional alternating current high voltage power source 72 by
suitable electrical connections (not shown) that would be apparent
to one of ordinary skill in the art. The system 70 includes a
diesel engine 46 in fluid communication with the integrated
non-thermal plasma reactor-diesel particulate filter 60. A plasma
and particulate treated exhaust stream 50 passes from the outlet 16
of the integrated NTP-DPF apparatus 60 to a catalytic converter 52
having a catalyst for further treating the plasma treated exhaust
stream 50, particularly for reducing nitrogen oxides in the plasma
treated exhaust stream 50.
[0061] While the invention has been described by reference to
certain preferred embodiments, it should be understood that
numerous changes could be made within the spirit and scope of the
inventive concepts described. Accordingly, it is intended that the
invention not be limited to the disclosed embodiments, but that it
have the full scope permitted by the language of the following
claims.
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