U.S. patent application number 13/960463 was filed with the patent office on 2013-12-05 for system and method for treatment of gases with reducing agents generated using steam reforming of diesel fuel.
This patent application is currently assigned to OLD DOMINION UNIVERSITY RESEARCH FOUNDATION. The applicant listed for this patent is Richard HELLER, Muhammad Arif MALIK, Karl H. SCHOENBACH. Invention is credited to Richard HELLER, Muhammad Arif MALIK, Karl H. SCHOENBACH.
Application Number | 20130318947 13/960463 |
Document ID | / |
Family ID | 46639175 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130318947 |
Kind Code |
A1 |
MALIK; Muhammad Arif ; et
al. |
December 5, 2013 |
SYSTEM AND METHOD FOR TREATMENT OF GASES WITH REDUCING AGENTS
GENERATED USING STEAM REFORMING OF DIESEL FUEL
Abstract
Systems and methods for treatment of a heated exhaust gas
including hydrocarbons are provided. A method includes providing a
first gas including a gaseous mixture of vaporized diesel fuel and
steam and treating the first gas using at least one corona
discharge including a combination of streamers to transform the
first gas into a second gas including volatile partially oxidized
hydrocarbons (PO--HC) and hydrogen gas (H.sub.2), the combination
of streamers including primarily surface streamers. The method also
includes extracting at least a portion of vaporized diesel fuel and
steam from the second gas to form a third gas and directing a
combination of the third gas and the exhaust gas into a nitrogen
oxides (NOx) reduction reactor.
Inventors: |
MALIK; Muhammad Arif;
(Norfolk, VA) ; SCHOENBACH; Karl H.; (Norfolk,
VA) ; HELLER; Richard; (Norfolk, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MALIK; Muhammad Arif
SCHOENBACH; Karl H.
HELLER; Richard |
Norfolk
Norfolk
Norfolk |
VA
VA
VA |
US
US
US |
|
|
Assignee: |
OLD DOMINION UNIVERSITY RESEARCH
FOUNDATION
Norfolk
VA
|
Family ID: |
46639175 |
Appl. No.: |
13/960463 |
Filed: |
August 6, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US2012/024249 |
Feb 8, 2012 |
|
|
|
13960463 |
|
|
|
|
61440664 |
Feb 8, 2011 |
|
|
|
Current U.S.
Class: |
60/274 ;
60/275 |
Current CPC
Class: |
F01N 2240/28 20130101;
B01D 53/9431 20130101; F01N 2240/30 20130101; F01N 3/2073 20130101;
B01D 2258/012 20130101; F01N 3/36 20130101; B01D 2251/208 20130101;
B01D 2259/818 20130101; F01N 3/0892 20130101; F01N 2240/02
20130101; F01N 2240/04 20130101 |
Class at
Publication: |
60/274 ;
60/275 |
International
Class: |
F01N 3/08 20060101
F01N003/08; F01N 3/36 20060101 F01N003/36 |
Claims
1. A method for treatment of a heated exhaust gas comprising
hydrocarbons, the method comprising: providing a first gas
comprising a gaseous mixture of vaporized diesel fuel and steam;
treating the first gas using at least one corona discharge
comprising a combination of streamers to transform the first gas
into a second gas comprising volatile partially oxidized
hydrocarbons (PO--HC) and hydrogen gas (H.sub.2), the combination
of streamers comprising primarily surface streamers; extracting at
least a portion of vaporized diesel fuel and steam from the second
gas to form a third gas; directing a combination of the third gas
and the exhaust gas into a nitrogen oxides (NOx) reduction
reactor.
2. The method of claim 1, wherein the step of providing further
comprises: directing a liquid mixture of liquid diesel fuel and
water into a heat exchanger; and applying the heated exhaust gas to
the heat exchanger to vaporize the liquid mixture and produce the
first gas.
3. The method of claim 1, wherein the step of treating further
comprises: providing one or more discharge chambers defined by a
plurality of dielectric sections, each of the discharge chambers
comprising at one or more sets of first and second electrodes for
producing electric fields in the discharge chambers, the plurality
of dielectric sections and the sets of first and second electrodes
arranged to define a volume in each of the discharge chambers that
inhibits the formation of volume-streamers, and the discharge
chambers being configured to prevent pulsed electric fields
generated in adjacent ones of the discharge chambers from
substantially interacting; directing the first gas into the
discharge chambers; generating the corona discharge in the
discharge chambers using a pulsed electric field generated by each
of the sets of the first and second electrodes in the discharge
chambers; and releasing the second gas from the discharge
chambers.
4. The method of claim 3, further comprising heating the discharge
chambers using the heated exhaust gas.
5. The method of claim 1, wherein the step of extracting further
comprises: directing the second gas into a heat exchanger; cooling
the second gas in the heat exchanger to condense water and liquid
diesel fuel from the second gas.
6. The method of claim 5, wherein the step of providing further
comprises: forming at least a portion of the first gas using the
condensed water and the condensed liquid diesel fuel.
7. An exhaust system, comprising: a nitrogen oxides (NOx) removal
reactor; an inlet portion configured for receiving a heated exhaust
gas comprising hydrocarbons and directing the heated exhaust gas
into the catalytic reactor; and a reformer system heated by the
heater exhaust gas, the reformer system comprising: a gas treatment
device for treating a first gas comprising a mixture of vaporized
diesel fuel and steam using at least one corona discharge
comprising a combination of streamers to transform the first gas
into a second gas comprising volatile partially oxidized
hydrocarbons (PO--HC) and hydrogen (H.sub.2), the combination of
streamers comprising primarily surface streamers, and a recycling
system for extracting at least a portion of vaporized diesel fuel
and steam from the second gas to form a third gas and directing the
third gas into the inlet portion.
8. The system of claim 7, wherein the reformer system further
comprises a first heat exchanger for receiving a liquid mixture of
liquid diesel fuel and water and generating the first gas, wherein
the first heat exchanger is configured for generating the first gas
by vaporizing the liquid mixture using the heated exhaust gas.
9. The system of claim 8, wherein the heat exchanger is disposed in
the inlet portion.
10. The system of claim 8, wherein the recycling system comprises:
a second heat exchanger coupled to an outlet of the plasma reactor
and configured for producing the third gas by condensing water and
liquid diesel fuel from the second gas; a recycle supply line for
directing the condensed water and the condensed liquid diesel fuel
from the second heat exchanger to the first heat exchanger; and a
reactant supply line for directing the third gas from the second
heat exchanger to the inlet portion.
11. The system of claim 8, further comprising: a water source for
providing the water to the first heat exchanger; and a fuel source
for providing the liquid diesel fuel to the first heat
exchanger.
12. The system of claim 1, wherein the gas treatment device
comprises one or more discharge chambers defined by a plurality of
dielectric sections, each of the discharge chambers comprising at
one or more sets of first and second electrodes for producing
electric fields in the discharge chambers, wherein the plurality of
dielectric sections and the sets of first and second electrodes are
arranged to define a volume in each of the discharge chambers that
inhibits the formation of volume-streamers, and wherein the
discharge chambers being configured to prevent pulsed electric
fields generated in adjacent ones of the discharge chambers from
substantially interacting.
13. The system of claim 12, further comprising heating the
discharge chambers using the heated exhaust gas.
14. The system of claim 12, wherein the discharge chambers are
disposed in the inlet portion.
15. The system of claim 12, wherein the NOx removal reactor
comprises at least one of a hydrocarbon selective catalytic
reduction (H-SCR) reactor and a NOx adsorbent.
16. A diesel fuel powered system, comprising: a diesel fuel engine
comprising an exhaust outlet for releasing exhaust gas; a
hydrocarbon selective catalytic reduction (H-SCR) reactor; an inlet
portion configured for directing the exhaust gas from the exhaust
outlet to the H-SCR reactor; a gas treatment device at least
partially disposed in the inlet portion, the gas treatment device
configured for treating a first gas comprising a mixture of
vaporized diesel fuel and steam using at least one corona discharge
comprising a combination of streamers to transform the first gas
into a second gas comprising volatile partially oxidized
hydrocarbons (PO--HC) and hydrogen (H.sub.2), the combination of
streamers comprising primarily surface streamers, a first heat
exchanger at least partially disposed in the inlet portion and
configured for generating the first gas from water and liquid
diesel fuel using a heat of the exhaust outlet; a recycling system
coupled to the plasma reactor to receive the second gas, the
recycling system configured for extracting liquid diesel fuel and
water from the second gas to form a third gas, directing the third
gas into the inlet portion, and directing the extracted liquid
diesel fuel and the extracted water into the first heat
exchanger.
17. The system of claim 16, wherein the recycling system comprises:
a second heat exchanger coupled to an outlet of the plasma reactor
and configured for producing the third gas by condensing water and
liquid diesel fuel from the second gas; a recycle supply line for
directing the condensed water and the condensed liquid diesel fuel
from the second heat exchanger to the first heat exchanger; and a
reactant supply line for directing the third gas from the second
heat exchanger to the inlet portion.
18. The system of claim 16, further comprising: a water source for
providing the water to the first heat exchanger; and a fuel source
for providing the liquid diesel fuel to the first heat exchanger
and the diesel fuel engine.
19. The system of claim 16, wherein the gas treatment device
comprises one or more discharge chambers defined by a plurality of
dielectric sections, each of the discharge chambers comprising at
one or more sets of first and second electrodes for producing
electric fields in the discharge chambers, wherein the plurality of
dielectric sections and the sets of first and second electrodes are
arranged to define a volume in each of the discharge chambers that
inhibits the formation of volume-streamers, and wherein the
discharge chambers being configured to prevent pulsed electric
fields generated in adjacent ones of the discharge chambers from
substantially interacting.
20. The system of claim 19, wherein the discharge chambers are
disposed in the inlet portion.
21. The system of claim 16, wherein the first heat exchanger is
disposed in the inlet portion.
22. An exhaust system, comprising: a nitrogen oxides (NOx) removal
reactor; an inlet portion configured for receiving a heated exhaust
gas comprising hydrocarbons and directing the heated exhaust gas
into the catalytic reactor; and a reformer system heated by the
heater exhaust gas in the inlet portion, the reformer system
comprising a plasma reactor for treating a first gas comprising a
mixture of vaporized diesel fuel and steam using at least one
corona discharge comprising volume streamer and surface streamers
to transform the first gas into a second gas comprising volatile
partially oxidized hydrocarbons (PO--HC) and hydrogen (H.sub.2),
and a recycling system for extracting at least a portion of
vaporized diesel fuel and steam from the second gas to form a third
gas and for directing the third gas into the inlet portion, wherein
the plasma reactor comprises a plurality of dielectric sections
defining two or more discharge chambers for treating the first gas,
first and second electrodes disposed in each of the discharge
chambers, and electrically conductive shield portions positioned
between adjacent ones of the discharge chambers, and wherein the
plurality of dielectric sections and the first and second
electrodes are arranged so that a greater portion of overall energy
density within the discharge chambers is due to the
surface-streamers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to PCT patent application
No. PCT/US2012/024249, filed Feb. 8, 2012, which claims priority to
U.S. Provisional Patent Application Ser. No. 61/440,664, filed Feb.
8, 2011, both of which are hereby incorporated by reference in
their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to systems for treating gases
including pollutants. More specifically, the invention relates to
systems and methods for treating gases including pollutants using
reducing agents generated via steam reforming of diesel fuel with a
corona discharge plasma reactor.
[0004] 2. Background
[0005] Diesel exhaust contains pollutants like CO, hydrocarbons
(HC), nitrogen oxides (NOx), and soot particles that need to be
removed before it can be safely released into the environment. In
general, about ninety percent of the nitrogen oxides exist as
nitrogen monoxide (NO) which is typically difficult to destroy. The
remaining nitrogen oxides are typically composed of nitrogen
dioxide (NO.sub.2) that can be destroyed by hydrocarbon selective
catalytic reduction (H-SCR) or by urea selective catalytic
reduction U-SCR. In general, several technologies based on
oxidation catalysts and diesel particulate filters (DPF) for
removal of CO, HC, and soot particles are available. However,
technologies for destruction/removal of NOx are still being
developed.
SUMMARY
[0006] The various embodiments are directed to systems and methods
for treatment of gases. In a first embodiment, a method for
treatment of a heated exhaust gas including hydrocarbons is
provided. The method includes providing a first gas including a
gaseous mixture of vaporized diesel fuel and steam and treating the
first gas using at least one corona discharge including a
combination of streamers to transform the first gas into a second
gas including volatile partially oxidized hydrocarbons (PO--HC) and
hydrogen gas (H.sub.2), the combination of streamers including
primarily surface streamers. The method also includes extracting at
least a portion of vaporized diesel fuel and steam from the second
gas to form a third gas and directing a combination of the third
gas and the exhaust gas into a nitrogen oxides (NOx) reduction
reactor. The method can also include heating the discharge chambers
using the heated exhaust gas.
[0007] In the method, the step of providing can include directing a
liquid mixture of liquid diesel fuel and water into a heat
exchanger and applying the heated exhaust gas to the heat exchanger
to vaporize the liquid mixture and produce the first gas.
[0008] The step of treating can include providing one or more
discharge chambers defined by a plurality of dielectric sections,
each of the discharge chambers including at one or more sets of
first and second electrodes for producing electric fields in the
discharge chambers, the plurality of dielectric sections and the
sets of first and second electrodes arranged to define a volume in
each of the discharge chambers that inhibits the formation of
volume-streamers, and the discharge chambers being configured to
prevent pulsed electric fields generated in adjacent ones of the
discharge chambers from substantially interacting. The step of
treating can also include directing the first gas into the
discharge chambers, generating the corona discharge in the
discharge chambers using a pulsed electric field generated by each
of the sets of the first and second electrodes in the discharge
chambers, and releasing the second gas from the discharge
chambers.
[0009] The step of extracting can include directing the second gas
into a heat exchanger and cooling the second gas in the heat
exchanger to condense water and liquid diesel fuel from the second
gas. The step of providing can include forming at least a portion
of the first gas using the condensed water and the condensed liquid
diesel fuel.
[0010] In a second embodiment of the invention, an exhaust system
is provided. The system can include a nitrogen oxides (NOx) removal
reactor, an inlet portion configured for receiving a heated exhaust
gas including hydrocarbons and directing the heated exhaust gas
into the catalytic reactor, and a reformer system heated by the
heater exhaust gas. The reformer system can include a gas treatment
device for treating a first gas including a mixture of vaporized
diesel fuel and steam using at least one corona discharge including
a combination of streamers to transform the first gas into a second
gas including volatile partially oxidized hydrocarbons (PO--HC) and
hydrogen (H.sub.2), the combination of streamers including
primarily surface streamers and a recycling system for extracting
at least a portion of vaporized diesel fuel and steam from the
second gas to form a third gas and directing the third gas into the
inlet portion. In some configurations, the heat exchanger is
disposed in the inlet portion. Further, the NOx removal reactor
includes at least one of a hydrocarbon selective catalytic
reduction (H-SCR) reactor and a NOx adsorbent.
[0011] The reformer system can include a first heat exchanger for
receiving a liquid mixture of liquid diesel fuel and water and
generating the first gas, where the first heat exchanger is
configured for generating the first gas by vaporizing the liquid
mixture using the heated exhaust gas. The system can also include a
water source for providing the water to the first heat exchanger
and a fuel source for providing the liquid diesel fuel to the first
heat exchanger.
[0012] The recycling system can include a second heat exchanger
coupled to an outlet of the plasma reactor and configured for
producing the third gas by condensing water and liquid diesel fuel
from the second gas, a recycle supply line for directing the
condensed water and the condensed liquid diesel fuel from the
second heat exchanger to the first heat exchanger, and a reactant
supply line for directing the third gas from the second heat
exchanger to the inlet portion.
[0013] The gas treatment device can include one or more discharge
chambers defined by a plurality of dielectric sections, each of the
discharge chambers including at one or more sets of first and
second electrodes for producing electric fields in the discharge
chambers, where the plurality of dielectric sections and the sets
of first and second electrodes are arranged to define a volume in
each of the discharge chambers that inhibits the formation of
volume-streamers, and where the discharge chambers being configured
to prevent pulsed electric fields generated in adjacent ones of the
discharge chambers from substantially interacting. In some cases, a
heating the discharge chambers can be provided using the heated
exhaust gas. Further, the discharge chambers can be disposed in the
inlet portion.
[0014] In third embodiment of the invention, a diesel fuel powered
system is provided. The system includes a diesel fuel engine
including an exhaust outlet for releasing exhaust gas, a
hydrocarbon selective catalytic reduction (H-SCR) reactor, an inlet
portion configured for directing the exhaust gas from the exhaust
outlet to the H-SCR reactor, and a gas treatment device at least
partially disposed in the inlet portion, the gas treatment device
configured for treating a first gas including a mixture of
vaporized diesel fuel and steam using at least one corona discharge
including a combination of streamers to transform the first gas
into a second gas including volatile partially oxidized
hydrocarbons (PO--HC) and hydrogen (H.sub.2), the combination of
streamers including primarily surface streamers. The system also
includes a first heat exchanger at least partially disposed in the
inlet portion and configured for generating the first gas from
water and liquid diesel fuel using a heat of the exhaust outlet and
a recycling system coupled to the plasma reactor to receive the
second gas, the recycling system configured for extracting liquid
diesel fuel and water from the second gas to form a third gas,
directing the third gas into the inlet portion, and directing the
extracted liquid diesel fuel and the extracted water into the first
heat exchanger. The first heat exchanger can be disposed in the
inlet portion.
[0015] The system can also include a water source for providing the
water to the first heat exchanger and a fuel source for providing
the liquid diesel fuel to the first heat exchanger and the diesel
fuel engine.
[0016] The recycling system can include a second heat exchanger
coupled to an outlet of the plasma reactor and configured for
producing the third gas by condensing water and liquid diesel fuel
from the second gas, a recycle supply line for directing the
condensed water and the condensed liquid diesel fuel from the
second heat exchanger to the first heat exchanger, and a reactant
supply line for directing the third gas from the second heat
exchanger to the inlet portion.
[0017] The gas treatment device can include one or more discharge
chambers defined by a plurality of dielectric sections, each of the
discharge chambers including at one or more sets of first and
second electrodes for producing electric fields in the discharge
chambers, where the plurality of dielectric sections and the sets
of first and second electrodes are arranged to define a volume in
each of the discharge chambers that inhibits the formation of
volume-streamers, and where the discharge chambers being configured
to prevent pulsed electric fields generated in adjacent ones of the
discharge chambers from substantially interacting. The discharge
chambers can be disposed in the inlet portion.
[0018] In a fourth embodiment of the invention, an exhaust system
is provided. The system includes a nitrogen oxides (NOx) removal
reactor, an inlet portion configured for receiving a heated exhaust
gas including hydrocarbons and directing the heated exhaust gas
into the catalytic reactor, and a reformer system heated by the
heater exhaust gas in the inlet portion, the reformer system
including a plasma reactor for treating a first gas including a
mixture of vaporized diesel fuel and steam using at least one
corona discharge including volume streamer and surface streamers to
transform the first gas into a second gas including volatile
partially oxidized hydrocarbons (PO--HC) and hydrogen (H.sub.2),
and a recycling system for extracting at least a portion of
vaporized diesel fuel and steam from the second gas to form a third
gas and for directing the third gas into the inlet portion.
[0019] In the system, the plasma reactor includes a plurality of
dielectric sections defining two or more discharge chambers for
treating the first gas, first and second electrodes disposed in
each of the discharge chambers, and electrically conductive shield
portions positioned between adjacent ones of the discharge
chambers. Further, the plurality of dielectric sections and the
first and second electrodes are arranged so that a greater portion
of overall energy density within the discharge chambers is due to
the surface-streamers.
DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A and 1B show top and side views, respectively, of a
surface-streamer based plasma reactor that is useful for describing
the various embodiments of the invention;
[0021] FIG. 2 is a partial cross-section diagram of a first
exemplary configuration for a gas treatment device in accordance
with an embodiment of the invention;
[0022] FIGS. 3A and 3B are partially exploded and assembled view,
respectively, of one exemplary configuration for a gas treatment
device in accordance with an embodiment of the invention;
[0023] FIG. 4 is a partial cross-section diagram of another
exemplary configuration for a gas treatment device in accordance
with an embodiment of the invention;
[0024] FIG. 5 is a schematic of an exemplary diesel fuel powered
system configured in accordance with an embodiment
[0025] FIG. 6 illustrates a system including a gas treatment
device, configured in accordance with an embodiment of the
invention, and supporting electrical circuitry.
[0026] FIG. 7 is a detailed block diagram of a computing device
which can be implemented as a control system.
[0027] FIG. 8 is a bar chart showing a comparison of energy cost
for partial oxidation of organic pollutants from air and reduction
of nitric oxide from nitrogen in pulsed corona discharges in air
(conventional plasma reactors) and the sliding discharge
reactor.
DETAILED DESCRIPTION
[0028] The invention is described with reference to the attached
figures, wherein like reference numerals are used throughout the
figures to designate similar or equivalent elements. The figures
are not drawn to scale and they are provided merely to illustrate
the instant invention. Several aspects of the invention are
described below with reference to example applications for
illustration. It should be understood that numerous specific
details, relationships, and methods are set forth to provide a full
understanding of the invention. One having ordinary skill in the
relevant art, however, will readily recognize that the invention
can be practiced without one or more of the specific details or
with other methods. In other instances, well-known structures or
operations are not shown in detail to avoid obscuring the
invention. The invention is not limited by the illustrated ordering
of acts or events, as some acts may occur in different orders
and/or concurrently with other acts or events. Furthermore, not all
illustrated acts or events are required to implement a methodology
in accordance with the invention.
[0029] As described above, a principal concern in the treatment of
diesel engine exhaust and other fossil fuel engine exhaust is the
destruction/removal of NOx, and particularly the destruction of NO.
One method of dealing with NO is to oxidize NO into NO.sub.2 using
oxidation catalysts and thereafter using H-SCR or U-SCR to
eliminate the NO.sub.2. However, such an approach generally
requires on-board supply of the reducing agents, i.e.,
hydrocarbons, hydrogen or urea. In the case of a diesel fuel
system, diesel fuel itself comprises of hydrocarbons, but these
hydrocarbons are generally long chain hydrocarbons and aromatic
compounds that are not effective reducing agents in H-SCR
processes. A solution is to reform the diesel fuel to obtain
Hydrogen (H.sub.2) and partially oxidized hydrocarbons (PO--HC),
which are effective reducing agents for the H-SCR process.
[0030] One option for reforming fuels is to use plasma treatments.
Plasma, i.e., a partially ionized gas, can be formed by high
voltage electrical discharges. The plasma can be thermal where ions
as well as neutral particles are close to thermal equilibrium or it
can be non-thermal where electrons are selectively heated while the
heavier ions and neutral particles remain close to room
temperature. For example, high voltage pulse of short rise time and
short duration are applied between the electrodes in pulsed corona
discharges. Electrons, being light weight, accelerate to high
energy state while the heavier ions do not have sufficient time to
accelerate to high energy states during the voltage pulse. The high
energy electrons ultimately collide with ambient gas molecule and
cause dissociation, excitation or ionization. These processes
produce chemically active species, such as N, O, O.sub.3, etc. The
high energy electrons and chemically active species can react with
and transform the hydrocarbon molecules. However, conventional
thermal and non-thermal plasma reactors typically consume large
amounts of energy. Further, to treat a large volume of gas
efficiently, the non-thermal plasma reactors typically occupy a
substantially large volume. As a result, assembling a lightweight,
compact exhaust system that uses steam reforming based on a plasma
reactor is typically difficult using conventional non-thermal
plasma reactor configurations.
[0031] Accordingly, the various embodiments provide new exhaust
systems and methods utilizing steam reforming based on
high-efficiency, compact surface-plasma reactors using pulsed
corona discharges. Such reactors generally consume significantly
less energy as compared to conventional volume-plasma reactors for
conversions of the hydrocarbons. In particular, a plasma reactor
configuration is provided in the exhaust system that includes a
stacked arrangement of multiple discharge chambers that can be
operated in parallel. The compact size of these surface-plasma
reactors is advantageous, particularly for applications in
vehicles. The operation and configuration of such a plasma reactor
is described below with respect to FIGS. 1-4.
[0032] FIGS. 1A and 1B show top and side views, respectively, of a
plasma reactor 100, configured for encouraging primarily
surface-streamers, which is useful for describing the invention. As
shown in FIGS. 1A and 1B, the reactor 100 is an enclosure defining
a discharge volume or chamber 102. The discharge chamber 102 is
defined by a collection of surfaces. For example, as shown in FIGS.
1A and 1B, the discharge chamber is defined by opposing upper and
lower dielectric portions or surfaces 104, opposing dielectric end
portions 106, and lateral or side portions 108.
[0033] The reactor 100 can also include an inlet a 114 and an
outlet 116 for directing gas in and out, respectively, of the
discharge chamber 102. In the configuration illustrated in FIGS.
1A-1B, the reactor 100 is shown as including a single inlet 114 and
a single outlet 116 positioned at end portions 106. However, the
number and placement of inlets and outlets can vary for reactor
100.
[0034] The discharge chamber 102 further includes electrodes 110
and 112 for producing plasma in the discharge chamber 102 using a
short high voltage pulse, such as pulses less than 1, 10, or 100
microseconds. Use of a short pulse prevents arcing. As shown in
FIG. 1A, the reactor 100 includes an anode electrode 110. In FIG.
1, an anode electrode 110 is shown as a wire inserted across
discharge chamber 102. Electrode 110 may also be a threaded rod,
sharp edge, or any other localizing configuration of electrode
capable of producing streamers, as is known to those in the field
and may be appropriate for the application.
[0035] Reactor 100 also includes one or more cathode electrodes
112. In the configuration illustrated in FIGS. 1A and 1B, the
second electrode is shown as a solid electrical conductor disposed
on an inner surface of lateral side portions 108. However, lateral
side portions 108 and electrodes 112 can be integrally formed.
Further, the cathode electrodes 112 can also be in the form of a
wire mesh, a plate, a wire, or other conductive electrode
configuration known in the art. Additionally, the lateral side
portions 108 and the electrodes 112 can be configured to permit the
flow of gas into and out of gas discharge chamber 102 through
cathode electrodes 112. For example, by positioning from gas inlet
114 into reactor 100 along lateral side portions 108 and sizing or
configuring cathode electrodes 112 to allow gases to flow through
cathode electrodes 112 and into discharge chamber 102. After
treatment, the gas exits through another of cathode electrodes 112
and side portion 108 by gas outlet 116.
[0036] As shown in FIGS. 1A-1B, reactor 100 shows a substantially
wire-to-plate arrangement of electrodes 110 and 112. As shown in
FIG. 1A, the anode electrode 110, in this case a wire, is located
at equal distance to the two cathode electrodes 112. However, the
various embodiments of the invention are not limited to this
exemplary configuration for a reactor. For example, a position of
anode electrode 110 can vary and need not be exactly equidistant
between electrodes 112. Further, electrode 110 can be disposed on
or near a first of dielectric portions 104. However, the various
embodiments are not limited in this regard and the position of
electrode 110 with respect to dielectric portions 104 can vary.
That, is the electrode 110 can be either placed on or near either
of dielectric portions 104, equidistant between the two surface
104, or any position in between, as long as the distance of the
wire to the sheets is small enough such that surface streamers are
primarily generated in the reactor 100.
[0037] Further, the various embodiments are not limited to
wire-to-plate configurations. Thus, the anode and cathode
electrodes can be arranged in a wire-to-wire configuration, a
point-to-wire configuration, or a point-to-plate configuration, to
name a few. Further, the roles of the electrodes in the various
embodiments can be reversed. That is, electrode 110 and electrode
112 can be switched to provide a cathode and an anode,
respectively.
[0038] In one exemplary configuration of reactor 100, it can be
constructed using sheets or films consisting of glass, ceramic, or
other high temperature resistant dielectric materials, as
dielectric surfaces 104, a stainless steel wire of 150 micro-meter
diameter as anode electrode 110, aluminum strips of 6 mm thickness
as cathode electrodes 112. End portions 106 can also be formed
using glass, ceramic, or other high temperature resistant
dielectric materials. An example of a suitable high temperature
dielectric material is MACOR.RTM., developed and sold by Corning
Incorporated of New York, N.Y. However, the various embodiments are
not limited to the exemplary materials described above. For
example, the electrodes 110 and 112 can be fabricated from any
electrically conducting or semi-conducting materials. However,
metals, such as stainless steel, copper, silver, tungsten, or
alloys thereof would provide superior performance.
[0039] Exemplary dimensions for reactors using such materials and
the typically achievable energy per pulse are listed in Table
1.
TABLE-US-00001 TABLE 1 Dimensions of discharge spaces of three
reactors employed. Length Width Height Energy per pulse Reactor Cm
cm Cm J .+-. 1.sigma. 1 8 10 0.2 0.0085 .+-. 0.002 2 30 9 0.2 0.035
.+-. 0.008 3 30 9 1.4 0.034 .+-. 0.007 4 15 ID**: 4.5 -- 0.10 .+-.
0.01
In Table 1, Reactor 4 is a conventional coaxial reactor (not shown)
with the discharge gap defined by the diameter of the cylinder and
operating in a volume-streamer mode. Reactors 1, 2, and 3 are
reactors configured in accordance with FIGS. 1A and 1B and
operating in surface-streamer mode. The dimensions and achievable
energy per pulse for Reactor 4 is shown for purposes of
comparison.
[0040] In addition to the configuration described above, the ends
of the first electrodes 110 within the discharge chamber 102 can be
insulated to eliminate surface-streamer at the end portions 106.
For example, a 2.5 cm part each end of the electrodes can be used
to insulate electrodes 110 and 112 to eliminate surface-streamers
at the end fittings. Accordingly, the effective length of the
electrodes would be 5 cm less than that listed above.
[0041] Those skilled in the art will recognize that the
configuration of the discharge chamber, the gas, and the electrodes
will vary the effective length at which the formation of streamers
is effectively constrained so that surface-streamers play a primary
role in energy density. For example, spacing between the dielectric
surfaces 104 may be used to reduce the dimensions of discharge
chamber 102 so as to constrain the formation of volume-streamers,
given the electrode configuration described above. In the
embodiment of FIG. 1, a distance of 10 mm between dielectric
surfaces 104 was shown to be effective to significantly reduce or
eliminate the formation of volume-streamers. Smaller distances are
preferable in that they increase the role of surface-streamers with
a corresponding increase in energy density. The design of a plasma
reactor with a discharge chamber, in which surface-streamers are
predominant, is described in U.S. Pat. No. 7,298,092 to Malik et
al., issued Nov. 20, 2007, the contents of which are hereby
incorporated in their entirety.
[0042] Although the plasma reactors described above can generate a
sufficient volume of surface-streamers to provide effective
treatment, combining several of these reactors into a small space
can be difficult. For example, where two of the reactors shown in
FIGS. 1A and 1B are placed directly on top of each other or
constructed using a common one of dielectric portions 104 and
operated in parallel using a common power supply, plasma will
typically be observed in one chamber only. This is believed to be
due to positive surface charge that the surface plasma leaves on
the dielectric surface in contact with the plasma. This charge on
one side of the dielectric induces an opposite charge on the other
side, which appears to change or interact with the electric field
distribution in the adjacent discharge chamber. As a result, this
interaction results in an electric field distribution which is not
favorable to plasma formation. In other words, when two
surface-plasma reactors are operated adjacent to each other, they
can become electrically coupled with each other. Normally, this can
occur is the electrical field of one of the reactors is
sufficiently strong causing accumulation of charges on an opposing
dielectric surface. As a result, plasma formation will occur in one
reactor only, decreasing treatment efficiency. As a result,
combining a number of such reactors in a small space will not
result in improved treatment of gases.
[0043] Accordingly, in the various embodiments, the exhaust system
is configured to include a reforming system to include adjacent
surface-plasma reactors with shield portions to prevent the
inducement of opposite charges in one reactor due to surface plasma
discharge in an adjacent chamber. Thus, a reforming system for an
exhaust system can be formed by scaling up a surface-plasma reactor
by operating multiple reactors in parallel or series and positioned
adjacent to each other, by separating them with a shield portion
held at a reference voltage.
[0044] FIG. 2 is a partial cross-section diagram of a first
exemplary configuration for a gas treatment device 200 in
accordance with an embodiment of the invention. In particular, FIG.
2 is a stacked arrangement of two of reactor 100 (reactors 100A and
100B), where the cross section shown in FIG. 2 is a portion of the
cross-section along cutline 2-2 in FIG. 1 for each of reactors 100A
and 100B. That is, each of reactors 100A and 100B is configured
substantially similar to reactor 100 in FIG. 1.
[0045] The partial cross-section of device 200 shows the top and
bottom dielectric portions 104A and 104B for each of reactor 100A
and 100B, respectively. In device 200, the decoupling between
reactors 100A and 100B is provided by introducing an electrically
conductive shield portion 202 between the reactors 100A and 100B.
Particularly, the shield portion 202 is disposed between the
contacting ones of dielectric portions 104A and 104B. Thus, this
shield portion 202 can decouple the two reactors 100A and 100B by
providing a conducting medium which prevents the induction of
charges on the dielectric which is part of the neighboring
reactor.
[0046] In operation, the shield portion 202 is connected to a
reference voltage that is the same or lower than that of the
electrodes in each of reactor 100A and 100B. For example, the
shield portion 202 can be coupled to ground. As a result, the
electric field generated in first of discharge chambers 102A is
effectively blocked from entering a second of discharge chambers
102B. The electric charge induced on the dielectric surface is
transported by the conductive shield. Accordingly, the lack of
induced charges results in the ability to generate plasma in both
adjoining discharge chambers 102A and 102B.
[0047] In some embodiments of the invention, the shield portion 202
and the electrodes in reactors 100A and 100B can be separately
biased, as described above. However, in some configurations, the
shield portion 202 and the cathode electrodes in reactors 100A and
100B can be biased and/or electrically connected. Such a
configuration simplifies the circuitry required for operating
device 200. That is, separate circuits are not required for biasing
shield portion 202 and the cathode electrodes in reactors 100A and
100B. Further, since these portions are substantially adjacent to
each other, a simpler wiring for these portions can be
provided.
[0048] In the configuration shown in FIG. 2, two separate reactor
chambers are shown, separated by the shield portion. However, the
various embodiments of the invention are not limited in this
regard. In other embodiments, the reactors can share a common
dielectric portion, where the dielectric portion includes a shield
portion embedded or otherwise integrally formed within the common
dielectric portion.
[0049] Additionally, the shield portion can be formed in several
ways. For example, in some embodiments of the invention, the shield
portion can be formed using a sheet or foil of electrically
conductive material. For example, the sheet or foil can consist of
a metal or metal alloy. However, the various embodiments of the
invention are not limited to shield portions consisting of metallic
conductors. Rather, non-metallic conductors can also be used
without limitation. Further, the various embodiments are not
limited to solely a sheet-type or foil-type shield portions. In
some configurations, a perforated sheet or foil can also be used to
provide the shield portion. In yet other configurations, the
electrically conductive materials of the shield portion can be
arranged to form a mesh or screen. In still other configurations, a
plurality of shield portions can be used, each coupled to a
reference voltage.
[0050] Referring now to FIGS. 3A and 3B, there is shown one
exemplary configuration of a gas treatment device 300, arranged in
accordance with an embodiment of the invention. FIG. 3A is a
partially exploded view of device 300. FIG. 3B is an assembled view
of device 300. As shown in FIGS. 3A and 3B, device 300 includes a
first reactor 302 and a second reactor 304. Each of reactors 302
and 304 includes a discharge chamber 306, defined by a stack of
layers. In particular, the stack includes a first dielectric layer
308, a second dielectric layer 310, and a spacer layer 312 disposed
between dielectric layers 308 and 310.
[0051] In the configuration shown in FIGS. 3A and 3B, the stack of
layers 308-312 can be formed using layers or sheets of dielectric
materials, as described above with respect to FIG. 1. However, the
various embodiments of the invention are not limited in this
regarding and any other dielectric materials can be used for
forming layers 308-312. To define discharge chamber 306, layers
308-312 are configured to provide an enclosure. In particular,
dielectric layers 308 and 310 are configured to be substantially
solid to provide upper and lower surfaces of such an enclosure. The
side surfaces of the enclosure are provided by the spacer layer
312. In particular, spacer layer 312 includes an opening for
defining the discharge chamber 306 between layers 308 and 312.
Accordingly, by adjusting the size of the opening in spacer layer
312 and the thickness of spacer layer 312, the volume of discharge
chamber 306 can be varied. Accordingly, as described above, this
opening size and thickness can be selected to adjust the amount of
surface- and volume-streamers for the discharge chamber.
[0052] Gas flow into the discharge chamber 306 can be provided
using an inlet 314 and an outlet 316. In FIGS. 3A and 3B, the inlet
314 and the outlet 316 are shown as being incorporated into first
dielectric layer 308. However, the various embodiments of the
invention are not limited in this regard. Rather inlet 314 and
outlet 316 can be formed in any of layers 308-312. Further the
inlet 314 and outlet 316 of each of reactors 302 and 304 can be
coupled to provide each serial or parallel communication of gases
between the reactors 302 and 304. Such a communication can be
provided using conduit or tubing portions (not shown).
[0053] However, gas communication between the reactors 302 and 304
is not limited to using conduit or tubing portions. For example, as
shown in FIGS. 3A and 3B, reactors 302 and 304 are in a stacked
configuration, where a second dielectric layer 310 of reactor 302
faces a second dielectric layer 310 of reactor 304. Accordingly,
the reactors 302 and 304 can be configured to allow gas
communication via respective ones of dielectric layer 310. In
particular, dielectric layer 310 in each of reactors 302 and 304
can include any arrangement of openings such that when reactors 302
and 304 are stacked on each other, the discharge chamber 306 of
reactors 302 and 304 are in gas communication. Accordingly, the use
of conduits can be limited for purposes of directing a gas in or
out of device 300.
[0054] In reactors 302 and 304, plasma streamers in a corresponding
discharge chamber 306 are formed via anode electrode 318 and
cathode electrodes 320. Although electrodes 318 and 320 are
referred to as anode and cathode electrodes, respectively, this is
for illustrative purposes only. In the various embodiments of the
invention, these roles can be reversed, as described above with
respect to FIGS. 1A and 1B. As shown in FIG. 3A, cathode electrodes
320 are formed by providing an electrically conductive surfaces
along two facing sides of discharge chamber 306. In particular, an
electrically conductive material is disposed on portions of spacer
312, such that two facing and substantially parallel electrodes are
formed within discharge chamber 306. Anode electrode 318 is then
formed using a wire extending across the opening in spacer layer
312, as shown in FIG. 3A. In particular, the wire for anode
electrode 318 is disposed in discharge chamber 306 so that it
extends substantially parallel and between to the cathode
electrodes 320 formed on spacer layer 312. Further, the wire is
disposed in discharge chamber 306 to provide an electrode that is
substantially equidistant from each of cathode electrodes 320. That
is, in a substantially wire-to-plate relationship. However, other
relationships can be used in the various embodiments of the
invention, as described above with respect to FIGS. 1A and 1B.
[0055] Although FIG. 3 shows a wire for forming anode electrode
318, the various embodiments of the invention are not limited in
this regard, as described above with respect to FIG. 1. In the
various embodiments, the structure for anode electrode 318 can
vary. Rather, any configuration that results in a greater electric
field density at or near the anode electrode 318, as compared to
cathode electrodes 320, can be used in the various embodiments of
the invention. Accordingly, one or more pin-like or blade-like
structures can also be provided to form anode electrode 318.
Further, although the wire forming anode electrode 318 is shown as
extending along the entire width or length of the opening in spacer
layer 312, the various embodiments are not limited in this regard.
In other configurations, a wire or blade-type structure for anode
electrode 318 can extend only along a portion of the opening. In
still other configurations, a series of wires, pin-type structures,
or blade-type structures can be used over a portion or the entire
length or width of the opening in spacer layer 312.
[0056] In operation, a voltage can be applied to anode electrode
318 via a portion of the wire forming anode electrode extending
through spacer layer 312. However, alternatively or in addition to
such a wire portion, spacer layer 312 or other portions of reactors
302 and 304 can be configured to include any type of connector
structure for providing a voltage for anode electrode 318. Thus,
such structures can be disposed on or extend through one or more
portions of any of layers 308, 310, and 312. Similarly, a voltage
can be applied to cathode electrodes 320 via a portion of the
electrically conductive surfaces extending to outer surfaces of
spacer layer 312. Thus, alternatively or in addition to such
portions, spacer layer 312 or other portions of reactors 302 and
304 can be configured to include any type of connector structure
for providing a voltage for cathode electrodes 320. Preferably,
dielectric isolation can be provided between the anode electrode
318 for reactors 302 and 304. For example, as shown in FIGS. 3A and
3B, portions of dielectric layer 310 can extend along a length of
anode outside the discharge chamber 306. Thus, such structures can
also be disposed on or can also extend through one or more portions
of any of layers 308, 310, and 312.
[0057] To provide decoupling between reactors 302 and 304, a shield
portion for the device 300 can be formed by providing an
electrically conductive portion between inner dielectric layers 310
and thereafter connecting this shield portion to a reference or
ground voltage, as described above. However, as shown in FIGS. 3A
and 3B, for each of reactors 302 and 304, a shield portion 322 is
provided that is electrically connected to the cathode electrodes
320 of a corresponding one of reactors. Thus, a single voltage can
be provided for the shield portion 322 and cathode electrodes 320
for the reactors 302 and 304 in device 300. Thus reduces
requirements and complexity for a circuit providing power to device
300.
[0058] Additionally, to further reduce wiring requirements for
device 300, the shield portion 322 and cathode portions 320 can be
configured in each of reactors 302 and 304 so that the assembling
of device 300 automatically electrically connects these portions in
reactors 302 and 304. For example, as shown in FIG. 3A, shield
portion 322 is disposed on an outer surface of second dielectric
layer 310 in each of reactors 302 and 304. Thus, when device 310 is
assembled as shown in FIG. 3B, the shield portion 322 of reactor
302 is placed in physical and electrical contact with the shield
portion 322 of reactor 304. Accordingly, if a reference of ground
voltage is applied to shield portion 322 or either of cathode
electrodes 320 in reactor 302 or reactor 304, all of these portions
in both of reactors 302 and 304 are biased to the same reference
voltage. In the some embodiments of the invention, the reference
voltage can be a ground potential. However, the invention is not
limited in this regard and the reference voltage can be any voltage
suitable for electrodes 320. That is, at least the voltage
difference provided between electrodes 318 and 320 should be
provided between electrode 318 and shield portion 322.
[0059] In the various embodiments, the connection between shield
portion 322 and cathode electrodes 320 can be provided in various
ways. In some configurations, electrically conductive wires and/or
any other types of electrically conductive elements or structures
can be used to provide the connection. In the configuration shown
in FIGS. 3A and 3B, this connection is provided by forming shield
portion 322 and cathode electrodes 320 using a continuous
electrically conductive portion, such as an electrically conductive
foil or sheet. In such configurations, foil or sheet can be
configured as follows. First, a foil or sheet can be provided, with
first and second ends that extend along the outer surface of second
dielectric layer 310 that corresponds to at least discharge chamber
306. The first end of the foil or sheet can be wrapped around a
first side portion of spacer layer 312 and the second end can be
wrapped around a second side portion of spacer layer 312 facing the
first side portion. As a result, a single electrically conductive
portion, extending along the outer surface of each of reactors 302
and 304 defines both the shield portion 322 and cathode electrodes
320.
[0060] In some configurations, the shield portion 322 can
optionally extend around each of reactors 302 and 304. For example,
in some configurations, an additional shield portion 324 can be
formed on an exterior surface of outer dielectric layer 308. In
operation, the additional shield portion 324 can then be coupled to
the cathode electrodes 320 and shield portion 322. In another
configuration, the additional shield portion 324 for reactors 302
and 304 can be formed by wrapping another foil or sheet around the
assembled chambers, i.e., around the outer sides of layers 308 as
well as around the sides of the chambers. In such a configuration,
the foil defining additional shield portion 324 can be wrapped so
as to make electrical contact with electrodes 320 on the sides of
the chambers 302 and 304, and thus electrically couple shield
portion 322 to shield portion 324.
[0061] Such a configuration provides improved performance, in
particular as compared to a single reactor system, such as that
described in FIGS. 1A and 1B. In particular, where a test reactor
was constructed in accordance with FIGS. 3A and 3B and with an
additional shield portion 324 for reactors 302 and 304, the present
inventor has found that the electrical power consumed in the plasma
in such a system was 0.33 W. In contrast, the present inventors
have found that electrical power consumed in the plasma was 0.028 W
in the case of a device configured in accordance with the single
reactor configuration illustrated in FIGS. 1A and 1B and having
similar dimensions, a .about.10.times. increase. The power (P) was
calculated by the following formula: P=(.intg.VI dt)f. The voltage
pulse was the same in the two cases, with a peak voltage value of
.about.30 kV, and the pulse frequency .about.10 Hz was also the
same. Thus, the increase in power is due to corresponding increase
in current flowing through the discharge gap during the pulse when
the shield portion extends around the discharge chambers.
[0062] The coupling between the first and second reactors is
reduced or eliminated by providing a shield portion therebetween.
However, the various embodiments of the invention are not limited
in this regard. As described above, the principal difficulty in
generating plasma in two adjacent chambers is the induction of
charges on a dielectric surface of a reactor adjacent to another
reactor in which plasma is being formed. Accordingly, another
embodiment of the invention involves forming plasma in adjacent
chambers, without a shield portion therebetween, that fails to
induce charges on neighboring dielectric layers. Accordingly,
another aspect of the invention provides for plasma formation using
a staggered-discharge approach. That is, the adjacent reactors are
configured such that the discharge for forming plasma in a first
reactor and the discharge for forming plasma in a second, adjacent
chamber reactor occur in non-overlapping portions. This is
conceptually illustrated with respect to FIG. 4.
[0063] FIG. 4 is a partial cross-section diagram of another
exemplary configuration for a gas treatment device 400 in
accordance with an embodiment of the invention. In particular, FIG.
4 is a stacked arrangement of two of reactor 100 (reactors 100A and
100B), where the cross section shown in FIG. 4 is a portion of the
cross-section along cutline 2-2 in FIG. 1 for each of reactors 100A
and 100B. Each of reactors 100A and 100B are configured
substantially similar to reactor 100 in FIG. 1. Thus, the partial
cross-section of device 400 shows the top and bottom dielectric
portions 104A and 104B for each of reactors 100A and 100B,
respectively, that defines respective ones of discharge chambers
102A and 102B. In device 400, the decoupling between reactors 100
is provided by staggering the portions of each discharge chamber in
device 400 that are to be discharged.
[0064] This staggering can be provided in several ways. For
example, in one configuration, the electrodes 110 and 112 in each
discharge chamber 102 can be configured such that when device 200
is assembled, the electrodes that are being biased at the same time
do not substantially overlap. For example, as shown in FIG. 4, only
the electrodes associated with an upper portion 402 in a first
reactor 100 and the electrodes associated with a lower portion 404
in a second reactor 100 are configured to provide a plasma in
portions "A" and "B" in device 200. Thus, any charges induced in an
adjacent discharge chamber not induced in a portion of the
discharge chamber associated with generation of plasma. That is,
the charges induced in portion "C" of the second reactor 100 by the
plasma in portion "A" of first reactor 100 are inconsequential,
since the plasma in second reactor 100 is limited to portion "B".
Similarly, the charges induced in portion "D" of the first reactor
100 by the plasma in portion "B" of second reactor 100 are
inconsequential, since the plasma in first reactor 100 is limited
to portion "A". However, in such a configuration, since only a
portion of the volume of each discharge chamber is used, the
efficiency may be reduced.
[0065] In some configurations overlapping portions can be provided
by controlling a timing of discharges in device 400. In particular,
the timing associated with biasing of the electrodes for these
portions can be controlled so that only non-overlapping portions
are biased at the same time. Thus, at any one time, only one set of
electrodes, associated with non-overlapping portions, are
concurrently biased. Such a configuration is advantageous, since
switching between the different sets of non-overlapping electrode
portions permits a majority of the volume of each discharge chamber
102 in device 400 to be used. Accordingly, a greater efficiency can
be achieved.
[0066] The gas treatment devices described in FIGS. 2-4 can be
incorporated into an exhaust system, as described below with
respect to FIG. 5, to provide steam reforming for reducing
pollutants in exhaust gases. FIG. 5 is a schematic of an exemplary
diesel fuel powered system 500 configured in accordance with an
embodiment. For purposes of FIG. 5, some minor components, such as
valves, pumps, electrical wiring, and control systems, to name a
few, are not shown for ease of illustration.
[0067] System 500 includes an engine 502, powered using diesel fuel
from a fuel reservoir 504. The system 500 includes an engine air
inlet 506 for providing air to engine 502 and an engine exhaust
outlet 508 for directing exhaust gas from engine 502. The engine
exhaust outlet 508 can be connected to an exhaust system 510 for
treating the exhaust gas from engine 502.
[0068] Exhaust system 510 can include an inlet portion 512, an
outlet portion 514, and a NOx removal reactor 516 therebetween,
such as a hydrocarbon selective catalytic reduction (H-SCR)
reactor, a NOx adsorbent, or a combination of both. In some
configurations, the inlet portion 512 can include a diesel
particulate filer (DPF) 518 and an oxidation catalyst 520 to remove
particulates, CO, and to oxidize NO to NO.sub.2. Additionally,
exhaust system, 510 can include a reforming system 522.
[0069] The reforming system 522 can include a water source 524, a
diesel fuel source 504, a first heat exchanger 526, a gas treatment
device 528, and a recycling system 530. The recycling system 530
can include a treated gas collection line 532 feeding a second heat
exchanger 534, which in turns feeds a reactant supply line 536
coupled to the inlet portion 512 and a recycle supply line 538
coupled to the first heat exchanger 526.
[0070] System 500 operates as follows. Initially, engine 502 begins
to operate. That is fuel from fuel source 504 and air (via air
inlet 506) are fed into engine 502 and engine 502 produces exhaust
gas at outlet 508. The operation of such engines is well-known to
those of ordinary skill in the art and will not be described here.
The exhaust gas then propagates through exhaust system 510 for
treatment.
[0071] First, as described above, the exhaust gas can pass through
DPF 518 and oxidation catalyst 520 to remove particulates, CO, and
to oxidize NO to NO.sub.2. Second, as the exhaust gas reaches
reactor 516, the exhaust gas can be combined with volatile PO--HC
and H.sub.2 produced by the reforming system 522 to be utilized in
the H-SCR process for reduction of NOx. Further, in the case where
a NOx adsorbent is used, the PO--HC and H.sub.2 can be used to
regenerate the adsorbent material.
[0072] The reforming system 522 operates as follows to produce
volatile PO--HC and H.sub.2. First, liquid diesel fuel from fuel
source 504 and water from water source 524 is transferred to first
heat exchanger 526. In some embodiments, the liquid diesel fuel and
the water can be transferring using a fuel pump 540 and a water
pump 542, respectively. However, the various embodiments are not
limited in this regard and a system relying on gravity can also be
used.
[0073] Once the liquid diesel fuel and the water reach the first
heat exchanger 526, these are vaporized to produce a first gas,
consisting of a mixture of vaporized diesel fuel and steam. In the
various embodiments, to reduce the power requirements of the
reforming system 522, the heat exchanger 526 is in contact with or
at least partially disposed in the inlet portion 512. In such a
configuration, rather than relying on an external source of heat to
vaporize the liquid diesel fuel and water, the heat present in the
exhaust gas (typically >100.degree. C.) is utilized to introduce
the necessary heat for causing vaporization. In some embodiments,
the first heat exchanger 526 can be contained entirely within inlet
portion 512.
[0074] The first gas can then be directed into gas treatment device
528. The gas treatment device can be configured in accordance with
any of the configurations in FIGS. 1-4. However, the configuration
in FIGS. 2-4 will generally provide a more efficient and compact
arrangement for gas treatment device 528. Operation of gas
treatment device 528 results in at least some of the hydrocarbons
in the vaporize diesel fuel to be converted to volatile PO--HC and
H.sub.2, thus resulting in a second gas to be formed that includes
the volatile PO--HC and H.sub.2, as well as any non-reacted
vaporized diesel fuel and steam. In the various embodiments, to
further reduce the power requirements of the reforming system 522,
the gas treatment system 528 can also be in contact with or at
least partially disposed in the inlet portion 512. In such a
configuration, an external source of heat would not be required to
maintain the liquid diesel fuel and water and water in a vaporized
state, as the heat present in the exhaust gas (typically
>100.degree. C.) is utilized to introduce the necessary heat for
maintaining vaporization. In some embodiments, the gas treatment
system 528 can be contained entirely within inlet portion 512.
[0075] The second gas, produced by gas treatment device 528, can
then be directed from gas treatment device 528 to the second heat
exchanger 534 in recycling system 530 via gas collection line 532.
The second gas is then cooled in second heat exchanger 534 using
air or any other gas to reduce the temperature of the second gas
below 100.degree. C. and cause condensation of at least a portion
of the diesel fuel and steam remaining in the second gas. As a
result, a third gas, primarily volatile PO--HC and H.sub.2 and a
liquid mixture of diesel fuel and water are produced. The liquid
mixture can be redirected into the first heat exchanger 526 via
recycle supply line 538, where it can be re-vaporized and
subsequently retreated using gas treatment device 528. The third
gas can be concurrently redirected into inlet portion 512, to
combine with the exhaust gas prior to reactor 516.
[0076] The system and method described above is particularly
advantageous because it utilizes existing infrastructure, i.e.,
fuel tank 504 for providing fuel to engine 502, surplus heat of the
exhaust gas to vaporize the liquid diesel fuel and water, and
electrical power required for the gas treatment device 528 can be
generated by an alternator or other electrical power generating
device already present in the system.
[0077] Further, the system and method described above are different
from previously available systems in various ways. For example,
conventional catalytic steam reforming of fuel generally requires
the heating of gases to higher temperatures than possible with the
configuration or materials that would be used for the system of
FIG. 5. That is, temperatures in the range of 3000K to 10,000K are
typically required for steam reforming, which normally result in
heat losses and material compatibility issues. In contrast, stream
reforming in accordance with the various embodiments can be
performed at the significant lower temperatures associated with
vehicle engine exhaust, typically less than 500K. Further, such
systems generally suffer from frequent catalyst deactivation. In
contrast, the plasma processes possible for the gas treatment
devices of FIGS. 1-4 can tolerate the impurities that are
responsible for the catalyst deactivation. Additionally, even in
systems where partial oxidation of diesel fuel is performed using
plasma reactor, several major drawbacks have been reported. First,
fire hazard limits the allowed concentration of fuel to be very
low. That is, the lower explosive or flammable limits for gasoline
and kerosene are 1.4% and 0.7% concentrations, respectively. Thus,
if the concentration of these fuels in air is higher than these
values, the likelihood of an explosion is high. Second, the amount
of hydrogen in the product gases resulting from such processes is
relatively low because a fraction of it is consumed by surplus
oxygen by following reactions: partial oxidation
C.sub.nH.sub.m+(n/2)O.sub.2.fwdarw.nCO+(m/2)H.sub.2, water
formation 2H.sub.2+O.sub.2.fwdarw.2H.sub.2O. Finally, cock or wax
deposition on electrodes typically poses a problem in these
processes.
[0078] In contrast, configurations in accordance with the various
embodiments provide steam reforming that allows higher
concentrations of hydrocarbons to be treated without fire hazard
and without cock or wax deposition on electrodes. For example, the
inclusion of steam allows for concentrations up to 20%. Further,
such steam reforming yields more hydrogen from water vapors in
addition to the hydrogen coming from hydrocarbons by reactions such
as the following:
C.sub.nH.sub.m+nH.sub.2O.fwdarw.nCO+(n+(m/2))H.sub.2, and
2H.sub.2O+CO.fwdarw.H.sub.2+CO.sub.2.
[0079] Additionally, the systems and methods described above
provide additional advantages. For example, although steam
reforming of light hydrocarbons, i.e., methane, propane, and hexane
can be performed using non-thermal plasmas, in the diesel engine
setup, additional fuel tanks and related infrastructure would be
required. Further, such processes are generally limited to gaseous
fuels or require dilution of the process gas with some inert gas,
increasing overall complexity of the system. Also, the non-thermal
plasmas typically reported for reforming light hydrocarbons are
generally inefficient compared with the surface-plasma of this
embodiment.
[0080] The present configuration also produces plasma in gas phase
which is different from arc discharges directly in liquid fuels.
Such arc discharges in liquids are close to thermal plasma, where
energy wastage as heat loses is a problem. Further, such discharges
also generally result in cracking of diesel fuel that produces many
solid carbon particles and light hydrocarbons along with hydrogen.
The solid carbon needs to be filtered out continually from the fuel
as they are electrically conductive particles that interfere with
the plasma process. Further, PO--HC is not produced in this process
as there is no source of oxygen in the system. As a result
additional filtering and processing would be needed, as compared to
the system and methods described above.
[0081] FIG. 6 illustrating a system including a gas treatment
device 602, configured in accordance with an embodiment of the
invention, and supporting electrical circuitry. In operation, a
high voltage pulse can be applied to device 602. In the various
embodiments, the pulse can be formed using a capacitive discharge
circuit or an inductive discharge circuit. In the case of a
capacitive discharge circuit, the pulse forming element can be
single or multiple capacitors 656, where one of them could be used
to change the polarity of the pulse. It can also be combinations of
capacitors and inductors, which form a pulse forming circuit, or
cables and other pulse forming lines. In the case of an inductive
discharge circuit, the pulse forming element can be an inductor or
a combination of inductors and capacitors, which form a pulse
forming circuit, or combinations thereof. The capacitive storage
elements are charged by a power supply 650, either through a
resistor 655 or in a pulsed mode through an inductor. In the case
of capacitive discharges, the switch must be a closing switch, e.g.
a spark gap switch 625 or any other high power closing switch. The
switch should be preferably controllable, e.g. triggereable with a
trigger generator 651. In case of a an inductive storage system,
the switch needs to be an opening switch. The circuit also contains
resistors which are placed in parallel 655 or in series to the
load, the reactor 602. The pulse is generated by closing the switch
625, or in the case of an inductive circuit, opening a switch. This
pulse was applied to high voltage electrode node 657 (i.e., the
anode electrode), while counter electrode node 658 (i.e., the
cathode electrode and/or shield portions) was grounded (i.e.,
coupled to ground node 653). A control system 660 can be provided
to monitor and control the various elements in system 600. Other
components can also be provided, such as resistor 654 for providing
a voltage divider for measuring voltage. The pulse duration
preferably is short enough to prevent the occurrence of a
transition from streamer to arc. Those skilled in the art will
readily see that a variety of circuits may be used and pulses
having different characteristics may readily be achieved.
[0082] Referring now to FIG. 7, there is provided a detailed block
diagram of a computing device 700 which can be implemented as
control system 660. Although various components are shown in FIG.
7, the computing device 700 may include more or less components
than those shown in FIG. 7. However, the components shown are
sufficient to disclose an illustrative embodiment of the invention.
The hardware architecture of FIG. 7 represents only one embodiment
of a representative computing device for controlling a jointed
mechanical device.
[0083] As shown in FIG. 7, computing device 700 includes a system
interface 722, a Central Processing Unit (CPU) 706, a system bus
710, a memory 716 connected to and accessible by other portions of
computing device 700 through system bus 710, and hardware entities
714 connected to system bus 710. At least some of the hardware
entities 714 perform actions involving access to and use of memory
716, which may be any type of volatile or non-volatile memory
devices. Such memory can include, for example, magnetic, optical,
or semiconductor based memory devices. However the various
embodiments of the invention are not limited in this regard.
[0084] In some embodiments, computing system can include a user
interface 702. User interface 702 can be an internal or external
component of computing device 700. User interface 702 can include
input devices, output devices, and software routines configured to
allow a user to interact with and control software applications
installed on the computing device 700. Such input and output
devices include, but are not limited to, a display screen 704, a
speaker (not shown), a keypad (not shown), a directional pad (not
shown), a directional knob (not shown), and a microphone (not
shown). As such, user interface 702 can facilitate a user-software
interaction for launching software development applications and
other types of applications installed on the computing device
700.
[0085] System interface 722 allows the computing device 700 to
communicate directly or indirectly with the other devices, such as
an external user interface or other computing devices.
Additionally, computing device can include hardware entities 714,
such as microprocessors, application specific integrated circuits
(ASICs), and other hardware. As shown in FIG. 7, the hardware
entities 714 can also include a removable memory unit 716
comprising a computer-readable storage medium 718 on which is
stored one or more sets of instructions 720 (e.g., software code)
configured to implement one or more of the methodologies,
procedures, or functions described herein. The instructions 720 can
also reside, completely or at least partially, within the memory
716 and/or within the CPU 706 during execution thereof by the
computing device 700. The memory 716 and the CPU 706 also can
constitute machine-readable media.
[0086] While the computer-readable storage medium 718 is shown in
an exemplary embodiment to be a single storage medium, the term
"computer-readable storage medium" should be taken to include a
single medium or multiple media (e.g., a centralized or distributed
database, and/or associated caches and servers) that store the one
or more sets of instructions. The term "computer-readable storage
medium" shall also be taken to include any medium that is capable
of storing, encoding or carrying a set of instructions for
execution by the machine and that cause the machine to perform any
one or more of the methodologies of the present disclosure.
[0087] The term "computer-readable storage medium" shall
accordingly be taken to include, but not be limited to solid-state
memories (such as a memory card or other package that houses one or
more read-only (non-volatile) memories, random access memories, or
other re-writable (volatile) memories), magneto-optical or optical
medium (such as a disk or tape). Accordingly, the disclosure is
considered to include any one or more of a computer-readable
storage medium or a distribution medium, as listed herein and to
include recognized equivalents and successor media, in which the
software implementations herein are stored.
[0088] System interface 722 can include a network interface unit
configured to facilitate communications over a communications
network with one or more external devices. Accordingly, a network
interface unit can be provided for use with various communication
protocols including the IP protocol. Network interface unit can
include, but is not limited to, a transceiver, a transceiving
device, and a network interface card (NIC).
[0089] As noted above, those skilled in the art will recognize that
such a plasma reactor may not only be used with conventional gas
treatment, but also for decontamination, odor control, etc. While
the description above refers to particular embodiments of the
invention, it will be understood that many modifications may be
made without departing from the spirit thereof. The accompanying
claims are intended to cover such modifications as would fall
within the true scope and spirit of the invention.
[0090] For example, although the various embodiments have been
discussed above with respect to hydrocarbons, the methods described
herein are equally application to removing other types of
contaminants from air and other gases. One potential use of the
systems and methods of the various embodiments is for the reduction
of sulfur contents from liquid fossil fuels is important for
production of good quality environment friendly fuels. Accordingly,
the systems and methods of the various embodiments can be used in
hydro-desulfurization by employing hydrogen and suitable catalysts
to break carbon-sulfur bond in the sulfur containing compounds and
make hydrogen-sulfur bonds to convert sulfur into gaseous hydrogen
sulfide. The systems and methods of the various embodiments can
also be used for oxidative desulfurization to provide an alternate
technique to oxidize the sulfur compounds into higher oxidation
states, like sulfones or sulfoxides which can be extracted from the
fuels. A non-thermal plasma based technique can be used as a source
of oxidizing agents for oxidative desulfurization.
[0091] Previous experiments with plasma reactors in which the
insulating walls were designed to confine the plasma in narrower
spaces, showed that the efficiency of these sliding discharges for
oxidation of organic compounds in air can be increased by more than
500% as illustrated in FIG. 8. FIG. 8 is a bar chart showing a
comparison of energy cost for partial oxidation of organic
pollutants from air and reduction of nitric oxide from nitrogen in
pulsed corona discharges in air (conventional plasma reactors) and
the sliding discharge reactor.
[0092] As noted above, introduction of a shield around the
discharge chamber allows increasing the energy density in the
plasma, shown in FIG. 8 to be about forty times, without loss of
efficiency for the chemical reactions that makes the plasma reactor
compact and scalable for high throughput relevant to commercial
applications. The reasons for these dramatic improvements in energy
deposition and efficiency are assumed to be due to: i) the
increased interaction of the sliding discharges with the solid
surfaces that supplies additional free electrons through
bombardment of charged particles on the surface or thermionic/photo
emissions and ii) adsorption and stabilization of short lived
active species on the surfaces that otherwise would be destroyed in
the gas phase. A similar improvement in efficiency can be provided
in oxidation of sulfur compounds.
[0093] For such processes, the sliding discharges of the various
embodiments can operate in air as well as in presence of any
proportion of water vapors in the process gas. The plasma in water
vapors (steam) simultaneously produces reducing agents and
oxidizing agents. These agents can be utilized to reduce and/or
oxidize organic compounds. Oxidation of benzene a representative
organic compound has already been demonstrated and desulfurization
in accordance with the various embodiments would occur in a similar
fashion, by simultaneously oxidizing a fraction of sulfur compounds
and reduction of the remaining fraction from fossil fuels.
[0094] The systems and methods of the various embodiments can also
be used to provide a plasma device that operates as an air filter
for destroying any air borne toxic chemical, bacterial or viral
agent. In order to obtain breathable air, it is desirable to
mitigate unwanted by-products of plasma, such as ozone and nitrogen
oxides. This can be achieved by employing suitable catalysts in the
plasma device. For example, some crystalline forms of aluminum
oxide can enhance ozone while some other crystalline forms of the
same material can destroy ozone in the plasma device. Since the
plasma device of the various embodiments is compact and easily
scalable by stacking and operating multiple discharge chambers in
parallel, it can be utilized to form an air filter for destroying
air borne toxic chemical, bacterial or viral agent.
[0095] In the case of the proposed shielded sliding discharge
device of the various embodiments, the dielectric surface in
contact with the plasma can itself act as a catalyst or a suitable
catalyst can be deposited on the dielectric surface. A layer of
porous ceramic layer can be deposited on the dielectric to provide
large area catalyst support for this purpose. This combination of
compact plasma device and catalyst can potentially be developed as
a device for protection against chemical and biological warfare
agents.
[0096] Applicants present certain theoretical aspects above that
are believed to be accurate that appear to explain observations
made regarding embodiments of the invention. However, embodiments
of the invention may be practiced without the theoretical aspects
presented. Moreover, the theoretical aspects are presented with the
understanding that Applicants do not seek to be bound by the theory
presented.
[0097] While various embodiments of the invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. Numerous
changes to the disclosed embodiments can be made in accordance with
the disclosure herein without departing from the spirit or scope of
the invention. Thus, the breadth and scope of the invention should
not be limited by any of the above described embodiments. Rather,
the scope of the invention should be defined in accordance with the
following claims and their equivalents.
[0098] Although the invention has been illustrated and described
with respect to one or more implementations, equivalent alterations
and modifications will occur to others skilled in the art upon the
reading and understanding of this specification and the annexed
drawings. In addition, while a particular feature of the invention
may have been disclosed with respect to only one of several
implementations, such feature may be combined with one or more
other features of the other implementations as may be desired and
advantageous for any given or particular application.
[0099] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. Furthermore, to the extent
that the terms "including", "includes", "having", "has", "with", or
variants thereof are used in either the detailed description and/or
the claims, such terms are intended to be inclusive in a manner
similar to the term "comprising."
[0100] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
* * * * *