U.S. patent application number 12/335934 was filed with the patent office on 2010-06-17 for emissions control system and method.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Gregg Anthony Deluga, Arnaldo Frydman, Gregory Ronald Gillette, Daniel Hancu, Ke Liu, Daniel George Norton, Frederic Vitse, Benjamin Hale Winkler.
Application Number | 20100146947 12/335934 |
Document ID | / |
Family ID | 42238935 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100146947 |
Kind Code |
A1 |
Liu; Ke ; et al. |
June 17, 2010 |
EMISSIONS CONTROL SYSTEM AND METHOD
Abstract
A system comprising a fuel converter comprising a catalyst
composition capable of converting a fuel into a selected one or
both of a syngas reductant and a short chain hydrocarbon reductant,
wherein the catalyst composition comprises: cracking sites that
perform a cracking function when a temperature of an exhaust fluid
is greater than a predetermined threshold temperature, wherein the
cracking function converts long chain hydrocarbon molecules to
short chain hydrocarbon molecules; and partial oxidation sites that
perform a catalytic partial oxidation function when the temperature
of the exhaust fluid is less than the predetermined threshold
temperature, wherein the catalytic partial oxidation function
oxidizes the fuel to produce the syngas reductant; and a selective
catalytic reduction catalyst reactor in fluid communication with
the fuel converter and the exhaust fluid.
Inventors: |
Liu; Ke; (Rancho Santa
Margarita, CA) ; Deluga; Gregg Anthony; (Playa del
Rey, CA) ; Frydman; Arnaldo; (Houston, TX) ;
Gillette; Gregory Ronald; (Houston, TX) ; Hancu;
Daniel; (Niskayuna, NY) ; Norton; Daniel George;
(Niskayuna, NY) ; Vitse; Frederic; (Knoxville,
TN) ; Winkler; Benjamin Hale; (Albany, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
42238935 |
Appl. No.: |
12/335934 |
Filed: |
December 16, 2008 |
Current U.S.
Class: |
60/295 ;
60/299 |
Current CPC
Class: |
Y02A 50/2325 20180101;
F01N 3/2073 20130101; C01B 2203/0277 20130101; C01B 3/386 20130101;
C01B 2203/16 20130101; C01B 2203/0261 20130101; F01N 2610/04
20130101; C10G 11/02 20130101; C01B 2203/1047 20130101; F01N
2610/03 20130101; C01B 3/26 20130101 |
Class at
Publication: |
60/295 ;
60/299 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Claims
1. A system comprising: a fuel converter comprising a catalyst
composition capable of converting a fuel into a selected one or
both of a syngas reductant and a short chain hydrocarbon reductant,
wherein the catalyst composition comprises: cracking sites that
perform a cracking function when a temperature of an exhaust fluid
is greater than a predetermined threshold temperature, wherein the
cracking function converts long chain hydrocarbon molecules to
short chain hydrocarbon molecules; and partial oxidation sites that
perform a catalytic partial oxidation function when the temperature
of the exhaust fluid is less than the predetermined threshold
temperature, wherein the catalytic partial oxidation function
oxidizes the fuel to produce the syngas reductant; and a selective
catalytic reduction catalyst reactor in fluid communication with
the fuel converter and the exhaust fluid.
2. The system of claim 1, further comprising an engine in fluid
communication with a fuel tank and the selective catalytic
reduction catalyst reactor, wherein the engine is located
downstream of the fuel tank and upstream of the selective catalytic
reduction catalyst reactor.
3. The system of claim 1, further comprising a controller operable
to control a flow of the exhaust fluid to the fuel converter.
4. The system of claim 3, wherein the controller permits the flow
of the exhaust fluid to the fuel converter when the temperature of
the exhaust fluid is less than the predetermined threshold
temperature.
5. The system of claim 3, wherein the control of exhaust fluid flow
is effective to change an oxygen to carbon molar ratio in the fuel
in the fuel converter.
6. The system of claim 1, further comprising a controller operable
to control the flow of fuel to the fuel converter and thus control
the production of the syngas reductant and/or the short-chain
hydrocarbon reductant.
7. The system of claim 1, wherein the cracking sites comprise a
zeolite and the partial oxidation sites comprise a dispersed noble
metal.
8. The system of claim 1, wherein the catalyst composition
comprises a platinum group metal dispersed on a catalyst
support.
9. The system of claim 8, wherein the platinum group metal
comprises platinum, rhodium, palladium, iridium, osmium, ruthenium,
or a combination comprising at least one of the foregoing.
10. The system of claim 8, wherein the catalyst composition
comprises about 0.1 weight percent to about 20 weight percent of
the platinum group metal.
11. The system of claim 9, wherein the platinum group metal further
comprises one or more base metals from Group VIII, Group IB, Group
VB or Group VIB of the Periodic Table of Elements.
12. The system of claim 8, wherein the catalyst support comprises a
monolith, wherein the monolith comprises foam, metal foil, fibers,
or a combination comprising at least one of the foregoing.
13. The system of claim 1, wherein the catalyst composition is
trimetallic.
14. The system of claim 13, wherein the trimettalic catalyst
composition is rhodium-platinum-iridium in proper
stoichiometry.
15. The system of claim 13, wherein the catalyst composition
further comprises a promoter configured to enhance the dispersion
of the platinum group metal.
16. The system of claim 15, wherein the promoter comprises rhenium,
rhodium, palladium, ruthenium, iridium, platinum, lanthanum,
cerium, chromium, gallium, or a combination comprising at least one
of the foregoing.
17. The system of claim 1, wherein the syngas reductant and/or the
short-chain hydrocarbon reductant control a nitrogen oxide content
of the exhaust fluid in the selective catalytic reduction catalyst
reactor.
18. A vehicle or stationary generator employing the system of claim
1.
19. A locomotive employing the system of claim 1 on board.
20. A method, comprising: determining a measured temperature of an
exhaust fluid; performing a catalytic partial oxidation of a fuel
to a syngas reductant when the measured temperature is less than a
predetermined threshold value, or converting a long chain
hydrocarbon molecules into a short chain hydrocarbon reductant, in
the presence of a catalyst composition, when the measured
temperature is greater than the predetermined threshold value;
reacting the syngas reductant and/or the short chain hydrocarbon
reductant with the exhaust fluid in the presence of a selective
catalytic reduction catalyst; and controlling a concentration of a
component of the exhaust fluid based on the measured
temperature.
21. The method of claim 20, wherein the converting occurs in a fuel
converter, and wherein the fuel converter comprises a ratio of
oxygen to carbon (O.sub.2/C) in a range of from about 0.10 to about
0.75.
22. The method of claim 20, wherein controlling the concentration
comprises reducing a nitrogen oxide content in the exhaust
fluid.
23. The method of claim 20, further comprising regenerating the
catalyst composition by diverting a portion of the exhaust fluid to
the catalyst composition when the measured temperature is less than
the predetermined threshold value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present disclosure includes embodiments that relate to
systems for controlling emissions. The disclosure further includes
embodiments that relate to a method for controlling emissions.
[0003] 2. Discussion of Art
[0004] Some vehicles may emit nitrogen oxides (NO.sub.x) during
use. Such emissions may be undesirable.
[0005] Emission controls have included engine modification and
exhaust gas treatment. It may be desirable to have a system for
emissions control that differs from those systems currently
available. It may be desirable to have a method of controlling
emissions that differs from those methods that currently
available.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Disclosed herein are systems and methods for controlling
emissions. In one embodiment, the method of controlling emissions
includes a system comprising a fuel converter comprising a catalyst
composition capable of converting a fuel into a selected one or
both of a syngas reductant and a short chain hydrocarbon reductant,
wherein the catalyst composition comprises: cracking sites that
perform a cracking function when a temperature of an exhaust fluid
is greater than a predetermined threshold temperature, wherein the
cracking function converts long chain hydrocarbon molecules to
short chain hydrocarbon molecules; and partial oxidation sites that
perform a catalytic partial oxidation function when the temperature
of the exhaust fluid is less than the predetermined threshold
temperature, wherein the catalytic partial oxidation function
oxidizes the fuel to produce the syngas reductant; and a selective
catalytic reduction catalyst reactor in fluid communication with
the fuel converter and the exhaust fluid.
[0007] A method for controlling emissions includes determining a
measured temperature of an exhaust fluid; performing a catalytic
partial oxidation of a fuel to a syngas reductant when the measured
temperature is less than a predetermined threshold value, or
converting a long chain hydrocarbon molecules into a short chain
hydrocarbon reductant, in the presence of a catalyst composition,
when the measured temperature is greater than the predetermined
threshold value, reacting the syngas reductant and/or the short
chain hydrocarbon reductant with the exhaust fluid in the presence
of a selective catalytic reduction catalyst; and controlling a
concentration of a component of the exhaust fluid based on the
measured temperature.
[0008] The above described and other features are exemplified by
the following Figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Referring to the exemplary drawings wherein like elements
are numbered alike in the several Figures:
[0010] FIG. 1 is a schematic depiction of one exemplary embodiment
of the system 10; and
[0011] FIG. 2 is a schematic depiction of one exemplary embodiment
of a rotary fuel converter.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present disclosure includes embodiments that relate to
systems and methods of controlling emissions. Systems and methods
for controlling emissions may reduce the nitrogen oxides (NO.sub.x)
emissions from the exhaust stream of a vehicle or a stationary
source. Vehicles may include, for example, locomotives, marine
vessels, off-highway vehicles, tractor-trailer rigs, passenger
vehicles, and the like. Emissions control refers to the ability to
affect the compositional make-up of an exhaust gas stream. As
exhaust gas is a mixture of components, the reduction of one
component almost invariably increases the presence of another
component. For clarity of discussion, the chemical reduction of
NO.sub.x is used as a non-limiting example of emission reduction
insofar as the concentration of a determined species within the
exhaust gas stream is controlled.
[0013] The system utilizes the fuel for the engine as a reductant
to reduce NO.sub.x emissions. The system converts the already
on-board fuel into a broad range of reductants. The system
advantageously utilizes short-chain hydrocarbons, hydrogen
(H.sub.2), and carbon monoxide (CO) obtained from a fuel conversion
reactor to reduce NO.sub.x emissions. The fuel converter converts
fuel, for instance diesel fuel, into a hydrogen-rich syngas,
short-chain hydrocarbons, which can include small amounts of
H.sub.2 and CO present as by-products, or some combination of the
two. These are mixed with the exhaust stream and facilitate a
reduction of NO.sub.x emissions in the presence of a hydrocarbon
based selective catalytic reduction (SCR) catalyst bed. The
short-chain hydrocarbons and/or the hydrogen-rich syngas generated
in-situ from the fuel converter will react with the NO.sub.x in the
exhaust stream and reduce NO.sub.x to nitrogen at the surface of a
selective catalytic reduction (SCR), thereby reducing NO.sub.x
emissions from the vehicle. The system can be advantageously
utilized on board in all types of vehicles that employ internal
combustion engines powered by hydrocarbon-based fossil fuels or
isolated units that have no access to other reductants. The system
can also be utilized on board in all types of locomotives that
employ engines and turbines powered by hydrocarbon-based fossil
fuels. In one embodiment, the hydrocarbon-based fossil fuels are
liquids. In particular, the system can be utilized in vehicles that
employ diesel engines. Locomotives that employ diesel engines and
diesel turbines can use the system on board for reduction of
NO.sub.x emissions. The system can be also utilized in stationary
combustion sources burning hydrocarbon-based fuels. The system
described herein does not require the need for additional reductant
chemicals or the storage equipment required to be on-board
therewith.
[0014] The system converts the already on-board fuel into a broad
range or reductants by utilizing a fuel converter that can operate
in a auto-thermal cracking (ATC) mode, a catalytic partial
oxidation (CPO) mode, or a combination thereof. The flexibility of
operating between these two modes can generate either short chain
hydrocarbon reductants (i.e., light hydrocarbons) in the ATC mode,
or hydrogen-rich syngas via the CPO mode. All of the reductants can
be produced from the fuel on board. The flexible design of the fuel
converter is a result of the catalyst composition disposed therein.
The catalyst composition is capable of converting the on-board fuel
into a selected one or both of the hydrogen-rich syngas reductant
and the short chain hydrocarbon reductant. The catalyst composition
includes cracking sites that perform a cracking function when a
temperature of an exhaust fluid is greater than a predetermined
threshold temperature, wherein the cracking function converts long
chain hydrocarbon molecules to short chain hydrocarbon molecules.
The catalyst composition further includes oxidation sites that
perform a catalytic partial oxidation function when the temperature
of the exhaust fluid is less than the predetermined threshold
temperature, wherein the catalytic partial oxidation function
oxidizes the fuel to produce the hydrogen-rich syngas reductant. In
one embodiment, the predetermined threshold temperature is about
150 to about 400 degrees Celsius
[0015] With reference now to FIG. 1, an example of system 10 for
the reduction of NOx emissions comprises a fuel tank 12, a fuel
converter 14, a SCR catalyst reactor 16 and an engine 18. The fuel
tank 12 is upstream of the fuel converter 14 and the SCR catalyst
reactor 16. The fuel tank 12, the fuel converter 14, and the SCR
catalyst reactor 16 are in fluid communication with one another.
The fuel converter 14 is located between the fuel tank 12 and the
SCR catalyst reactor 16 and is upstream of the SCR catalyst reactor
16. The engine 18 is located downstream of the fuel tank 12 and in
fluid communication with the fuel tank 12. The engine is located
upstream of the fuel converter 14 and the SCR catalyst reactor 16
and is in fluid communication with both the fuel converter 14 and
the SCR catalyst reactor 16.
[0016] The system 10 can also employ two optional separators--a
first separator 20 and a second separator 22. The optional
separators 20 and 22 comprise distillation columns (with optional
vacuum systems), packed columns, membranes, condensers,
centrifuges, or the like that can be used to separate aromatics
from paraffins or long-chain hydrocarbons from the short-chain
hydrocarbons. In one embodiment, aromatics are separated from the
hydrocarbons in the separator 20, while heavy hydrocarbons are
separated from the short-chain hydrocarbons in the separator 22.
The heavy hydrocarbons are recycled to the fuel tank 12 so that
they can be consumed in the engine 18.
[0017] In one embodiment, the system 10 can further comprise a
controller 23 operable to control a flow of the exhaust fluid to
the fuel converter 14. As will be described in greater detail
below, the controller 24 can permit the flow of the exhaust fluid
to the fuel converter 14 when the temperature of the exhaust fluid
is less than a predetermined threshold temperature. The system 10
can still further include a second controller 24, which is operable
to control the flow of fuel to the fuel converter 14, and thus
control the production of the syngas reductant and/or the
short-chain hydrocarbon reductant.
[0018] The term "fluid communication" encompasses the containment
and/or transfer of compressible and/or incompressible fluids
between two or more points in the system 10. Examples of suitable
fluids are gases, liquids, combinations of gases and liquids, or
the like. The use of pressure transducers, thermocouples, flow,
hydrocarbon, NOx sensors aid in communication and control. In one
embodiment, computers can be used to aid in the flow of fluids in
the system. The term "on-board" refers to the ability of a vehicle
or locomotive to host the system 10 in its entirety aboard the
vehicle or locomotive.
[0019] A variety of fuels may be stored in the fuel tank 12 and
used in the system 10. In one embodiment, the fuel is a
hydrocarbon-based fossil fuel. It is desirable for the
hydrocarbon-based fossil fuel to be a liquid. Examples of suitable
liquids are diesel, gasoline, jet-fuel, logistic fuel (JP-8),
kerosene, fuel oil, bio-diesel, or the like, or a combination
comprising at least one of the foregoing hydrocarbon-based fossil
fuels. As will be discussed in further detail below, the fuel
converter 14 converts long-chain hydrocarbons to short-chain
hydrocarbons which are then used to reduce NOx in the exhaust.
Long-chain hydrocarbons are hydrocarbons that have 9 or more carbon
atoms. In an exemplary embodiment, an exemplary long-chain
hydrocarbon is diesel. Short-chain hydrocarbons are those that have
8 or less carbon atoms. Exemplary short-chain hydrocarbons are
those having about 2 to about 8 hydrocarbons. Short-chain
hydrocarbons are also termed paraffinic hydrocarbons. Paraffinic
hydrocarbons can be saturated or unsaturated.
[0020] As mentioned above, the fuel converter 14 comprises a fixed
bed reactor that comprises a catalyst composition. It is desirable
for the catalyst composition to be able to operate under conditions
that vary from oxidizing at the inlet of the reactor to reducing
conditions at the exit of the reactor. The catalyst should be
capable of operating effectively and without any thermal
degradation from a temperature of about 200 to about 900.degree. C.
The catalyst should operate effectively in the presence of air,
carbon monoxide, carbon dioxide, water, alkanes, alkenes, cyclic
and linear compounds, aromatic hydrocarbons and sulfur-containing
compounds. The catalyst composition should provide for low levels
of coking such as by preferentially catalyzing the reaction of
carbon with water to form carbon monoxide and hydrogen thereby
permitting the formation of only a low level of carbon on the
surface of the catalyst. The catalyst composition should be able to
resist poisoning from such common poisons such as sulfur and
halogen compounds. Moreover, an exemplary catalyst composition may
satisfy all of the foregoing requirements simultaneously.
[0021] In one embodiment, the catalyst composition contained in the
fuel converter 14 is bifunctional, i.e., it serves to crack heavier
hydrocarbons to light hydrocarbons, while simultaneously preventing
poisoning of the catalyst composition from coke depositions. Coke
build-up that occurs during the cracking of hydrocarbons while
using traditional zeolite cracking catalysts during processes such
as fluidized catalytic cracking (FCC) deactivates the catalyst. The
bifunctional catalyst advantageously slows down coke build-up rate
on the surface of cracking catalysts, thus allowing it to continue
being active for cracking hydrocarbons, which would normally not
occur on conventional cracking catalysts operating under similar
conditions.
[0022] In the catalyst composition, since the catalytic partial
oxidation reaction is an exothermic reaction, while cracking is an
endothermic reaction, the heat generated at a catalytic partial
oxidation site facilitates the endothermic cracking reaction and
also facilitates the oxidation of coke. In one embodiment, the
catalytic partial oxidation sites are used to oxidize the coke away
from the cracking sites to keep the cracking sites clean and
active.
[0023] The use of a fuel converter 14 that employs the catalytic
composition is advantageous in that it may use only a single fixed
bed reactor to convert diesel fuel to a mixture of short-chain
hydrocarbons and hydrogen-rich syngas. This mixture of short-chain
hydrocarbons and syngas can be used as a reducing agent for NOx
reduction in diesel engine exhaust and will be discussed later. If
desired, the fuel converter can employ more than one fixed bed
reactor to improve productivity. For example, the catalytic
converter can employ about 2 to about 6 fixed bed reactors if
desired.
[0024] The catalytic partial oxidation sites generally comprise
noble metals that perform the catalytic partial oxidation function.
The catalytic partial oxidation sites comprise one or more
"platinum group" metal components. As used herein, the term
"platinum group" metal implies the use of platinum, palladium,
rhodium, iridium, osmium, ruthenium or mixtures thereof. Exemplary
platinum group metal components are rhodium, platinum and
optionally, iridium. The catalyst composition generally comprises
about 0.1 to about 20 wt % of the platinum group metal. The
platinum group metal components may optionally be supplemented with
one or more base metals, particularly base metals of Group VIII,
Group IB, Group VB and Group VIB of the Periodic Table of Elements.
Exemplary base metals are iron, cobalt, nickel, copper, vanadium
and chromium.
[0025] The cracking sites generally comprise a zeolite. The
zeolites generally have a silica-to-alumina mole ratio of at least
about 12. In one embodiment, a zeolite having a silica-to-alumina
mole ratio of about 12 to about 1000 is used. In one embodiment, a
zeolite having a silica-to-alumina mole ratio of about 15 to about
500 is used. Examples of suitable zeolites are RE-Y (rare earth
substituted yttria), USY (ultrastable yttria zeolite), RE-USY
ZSM-5, ZSM-11, ZSM-12, ZSM-35, zeolite beta, MCM-22, MCM-36,
MCM-41, MCM-48, or the like, or a combination comprising at least
one of the foregoing zeolites.
[0026] Zeolites also contemplated for use in this process are the
crystalline silicoaluminophosphates (SAPO). Examples of suitable
silicoalumino-phosphates include SAPO-11, SAPO-34, SAPO-31, SAPO-5,
SAPO-18, or the like, or a combination comprising at least one of
the foregoing silicoaluminophosphates.
[0027] The platinum group catalysts along with other base metal
catalysts are washcoated onto the molecular sieves to form the
catalytic composition. In one embodiment, the catalytic partial
oxidation sites comprise about 0.1 to about 5.0 weight percent (wt
%) of the total weight of the catalytic composition. In a preferred
embodiment, the catalytic partial oxidation sites comprise about
0.3 to about 1.0 wt % of the total weight of the catalytic
composition.
[0028] In one embodiment, the bifunctional catalyst composition of
the fuel converter can comprise a combination of metals forming a
uniform phase, such as trimetallic catalysts. An exemplary
trimetallic catalyst is rhodium-platinum-iridium in proper
stoichiometry to aid catalyst phase uniformity.
[0029] Catalyst supports may comprise alumina, titania, zirconia,
ceria, silicon carbide or any mixture of these materials.
Typically, the catalyst support comprises gamma-alumina with high
surface area comprising impurities of at least about 0.2% by weight
in one embodiment and at least about 0.3% by weight in another
embodiment. The catalyst support may be made by any method known to
those of skill in the art, such as co-precipitation, spray drying
or sol-gel methods for example. The catalyst substrates can be
foam, metal foil, fibrous metal, monolith, and the like. The
substrates can be wash coated with the metal oxides before
dispersion of, for example, the trimetallic catalyst composition
onto the substrate.
[0030] A refractory support can further be included with the
bifunctional catalyst composition to enhance stability of catalytic
partial oxidation sites when sulfur and steam are present in a feed
stream to the fuel converter.
[0031] Further, promoters can be used to enhance the dispersion of
the trimetallic catalyst composition on the substrate. Exemplary
promoters can include, without limitation, rhenium, rhodium,
palladium, ruthenium, iridium, platinum, lanthanum, cerium,
chromium, oxides thereof, and a combination comprising at least one
of the foregoing.
[0032] In one embodiment, the trimetallic catalyst composition
system comprises 0.2 wt % rhodium, 0.2 wt % iridium, and 0.3 wt %
platinum, based on a total weight of the catalyst composition,
dispersed on an alumina foam support washcoated with 5 wt % cerium,
0.5 wt % zirconium, and 0.01 wt % yttrium alumina.
[0033] In another embodiment, a wash-coated support substrate with
a doped alumina wash coat can be used in order to maintain a gamma
alumina phase of the composition, rather than the alpha alumina
phase. Such an example could be chromium-europium doped alumina
that is then wash coated onto a support. Chromium can form a
Sapphire support substrate structure and europium can form defects
within that structure. These crystals can then stabilize the
overall structure of alumina into the gamma phase, thereby
increasing catalyst stability.
[0034] In an exemplary embodiment, in one method of operating the
fuel converter 14, a gas-assisted nozzle is utilized to atomize the
fuel at a low-pressure inlet into the fuel converter 14 (not
shown). The fuel, which primarily comprises heavy hydrocarbons
undergoes cracking to form the short hydrocarbons. The short
hydrocarbons are then used to reduce the NOx emitted in the engine
exhaust. The reduction of the NOx with the short hydrocarbons
occurs in the presence of an SCR catalyst as will be detailed
later.
[0035] A portion of the hot exhaust gas that is emitted by the
locomotive engine can be used as a secondary gas for atomizing the
fuel. Air can also be employed as the secondary gas for atomizing
the fuel. In an exemplary embodiment, a portion of the exhaust
stream is combined with air to form the secondary gas to facilitate
the catalytic partial oxidation reaction. The amount of hot engine
exhaust gas is effective to light off the catalytic partial
oxidation reaction in the fuel converter 14. The heat released from
the exothermic catalytic partial oxidation reaction will drive the
endothermic cracking reaction forward. Water present in the exhaust
stream can facilitate the reduction of coke formation on the
catalyst.
[0036] In one embodiment, in order to light off the catalytic
partial oxidation reaction, the oxygen/carbon (O2/C) mole ratio in
the feed gas that is supplied to the fuel converter is in an amount
of about 0.01 to about 0.5. In another embodiment, the
oxygen/carbon (O2/C) mole ratio in the feed gas is in an amount of
about 0.05 to about 0.4. In yet another embodiment, the
oxygen/carbon (O2/C) mole ratio in the feed gas is in an amount of
about 0.1 to about 0.3. An exemplary (O2/C) mole ratio in the feed
gas is in an amount of about 0.1.
[0037] The temperature of the fuel converter is maintained at about
550.degree. C. to about 650.degree. C., during the conversion of
long-chain hydrocarbons to short-chain hydrocarbons. In one
embodiment, the temperature of the fuel converter is maintained at
about 580.degree. C. to about 640.degree. C., during the conversion
of long-chain hydrocarbons to short-chain hydrocarbons. An
exemplary temperature is about 600 to about 620.degree. C. At about
600 to about 620.degree. C., the deposition of sulfate groups
derived from sulfur containing organic compounds will be reduced
and hence the sulfur tolerance of the system 10 is enhanced.
[0038] If coke species accumulate on the catalyst composition in
the fuel converter during the catalytic partial oxidation process,
the flow rate of engine exhaust gas (which contains considerable
quantity of oxygen and water) can be periodically increased to burn
and steam the coke off and to regenerate the hybrid catalyst
activity. A single valve (not shown) can also periodically be used
to increase the flow rate of engine exhaust gas and/or air to burn
the coke off.
[0039] In one embodiment, in order to burn off coke that is
deposited on the catalytic composition, the O2/C mole ratio in the
feed gas to the diesel converter can be varied in an amount of
about 0.1 to about 0.75. In one embodiment, in order to burn off
coke that is deposited on the catalytic composition, the O2/C mole
ratio in the feed gas to the diesel converter can be varied in an
amount of about 0.2 to about 0.55. An exemplary O2/C mole ratio in
the feed gas to the diesel converter is about 0.5.
[0040] The temperature of the fuel converter is maintained at about
550.degree. C. to about 750.degree. C., during the burning off coke
that is deposited on the catalytic composition. In one embodiment,
the temperature of the fuel converter is maintained at about
600.degree. C. to about 720.degree. C., during the burning off coke
that is deposited on the catalytic composition. In another
embodiment, the temperature of the fuel converter is maintained at
about 620.degree. C. to about 710.degree. C., during the burning
off coke that is deposited on the catalytic composition. An
exemplary temperature is about 650 to about 700.degree. C. during
the burning off coke that is deposited on the catalytic
composition.
[0041] The use of the catalytic composition in conjunction with an
increased exhaust gas and/or air flow to burn off the coke is
advantageous in that it overcomes the need for a system comprising
two reactors to perform the cracking and regeneration functions.
Noble metals such as rhodium, iridium and platinum are also
oxidation catalysts, and they will also help to burn the coke more
efficiently off the zeolite cracking catalyst. The noble metal
promotes oxidation of coke into carbon dioxide and minimizes or
completely avoids formation of carbon monoxide during the coke
oxidation process.
[0042] In another embodiment, in another method of operating the
fuel converter 14, the fuel converter 14 can comprise a rotary
reactor, wherein the inlet port of such a reactor can be
periodically rotated through a first small angle. FIG. 2 is an
exemplary embodiment or a rotary reactor 100 that can be used as a
fuel converter. The rotary reactor 100 comprises 4 reaction
chambers 102, 104, 106, and 108 each of which contains the catalyst
composition. Each reaction chamber also comprises an inlet port 110
that is used to permit feed gases into the reactor. The chambers
and the inlet ports can be rotated about a shaft 112.
[0043] The rotation of the inlet port can be conducted
automatically via a computer. By rotating the inlet port of the
reactor, a small portion of the reactor can be subjected to the
high temperature exhaust gases. The coke disposed upon the catalyst
composition contained in this small portion of the reactor is
oxidized by the hot exhaust gases and removed. Thus a small portion
of the catalyst composition is completely regenerated, and the
inlet port can be rotated through a second small angle in order to
regenerate another portion of the catalyst. The rotation can be
continued throughout the process to continuously convert long-chain
hydrocarbons to short-chain hydrocarbons and syngas without
significant catalyst deactivation due to coking. As noted above,
syngas comprises hydrogen and carbon monoxide, both of which are
useful reducing agents when exhaust gases having a low temperature
are used. The use of the continuously operating fuel converter 14
permits it to be used on-board in vehicles and locomotives.
[0044] The short-chain hydrocarbons obtained from the fuel
converter 14 are then permitted to flow to the SCR catalyst reactor
16, where they are used to reduce the NOx in the engine exhaust
stream. The reduction of NOx occurs over a selective catalytic
reduction catalyst. Examples of suitable selective catalytic
reduction catalysts are metals such as silver, gallium, cobalt,
molybdenum, tungsten, indium, bismuth, vanadium or a combination
comprising at least one of the foregoing metals in a binary,
ternary or quaternary mixture disposed upon a suitable support.
Oxides of metals can be used as catalysts if desired. Oxides of
metals can also be used as catalyst supports. Examples of suitable
metal oxide supports are alumina, titania, zirconia, ceria, silicon
carbide, or a combination comprising at least one of the foregoing
supports.
[0045] The short-chain hydrocarbons can be used to reduce NO.sub.x
in the exhaust stream, according to the following overall reaction
(1).
NO.sub.x+O.sub.2+organic reductant.fwdarw.N.sub.2+CO.sub.2+H.sub.2O
(1)
[0046] The exhaust stream usually comprises air, water, CO,
CO.sub.2, NO.sub.x, SO.sub.x, H.sub.2O and may also comprise other
impurities. Water contained in the exhaust stream is generally in
the form of steam. Additionally, uncombusted or incompletely
combusted fuel may also be present in the exhaust stream. The
short-chain hydrocarbon molecules comprising less than or equal to
about 8 carbon atoms along with CO and H.sub.2 is fed into the
exhaust stream to form a gas mixture, which is then fed through the
selective catalytic reduction catalyst. Sufficient oxygen to
support the NO.sub.x reduction reaction may already be present in
the exhaust stream. If the oxygen present in the exhaust stream is
not sufficient for the NO.sub.x reduction reaction, additional
oxygen gas may also be introduced into the exhaust stream in the
form of air. In some embodiments the gas mixture comprises from
about 1 mole percent (mole %) to about 21 mole % of oxygen gas. In
some other embodiments the gas mixture comprises from about 1 mole
% to about 15 mole % of oxygen gas.
[0047] The NO.sub.x reduction reaction may take place over a range
of temperatures. In one embodiment, the reduction reaction can
occur at a temperature of about 200.degree. C. to about 600.degree.
C. In another embodiment, the reduction reaction can occur at a
temperature of about 300.degree. C. to about 500.degree. C. In yet
another embodiment, the reduction reaction can occur at a
temperature of about 350.degree. C. to about 450.degree. C.
[0048] If syngas is produced during the conversion of heavy
hydrocarbons to short-chain hydrocarbons in the fuel converter 14,
then reduction of NO.sub.x in the SCR catalyst reactor 16 with the
short-chain hydrocarbons and syngas can take place at temperatures
of as low as about 150.degree. C., according to the following
reaction (2).
NO.sub.x+H.sub.2+CO+organic
reductant.fwdarw.N.sub.2+H.sub.2O+CO.sub.2 (2)
[0049] In one embodiment, reaction (2) occurs at a temperature of
about 100 to about 500.degree. C. In another embodiment, the
reaction occurs at a temperature of about 150 to about 350.degree.
C. The system 10 detailed above provides many advantages that make
it useful in diesel locomotives. The catalyst composition
advantageously displays both a cracking function as well as a
catalytic partial oxidation function. This reduces the need for a
system having two reactors with multiple hot valves, which
alternately switches between cracking and regeneration modes
thereby reducing costs.
[0050] Additionally, the use of a simple air-valve to periodically
increase the flow rate of engine exhaust gas and/or air to burn the
coke off, also reduces the need for a system having two or more
reactors. The use of the gas-assisted nozzle facilitates the
atomization of the long-chain hydrocarbons such as diesel at a low
pressure. In one embodiment, the fuel pressure is less than or
equal to about 8 bar (8.15 kg/cm.sup.2) and the air pressure is
less than or equal to about 6.5 bar (6.62 kg/cm.sup.2) prior to
entry into the fuel converter 14. In one embodiment, the fuel
pressure is less than or equal to about 6 kg/cm.sup.2 and the air
pressure is less than or equal to about 4.5 bar kg/cm.sup.2 prior
to entry into the fuel converter 14. In yet another embodiment, the
fuel pressure is less than or equal to about 4.5 kg/cm.sup.2 and
the air pressure is less than or equal to about 3.5 bar kg/cm.sup.2
prior to entry into the fuel converter 14.
[0051] In addition, the use of a fuel converter 14 that can rotate
(i.e., functions as a rotary reactor) permits regeneration of the
entire catalyst bed thereby permitting continuous operation. This
allows for an effective on-board utility while reducing operating
and maintenance costs.
[0052] The system 10 advantageously uses hot exhaust gases from the
exhaust stream to light off the catalytic partial oxidation
function of the catalyst composition. This permits integration of
the system 10 with the exhaust system to improve the efficiency of
the fuel converter 14. The use of hot exhaust gases advantageously
facilitates the production of syngas, which can be used to reduce
the NO.sub.x concentration at lower temperatures. In addition, the
hydrogen contained in the syngas minimizes coke formation.
[0053] Turning back now to FIG. 1, an optional separator 20 is
located down stream of the fuel tank 12 and upstream of the fuel
converter 14 and is in fluid communication with the fuel tank 12
and the fuel converter 14. A feed back loop between the first
separator 20 and the fuel tank 12 serves to recycle heavy
hydrocarbons species to the fuel tank 12 or engine 18. The first
separator comprises distillation columns with optional vacuum
systems, membranes, condensers, centrifuges, or combinations
thereof that can be used to separate aromatic heavy hydrocarbons
from the paraffinic short-chain hydrocarbons, and wherein the
aromatics output from the first separator is recycled back to the
fuel tank, and the paraffinic hydrocarbons are fed to the fuel
converter.
[0054] An additional optional separator 22 can also be located
between the fuel converter 14 and the SCR catalyst reactor 16. The
second separator 22 is located down stream of the fuel converter 14
and upstream of the SCR catalyst reactor 16. The second separator
22 is in fluid communication with the fuel converter 14 and
upstream of the SCR catalyst reactor 16. A feed back loop between
the second separator 22 and the fuel tank 12 serves to recycle
heavy hydrocarbons to the fuel tank 12 or engine 18. Separator 22
seeks to increase fuel efficiency and increase the robust nature of
the SCR catalyst while separator 20 seeks to improve the
reliability of the fuel converter and increase fuel efficiency. As
noted above, the separators are optional. However, in one
embodiment, either the first separator 20 or the second separator
22 can be used in the system. In yet another embodiment, both the
first separator 20 and the second separator 22 can be used in the
system. It is generally desirable to use the second separator due
to its low cost and low fuel consumption. Additionally, the second
separator 22 introduces more robustness to the system of producing
a rich-stream in useful reductants to the SCR system.
[0055] In an exemplary embodiment, the second separator 22 can be a
simple packed column e.g., a vessel with some packing material such
as pall rings packed inside a column with either some coils or a
jacket where cooling water at a temperature of about 70 to about
99.degree. C. available on the locomotive will flow through and
maintain the column temperature at about 100 to about 200.degree.
C. In another embodiment, a cooled knock-out plate or a condenser
operating at a temperature of about 90 to about 150.degree. C. with
heated return lines can be used to return the heavy hydrocarbons to
the fuel tank 12 or engine 18. This facilitates uniform viscosity
and flow characteristics for the heavy hydrocarbons that are
returned to the fuel tank 12 or the engine 18.
[0056] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. Ranges disclosed herein are inclusive and combinable
(e.g., ranges of "up to about 25 wt %, or, more specifically, about
5 wt % to about 20 wt %", is inclusive of the endpoints and all
intermediate values of the ranges of "about 5 wt % to about 25 wt
%," etc.). "Combination" is inclusive of blends, mixtures, alloys,
reaction products, and the like. Furthermore, the terms "first,"
"second," and the like, herein do not denote any order, quantity,
or importance, but rather are used to distinguish one element from
another, and the terms "a" and "an" herein do not denote a
limitation of quantity, but rather denote the presence of at least
one of the referenced item. The modifier "about" used in connection
with a quantity is inclusive of the stated value and has the
meaning dictated by context, (e.g., includes the degree of error
associated with measurement of the particular quantity). The suffix
"(s)" as used herein is intended to include both the singular and
the plural of the term that it modifies, thereby including one or
more of that term (e.g., the colorant(s) includes one or more
colorants). Reference throughout the specification to "one
embodiment", "another embodiment", "an embodiment", and so forth,
means that a particular element (e.g., feature, structure, and/or
characteristic) described in connection with the embodiment is
included in at least one embodiment described herein, and may or
may not be present in other embodiments. In addition, it is to be
understood that the described elements may be combined in any
suitable manner in the various embodiments.
[0057] 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 the
embodiments of the invention belong. 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 the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0058] While the disclosure has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *