U.S. patent application number 12/751183 was filed with the patent office on 2011-10-06 for emission treatment system and method of operation.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Dan Hancu, Larry Neil Lewis, Daniel George Norton, Benjamin Hale Winkler.
Application Number | 20110239622 12/751183 |
Document ID | / |
Family ID | 44708011 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110239622 |
Kind Code |
A1 |
Hancu; Dan ; et al. |
October 6, 2011 |
EMISSION TREATMENT SYSTEM AND METHOD OF OPERATION
Abstract
An emission treatment system is provided. The emission treatment
system comprises a separation system and a selective catalytic
reduction (SCR) catalyst. The separation system comprises a
separator, a fuel inlet disposed to supply fuel to the separator, a
first fuel outlet and a second fuel outlet respectively disposed to
carry away fuel from the separator. The SCR catalyst comprises a
catalyst composition comprising silver and templated metal oxide
substrate. The emission treatment system is designed such that the
separation system is configured to be in fluid communication with
the SCR catalyst through the first fuel outlet during operation. A
system including the emission treatment system and a combustion
engine is also provided. Method of increasing NOx reduction
efficiency of the SCR catalyst using fuel fraction is
discussed.
Inventors: |
Hancu; Dan; (Clifton Park,
NY) ; Winkler; Benjamin Hale; (Albany, NY) ;
Norton; Daniel George; (Niskayuna, NY) ; Lewis; Larry
Neil; (Scotia, NY) |
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
44708011 |
Appl. No.: |
12/751183 |
Filed: |
March 31, 2010 |
Current U.S.
Class: |
60/274 ; 422/173;
422/177; 60/297; 60/303 |
Current CPC
Class: |
B01D 53/9418 20130101;
B01D 2255/2092 20130101; F01N 2330/06 20130101; F01N 2370/04
20130101; F01N 2240/30 20130101; F01N 2610/03 20130101; Y02T 10/12
20130101; B01D 2255/9207 20130101; B01D 53/90 20130101; Y02T 10/24
20130101; B01D 2255/30 20130101; B01D 2257/404 20130101; F01N
2330/48 20130101; B01D 2251/208 20130101; F01N 3/2066 20130101;
F01N 3/2828 20130101; F01N 2240/16 20130101; F01N 2240/02 20130101;
B01D 2255/104 20130101 |
Class at
Publication: |
60/274 ; 60/297;
60/303; 422/177; 422/173 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/035 20060101 F01N003/035; F01N 3/10 20060101
F01N003/10 |
Claims
1. An emission treatment system comprising: a separation system
comprising a separator, a fuel inlet disposed to supply fuel to the
separator, a first fuel outlet and a second fuel outlet
respectively disposed to carry away fuel from the separator; and a
selective catalytic reduction (SCR) catalyst comprising a catalyst
composition comprising silver and templated metal oxide substrate,
wherein the separation system is configured to be in fluid
communication with the SCR catalyst through the first fuel outlet
during operation.
2. The emission treatment system of claim 1, wherein the separator
comprises a flash heater.
3. The emission treatment system of claim 1, wherein the separator
comprises a distillation unit.
4. The emission treatment system of claim 1, wherein the separator
comprises a membrane.
5. The emission treatment system of claim 1, wherein the separator
comprises a heat exchanger.
6. The emission treatment system of claim 1, wherein the separator
comprises a bubbling column.
7. The emission treatment system of claim 1, wherein the templated
metal oxide comprises alumina or silica-alumina.
8. The emission treatment system of claim 1, wherein the catalyst
composition has a surface area in the range of about 250 to about
600 m.sup.2/gm.
9. The emission treatment system of claim 1, wherein the templated
metal oxide has periodically arranged templated pores, wherein the
average diameter of the pores is in a range of from about 2
nanometers to about 100 nanometers and the pores have a periodicity
in a range of from about 50 Angstrom to about 130 Angstrom.
10. The emission treatment system of claim 1, wherein the substrate
further comprises an additional dopant material selected from the
group consisting of zirconium, yttrium, iron, gallium, indium,
tungsten, zinc, platinum, and rhodium.
11. The emission treatment system of claim 1, wherein the separator
is configured to receive fuel through the fuel inlet, separate the
fuel into a first fraction having a maximum boiling point at a
temperature that is in the range from about 70 degrees Celsius to
about 360 degrees Celsius and a second fraction of fuel having a
boiling point above said temperature, and dispose the first
fraction into the first fuel outlet.
12. The emission treatment system of claim 11, wherein the maximum
boiling point is at a temperature that is in the range from about
100 degrees Celsius to about 225 degrees Celsius.
13. The emission treatment system of claim 12, wherein the
temperature is about 225 degrees Celsius.
14. The emission treatment system of claim 1, wherein the separator
is configured to receive fuel through the fuel inlet, separate the
fuel into a first fraction having a minimum boiling point at a
temperature that is in the range from about 70 degrees Celsius to
about 360 degrees Celsius and a second fraction of fuel having a
boiling point below said temperature, and dispose the first
fraction into the first fuel outlet.
15. The emission treatment system of claim 14, wherein the minimum
boiling point is at a temperature that is in the range from about
300 degrees Celsius to about 360 degrees Celsius.
16. The emission treatment system of claim 1, wherein the
separation system comprises a first separator and a second
separator, and wherein the first fuel outlet of the first separator
is the fuel inlet of the second separator.
17. A system comprising: a fuel tank adapted to supply a fuel; a
combustion engine configured to receive the fuel and create an
exhaust stream; and an emission treatment system configured to
receive at least a portion of the exhaust stream wherein the
emission treatment system comprises: a separation system comprising
a fuel inlet disposed to receive fuel from the fuel tank, a
separator configured to receive fuel through the fuel inlet, a
first fuel outlet and a second fuel outlet respectively disposed to
carry away fuel from the separator; and an SCR catalyst comprising
a catalyst composition comprising silver and a templated metal
oxide substrate, wherein the separation system is in fluid
communication with the SCR catalyst through the first fuel
outlet.
18. The system of claim 17, wherein the separation system is in
fluid communication with the combustion engine through the second
fuel outlet.
19. The system of claim 17, wherein the separator comprises a flash
heater.
20. The system of claim 17, wherein the separator comprises a
distillation unit.
21. The system of claim 17, wherein the templated metal oxide
comprises alumina or silica-alumina.
22. The system of claim 17, wherein the catalyst composition has a
surface area in the range of about 250 to about 600 m.sup.2/gm.
23. The system of claim 17, wherein the templated metal oxide has
periodically arranged templated pores, wherein the average diameter
of the pores is in a range of from about 2 nanometers to about 100
nanometers and the pores have a periodicity in a range of from
about 50 Angstrom to about 130 Angstrom.
24. The system of claim 17, wherein the substrate further comprises
an additional dopant material selected from the group consisting of
zirconium, yttrium, iron, gallium, indium, tungsten, zinc,
platinum, and rhodium.
25. The system of claim 17, wherein the separator is configured to
receive fuel through the fuel inlet, separate the fuel into a first
fraction having a maximum boiling point at a temperature that is in
the range from about 70 degrees Celsius to about 350 degrees
Celsius and a second fraction having a boiling point above said
temperature, and dispose the first fraction into the first fuel
outlet.
26. The system of claim 25, wherein the maximum boiling point is at
a temperature that is in the range from about 100 degrees Celsius
to about 225 degrees Celsius.
27. The system of claim 26, wherein the maximum boiling point is at
a temperature that is in the range from about 150 degrees Celsius
to about 200 degrees Celsius.
28. The system of claim 17, wherein the separator is configured to
receive fuel through the fuel inlet, separate the fuel into a first
fraction having a minimum boiling point at a temperature that is in
the range from about 70 degrees Celsius to about 350 degrees
Celsius and a second fraction having a boiling point below said
temperature, and dispose the first fraction into the first fuel
outlet.
29. The system of claim 28, wherein the minimum boiling point is at
a temperature that is in the range from about 300 degrees Celsius
to about 360 degrees Celsius.
30. A system comprising: a fuel tank adapted to supply a fuel; a
combustion engine configured to receive the fuel and create an
exhaust stream; and an emission treatment system configured to
receive at least a portion of the exhaust stream wherein the
emission treatment system comprises: a separation system
comprising: a fuel inlet disposed to receive fuel from the fuel
tank, a separator configured to receive fuel through the fuel
inlet, separate the fuel using a flash heater to a first fraction
having a maximum boiling point at a temperature that is in the
range from about 70 degrees Celsius to about 360 degrees Celsius
and a second fraction having a boiling point above said temperature
range, dispose the first fraction from the separator to a first
fuel outlet, and dispose the second fraction from the separator to
a second fuel outlet; and an SCR catalyst comprising a catalyst
composition comprising silver and a templated metal oxide
substrate, wherein the separation system is in fluid communication
with the SCR catalyst and combustion engine through the first fuel
outlet and second fuel outlet, respectively.
31. A system comprising: a fuel tank adapted to supply a fuel; a
combustion engine configured to receive the fuel and create an
exhaust stream; and an emission treatment system configured to
receive at least a portion of the exhaust stream wherein the
emission treatment system comprises: a separation system
comprising: a fuel inlet disposed to receive fuel from the fuel
tank, a separator configured to receive fuel through the fuel
inlet, separate the fuel using a flash heater to a first fraction
having a minimum boiling point at a temperature that is in the
range from about 70 degrees Celsius to about 360 degrees Celsius
and a second fraction having a boiling point below said temperature
range, dispose the first fraction from the separator to a first
fuel outlet, and dispose the second fraction from the separator to
a second fuel outlet; and an SCR catalyst comprising a catalyst
composition comprising silver and a templated metal oxide
substrate, wherein the separation system is in fluid communication
with the SCR catalyst and combustion engine through the first fuel
outlet and second fuel outlet, respectively.
32. A method of reducing nitrogen oxides in an exhaust stream,
comprising: passing a fuel through a fuel inlet of a separation
system; fractionating the fuel into a first fraction and a second
fraction using a separator in the separation system, wherein the
first fraction has a different average boiling point than the
second fraction; passing the first fraction through a first fuel
outlet of the separation system to an SCR catalyst comprising a
catalyst composition comprising silver and a templated metal oxide
substrate; and passing a second fraction through a second fuel
outlet of the separation system to a combustion engine, wherein the
combustion engine is configured to create the exhaust stream and
the SCR catalyst reduces nitrogen oxides present in the exhaust
stream created by the combustion engine.
33. The method of claim 32, wherein the catalyst composition
reduces the nitrogen oxides at a temperature greater than about 275
degrees Celsius.
34. The method of claim 32, wherein the fuel comprises at least one
element selected from the group consisting of diesel fuel, ULSD,
biodiesel fuel, Fischer-Tropsch fuel, gasoline, kerosene, and
ethanol.
35. The method of claim 32, wherein the fuel comprises at least one
of ultra low sulfur diesel fuel and biodiesel.
36. The method of claim 32, wherein the fuel comprises ultra low
sulfur diesel fuel.
37. The method of claim 32, wherein the first fraction in first
fuel outlet comprises lower boiling point fuel than the second
fraction.
38. The method of claim 37, wherein the first fraction comprises at
least one compound selected from the group consisting of an
alcohol, kerosene, and ester.
39. The method of claim 37, wherein the first fraction comprises
the fuel in a vapor state.
40. The method of claim 37, wherein the first fraction has a
maximum boiling point less than about 360 degrees Celsius.
41. The method of claim 40, wherein the maximum boiling point is in
the range from about 100 degrees Celsius to about 225 degrees
Celsius.
42. The method of claim 32, wherein the first fraction in first
fuel outlet comprises higher boiling point fuel than the second
fraction.
43. The method of claim 42, wherein the first fraction comprises
biodiesel.
44. The method of claim 42, wherein the first fraction comprises
the fuel in a liquid state.
45. The method of claim 42, wherein the first fraction has a
minimum boiling point greater than about 250 degrees Celsius.
46. The method of claim 45, wherein the minimum boiling point is in
the temperature range from about 300 degrees Celsius to about 360
degrees Celsius.
Description
BACKGROUND
[0001] The invention relates generally to an efficient emission
treatment system and method of operating the emission treatment
system.
[0002] Exhaust streams generated by the combustion of fossil fuels
in, for example, furnaces, ovens, and engines, contain nitrogen
oxides (NOx) that are undesirable pollutants. There is a growing
need to have efficient and robust emission treatment systems to
treat the NOx emissions.
[0003] In selective catalytic reduction (SCR) using hydrocarbons
(HC), hydrocarbons serve as the reductants for NOx conversion.
Hydrocarbons employed for HC-SCR include relatively small molecules
like methane, ethane, ethylene, propane and propylene as well as
longer linear hydrocarbons like hexane, octane, etc. or branched
hydrocarbons like iso-octane. The injection of several types of
hydrocarbons has been explored in some heavy-duty diesel engines to
supplement the HC in the exhaust stream. From an infrastructure
point of view, it would be advantageous to employ an on-board
diesel fuel as the hydrocarbon source for HC-SCR.
[0004] Fuels, including gasoline or diesel fuels containing sulfur
lead to a number of disadvantages when trying to clean-up the
exhaust gases by some form of catalytic after-treatment. During the
combustion process, sulfur in the fuel gets converted to sulfur
dioxide (SO.sub.2), which poisons some catalysts. Further poisoning
happens from the formation of base metal sulphates from the
components of a catalyst compositions, which sulphates can act as a
reservoir for poisoning sulfur species within the catalyst.
[0005] When the SCR catalysts absorb the NOx in the exhaust gas,
they also absorb sulfur oxides (SOx) in the exhaust gas. The sulfur
oxides poison the catalysts, and the NOx absorption performance
declines as the poisoning by SOx increases.
[0006] In conventional NOx trap devices, the amount of SOx trapped
at the catalyst is computed and when the computed amount reaches an
upper limit, the air-fuel ratio of the air-fuel mixture supplied to
engine is temporarily enriched and the exhaust gas temperature is
increased. Due to the increase of temperature of the exhaust gas,
the SOx trapped by the catalyst is released, and the NOx trapping
performance of the catalyst is recovered. This operation is termed
desulfating of the catalyst. Also in the NOx trapping systems, two
sets of catalyst are required, so that one can be used while the
other one is getting regenerated. Therefore, it is desirable to
have an emission treatment system with properties and
characteristics that has enhanced sulfur tolerance without severe
degradation of the NOx reduction activity.
BRIEF DESCRIPTION
[0007] In one embodiment, an emission treatment system is
presented. The emission treatment system comprises a separation
system and a selective catalytic reduction (SCR) catalyst. The
separation system comprises a separator, a fuel inlet disposed to
supply fuel to the separator, a first fuel outlet and a second fuel
outlet respectively disposed to carry away fuel from the separator.
The SCR catalyst comprises a catalyst composition comprising silver
and templated metal oxide substrate. The emission treatment system
is designed such that the separation system is configured to be in
fluid communication with the SCR catalyst through the first fuel
outlet during operation.
[0008] In one embodiment, a system is provided. The system includes
a fuel tank adapted to supply a fuel, a combustion engine
configured to receive the fuel and create an exhaust stream, and an
emission treatment system configured to receive at least a portion
of the exhaust stream. The emission treatment system includes a
separation system and an SCR catalyst. The separation system
comprises a fuel inlet disposed to receive fuel from the fuel tank,
a separator configured to receive fuel through the fuel inlet, a
first fuel outlet and a second fuel outlet disposed to carry away
fuel from the separator. The SCR catalyst comprises a catalyst
composition comprising silver and templated metal oxide substrate.
The emission treatment system is designed such that the separation
system is configured to be in fluid communication with the SCR
catalyst through the first fuel outlet during operation.
[0009] In one embodiment, a system is provided. The system includes
a fuel tank adapted to supply a fuel, a combustion engine
configured to receive the fuel and create an exhaust stream, and an
emission treatment system configured to receive at least a portion
of the exhaust stream. The emission treatment system includes a
separation system and an SCR catalyst. The separation system
comprises a fuel inlet disposed to receive fuel from the fuel tank,
a separator configured to receive fuel through the fuel inlet and
to separate the fuel using a flash heater to two fractions: A first
fraction having a maximum boiling point at a temperature in a range
from about 70.degree. C. to about 360.degree. C. and a second
fraction having a boiling point above said temperature range. The
separation system further comprises a first fuel outlet, and a
second fuel outlet. The SCR catalyst of the emission treatment
system includes a catalyst composition comprising silver and a
templated metal oxide substrate. In this embodiment, the separation
system is in fluid communication with the SCR catalyst through the
first fuel outlet and the separation system is in fluid
communication with the combustion engine through the second fuel
outlet.
[0010] In one embodiment, a system is provided. The system includes
a fuel tank adapted to supply a fuel, a combustion engine
configured to receive the fuel and create an exhaust stream, and an
emission treatment system configured to receive at least a portion
of the exhaust stream. The emission treatment system includes a
separation system and an SCR catalyst. The separation system
comprises a fuel inlet disposed to receive fuel from the fuel tank,
a separator configured to receive fuel through the fuel inlet and
to separate the fuel using a flash heater into two fractions: A
first fraction having a minimum boiling point at a temperature in a
range from about 70.degree. C. to about 360.degree. C., and a
second fraction having a boiling point below said temperature
range. The separation system further comprises a first fuel outlet,
and a second fuel outlet. The SCR catalyst of the emission
treatment system includes a catalyst composition comprising silver
and a templated metal oxide substrate. In this embodiment, the
separation system is in fluid communication with the SCR catalyst
through the first fuel outlet and the separation system is in fluid
communication with the combustion engine through the second fuel
outlet.
[0011] In one embodiment, a method of reducing nitrogen oxides in
an exhaust stream is disclosed. The method comprises the steps of
passing a fuel through a fuel inlet of a separation system,
fractionating the fuel into a first fraction and a second fraction
using a separator in the separation system such that the first
fraction has a different average boiling point than the second
fraction, passing the first fraction through a first fuel outlet of
the separation system to an SCR catalyst and passing a second
fraction through a second fuel outlet of the separation system to a
combustion engine. The SCR catalyst comprises a catalyst
composition that includes silver and a templated metal oxide
substrate. The combustion engine is configured to create the
exhaust stream and the SCR catalyst reduces nitrogen oxides present
in the exhaust stream created by the combustion engine.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a schematic diagram of a system in accordance with
one embodiment of the invention;
[0013] FIG. 2 is a schematic diagram of a separation system in
accordance with one embodiment of the invention;
[0014] FIG. 3 is a graphical representation of result of fuel
sensitivity performance experiment in accordance with one
embodiment of the invention;
[0015] FIG. 4 is a graph of experimental results for the
performance of a GaAg monolith with ULSD and biodiesel, in
accordance with one embodiment of the invention;
[0016] FIG. 5 is a graphical representation of NOx reduction
efficiency degradation in accordance with one embodiment of the
invention;
[0017] FIG. 6 is a graphical representation of NOx reduction
efficiency degradation in accordance with one embodiment of the
invention;
[0018] FIG. 7 is a graphical representation of NOx reduction
performation in accordance with one embodiment of the
invention;
[0019] FIG. 8 is a graphical representation of NOx reduction
performation in accordance with one embodiment of the
invention.
DETAILED DESCRIPTION
[0020] The systems and methods described herein include embodiments
that relate to a system comprising internal combustion engines and
emission treatment systems employed to treat the exhaust gases from
the combustion engines. The emission treatment systems include
embodiments that relate to a system using the catalyst composition
for reducing nitrogen oxides and separation systems that facilitate
robust performance of catalyst compositions. Generally, disclosed
is a NOx selective reduction catalyst (SCR) and emission treatment
system for reducing NOx in exhaust gas discharged from a combustion
device. Suitable combustion devices may include furnaces, ovens, or
engines.
[0021] In the following specification and the claims that follow,
the singular forms "a", "an" and "the" include plural referents
unless the context clearly dictates otherwise.
[0022] As used herein, without further qualifiers, "mesoporous"
refers to a material containing pores with diameters in a range of
from about 2 nanometers to about 50 nanometers. A catalyst is a
substance that can cause a change in the rate of a chemical
reaction without itself being consumed in the reaction. Templating
refers to a controlled patterning; and, templated refers to
determined control of an imposed pattern and may include molecular
self-assembly. A monolith may be a ceramic block having a number of
channels, and may be made by extrusion of clay, binders and
additives that are pushed through a dye to create a structure.
Approximating language, as used herein throughout the specification
and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term such as "about" is not to be limited to
the precise value specified. In some instances, the approximating
language may correspond to the precision of an instrument for
measuring the value. All temperatures given herein are for the
atmospheric pressure. One skilled in the art would appreciate that
the boiling points can vary with respect to the ambience pressure
of the fuel.
[0023] In one embodiment, a system is provided. The system
comprises a fuel tank, a combustion engine, and an emission
treatment system. A fuel tank is a storage place for fuel or a
continuous supply of fuel. Fuel may be of different kinds that are
used to run the combustion engines. In one embodiment, fuel
comprises a material selected from the group consisting of diesel
fuel, ultra low sulfur diesel (ULSD), biodiesel fuel,
Fischer-Tropsch fuel, gasoline, ethanol, kerosene, and any
combination thereof. In a further embodiment, the fuel comprises
diesel fuel or biodiesel fuel. In one embodiment, the fuel
comprises a non-biodiesel fuel selected from the group consisting
of diesel fuel, ULSD, Fischer-Tropsch fuel, gasoline, kerosene, and
ethanol. In one embodiment, the fuel comprises a non-biodiesel fuel
selected from the group consisting of diesel fuel, ULSD,
Fischer-Tropsch fuel, kerosene, and gasoline. In a further
embodiment, the fuel comprises ULSD.
[0024] In another embodiment, the fuel comprises a biodiesel fuel
or a combination comprising a biodiesel fuel. In a further
embodiment, the fuel comprises a mixture of biodiesel fuel and at
least one non-biodiesel fuel. In a certain embodiment, the fuel
comprises a mixture of ULSD and biodiesel. In one particular
embodiment, the ULSD fuel does not contain any intentionally
premixed alcohols. In one embodiment, while referring to a
particular fuel, the fuel may comprise the native ingredients and
kerosene in the fuel. For example, in a fuel consisting essentially
of ULSD, there is no intentional pre-mixing of any alcohols along
with ULSD fuel. However, some amount of kerosene may be present as
a part of the commercial ULSD. In another example, in a fuel
consisting essentially of biodiesel, there is no intentional
pre-mixing of any alcohols along with biodiesel. However, a small
amount of diesel and kerosene may be present as a part of the
commercial or indigenous biodiesel. Similarly in a fuel mixture
consisting essentially of ULSD and biodiesel, there is no
intentional pre-mixing of any alcohols along with ULSD and
biodiesel. However, a small amount of kerosene may be present as a
part of the commercial or indigenous ULSD and biodiesel.
[0025] A combustion engine is any engine that accepts fuel,
performs an action by burning fuel and emits an exhaust stream. In
one embodiment, the combustion engine is an internal combustion
engine in which the combustion of a fuel occurs with an oxidizer in
a combustion chamber resulting in an expansion of the high
temperature and pressure gases that can be applied to move a
movable component of the engine. Examples of combustion engines
include gasoline engines, diesel engines, and turbines.
[0026] An emission treatment system works on an exhaust stream of
the combustion engine and reduces harmful emissions in the exhaust
stream. In one embodiment, the emission treatment system is
configured to receive at least a portion of the exhaust stream.
Further, the treatment system comprises a separation system that
includes a separator, a fuel inlet to the separator, and at least
two fuel outlets. The separator separates the contents of fuel into
two fractions and sends out the fractions through the two fuel
outlets. In general, the two fractions are such that one fraction
is a fuel component used, for example, for the operation of the
combustion engine, or for some other purpose, and the other
fraction is a reductant component, generally comprising reductant
species ("reductants") suitable for use in NOx reduction. Apart
from receiving one fraction of fuel from the separator, the engine
may or may not additionally receive fuel from the fuel tank
directly depending on the fuel fraction production and the
requirement of the fuel in the engine and the reductant in SCR
catalyst. Similarly, in one embodiment, the fuel coming from the
separator to the engine can be redirected fully or partially to the
fuel tank or another temporary storage tank depending on the fuel
fraction production and the requirement of the fuel in the
combustion engine at that time. At least a portion of the fuel is
burned in the engine during operation of the engine and an emission
of exhaust gases are produced thereby. The exhaust gases, thus
produced, are discharged to an SCR catalyst of an emission
treatment system, where the emission is treated.
[0027] FIG. 1 is a schematic diagram of an example of a system 10
comprising a fuel tank 12 adapted to supply a fuel, a combustion
engine 14 configured to receive the fuel and create an exhaust
stream, and an emission treatment system 16 configured to receive
at least a portion of the exhaust stream. The emission treatment
system 16 comprises a separation system 20 and an SCR catalyst 30.
The separation system 20 comprises a fuel inlet 22 disposed to
receive fuel from the fuel tank 12, a separator 24 configured to
receive fuel through the fuel inlet 22, a first fuel outlet 26 and
a second fuel outlet 28 disposed to carry away fuel from the
separator 24. The separation system 20 is in fluid communication
with the SCR catalyst 30 through the first fuel outlet 26.
[0028] In one embodiment, two fractions of the fuel are separated
in the separator based on the vapor pressures of the fractions. In
a further embodiment, the fractions are separated based on their
boiling points. In general, the smaller chain molecules such as,
for example, methane, ethylene, and propylene are lighter and have
lower boiling points compared to bigger molecules. In some
embodiments, separation of lighter and heavier hydrocarbons can be
carried out through separation based on their boiling points. In
one embodiment, the lighter and heavier hydrocarbons can also be
separated by mechanical separation means such as membranes.
[0029] The fractionations using vapor pressure or boiling points
can be carried out in several ways. In one embodiment, the fuel is
distilled at temperature and/or pressure ranges suitable for
separating the required fractions. In another embodiment, the fuel
is flash heated, passed through a bubble chamber, or subjected to a
heat exchanger for fractionation. In one embodiment, the fraction
of fuel having the higher boiling point is in the vapor state. In a
further embodiment, the fraction of fuel in the vapor state is used
as a reductant to the SCR catalyst. In another embodiment, the
fraction of fuel in the vapor state is condensed, optionally
stored, and then used as a reductant to the SCR catalyst. In one
embodiment, the fraction of fuel having lower boiling point is in
the liquid state.
[0030] In another embodiment, the fractions are separated by the
molecular sizes of the fuel. In one embodiment, the reductant is a
hydrocarbon having an average carbon chain length of about 2 carbon
atoms to about 24 carbon atoms. In a further embodiment, the carbon
chain length is in the range of about 10 carbon atoms to about 16
carbon atoms. In one embodiment, the reductant is an oxygenated
hydrocarbon, such as ethanol. Fractionations by molecular sizes can
be carried out using molecular sieves and/or membranes.
[0031] In one embodiment, the SCR catalyst 30 comprises a catalyst
composition. In a further embodiment, the catalyst composition
includes silver and templated metal oxide. The silver acts as a
catalyst metal and the templated metal oxide acts as a catalyst
substrate.
[0032] Suitable catalyst substrate may include an inorganic
material. Suitable inorganic materials may include, for example,
oxides, carbides, nitrides, hydroxides, carbonitrides, oxynitrides,
borides, or borocarbides. In one embodiment, the inorganic oxide
may have hydroxide coatings. In one embodiment, the inorganic oxide
may be a metal oxide. The metal oxide may have a hydroxide coating.
Other suitable metal inorganics may include one or more metal
carbides, metal nitrides, metal hydroxides, metal carbonitrides,
metal oxynitrides, metal borides, or metal borocarbides. Metallic
cations used in the foregoing inorganic materials can be transition
metals, alkali metals, alkaline earth metals, rare earth metals, or
the like.
[0033] In one embodiment, the catalyst substrate includes oxide
materials. In one embodiment, the catalyst substrate includes
alumina, zirconia, silica, zeolite, or any mixtures comprising
these elements. The desired properties of the catalyst substrate
include, for example, a relatively small particle size and high
surface area. In one embodiment, the powder of the catalyst
substrate has an average diameter that is less than about 100
micrometers. In one embodiment, the average diameter is less than
about 50 micrometers. In a further embodiment, the average diameter
is from about 1 micrometer to about 10 micrometers. The catalyst
substrate powders may have a surface area greater than about 100
m.sup.2/gram. In one embodiment, the surface area of the catalyst
substrate powder is greater than about 200 m.sup.2/gram. In one
embodiment, the surface area is in a range of from about 200
m.sup.2/gram to about 500 m.sup.2/gram, and, in another embodiment,
from about 300 m.sup.2/gram to about 600 m.sup.2/gram.
[0034] One way of forming templated substrates is by employing
templating agents. Templating agents facilitate the production of
catalyst substrates containing directionally aligned forms. The
templating agent may be a surfactant, a cyclodextrin, a crown
ether, or mixtures thereof. An example of a useful templating agent
is octylphenol ethoxylate, commercially available as TRITON
X-114.RTM..
[0035] The catalyst substrate may have periodically arranged
templated pores of determined dimensions. The dimensions can
include pore diameter, degree of curvature, uniformity of the inner
surface, and the like. The median diameter of the pores, in some
embodiments, is greater than about 2 nm. The median diameter of the
pores, in one embodiment, is less than about 100 nm. In some
embodiments, the median diameter of the pores is in a range from
about 2 nm to about 20 nm. In another embodiment, the diameter is
from about 20 nm to about 60 nm and in yet another embodiment, the
diameter is from about 60 nm to about 100 nm. The pores in some
embodiments have a periodicity greater than about 50 .ANG.. The
pores in some embodiments have a periodicity less than about 150
.ANG.. In one embodiment, the pores have a periodicity in the range
of from about 50 .ANG. to about 100 .ANG.. In another embodiment,
the pores have a periodicity in the range from about 100 .ANG. to
about 150 .ANG..
[0036] In certain embodiments, the pore size has a narrow monomodal
distribution. In one embodiment, the pores have a pore size
distribution polydispersity index that is less than 1.5. As used
herein, the polydispersity index is a measure of the distribution
of pore diameter in a given sample. In a further embodiment, the
polydispersity index is less than 1.3, and in a particular
embodiment, the polydispersity index is less than 1.1. In one
embodiment, the distribution of diameter sizes may be bimodal, or
multimodal.
[0037] The catalyst composition can include a catalytic metal along
with the catalyst substrates. Suitable catalyst metal may include
one or more of gallium, indium, rhodium, palladium, ruthenium, and
iridium. Other suitable catalyst metal includes transition metal
elements. Suitable catalyst metal also includes one or more of
platinum, gold, and silver. In one embodiment, the catalyst metal
comprises silver. In one particular embodiment, the catalyst metal
is substantially 100% silver.
[0038] The catalyst metal may be present in an amount of at least
about 0.5 mole percent of the substrate. In one embodiment, the
catalyst metal is present in an amount equal to or greater than 3
mole percent of the substrate. In one embodiment, the amount of
catalyst metal present is about 6 mole percent of the catalyst
substrate. In one embodiment, the catalytic metal may be present in
an amount in a range of from about 1 mole percent to about 9 mole
percent of the substrate.
[0039] The SCR catalysts can have different dopants that enhance
reduction activity and stability of the catalysts. In one
embodiment, the dopants may be selected from the group consisting
of zirconium, iron, gallium, indium, tungsten, zinc, platinum, and
rhodium. In one embodiment, the dopant comprises zirconium. In
another embodiment, the dopant comprises rhodium and in yet another
embodiment, the dopant comprises both gallium and indium. In one
embodiment, the dopant may be present in an amount in a range of
from about 0.1 mole percent to about 20 mole percent, of the
substrate material. In a further embodiment, the dopant may be
present in an amount in a range of from about 0.1 mole percent to
about 5 mole percent, of the substrate material. In a particular
embodiment, the dopant may be present in an amount in a range of
from about 0.5 mole percent to about 3 mole percent, of the
substrate material.
[0040] One useful NOx reduction catalyst is silver-templated
alumina (Ag-TA) catalyst. In some embodiments, the inventors
studied the reduction efficiency of NOx reduction catalysts by
taking Ag-TA as an example.
[0041] In one embodiment, the fuel fractionated based on the
boiling point is used in the emission treatment system such that
the lower boiling point fraction is taken out through the first
fuel outlet 26 to the SCR catalyst 30. Trial evaluations of such a
system have found this fraction to be a better reductant than the
fuel itself. That is, the emission treatment system was found to be
more efficient in NOx reduction when the lower boiling fraction of
the fuel was used as a reductant in comparison with using a
non-fractionated, stock fuel itself as a reductant. An efficiency
increase of the emission treatment system when using a lower
boiling point fraction of the fuel was also observed with an
emission treatment system having a sulfur treated HC-SCR catalyst.
A sulfur treated catalyst is defined herein as a catalyst that is
exposed to an amount of sulfur that is capable of reducing the
performance efficiency of the catalyst by more than about 5%. Use
of lower boiling point fuel fraction for NOx reduction
significantly improves the NOx conversion performance of the HC-SCR
after sulfur treatment when compared to the non-fractionated fuel.
This property is particularly useful in applications where the
catalyst is likely to experience some sulfur exposure. The
advantages include improved performance of the catalyst and hence
lower usage amounts of catalyst. The fuels that are beneficial for
use as a lower boiling point fraction for increased reduction
efficiency of the NOx reduction HC-SCR catalyst include diesel
fuel, ULSD, Fischer-Tropsch fuel, gasoline, ethanol, kerosene, and
any combination thereof. Tests have indicated that the lower
boiling point fraction of diesel is a better reductant than the
higher boiling point fraction of diesel on the Ag-TA catalyst.
[0042] In another embodiment, the fuel fractionated based on the
boiling point is used in the emission treatment system such that
the higher boiling point fraction is taken out through the first
fuel outlet 26 to the SCR catalyst 30. In some situations, the
higher boiling point fuel was found to be a better reductant than
the fuel itself by improving the NOx conversion performance of the
HC-SCR. One example of a fuel that is beneficial to be used as a
higher boiling point fraction for increased reduction efficiency of
the NOx reduction HC-SCR catalyst is a biodiesel/diesel fuel
mixture such as B20. One skilled in the art would predict that a
higher boiling point fraction of a mixture comprising biodiesel may
also increase the reduction efficiency of the emission treatment
system comprising a sulfur treated HC-SCR catalyst.
[0043] In one embodiment, separator 24 of the emission treatment
system 16 is configured to receive fuel through the fuel inlet 22
and to separate the fuel into two fractions. A first fraction has a
maximum boiling point at a temperature of about 360.degree. C. and
the second fraction of fuel has a boiling point above that of the
first fraction. The maximum boiling point of a fraction as used
herein denotes the theoretical temperature at which all the
ingredients of the fraction will evaporate, when subjected to
heating at atmospheric pressure.
[0044] In one embodiment, the separator 24 is configured to
fractionate the incoming fuel into two fractions with a first
fraction having a maximum boiling point at a temperature that
ranges from about 70.degree. C. to about 360.degree. C. and the
second fraction of fuel having a boiling point above that of the
first fraction. Therefore, depending on the maximum boiling point
of the first fraction, the second fraction of this fractionation
may have a minimum boiling point greater than a temperature that
ranges from about 70.degree. C. to about 360.degree. C. In one
embodiment, the separator 24 is configured to fractionate the
incoming fuel into two fractions with a first fraction having a
maximum boiling point at a temperature that ranges from about
100.degree. C. to about 225.degree. C. and the second fraction of
fuel having a boiling point above that of the first fraction. In a
further embodiment, the temperature of separation of two fractions
is about 225.degree. C.
[0045] In another embodiment, the separator 24 is configured to
fractionate the incoming fuel into two fractions with a first
fraction having a minimum boiling point at a temperature that is in
a range from about 70.degree. C. to about 360.degree. C. and the
second fraction of fuel having a boiling point below that of the
first fraction. Therefore, depending on the minimum boiling point
of the first fraction, the second fraction of this fractionation
may have a maximum boiling point lower than a temperature that
ranges from about 70.degree. C. to about 360.degree. C. In a
further embodiment, the first fraction has a minimum boiling point
at a temperature that is in a range from about 225.degree. C. to
about 360.degree. C. and the second fraction of fuel that has a
boiling point below that of the first fraction. In a further
embodiment, the minimum boiling point of the first fraction is at a
temperature that is in the range of about 300.degree. C. to about
360.degree. C.
[0046] Depending on the type of fuel used and advantage of using
low boiling point fraction or high boiling point fraction for the
efficiency increase of the SCR catalyst, the suitable fuel fraction
can be transferred to the SCR catalyst 30, and the other fraction
can be routed to the combustion engine 14 or to a storage tank, as
required. For example, in one embodiment, the separator function is
fixed in providing a first fraction of low boiling point fuel and a
second fraction of high boiling point fuel, and the separator
outlets 26, 28 feeding the SCR catalyst 30 and combustion engine 14
respectively, are switched depending on the fuel fractionation. In
another embodiment, keeping the first fuel outlet 26 and second
fuel outlet 28 fixed to the SCR system 30 and the combustion engine
14 respectively, the function of the separator is modified in
providing a first fraction of lower boiling point or higher boiling
point fuel, depending on the requirement. Thus, by adjusting the
outlet connection or the separator function, each fraction is
routed to the proper outlet, depending on which fraction (high
boiling point or low boiling point) is desired for use as a
reductant.
[0047] In one embodiment, a method of reducing nitrogen oxides in
an exhaust stream is disclosed. The method comprises the steps of
passing a fuel through a fuel inlet 22 (FIG. 1) of a separation
system 20 and fractionating the fuel into a first fraction and a
second fraction using a separator 24 in the separation system 20
such that the first fraction has a different average boiling point
than the second fraction. The average boiling point as used herein
denotes the mean boiling point of the total constituents of a
particular fraction, averaged to accommodate different variations
such as, for example, the operators, source of fuel, ambient
temperatures, and type of separation equipment.
[0048] The method further includes passing the first fraction
through a first fuel outlet 26 of the separation system 20 to an
SCR catalyst 30. The SCR catalyst 30 used herein comprises a
catalyst composition that includes a silver catalyst and a
templated metal oxide substrate. The second fraction of fuel can be
directly fed to the combustion engine 14, fed back to the fuel tank
12 or partially or fully stored in a storage tank (not shown). In
one embodiment of the method, the second fraction of the fuel
passes through a second fuel outlet 28 of the separation system 20
to a combustion engine 14. In one embodiment, the second fraction
of fuel is not fed back into the fuel tank that supplies fuel to
the separation system 20. In one embodiment, the combustion engine
operates on the second fraction of fuel received from the
separation system 20 and creates an exhaust stream that is fed into
the SCR catalyst 30 to reduce the harmful emissions of the exhaust
stream. In one particular embodiment, the SCR catalyst 30 is used
to reduce the nitrogen oxides present in the exhaust. In one
embodiment, the combustion engine receives fuel from a fuel tank or
fuel line in addition to the second fraction of fuel from the
separation system 20.
[0049] In one embodiment of the method, the first fraction of fuel
has a lower average boiling point than the second fraction of fuel.
The temperature of separation of two fractions in this embodiment
is in the range of about 70.degree. C. to 360.degree. C. In one
embodiment, the first fraction has a maximum boiling point that is
less than about 360.degree. C. The fuels that are normally used in
this embodiment include diesel fuel, ULSD, Fischer-Tropsch fuel,
gasoline, ethanol, kerosene, or any combinations thereof. In a
further embodiment, the first fraction has a maximum boiling point
in the temperature range of about 100.degree. C. to 225.degree. C.
In an associated embodiment, the first fraction has a maximum
boiling point in the temperature range of about 150.degree. C. to
200.degree. C. The fuel that is normally used in this embodiment
includes a diesel fuel and/or ULSD. In a further embodiment, the
fuel consists essentially of ULSD. In an associated embodiment, an
ULSD fuel is fractionated at a temperature of about 200.degree. C.
and the less boiling point fraction is used as reductant for NOx
reduction. In a further embodiment, the portion not used as a
reductant is used as engine fuel.
[0050] In an alternate embodiment of the method, the first fraction
of fuel has a higher average boiling point than the second fraction
of fuel. The temperature of separation of two fractions in this
embodiment is in the range of about 70.degree. C. to 360.degree. C.
Therefore, the first fraction has a minimum boiling point that is
equal to or greater than about 70.degree. C. The fuels that are
normally used in this embodiment include biodiesel fuel, diesel,
ULSD, Fischer-Tropsch fuel, kerosene, or any combinations thereof.
In a particular embodiment of the method, the temperature of
separation of two fractions is in the range of about 250.degree. C.
to 360.degree. C. Therefore, the first fraction has a minimum
boiling point that is equal to or greater than about 250.degree. C.
One fuel that is normally used in this embodiment includes a
mixture of biodiesel fuel and ULSD. In this embodiment, when the
separator separates the fuel into two fractions, the first fraction
is expected to consist essentially of biodiesel fuel that is fed
into the SCR catalyst 30. The second fraction is expected to
consist essentially of ULSD that is fed into the combustion engine
14, recirculated to the fuel tank 12, or stored in a storage tank
for further usage. In a further embodiment, the temperature of
separation of two fractions is in the range of about 300.degree. C.
to 360.degree. C. In an associated embodiment, the first fraction
has a minimum boiling point in the range of about 300.degree. C. to
360.degree. C. An example of a fuel that may be suitably applied in
this embodiment includes biodiesel fuel.
[0051] In one embodiment, multiple separators 24 can be used to
fractionate the fuel and advantageously feed the desired fractions
to the SCR catalyst 30 and the combustion engine 14 or to the fuel
storage tank. For example, in one embodiment, a fuel can be
fractionated in three different temperature zones using two
separators as shown in FIG. 2. In FIG. 2, the separation system 20
comprises a first separator 24 and a second separator 34, such that
the first fuel outlet 26 of the first separator is the fuel inlet
26 of the second separator 34. The fuel fractionated by the second
separator 34 has a first fuel outlet 36 and a second fuel outlet
38. Depending on the requirement of the reductant for higher
efficiency, any one fraction of the fuel, or any combinations of
two fractions of fuel can be fed in to the SCR system 30. In one
example, fuels having maximum boiling points above, for example,
100.degree. C. may be separated using a separator and another
separator can be used to further separate the fuel having maximum
boiling point above, for example, 225.degree. C. Thus in the above
example, the fuels can be fractionated into three fractions: a
first fraction with a maximum boiling point of 100.degree. C., a
second fraction with a minimum boiling point of 100.degree. C. and
maximum boiling point of 225.degree. C. and a third fraction with a
minimum boiling point of 225.degree. C. If the initial stock fuel
consisted essentially of ethanol, ULSD, and biodiesel, then, in one
embodiment, the SCR catalyst performance can be increased by
passing the first and third fractions as reductants while using the
second fraction for the functioning of combustion engine. In one
embodiment, a single separator 24 can be operated at different
temperatures at different times, depending on the variations such
as, for example, type of the inlet fuel and type of SCR catalyst
used.
[0052] The SCR catalyst 30 advantageously functions across a
variety of temperature ranges. In one embodiment, the catalyst
composition reduces the nitrogen oxides at a temperature greater
than about 275.degree. C. In a further embodiment, the catalyst
composition reduces NOx at a temperature greater than about
325.degree. C.
EXAMPLES
[0053] The following experiments were carried out for determining
the sensitivity of NO.sub.x catalyst to reductant composition by
using different fractions of diesel fuels taken from different
sources.
[0054] An Ag-TA catalyst composition in the form of a washcoated
monolith was considered as the catalytic material. In order to
understand the effect of reductant on a fresh catalyst, the
monolith used herein was used without being subjected to sulfur
treatment. The feed gas composition included 300 ppm NO, 7%
H.sub.2O, and 9% O.sub.2. Two different base ULSD fuels were
compared: One is a ULSD fuel blend designed for winter and
identified as ULSD-1, and another is a ULSD fuel blend designed for
summer and identified as ULSD-2. These compositions are the
variations of the stock fuel that are generally used as a reductant
in studies performed in a reactor that mimics an exhaust treatment
system of a locomotive engine. Fractions were distilled from these
two ULSD stock fuels. The fractionation was performed from room
temperature up to a cut off temperature of 200.degree. C. and the
portion that was vaporized and condensed was retained and named as
fraction 1. Temperature of reduction for these experiments were
considered as 450.degree. C., 400.degree. C., 350.degree. C., and
300.degree. C. with 1 hour of hold at each temperature.
[0055] Some of these fuels were tested using gas chromatography
(GC) and Nuclear Magnetic Resonance Spectroscopy (NMR). From the
results of these analytical tests (Not shown), it was observed that
the ULSD-1 had a much lighter composition than ULSD-2. One reason
for the difference in composition between the ULSD-1 and ULSD-2 may
be a possible addition of kerosene in the commercial winter blend
(ULSD-1) to lighten the fuel for winter in colder climates. The
fractionation process cuts out the longer chain, higher boiling
constituents in the ULSD.
[0056] The ULSD-1 and ULSD-2 fuels and fractions 1 of the ULSD-1
and ULSD-2 fuels were used as reductants to determine the
sensitivity of a Ag-TA catalyst to reductant composition. The
results of these fuel sensitivity performance experiments are shown
in FIG. 3. It is clear that the catalyst was sensitive to the
reductant composition, with the highest NO.sub.x conversion 52 and
54 coming from the fraction 1 of the ULSD-1 and ULSD-2,
respectively, compared to the unfractionated ULSD-1 and ULSD-2.
Between the unfractionated ULSD stock fuels, ULSD-1 resulted in
higher NOx conversion 56 than the NOx conversion 58 of ULSD-2,
which is likely due to the higher concentration of heavy molecules
and/or aromatic molecules in the ULSD-2 stock fuel.
[0057] FIG. 4 compares a NOx reduction performance of diesel,
biodiesel and a mixture of diesel and biodiesel (called as B20)
while using a washcoated monolith using GaAg catalyst for NOx
reduction. The comparison shows that biodiesel was a more effective
reductant than the diesel or the mixture of diesel and
biodiesel.
[0058] The NOx reduction efficiency degradation due to sulfur
poisoning was studied in the labs. The degradation of the Ag-TA
catalyst performance during the use of ULSD fuel was studied for a
fresh catalyst and a catalyst that had a deep sulfur (S) treatment
with 30 ppm SO.sub.2 for 12 hrs at 350.degree. C., and then tested
over a wide temperature range. Steady state performance at
temperatures lower than 400.degree. C. was strongly affected by the
deep S treatment, as can be observed from the comparison of NOx
reduction activity curve of the fresh catalyst 62 and the sulfur
treated catalyst 64 (FIG. 5).
[0059] NOx profile as a function of time revealed an interesting
feature for a sulfur (S) treated monolith washcoated with Ag-TA
catalyst and tested at 375.degree. C. (FIG. 6). NOx conversion
reached .about.50% soon after ULSD addition, and then rapidly
decreased to the steady state value of about 10% in the next 5
minutes. One possible explanation is that carbon is accumulating on
the surface upon diesel addition, and affects the performance. It
appears that the process is accelerated upon S exposure. This
indicates that deep S treatment deteriorates the ability of the
catalyst to remove accumulations of carbonaceous by-products
(coke). Therefore, one potentially attractive strategy is to use
fractionated diesel as reductant, as the heavier fractions in
diesel are likely be the primary source for carbon formation.
[0060] To test this hypothesis, the performance of the S treated
Ag-TA catalyst monolith was evaluated with lighter fraction of
diesel (boiling point<200.degree. C.). The NOx reduction
performance of the catalyst was higher for a fractionated diesel 66
than the unfractionated diesel fuel 68 in the temperature range of
about 325.degree. C. to about 375.degree. C. as shown in FIG. 7.
Moreover, the NOx activity as a function of time profile indicated
that the catalyst deactivation due to coking was higher for the
ULSD 72 in comparison with the fractionated diesel 74 as shown in
FIG. 8. This suggests that the emission treatment system comprising
Ag-TA catalyst composition had a higher sulfur tolerance when the
fractionated fuel was used in comparison with unfractionated
fuel.
[0061] The system and methods discussed herein can be applied for
improving the overall NO.sub.x conversion of the after treatment
system. The present study suggests different diesel formulations
may have varying effects on the catalyst. The system and methods
described herein may limit the variability of NOx conversion as a
function of fuel source as it would always take a beneficial
fraction from the fuel and eliminate the unfavorable fraction that
is likely to be the cause of coking of the catalyst.
[0062] The embodiments described herein are examples of
composition, system, and methods having elements corresponding to
the elements of the invention recited in the claims. This written
description may enable those of ordinary skill in the art to make
and use embodiments having alternative elements that likewise
correspond to the elements of the invention recited in the claims.
The scope of the invention thus includes composition, system and
methods that do not differ from the literal language of the claims,
and further includes other compositions and articles with
insubstantial differences from the literal language of the claims.
While only certain features and embodiments have been illustrated
and described herein, many modifications and changes may occur to
one of ordinary skill in the relevant art. The appended claims
cover all such modifications and changes.
* * * * *