U.S. patent application number 16/480457 was filed with the patent office on 2019-12-19 for apparatus and method for desulfation of a catalyst used in a lean burn methane source fueled combustion system.
This patent application is currently assigned to UMICORE AG & CO. KG. The applicant listed for this patent is UMICORE AG & CO. KG. Invention is credited to Xue HAN, John G. NUNAN.
Application Number | 20190383185 16/480457 |
Document ID | / |
Family ID | 61094527 |
Filed Date | 2019-12-19 |
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United States Patent
Application |
20190383185 |
Kind Code |
A1 |
HAN; Xue ; et al. |
December 19, 2019 |
APPARATUS AND METHOD FOR DESULFATION OF A CATALYST USED IN A LEAN
BURN METHANE SOURCE FUELED COMBUSTION SYSTEM
Abstract
An apparatus for reactivating a sulfur poisoned oxidation
catalyst operating in the exhaust of a lean burn, methane source
(as in natural gas) fueled combustion device as in an engine. The
reactivation includes desulfation of the poisoned catalyst through
the use of a CO supplementation apparatus in communication with the
control unit that is adapted to supplement the CO content in the
exhaust reaching the catalyst, while avoiding an overall rich
exhaust atmosphere at the catalyst. An example includes the added
supply of hydrocarbons to one or more, preferably less than all, of
the lean burn engine's combustion chambers such as by an ECU
controlled extra supply of NG (e.g., CNG) to some of the combustion
chambers. Also featured is a method for desulfation of an oxidation
catalyst of a lean burn CNG engine by supplying excess CO to the
exhaust reaching the catalyst while retaining an overall lean
state, and a method of assembling an apparatus for reactivating a
sulfur deactivated lean burn NG engine catalyst by assembling a CO
supplementation apparatus with a control unit.
Inventors: |
HAN; Xue; (Owasso, OK)
; NUNAN; John G.; (Tulsa, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UMICORE AG & CO. KG |
Hanau-Wolfgang |
|
DE |
|
|
Assignee: |
UMICORE AG & CO. KG
Hanau-Wolfgang
DE
|
Family ID: |
61094527 |
Appl. No.: |
16/480457 |
Filed: |
January 29, 2018 |
PCT Filed: |
January 29, 2018 |
PCT NO: |
PCT/EP2018/052169 |
371 Date: |
July 24, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 23/96 20130101;
F02M 21/0209 20130101; Y02A 50/2324 20180101; F01N 3/36 20130101;
F01N 9/00 20130101; Y02A 50/20 20180101; B01D 53/9495 20130101;
F01N 2610/06 20130101; Y02T 10/47 20130101; F02D 41/027 20130101;
F01N 2900/1612 20130101; Y02T 10/12 20130101; F01N 2370/02
20130101; F01N 2450/40 20130101; F01N 2550/02 20130101; F01N
2570/04 20130101; B01D 53/944 20130101; B01D 2255/1021 20130101;
F01N 11/00 20130101; F01N 2610/03 20130101; F02B 43/10 20130101;
F01N 2610/05 20130101; F02M 21/0215 20130101; Y02T 10/40 20130101;
B01D 53/9454 20130101; Y02C 20/20 20130101; F02B 2043/103 20130101;
F01N 3/101 20130101; F01N 2570/20 20130101; B01D 2255/1023
20130101; B01J 38/04 20130101; F01N 3/2825 20130101; F01N 2260/04
20130101; B01D 2251/204 20130101; B01J 23/44 20130101; F01N 3/103
20130101; F01N 3/206 20130101; F01N 2590/08 20130101; F01N 2610/146
20130101; B01D 53/96 20130101; F01N 3/0885 20130101; F01N 3/2033
20130101; Y02T 10/22 20130101; F01N 2590/10 20130101 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 3/10 20060101 F01N003/10; F01N 3/28 20060101
F01N003/28; F02B 43/10 20060101 F02B043/10; F02M 21/02 20060101
F02M021/02; F01N 9/00 20060101 F01N009/00; F01N 11/00 20060101
F01N011/00; F01N 3/36 20060101 F01N003/36; B01D 53/94 20060101
B01D053/94; B01D 53/96 20060101 B01D053/96; F02D 41/02 20060101
F02D041/02; B01J 23/44 20060101 B01J023/44; B01J 23/96 20060101
B01J023/96; B01J 38/04 20060101 B01J038/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2017 |
US |
15438029 |
Claims
1. An apparatus for catalytic treatment of exhaust from a lean
burn, methane sourced fuel combustion device, comprising: an
exhaust line adapted for receipt of exhaust from the combustion
device; a catalyst positioned for contact with exhaust traveling in
the exhaust line; a control unit; a CO supplementation apparatus in
communication with the control unit and adapted to supplement the
CO content in the exhaust reaching the catalyst, while avoiding an
overall rich exhaust atmosphere at the catalyst, so as to desulfate
the catalyst.
2. The apparatus of claim 1 wherein the catalyst is a Pd-based
catalyst.
3. The apparatus of claim 2 wherein the catalyst comprises Pd and
at least a second metal.
4. The apparatus of claim 3 wherein the second metal is Pt.
5. The apparatus of claim 1 wherein the CO supplementation
apparatus supplements the CO exhaust content by adding fuel to the
CO supplementation apparatus while retaining an overall lean burn
state at the catalyst during CO supplementation.
6. The apparatus of claim 5 wherein the CO supplementation
apparatus operates such that the lean state of the exhaust reaching
the catalyst during supplementation is retained at or greater than
lambda 1.1.
7. The apparatus of claim 6 wherein the CO supplementation
apparatus operates such that the percentage of CO content in the
exhaust is about 1.0% to <7.5% during supplementation.
8. The apparatus of claim 1 wherein the CO supplementation
apparatus provides a percentage of CO content in the exhaust that
is about 2.0% to 6.0% CO during supplementation and while the
exhaust is in a lean state at the catalyst.
9. The apparatus of claim 8 wherein the CO supplementation
apparatus provides a CO content in the exhaust that is about 2.5 to
4.0% CO by volume during supplementation and while the exhaust is
in a lean state at the catalyst.
10. The apparatus of claim 1 wherein the CO supplementation
apparatus includes a fuel injector device.
11. The apparatus of claim 10 wherein the fuel injector is in
communication with the control unit and is adapted to add fuel to
one or more combustion chambers of the lean burn engine.
12. The apparatus of claim 11 wherein the fuel injector device
feeds a fuel in common with one of the lean burn engine operation
fuels.
13. The apparatus of claim 10 wherein the fuel injector device of
the CO supplementation apparatus supplies less than a total number
of combustion chambers of the lean burn engine with added fuel.
14. The apparatus of claim 1 further comprising a catalyst sulfur
deactivation sensor in communication with the control unit.
15. The apparatus of claim 14 wherein the deactivation sensor
conveys information to the control unit informative of a level of
sulfur deactivation of the catalyst, and, when the control unit
determines a threshold value of sulfur deactivation has occurred,
initiates the CO supplemental apparatus to supplement the exhaust
flow with added CO.
16. The apparatus of claim 14 wherein the initiation of the CO
supplemental apparatus includes the triggering of an additional
supply of methane source fuel through one or more valves opened by
the control unit.
17. A system for rejuvenation of a catalyst comprising a natural
gas fuel source as the methane sourced fuel, a combustion device
and the apparatus of claim 1, with exhaust from the combustion
device being received in said exhaust line.
18. The system of claim 17 wherein the natural gas fuel source is a
CNG fuel source and the combustion device is an engine of a
moveable vehicle.
19. The system of claim 17 wherein the combustion device is a
stationary power plant boiler.
20. An apparatus for catalytic treatment of exhaust from a lean
burn, methane sourced fuel combustion device, comprising: an
exhaust line adapted for receipt of exhaust from the methane
sourced fuel combustion device; a catalyst positioned for contact
with exhaust traveling in the exhaust line; a control unit; CO
supplementation means, in communication with the control unit, for
supplementation of the CO content in the exhaust reaching the
catalyst, while avoiding an overall rich exhaust atmosphere at the
catalyst, so as to desulfate the catalyst.
21. A method of enhancing a catalyst performance in a lean burn.
methane source fueled combustion device, comprising: supplementing
to a predetermined level the CO content of the lean burn combustion
device exhaust through the use of a control unit so as to
rejuvenate the catalyst while retaining an overall lean burn state
in the exhaust reaching the catalyst during CO supplementation.
22. The method of claim 21 wherein the catalyst comprises Pd.
23. The method of claim 22 wherein the rejuvenation includes
supplementing the CO content reaching the catalyst so as to have CO
percentage by volume of 2.0% to 6.0% CO during supplementation
while retaining the exhaust gas at an overall lean state at the
catalyst during CO supplementation
24. The method of claim 22 wherein the CO percentage by volume is
2.5% to 4.0% CO during supplementation while retaining the exhaust
gas at an overall lean state at the catalyst during CO
supplementation.
25. The method of claim 22 wherein the rejuvenation includes
desulfation of the Pd inclusive catalyst by way of the CO
supplementation.
26. The method of claim 21 wherein the CO supplementation is
carried out by supplying additional fuel to one or more combustion
chambers of a combustion device in the form of an engine of a
mobile vehicle.
27. The method of claim 26 wherein the CO supplementation is
carried out by supplying a fuel source, that is also used as a fuel
source for normal engine running, to less than all available
combustion chambers of the lean burn engine.
28. The method of claim 27 wherein the methane source fuel is
CNG.
29. A method of assembling the catalytic treatment apparatus of
claim 1, comprising providing the catalyst in the exhaust line so
as to be positioned for contact with the exhaust of the lean burn
combustion device, and setting up the control unit for control
communication with the CO supplemental apparatus.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the technology of catalytically
converting emissions from a lean burn combustion device that is a
methane source fueled device. Examples of lean burn methane source
fueled combustion devices include stationary combustion units such
as those used in natural gas supplied power plants and methane
source fueled engines such as a natural gas fueled engine. An
example of a natural gas fueled engine includes a compressed
natural gas (CNG) fueled engine, and the invention is inclusive of
an apparatus and a method for catalytic conversion of exhaust gases
containing saturated hydrocarbons such as methane that are found in
the exhaust of such combustion devices. The present invention is
further inclusive of an apparatus and method directed at avoiding
sulfur degradation or deactivation of a catalyst used in the
emission control of the lean burn methane source fueled combustion
device (e.g., an engine such as a CNG engine) through a controlled
supply of CO while maintaining the exhaust at the catalyst in a
lean state.
BACKGROUND
[0002] Methane source fueled combustion devices (e.g., engines),
such as lean burn natural gas (NG) engines, are used world-wide for
both stationary power generation and mobile applications, inclusive
of passenger cars, busses and light and heavy duty trucks.
Increased consideration of NG (e.g., CNG) as a fuel supply has been
driven by reasons such as an increased availability via fracturing
gas extraction technology and also a recognition of potential
benefits on the environmental side (and associated assistance in
meeting present and anticipated exhaust emission regulations).
[0003] For instance, compared to diesel and gasoline engine rivals,
NG fuel sourced combustion devices generate fewer pollutants
relative to ozone, NO.sub.x, and particulate matter (PM). Also,
CO.sub.2 emissions are reduced because the H/C ratio of NG is about
double that of gasoline and diesel fuel.
[0004] In the context of the present application, reference to a
methane source fueled combustion device is inclusive of, for
example, a natural gas (NG) fed combustion chamber used in a
stationary power plant and a methane source fueled engine such as
an NG fueled engine (e.g., CNG). Methane source fuel supplies
include those obtained through oil exploration, coal mining and
ocean deposits of methane hydrates.
[0005] A further example of a lean burn methane source fueled
engine is inclusive of an NG running lean burn mobile vehicle
engine, with NG as a sole fuel source for the vehicle engine, as
well as the methane source fuel (e.g., NG fuel) as a fuel component
of a mixed fuel source supply system to the combustion device such
as one that uses NG (e.g., CNG) as a component in a flex-fuel or
dual-fuel vehicle (e.g., diesel and NG, or gasoline and NG fuel
sources). NG used in vehicles may be classified into CNG and
liquefied natural gas (LNG) according to a fuel supply method. The
CNG is gas compressed at about 200 atmospheres and is used in a
state of being stored in a high-pressure container. The LNG is a
cryogenic liquid fuel that is produced by condensing natural gas
through cooling of the natural gas to a temperature of -162.degree.
C. (-260.degree. F.) while at atmospheric pressure.
[0006] CNG relates to natural gas produced out of the ground in a
broad sense, but typically refers to combustible gas containing
small saturated hydrocarbons as a main ingredient such as methane,
ethane and propane with trace levels of butanes and pentanes. CNG
is largely classified into oil-field gas produced out of an oil
field, coal-field gas produced out of a coal field, and
water-soluble gas which is soluble and present in water regardless
of occurrence of oil or coal. Each of the coal-field gas and the
water-soluble gas contains methane as a main ingredient, and carbon
dioxide, oxygen, nitrogen, etc., and is often referred to as dry
gas since the gas is not liquefied by pressurization at room
temperature. The oil-field gas contains ethane, propane, butane,
etc., in addition to the methane, and is often referred to as wet
gas since the gas is liquefied by pressurization at room
temperature.
[0007] Natural gas engines, such as CNG engines, are representative
of engines having a fuel source that is predominately methane such
that these engines produce emissions that predominately include
non-combusted methane-CH.sub.4 (e.g., 85%) as well as often other
short-chain alkane species (e.g., ethane C.sub.2H.sub.6 and propane
C.sub.3H.sub.8). Thus, the development of catalysts for high
efficiency removal of saturated hydrocarbons, including methane, by
oxidation within an exhaust stream is of strategic importance.
[0008] Even with catalytic assistance, the removal of methane from
the exhaust stream is relatively difficult because the C--H bond
must be ruptured. A further feature of methane that makes initial
C--H bond cleavage difficult is the highly symmetric shape of
methane where all C--H bonds are distributed symmetrically about
the central carbon at about 109.degree. resulting in the sticking
coefficient of methane being very low on metal or metal oxide
surfaces. In the oxidation of higher alkanes, oxidation is
generally more easily achieved by the cleavage of C--C bonds. Since
the C--H bond is stronger, methane is more difficult to oxidize.
Since methane is known to be a powerful greenhouse gas with about
20 times the greenhouse potential of carbon dioxide, there has been
investigated the use of noble metals and base metals as catalysts
for stimulating the oxidation of methane by cleavage of the C--H
bond. Alumina, silica, thoria, and titania supported platinum and
palladium catalysts were evaluated in 1983 and 1985 (see C. F.
Cullis and B. M. Willatt, Journal of Catalysis, Vol. 83, p. 267,
1983; and V. A. Drozdov, P. G. Tsyrulnikov, V. V. Popovskii, N. N.
Bulgakov, E. M. Moroz, and T. G. Galeev, Reaction Kinetic Catalysis
Letters, Vol. 27, p. 425, 1985). These studies suggested that,
under the described conditions, an alumina supported palladium
catalyst is the most active, followed by an alumina supported
platinum catalyst.
[0009] In addition to the treatment of methane, the reduction of
non-methane hydrocarbons (NMHCs) from the exhaust of many of these
combustion devices (e.g., engines) has also been under
consideration and poses challenges. While diesel engines emit very
low concentrations of low molecular weight alkanes (e.g., ethane,
propane, etc.), these species account for the majority of NMHCs
emitted by lean-burn natural gas engines and a fraction equivalent
to the natural gas substitution rate for dual-fuel engines. In view
of this, more recent investigations have specifically targeted the
catalytic oxidation of un-combusted alkanes in order to meet
challenging regulatory requirements. For example, the U.S.
Environmental Protection Agency (EPA) NMHC requirement for
heavy-duty on-highway compression- and spark-ignition engines and
non-road compression ignition engines is 0.14 g NMHC/bhphr (0.19 g
NMHC/kWhr). Also, at least 60% methane conversion is required to
meet the stringent European regulations for THC limit values (Tier
Euro IV, effective from October 2005).
[0010] Accordingly, while methane source fueled engines such as NG
engines have the above described advantages (e.g., lower NO.sub.x
and particulate matter (PM) production); they also have the
drawback of the emission of non-combusted methane and, in many
instances, non-methane hydrocarbons (NMHCs).
[0011] Additional factors presenting challenges, in the emission
treatment of methane source fueled combustion devices, such as NG
operating engines, include the often relatively low operation
temperature (e.g., 400-450.degree. C.) of such devices, and
contaminants such as sulfur dioxide (e.g., 1 ppm or more) in, for
example, engine exhaust (e.g., SO.sub.2 present in the source of NG
or introduced to the exhaust stream such as from engine oil or
both).
[0012] As noted, it has been reported in the literature that
oxidation catalysts containing palladium are, under the described
conditions, more efficient as compared to platinum-based catalysts
in converting methane. However, while palladium-based catalysts
have been reported in the prior art to be the most active for
methane and NMHCs abatement relative to those studies, they are
also known in the art to have serious limitations. For instance,
these palladium based catalysts are highly sensitive to sulfur
poisoning and their activities toward CH.sub.4 oxidation
deteriorate very quickly in the presence of SO.sub.2 or SO.sub.3,
and even more quickly when placed in contact with H.sub.2S. Since
many methane source fueled combustion devices (such as mobile
vehicle or stationary engines, as in NG lean burn engines) contain
SO.sub.2 within the NG itself (e.g., 1-5 ppm) and/or originating
from lubricating oils used in many engines, it has been recognized
in the art the limitations of using palladium-based catalysts
despite their greater efficiency in methane and NMHC's abatement in
the exhaust stream. In addition, water vapor is known to be a
strong inhibitor on the catalytic activity of methane (and NMHC)
oxidation and therefore must also be considered.
[0013] Thus, it is understood in the art that the reduction of
unburned hydrocarbon emissions from methane source fueled
combustion devices such as engines, as in lean-burn NG engines and
dual or multi-fuel (e.g., diesel and natural gas) engines and the
like, is particularly challenging due to the stability of the
predominant short-chain alkane species released (e.g., methane,
ethane, and propane). Supported Pd-based oxidation catalysts are
generally considered the most active materials for the complete
oxidation of low molecular weight alkanes at temperatures typical
of lean-burn NG exhaust. However, these catalysts rapidly degrade
under realistic exhaust conditions with high water vapor
concentrations and traces of sulfur.
[0014] The mechanisms associated with sulfur poisoning and
regeneration of Pd-based catalysts used in the exhaust of lean burn
NG engines have been studied in the prior art. Examples of studies
in this regard can be seen in Leprince et al. Regeneration of
palladium based catalyst for methane abatement; Paper no.: 210
CIMAC Congress Kyoto 2004; Hu et al. Sulfur Poisoning and
Regeneration of Pd Catalyst under Simulated Emission Conditions of
Natural Gas Engine 2007-01-4037 SAE International; and Ottinger et
al. Desulfation of Pd-based Oxidation Catalysts for Lean-burn
Natural Gas and Dual-fuel Applications 2015-01-0991 SAE
International.
[0015] As described in the above articles, two primary desulfation
strategies have been investigated relative to reactivating poisoned
Pd-based catalysts in a lean burn NG engine environment: a) thermal
desulfation; and b) reductive desulfation.
[0016] Thermal recovery of Pd-based oxidation catalysts has been
found to be challenging due to the thermal stability of Pd-sulfur
species and the associated minimal sulfur release within suitable
(non-damaging) temperature ranges.
[0017] Reductive de-sulfation was found to be a better option under
the prior art than thermal de-sulfation alone. The above articles
describe conversion of the lean burn state in the NG engine with
periodic reductive events designed to convert, on a repeating
basis, the catalyst exhaust environment over the catalyst from an
overall lean air fuel ratio (lambda>1 lean state) to one that is
in an overall rich state (lambda<1 rich state). The generation
of rich exhaust gas mixtures for engines designed to run under lean
conditions is particularly difficult and can have a major negative
impact on the drivability and stable operation of the vehicle. In
other words, the above described articles all use an overall rich
atmosphere to reactivate the catalysts. The same approach of
converting a lean burn CNG engine's exhaust from lean to rich in an
effort to recover degraded catalyst activity is seen in PCT
Publication WO2015167318. One disadvantage of running the Pd-based
catalysts under rich conditions is that Pd sinters more rapidly
under rich vs. lean exhaust conditions so that re-generation at
high temperatures can be detrimental to the overall stability of
the catalyst over time. Moreover, an overall rich running state
presents a greater likelihood of an increased release of hydrogen
sulfide (H.sub.2S), which is a more toxic poison relative to Pd, as
compared to, for example, sulfur dioxide and other sulfides. An
overall lean running engine has a tendency to generate less of the
more toxic hydrogen sulfide poison.
[0018] Also, in the prior art rich regeneration conditions are
considered required since Pd is unique among the noble metals (as
in Pt, Pd and Rh) in that elemental S can be incorporated into the
bulk of Pd as well as being on the surface. To remove the bulk S,
repeated rich--lean cycling is considered required at high
temperatures (Ts>700-800.degree. C.). Under rich conditions the
elemental S comes to the surface of the Pd/PdO crystallites and
then under the lean condition it is readily oxidized to SO.sub.2
which is easily desorbed at low temperatures.
[0019] A further example of the prior art attempts to offset
deactivation of a Pd-based three-way catalyst ("TWC") provided in a
CNG engine system through periodic shifts to a rich (lambda<1)
atmosphere, is seen by US 2016/0108833. In U.S. '833 there is
described a technique, directed at (general) CNG engine catalyst
deterioration avoidance, involving engine control adjustments in
the air/fuel ratio from 1.0 (stoichiometric) to 0.99 (rich) when a
catalyst is sensed to be in a deteriorated state.
[0020] However, as noted above, when dealing with a normally
running lean burn engine, shifts from lean to rich states for the
purpose of CNG catalyst reactivation, are artificial and hard to
achieve by, for example, engine control, or require added
complexity and/or lower fuel efficiency. Also, as noted above, the
rich running state is considered to have a greater propensity to
generate the more toxic hydrogen sulfide as compared to a lean
running state.
[0021] Thus, the common approaches in the prior art to desulfate a
catalyst through either high temperature activation above
600.degree. C. or reductive atmosphere treatment, or a combination
of both, has proven to be lacking. For example, the temperature
required to regenerate a degraded CNG lean burn catalyst has been
found to be beyond the operating temperature range for a lean CNG
catalyst and the reducing atmosphere (e.g., by engine control) is
hard to achieve. Accordingly, the present invention is directed at
addressing such problems in the prior art (e.g., the present
invention is directed at avoiding or at least alleviating the
aforementioned problems associated with the above described various
lean burn combustion devices that are methane source fueled as to
result in methane coming in contact with the catalyst in
stream).
SUMMARY OF THE INVENTION
[0022] The present invention is aimed at addressing or alleviating,
at least to some degree, one or more of the above described
problems and limitations in the prior art, and takes a different
approach than the standard regeneration categories of thermal
and/or rich catalyst atmosphere regeneration described above. Under
the present invention, the different approach utilized to reverse
sulfur poisoning of a lean burn methane source fueled combustion
device (e.g., engine) emission catalyst, such as an NG engine
emission catalyst, includes utilizing engine control, not to create
an overall rich lambda atmosphere in the lean burn engine exhaust
contacting the catalyst device, but to reverse sulfur poisoning by
introducing more CO to the atmosphere in contact with the NG engine
catalyst, while retaining an overall lean status in the
emission.
[0023] As noted, the present invention takes into consideration
that methane is harder to burn as compared to CO. For instance,
depending on catalyst formulations and testing conditions, CO
light-off temperatures can be 200.degree. C. lower than that of
methane. By introducing more CO to the exhaust under the present
invention, the exotherm generated by CO oxidation can more readily
achieve a local thermal treatment effect on a sulfur degraded lean
burn methane source fueled (e.g., NG) combustion device (e.g., a
vehicle engine) catalyst so as to facilitate a reversal in sulfur
poisoning of that catalyst. Thus, a technique featured under the
present invention is one that effectively provides an in-situ
desulfation/regeneration using the heat from CO oxidation. A second
feature of the high and very rapid oxidation of CO over, for
example, a Pd CNG catalyst is that the "local" temperature at the
Pd crystallites will be very high while at the same time the "local
gas composition" may be close to stoichiometry or slightly rich due
to the very rapid consumption of oxygen at those localized regions,
coupled with limitations in the rate of diffusion of oxygen to the
Pd crystallites. Thus the presence of CO coupled with a very high
combustion rate can essentially achieve the same effect as that of
making the overall exhaust rich as by EMS adjustment, which is
highly unfavorable. In other words, the presence of high levels of
CO, with its associated fast removal of local environment oxygen
under the present invention, can essentially achieve the same
effect as that of making the overall exhaust rich, from the
perspective of the local environment where catalysis is occurring,
i.e. at the Pd/PdO crystallites. The present invention, with its
overall lean environment relative to the catalyst, also avoids the
degree of hydrogen sulfide generation that can occur under an
overall rich atmosphere such as that generated periodically in the
prior art rich-lean toggling. The present invention also features a
system wherein the added CO in the exhaust provides for a lessening
of the impact of water vapor in the exhaust in that CO conversion
is less inhibited by the presence of water vapor as compared to
methane.
[0024] As seen from the examples provided below, under the approach
of the present invention, the methane light off temperatures of a
sulfur poisoned catalyst can be significantly improved by
increasing CO in the feed gas stream and there is also achieved a
strong recovery of the catalyst after regeneration (e.g., a final
recovery that is about the same or preferably at least within
10-20.degree. C. of the initial light off of the catalyst prior to
poisoning). These improvements under the present invention can be
seen in the below described testing involving a simulated lean
exhaust mixture wherein there is maintained an overall lean
atmosphere. The light off temperature is shown under the approach
of the present invention to be lowered significantly (e.g., by
300.degree. C.) from the poisoned state. Also, under the present
invention, not only does the catalyst perform well when a
supplemented amount of CO is present; but, after the CO content is
reduced in subsequent light off tests/runs, the catalyst can
recover its activity to (or nearly to) a pre-sulfur poisoning
level. As further seen by the examples under the present invention,
improvements are found both when the exhaust mixture contains only
methane and when it contains methane plus other exhaust components
such as NMHC's (e.g., when the exhaust contains a mixture of
methane as well as the NMHC's ethane and propane).
[0025] Since lean burn combustion devices under consideration in
the present invention (e.g., such as lean burn combustion engines),
are not able to properly generate a sufficient amount of CO in the
exhaust to meet the intended states featured under the present
invention during normal running operations, to generate enough CO
there is featured under the present invention a CO increase
operation using a CO supplementation apparatus. As an example of a
CO increase operation in accord with the present invention, one or
more cylinders (often preferably less than all) of a lean burn,
methane sourced fueled engine such as an NG (e.g., CNG) fueled
engine are operated in an engine rich mode or richer mode
periodically. This rich mode or richer mode in one or more of the
engine cylinders is not designed to place the overall exhaust
atmosphere in contact with the catalyst into a rich state or
lambda<1, but is intended to generate an added quantity of CO to
that exhaust atmosphere to initiate an exotheric reaction relative
to the CO at the catalyst. The localized exotheric reactions lead
to an in-situ increase in temperature in the atmosphere at
associated locations on the catalyst as to provide for in-situ
removal of the catalyst poisoning sulfur at those locations on the
catalyst. Therefore, the sulfur poisoned catalyst will be
reactivated via a higher CO exhaust content and associated
exotherm. As a result of rich or richer in-cylinder combustion
conditions, more hydrogen will also be generated. The increased
hydrogen also helps in the localized reactivation of CNG catalysts
from sulfur poisoning while there is still maintained an overall
lean state at the catalyst.
[0026] The method of the present invention is inclusive of working
in the presence or absence of other non-methane hydrocarbon(s). In
addition, the desulfation effect achieved under the present
invention is CO concentration dependent. For example, under
embodiments of the present invention and test conditions used,
there is suggested that a CO concentration at or less than 1.6% is
not as effective as compared to when a CO concentration of at or
greater than 3.2% is utilized. The exact concentration of CO in the
exhaust and, for example, a required adjustment in engine
operation, will depend on the details of the engine operation with
respect to overall emissions, temperature at the catalyst, the
exhaust flow rate in relation to catalysts volume (i.e. GHSV) and
the location of the catalyst relative to the engine manifold. Thus,
different lean burn combustion devices, as in engines with
different exhaust configurations, will require different levels of
CO concentration in the exhaust for full regeneration. That is, the
excess CO added is added in an amount designed toward providing
highly efficient poison removal while avoiding toggling into an
overall rich state as that can lead to undesirable consequences
such as an increase in generation of highly catalyst degrading
hydrogen sulfide.
[0027] Also, embodiments of the present invention include exhaust
treatment with Pd-based catalysts, such as Pd only catalysts or
Pd-based catalysts with one or more added PGMs (platinum group
metals inclusive of ruthenium, rhodium, palladium, osmium, iridium,
platinum or any combination of the same). Examples include
combinations with Pd such as Pd/Rh or Pd/Pt or Pd/Pt/Rh catalysts
(as well as all possible combinations of the same, as well as
varying relative percentages with Pd preferably the highest
percentage amongst other PGM's). In addition, the Pd based catalyst
of the present invention can also include other non-PGM metal
combinations with the Pd such as other base metals of Cu, Ni, Fe,
Zr, or any combination of the same as a few examples. The inclusion
of base metals such as those described above can be with respect to
Pd alone or with respect to any of the PGM combinations described
above.
[0028] The composition of the oxidation catalyst of the present
invention, in addition to the above described catalytic metals, is
preferably inclusive of suitable supports on which the metal can be
highly dispersed and includes materials such as refractory oxides
and mixtures thereof, such as those selected from the group
consisting of .gamma.-Al.sub.2O.sub.3, .delta.-Al.sub.2O.sub.3,
.theta.-Al.sub.2O.sub.3, heteroatom doped transition Aluminas,
Silica, Ceria, Zirconia, Ceria-Zirconia based solid solutions,
Lanthanum oxide, Magnesia, Strontia, Titania, Tungsten oxide and
mixtures thereof. As described in the background, active alumina
supports (e.g., particles on which the metal catalyst is supported)
is preferable in many instances in catalytic treatment as in, for
example, CNG catalytic treatment.
[0029] Embodiments of the invention also include substrate supports
on which the Pd-based oxidation catalyst material, such as
dispersed Pd metal already supported on a refractory oxide, can be
supported. The Pd-based oxidation catalyst material applied to the
substrate support, for example, can be in the form of a washcoat
slurry. Suitable substrates include a flow through or wall-flow
honeycomb body, or it may take on a number of different forms,
including, for example, one or more corrugated sheets; a mass of
fibers or open-cell foam; a volume of porous particle bodies; and
other filter-like structures. Also, if a honeycomb body is
utilized, it may be made of suitable heat-resistant materials such
as metal and/or ceramic materials. Preferably, the honeycomb body
is composed of: cordierite, cordierite-alumina, silicon nitride,
mullite, zircon mullite, spodumene, alumina-silica magnesia, zircon
silicate, sillimanite, a magnesium silicate, zircon, petalite,
alpha-alumina, an aluminosilicate, silicon carbide (SiC), aluminum
titanate, or the like, and combinations thereof.
[0030] Under embodiments of the invention there is preferably
provided sufficient PGM (e.g., Pd loading) to perform the desired
functioning of the present catalyst. Suitable loading of such PGM
material includes Pd in the range of 20 to 500 g/ft.sup.3 or 40 to
400 g/ft.sup.3 or 50 to 250 g/ft.sup.3 with or without Pt. If Pt is
included with Pd it is preferably provided in the range of 10-100
g/ft.sup.3 with a ratio of Pd/Pt of 3:1 to 10:1, or 4:1 to 7:1, or
5:1 being preferred. As seen from the below described examples, the
ability to avoid sulfur degradation, and thus also the prior art
requirement to compensate for such poisoning (by an increased
catalytic material loading), provides in the present invention the
benefit of lower catalytic loading requirement for a given system.
In other words, an advantage provided by the present invention is
the potential for a reduction in PGM content (Pd in particular) in
the catalyst utilized. That is, with the lowering of the light off
temperature and avoidance of sulfur poisoning through in-situ
sulfur removal, the amount of PGM catalyst required to meet a
predetermined result is lowered.
[0031] An apparatus of the present invention features a catalytic
system that converts the exhaust gas of a methane source fueled
combustion device as in an engine (e.g., an NG such as a CNG)
fueled engine (e.g., a mobile vehicle engine such as that for a
passenger car, light or heavy duty truck, bus and the like)
operating in a lean state. The methane source fueled combustion
device can be operated with the methane source fuel as a sole fuel
source as in, for example, NG (e.g., CNG) as a sole fuel source in
a lean burn engine, or as a component of a multi-fuel source engine
(e.g., a flex-fuel or bi-fuel).
[0032] An example of a suitable catalyst for use with a lean burn
methane source fueled combustion device, such as an engine, as in a
CNG lean burn engine, features Pd supported on a rare earth
stabilized high surface alumina with optionally other stabilizers
and promoters also present such as transition metals inclusive of
Zr, and alkaline earth metals such as Mg, Ca, Sr and Ba. Suitable
rare earth alumina stabilizers include La, Pr, Nd, and Y as a few
examples, which listed stabilizer sources can be used individually
or in any of the potential combinations relative to the list
above.
[0033] The present invention includes a catalytic treatment
apparatus for catalytic treatment of exhaust of a lean burn methane
source fueled (e.g., NG as in a CNG fueled) combustion device
(e.g., an engine), comprising: an exhaust line of the combustion
device; a catalyst in the exhaust line; a control unit; and a CO
supplementation apparatus in communication with the control unit
and adapted to supplement the CO content (to achieve, for example,
a programmed, and, hence, predetermined CO content level) in the
exhaust reaching the catalyst so as to desulfate the catalyst while
avoiding an overall rich exhaust.
[0034] An arrangement of the invention features a catalyst that
comprises palladium supported on a rare earth stabilized high
surface area alumina, such as a Pd-only oxidation catalyst or an
oxidation catalyst that comprises Pd and at least a second
catalytic metal such as Pt.
[0035] An arrangement of the invention includes having the CO
supplementation apparatus supplement the CO exhaust content to a
predetermined level while retaining an overall lean burn state at
the catalyst (.lamda.>1.0).
[0036] For example, a mode of the catalytic treatment apparatus is
one that retains the lean state of the exhaust reaching the
catalyst, while the supplemental CO content is supplied by the CO
supplementation apparatus, such that the overall state of the
exhaust gas avoids entering into a rich state such that it is
maintained greater than stoichiometric as in .lamda.>1.0 (e.g.,
>1.0 to 20.0); or .lamda..gtoreq.1.1 to .ltoreq.10.0 and more
preferably .lamda..gtoreq.1.2 to 5.0 even more preferably
.lamda..gtoreq.1.5 to .ltoreq.2.5 with .lamda.=2.1 being suited for
some examples under the present invention. It is noted that,
relative to the broader ranges above, the upper end of these ranges
is combustion device system driven (there is utilized a suitable
combustion air level for purpose of the desired combustion effect
relative to the supplied fuel, while attaining the desired catalyst
driven desulfation emission result in accordance with the present
invention).
[0037] Additionally, an embodiment of the invention features a
percentage of CO content in the exhaust that is capable of
regeneration/desulfation of the catalyst as described above. The
exact concentration of CO needed will depend on such
characteristics as the exhaust composition from the lean operating
engine, catalyst temperature, and exhaust configuration. The CO
concentration that is supplied is at a level and duration that is
sufficient for reactivation, but retains an overall lean state in
the exhaust reaching the catalyst. For example, the CO
supplementation apparatus preferably provides a percentage CO
content in the exhaust that is about 1.0 to <7.5% by volume of
exhaust at the catalyst, as in 1.0% to 6%, or more preferably, for
many situations featured under the present invention, 1.6% to 4.0%,
and still more preferably 3% to 4% as in 3.2% to 3.6% by volume
(while the exhaust is maintained in an overall lean state at the
catalyst). The upper end of the range of 1.0 to <7.5 is an
example of a capped end as to overall CO presence in a system,
where if exceeded for some systems under the present invention
could lead to an undesirable shift from an overall still lean state
to one that is in an overall rich state (having the undesirable
characteristics such as described above, including an increased
propensity for the toxic hydrogen sulfide generation and higher
catalyst sintering potential).
[0038] An example of the invention further includes a CO
supplementation apparatus, an example of which includes a fuel
injector device, such as a fuel injector that is in communication
with a control unit and is adapted to add fuel to one or more
combustion chambers of the lean burn combustion device such as a
combustion engine. The fuel injector can be one that is also used
to inject a source fuel such as CNG in a CNG operating combustion
device such as a combustion engine, but which, under the present
invention, is controlled in a different manner than that used in
standard operation procedures to provide added CO to the exhaust
stream at the desired points in time. This can include a controlled
high frequency periodic input of added fuel to achieve the desired,
predetermined level of increase in CO content in the exhaust
output. Thus, an embodiment features the fuel injector device
feeding a common fuel as in CNG fuel of a sole CNG fuel running
combustion device such as a combustion engine or one of the
component fuels of a multi-fuel running NG combustion device such
as a combustion engine for the purpose of controlled CO
supplementation while retaining an overall lean state in the
exhaust reaching the catalyst.
[0039] One technique under the present invention for retaining an
overall lean state at the catalyst during a supplementation period
(wherein fuel is supplied for controlled CO supplementation) is to
have the fuel injector device of the CO supplementation apparatus
supply fuel to less than the total number of combustion chambers of
a lean burn engine.
[0040] An arrangement of the catalytic treatment apparatus of the
present invention further includes a catalyst sulfation
deactivation state sensor in communication with the control unit,
with the deactivation state sensor conveying, for example,
information to the control unit that is informative of a level of
sulfation deactivation of the catalyst, and when the control unit
determines a threshold value of sulfation deactivation has
occurred, initiates the CO supplemental apparatus to supplement the
exhaust flow with added CO as to achieve a desulfation effect (and
it is considered as well, under applicable conditions, that the CO
supplementation reverses the derogatory effect that the water
poison effect has on catalyst activity).
[0041] A further arrangement of the invention includes the CO
supplemental apparatus increasing the CO content by way of
providing an additional supply of an available fuel through the
opening of one or more fuel supply valves based on operation of the
control unit communicating with the CO supplement apparatus. Again,
this supplemental apparatus is designed to provide sufficient added
fuel to reach predetermined levels of added CO content in the
exhaust gas reaching the catalyst, but not so much as to lead to an
overall rich state in the exhaust reaching the catalyst.
[0042] The present invention is also inclusive of a method of
enhancing performance of a catalyst operating in a lean burn
(methane fuel sourced) combustion device (e.g., engine) exhaust
passageway that comprises supplementing the CO content of the lean
burn (methane fuel sourced) combustion device (e.g., engine)
exhaust so as to rejuvenate the catalyst (e.g., reactivate a sulfur
degraded catalyst) while retaining a lean burn state in the exhaust
reaching the catalyst during CO supplementation.
[0043] The present invention is also inclusive of a method of
enhancing a catalyst performance in a lean burn (methane fuel
sourced) combustion device (e.g., engine) exhaust passageway, that
includes supplementing the CO content of the lean burn engine
exhaust so as to reactivate the catalyst (e.g., reactivate the
catalyst by removal of sulfur build up on that catalyst) while
retaining an overall lean lambda state in the exhaust reaching the
catalyst during CO supplementation. For example, in an embodiment
of the invention there is featured a lean burn combustion device
(e.g., engine) oxidation catalyst with Pd as the, or one of the,
active PGM materials, which catalyst is operating in the exhaust
passageway of the (e.g., CNG) lean burn combustion device (e.g.,
engine) and is reactivated by adding, in a controlled fashion, to
the CO content of the exhaust, which facilitates the desulfation of
that catalyst.
[0044] The method also includes the above described CO
supplementation step (for increasing the CO content) which results
in an exhaust with added CO reaching a catalyst that has both Pd
and a second catalytic metal such as a second PGM metal (preferably
in a subordinate role relative to the Pd metal so as to constitute
a "Pd-based" catalyst). Examples of secondary PGM materials
including Pt and/or Rh
[0045] Embodiments of the invention feature supplementing a typical
CO amount used for non-supplemented or normal running of the lean
burn engine (e.g., CO contents of 0.1 to 0.5% or 1,000 to 5,000 PPM
of non-supplemental CO content in a normal running lean CNG engine
with 4300 PPM being used in the below described testing and
representing a baseline amount of non-supplemented CO content,
which the present invention supplements. The method of the present
invention is inclusive of a rejuvenation of an oxidation catalyst
used in a methane source fueled (e.g., an NG) lean burn combustion
device (e.g., engine) oxidation catalyst that includes
supplementing the CO content reaching the catalyst so as to have CO
percentage by volume of 1.0% to <7.5%, as in 1.0% to 6.0%, and
more preferably, for many embodiments of the present invention,
1.6% to 4.0% with greater than 2.0% being preferred under
illustrative set ups of the present invention, and more preferably
at or greater than 2.5%, and still more preferably at or greater
than 3.2%, with the upper end of these ranges being designed to
preclude a conversion of an overall lean state in the exhaust
reaching the catalyst to one that is rich while providing a good
source of supplemental CO or desulfation on the catalyst. For
example, arrangements of the invention are inclusive of a CO
content of 3 to 4%, as in 3.5% reaching the catalyst, such as a Pd
based catalyst (a Pd only or Pd/Pt combination as a few
examples).
[0046] The method of the present invention also includes a process
wherein the catalyst is a Pd based oxidation catalyst and
rejuvenation includes desulfation of the Pd based catalyst by way
of the CO supplementation wherein the CO supplementation is carried
out by supplying additional fuel to one or more combustion chambers
of the methane source fueled lean burn combustion devices (e.g.,
combustion engine). The CO generating fuel can be in common with
one of the fuel supplies used for combustion device (e.g.,
combustion engine) performance, or a fuel supply that is a
separate, independent (dedicated) fuel supply and not sourced from
the main combustion device's (e.g., combustion engine's) fuel
supply or a combination of each. While less preferable in many
applications, such as mobile applications, where the
supplementation apparatus can take advantage of preexisting
equipment in conjunction with a modified control unit or other
means to change the manner of normal operation of the system to
enhance CO content, alternate embodiments are inclusive of CO
source supply units or means as in pressurized tanks or chemical
reaction devices that include CO as an output reactant, or the
like, to provide the desired added level of CO content reaching the
catalyst. An example of a CO supplementation technique includes a
control unit triggered CO pulse additions to the exhaust flow
upstream or at the catalyst set up.
[0047] The present invention features a technique for maintaining
high activity in a catalyst contained in a catalytic emission
system for a lean burn NG or methane inclusive fuel sourced
combustion device (e.g., combustion engine) (either in conjunction
with an initial manufacture of a catalytic emissions system or
based on a conversion of a preexisting catalytic emissions system).
The technique is inclusive of a CO supplementation step which acts
to offset the problem of sulfation deactivation, particularly
relative to sulfur poisoning of a Pd containing oxidation catalyst
designed for light off of methane (alone or with other NMHC's
generated by such combustion devices (e.g., combustion engines)),
since Pd containing catalysts, while highly effective in catalytic
treatment of methane and other low molecular weight alkanes, have
been shown to be particularly sensitive to H.sub.2S and other
sulfur containing gases in the exhaust such as SO.sub.3 or
SO.sub.2.
[0048] An embodiment of the method of the present invention
includes CO supplementation by supplying (e.g., adding to a normal
run supply, such as by way of extending the duration of fuel
already being supplied, increasing the relative flow volume
associated with normal operation, or newly adding fuel to one or
more combustion chambers not intended for fuel supply at that time
under a normal run mode, or a combination of two or more of these
added supply techniques. As an example of a lean retention
supplementation mode involving added fuel supply relative to that
which would be supplied for a normal running mode (e.g., a peak
performance normal running mode), supplemental fuel is supplied to
less than all available combustion chambers of the methane source
fueled lean burn engine. For example, a portion of CNG fuel of a
lean burn CNG engine can be utilized for the purpose of added fuel
supply (as by ECU controlled valve opening and closing) to one or
more of the combustion chambers of the engine at a time when a
normal running mode does not dictate fuel supply to those chambers
or in an added quantity compared to that which would be supplied to
the chamber(s) during normal running mode. For example, the number
of combustion chambers and/or the amount of added fuel to the
combustion chambers can be controlled by the ECU control unit so as
to achieve a CO desulfation content of 1.0% to <7.5%, while
maintaining an overall lambda lean state, at least at the initial
contact of the exhaust with the catalyst. More preferably the
supplemental CO provides a CO content in the exhaust gas reaching
the catalyst of 2.5% to 4.0%, and more preferably 3.0 to 4.0%,
while the lean lambda state is maintained at a ratio value greater
than stoichiometric and preferably at least 1.1. Alternate
embodiments feature controlled or preset addition of CO via CO
supplementation using alternate CO supplementation means such as by
direct CO injection into the exhaust in front of the catalyst,
which is particularly suited for NG fuel sourced power plants.
[0049] The present invention is also inclusive of a method of
assembling the catalytic treatment apparatus of the present
invention or retrofitting a preexisting system by adding a CO
supplemental apparatus (for example, a CO supplemental apparatus or
means for supplementing the level of CO reaching the catalyst as in
an entirely separate assembly or one that makes use of preexisting
combustion system components, such as the fuel intake valve
assembly feeding a combustion chamber or the like, with appropriate
control unit modifications such as a replacement/supplementation of
a preexisting engine control unit or as an added independent CO
supplementation control unit preferably working in communication
with the preexisting engine control unit). The CO supplemental
apparatus is designed to increase CO supply to the catalyst while
retaining a lambda lean state in the exhaust reaching the catalyst.
For example, under either an initial manufacture of a catalytic
emissions treatment system or a retrofitting of a preexisting
system, there is carried out a setting up of a control unit to
communicate with an added or preexisting fuel injection system for
supplemental fuel supply above and beyond what is utilized in the
normal running procedure within one or more of the combustion
chambers so as to generate added CO while maintaining an overall
lean burn state in the exhaust reaching the catalyst being
reactivated (as in desulfating a Pd based catalyst from a prior
poisoning by SO.sub.2).
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] Both the foregoing general description and the following
detailed description are exemplary and explanatory only and are
intended to provide further explanation of the invention as
claimed. The below referenced accompanying drawings are included to
provide a further understanding of the invention; are incorporated
in and constitute part of this specification; illustrate
embodiments of the invention; and, together with the description,
serve to explain the principles of the invention.
[0051] FIG. 1 is a diagram showing the general construction of a
combustion device in the form of an internal combustion engine to
which the present invention is applied.
[0052] FIGS. 2A and 2B show different approaches involving the use
of a dedicated ECU with a CO supplementation apparatus that work
together to achieve an increase in the CO content for a given time
period or periods in the exhaust flow for the purposes of lean CNG
catalyst desulfation.
[0053] FIG. 3 shows a schematic illustration of a CNG test bench
equipment set up for carrying out tests such as the comparative and
present invention tests described herein.
[0054] FIG. 4 shows that in the absence of SO.sub.2 no further
deactivation is noted after the 1.sup.st light off test and the
performance stabilizes at light off 2.
[0055] FIG. 5 shows that the introduction of SO.sub.2 leads to a
rapid and dramatic loss of light off activity, and that activity is
not recovered after the initial S free light-off activity.
[0056] FIG. 6 shows test protocol information for CNG lean burn
engine testing wherein SO.sub.2 influence is investigated by
utilizing a standard lean 4% O.sub.2 gas blend with and without
SO.sub.2 addition (at 5 PPM).
[0057] FIG. 7 shows a comparative conversion vs. temperature for
methane light off involving a nominal (or non-supplemented) CO
supply with examples of multiple runs inclusive of initial runs
without SO.sub.2 supplied, runs with SO.sub.2 supplied, and
subsequent light offs again without SO.sub.2 supplied; and FIG. 7
further shows that the introduction of SO.sub.2 leads to a rapid
and dramatic loss of light off activity and further that a lean
high temperature pretreatment does not recover the initial S-free
light-off activity of the catalyst.
[0058] FIG. 8 shows a conversion vs. temperature methane light-off
graph of the present invention which features a supplemented CO
supply with multiple runs shown, inclusive of initial runs without
SO.sub.2 supplied, runs with SO.sub.2 supplied at 5 ppm,
desulfation runs with CO supplementation at 3.2%, and subsequent
light offs again without SO.sub.2 supplied or CO
supplementation.
[0059] FIG. 9 shows a conversion vs. temperature 95:4:1
(methane/ethane/propane) mix light-off graph of the present
invention which features a supplemented CO supply with multiple
runs shown inclusive of initial runs without SO.sub.2 supplied,
runs with SO.sub.2 supplied at 5 ppm, desulfation runs with CO
supplementation at 3.2%, and subsequent light offs again without
SO.sub.2 supplied or CO supplementation.
[0060] FIG. 10 shows a conversion vs. temperature 95:4:1
methane/ethane/propane mix light-off graph of the present invention
at a lower CO supplementation, which features a supplemented CO
supply with multiple runs shown inclusive of initial runs without
SO.sub.2 supplied, runs with SO.sub.2 supplied at 5 ppm,
desulfation runs with CO supplementation at 1.6%, and subsequent
light offs again without SO.sub.2 supplied or CO
supplementation.
[0061] FIG. 11 shows an additional example of the present invention
featuring a multi-catalyst system with at least the first or
upstream catalyst operating under a CO supplemented exhaust
atmosphere.
[0062] FIG. 12 shows an additional example of the present invention
with the combustion device being an NG stationary power plant.
DETAILED DESCRIPTION
[0063] FIG. 1 is a diagram showing the general construction of an
internal combustion engine to which the catalytic system or
catalytic treatment apparatus (CTA) of the present invention is
included. The FIG. 1 example features a multi-fuel (CNG and liquid
fuel such as gasoline) internal combustion device (engine) 1. The
internal combustion engine 1 shown in FIG. 1 is a spark-ignition
internal combustion engine having a plurality of cylinders. While
the internal combustion engine shown in FIG. 1 has four cylinders,
the number of the cylinders may be three or less or five or more
(e.g., 1, 2, 4, 6, 8 or 12 as engine examples featured in the
present invention).
[0064] The internal combustion engine 1 is connected with an intake
passage 3 and an exhaust passage 4. The intake passage 3 is a
passage used to deliver fresh air taken from the atmosphere to the
cylinders 2 of the internal combustion engine 1. The intake passage
3 is provided with an air cleaner 30. The air cleaner 30 is adapted
to trap dust in the air. The intake passage 3 is provided with an
air flow meter 31 at a location downstream of the air cleaner 30.
The air flow meter 31 outputs an electrical signal correlating with
the quantity (or mass) of air flowing in the intake passage 3. The
intake passage 3 is provided with a throttle valve 32 at a location
downstream of the air flow meter 31. The throttle valve 32 varies
the quantity of air supplied to the internal combustion engine 1 by
varying the channel cross sectional area of the intake passage
3.
[0065] The intake passage 3 downstream of the throttle valve 32
forks into four branch pipes, which are connected to the cylinders
2 respectively. To each branch pipe of the intake passage 3 are
attached a first fuel injection valve 5 for injecting CNG (an
example of a methane source fuel) into the respective cylinders,
and a second fuel injection valve 6 for injecting gasoline (liquid
fuel) into the respective cylinders. In an embodiment featuring CNG
as the sole fuel source, the second fuel valve 6 (and below
described liquid fuel supply and associated "fuel valve 6" control
means portion would be non-applicable).
[0066] The first fuel injection valve 5 is connected to a first
delivery pipe 50. The first delivery pipe 50 is connected to a
first fuel tank 52 via a first fuel passage 51. The first fuel tank
52 is connected with a filler port 53 provided on the body of a
vehicle via an inlet pipe 54. The filler port 53 is adapted to
open, in response to insertion of a fuel service nozzle at a CNG
fuel station or the like, to allow introduction of CNG supplied
through the fuel service nozzle into the inlet pipe 54. The CNG
introduced into the inlet pipe 54 through the filler port 53 is
stored in the first fuel tank 52.
[0067] The CNG stored in the first fuel tank 52 is supplied to the
first delivery pipe 50 through the first fuel passage 51 and then
distributed to the four first fuel injection valves 5 from the
first delivery pipe 50. The first fuel passage 51 is provided with
a shut-off valve 55. The shut-off valve 55 provides switching
between fuel injection and shut-off of the first fuel passage 51.
The shut-off valve 55 is closed while the internal combustion
engine 1 is not running (e.g. in the period during which the
ignition switch is off) and open while the internal combustion
engine 1 is running (e.g. in the period during which the ignition
switch is on). An example of a suitable shut-off valve 55 is an
electromagnetic valve that is opened when the engine is running and
electricity generated and closed when the engine is not running and
there is a reduction in electricity generated.
[0068] The first fuel passage 51 is provided with a regulator 56 at
a location downstream of the shut-off valve 55. The regulator 56
reduces the pressure of CNG supplied from the first fuel tank 52 to
a predetermined pressure (set pressure). To put it another way, the
regulator 56 is a valve device that adjusts or steps down a higher
input pressure sourced from the first fuel tank 52 to a desired
outlet pressure which is fed to the first fuel injection valves 5
which are set open or closed based on the control input of
controller 7. In this way the fuel pressure in the first fuel
passage 51 downstream of the regulator 56 or the fuel pressure
acting on the first fuel injection valves 5 and the first delivery
pipe 50 (which will be hereinafter referred to as the "fuel
injection pressure") is made equal to the set pressure determined
to be applicable by the controller 7.
[0069] The first fuel passage 51 is provided with a pressure sensor
57 at a location upstream of the shut-off valve 55. It is preferred
that the pressure sensor 57 be arranged at a location as close to
the first fuel tank 52 as possible.
[0070] The second fuel injection valves 6 are connected to a second
delivery pipe 60. The second delivery pipe 60 is connected to a
second fuel tank 62 via a second fuel passage 61. The second fuel
tank 62 is a tank that stores gasoline (or some other fuel source
such as diesel). The second fuel passage 61 is provided with a fuel
pump 63 for pumping up gasoline stored in the second fuel tank 62.
The fuel pump 63 is, for example, a turbine pump driven by an
electric motor. The gasoline pumped up by the fuel pump 63 is
supplied to the second delivery pipe 60 through the second fuel
passage 61 and then distributed to the four second fuel injection
valves 6.
[0071] The exhaust passage 4 is a passage used to cause burned gas
(exhaust gas) discharged from the cylinders 2 to be emitted to the
atmosphere after passing through an exhaust gas purification
catalyst device 40 and a silencer etc. Sensor apparatus 41 can
include an air/fuel equivalence ratio or A/F sensing means that
outputs an electrical signal correlating with the air-fuel ratio of
the measured region of the exhaust passage 4. The A/F sensor
outputs an electrical signal for determining the current air fuel
ratio across the catalyst device 40 and can take on a variety of
forms such as an oxygen sensor with associated voltage meter.
[0072] The air-fuel ratio (AFR) is the ratio between the mass of
air (M.sub.air) and mass of fuel (M.sub.fuel) in the fuel-mix at
any given moment. That is: (AFR=M.sub.air/M.sub.fuel). The mass is
the mass of all constituents that compose the fuel and air being
whether combustible or not. For example, a calculation of the mass
of natural gas (NG)--which often contains carbon dioxide
(CO.sub.2), nitrogen (N.sub.2), and various alkanes, includes the
mass of the carbon dioxide, nitrogen and all alkanes in determining
the mass of natural gas. The air-fuel equivalence ratio
(.lamda.--lambda) is the ratio of actual AFR to stoichiometry for a
given mixture. .lamda.=1.0 is at stoichiometry, rich mixtures
.lamda.<1.0, and lean mixtures .lamda.>1.0. An embodiment of
the present invention features the engine 1 set to operate at a
lean mixture or .lamda.>1.0 (e.g., 1.1 to 20)
[0073] The internal combustion engine 1 having the above-described
construction is equipped with an ECU 7. The ECU 7 is an electronic
control unit composed of, for example, a CPU, a ROM, a RAM, and a
backup RAM etc. The ECU 7 is electrically connected with various
sensors such as an accelerator position sensor 8 and a crank
position sensor 9 in addition to the air flow meter 31, the
determination sensor apparatus or means 41 (sensor apparatus or
means 41 can comprise a single sensor type or a multiple set of
different sensor functioning devices or types), and the pressure
sensor 57 mentioned above. The accelerator position sensor 8 is a
sensor that outputs an electrical signal correlating with the
position of the accelerator pedal (accelerator opening degree). The
crank position sensor 9 is a sensor that outputs an electrical
signal correlating with the rotational position of the crankshaft
of the internal combustion engine 1.
[0074] The ECU 7 is electrically connected with various components
such as the first fuel injection valves 5, the second fuel
injection valves 6, the shut-off valve 55, and the fuel pump 63.
The ECU 7 controls the above-mentioned various components based on
signal outputs from the above-mentioned various sensors. The ECU 7
of the present invention is able to control the relative on/off
states of the first fuel injection valves 5 such that there is
provided for independent control as to which injector(s) 5 are
feeding CNG into the cylinders and which injector(s) 5 are not.
[0075] The ECU 7 for the multi-fuel engine shown in FIG. 1 also
switches the fuel utilized based on the sensed current settings
such as the relative fuel level in each of the multi-fuel source
tanks 52 and 62.
[0076] Under the present invention's approach of introducing added
CO, via supplementation apparatus S of the CTA, for the purpose of
avoiding sulfation build up and/or providing for desulfation of any
sulfur build up on the catalyst device 40 shown in FIG. 1, the CO
introduction can be implemented on a preset time schedule or one
that is based on a monitoring of performance of the catalyst such
as by way of providing a deactivation monitoring sensor function to
sensor apparatus 42, which can be a dedicated measure of the state
of deactivation of the catalyst 40 (e.g., a methane bypass sensor)
or one that is multi-functional, but one that in any event provides
information indicative as to the present state of deactivation of
catalyst 40. In a preferred embodiment the CO supplementation is
tied in with the activity of catalyst 40 (e.g., a lower level of
activity due to sulfation poisoning can be sensed as by way of how
much methane escapes or bypasses the catalyst). If such a condition
is received by the ECU, appropriate CO supplementation activity can
be activated by the ECU and provided by supplementation apparatus
S.
[0077] Alternatively, if a preventive mode is desired the ECU 7 can
implement a preset supplemental fuel schedule to achieve the
desired repeated CO supplementation runs in the exhaust line at the
catalyst. In this mode, the ECU 7 (or an independent, dedicated
supplemental fuel implementation control unit with attributes
similar to the above described ECU 7) can be set up to initiate a
preset increase in CO present in the exhaust flow on a preset time
basis and time duration (e.g., periodic initiation of CO
supplementation for a time period sufficient to raise the CO level
in the exhaust gas as in an increase of CO in a range of 1.5% to 4%
concentration by volume for a sufficient period of time to achieve
a level of desulfation within the periodic interval of CO
supplementation). In many embodiments of the present invention,
however, CO supplementation is carried out after a perceived or
monitored level of sulfur build up and not on a fixed schedule that
provides supplemental CO without monitoring the sulfur build up on
the catalyst.
[0078] Implementation of the increase in CO is carried out under an
example of the invention by an increased fuel supply to the
combustion device (e.g., the CNG source or an alternate source, as
in another fuel source in a multi-fuel sourced engine or an
independent alternate fuel supply not utilized for general
combustion device performance). With reference to FIG. 1, this can
be carried out a CO supplementation step by adding or
supplementing, via the ECU control 7 and the CO supplementation
apparatus S, the amount of CNG fuel supplied to one or more of the
cylinders C1 to C4. For example, there can be carried out an ECU
triggered/controlled manipulation of the CO supplementation fuel
supply valving 5 for a period of time suited for a desired
desulfation result. For instance, valve manipulation can be
utilized, e.g., opening one or more valves that are normally
maintained in a closed state during the applicable normal running
period, or maintaining for a longer time one or more of the valves
in an open state, as compared to the normal run time period of the
valve(s) feeding the cylinder(s) with the CNG fuel supply.
[0079] Alternatively, an increased flow rate within a common time
period in one or more of the cylinders over that rate used for
normal running can be utilized for CO supplementation. That is,
some or all cylinders can have a supplemental CO supply above and
beyond what is implemented for a standard or typical flow condition
under that current engine operating condition, although care is
taken under the present invention to avoid altering an overall lean
engine operation to one that generates or passes into a rich
overall operation state. For example, there also can be utilized
the sensed lambda value for the engine operation, such as by way of
the interplay between sensor apparatus 41 and/or sensor apparatus
42 and the ECU monitoring of the lambda value such that a cap
voidance value (an early triggering if the tendency is suggesting
potential later entry into an overall rich condition if steps are
not taken currently) is set at, for example, stoichiometric or
close to stoichiometric on the lean side (e.g., 1.05) to retain
overall lean condition, but with an added amount of CO to the
exhaust stream.
[0080] Thus, under the present invention there can be monitored the
activity level associated with the oxidation catalyst by a sensing
of any indicator that is informative of sulfur poisoning in the
operation of the catalyst device 40. For example, such monitoring
can be by way of either sensor apparatus 42 or a combination of
sensor apparatus 41 and sensor apparatus 42, with one or both of
sensor apparatus 41 and sensor apparatus 42 being potentially
inclusive of multiple sensing functions. For example, one
preferred, direct approach is to monitor methane breakthrough past
catalyst device 40 with a methane sensor such as with sensor
apparatus 42 downstream of catalyst device 40. The sensed level of
methane breakthrough downstream of catalyst device 40 can be
determined with a methane level sensor function provided in sensor
apparatus 42, and the trigger CO supplementation need level can be
based on a preset range of lowered performance acceptance before a
triggering of the supplemental CO (and preferably also accompanying
H.sub.2 production). Preferably there is set a trigger level as to
catalyst degradation that maintains catalyst operation above a
regulated level so as to avoid the release of a quantity of methane
(and NMHC's if present) that would violate a regulatory set level.
In this way, there is avoided over implementation of the CO
supplementation due to sensing fluctuations, etc., while also
ensuring that the catalyst performance avoids violating a
regulatory standard under consideration.
[0081] A person skilled in the art, with the benefit of the present
description, would be able to provide an engine controller that can
be used here in order to be able to carry out the CO
supplementation strategy according to the invention for the
exhaust-gas purification system (Electronic Engine Controls, 2008,
ISBN Number: 978-0-7680-2001-4). Again, with the benefit of the
present disclosure, said person skilled in the art would also be
likewise familiar with sensors which may be taken into
consideration for measuring the CO supplementation criteria (e.g.,
NO.sub.x threshold values, methane levels, and lambda value) (e.g.,
see Christian Hageluken, Autoabgaskatalysoren,
Grundlagen-Herstellung-Entwicklung-Recycling-Okologie [Automobile
exhaust-gas catalytic converters,
fundamentals-production-development-recycling-ecology], Expert
Verlag, 2.sup.nd Edition, pages 188 et seq., in particular page 206
et seq.)
[0082] Although a variety of sensing parameters, such as the above
noted NO.sub.x passage level, can be used as an indicator of a
level of sulfur degradation in a catalyst, a direct methane escape
level monitoring can be utilized as to better rule out other
(non-sulfur degradation) causal issues that might influence a level
reading. Thus, sensor apparatus 42 can comprise a direct methane
detector that can determine the methane level in the exhaust flow
departing the catalyst device 40 and determine if there has been a
level of degradation in the methane conversion performance
indicating a sulfur degraded catalyst is present. In an alternate
embodiment, both sensor apparatus 41 and 42 function to monitor
methane levels in the respective gas flow regions (e.g., an
upstream region leading to the middle of the catalyst 40 and a
downstream region departing the middle of the catalyst 40 (as in
sensing at the release point of exhaust downstream of a catalytic
canister represented by catalyst device 40)). In this way the
amount of methane received by the catalyst and the amount of
methane not removed by the catalyst can be determined by the
methane amount differential between the upstream and downstream
monitoring locations such that a degraded catalyst can be
determined.
[0083] An additional example, as to the various approaches
available for monitoring for when a desulfation level suggests a CO
supplementation mode will be helpful, includes dispensing with the
attachment of sensors such as downstream of the lean burn engine
catalyst 40. Rather, reliance is placed on respective CO
supplementation criteria (sulfur degraded catalyst performance
criteria) that is/are obtained on the basis of the data of the
engine characteristic (historical data for that engine or that type
of engine operating under similar conditions) and by computer
calculation. For example, poorer engine performance for a given set
of circumstances can be monitored and used as an indicator of
catalyst attributable to sulfur poisoning catalyst degradation. A
direct measurement of methane bypass levels or characteristics is,
however, better suited under many examples of the present invention
as it is better able to rule out other types of degrading
influences on the catalyst such as a high temperature/sintered
degraded catalysts.
[0084] As described above and as seen in FIG. 1, sensor apparatus
41 and/or 42 is/are preferably designed to include either or both
of a function of monitoring the oxidation performance of catalyst
device 40 relative to oxidation of a component in the exhaust flow
of the NG (e.g., CNG) engine and a direct measurement of methane
bypass. For example, sensor apparatus 41 and/or 42 is/are designed
to sense the level of activity of the catalyst, as by a monitoring
of methane passing past the catalyst and/or by any one of the other
techniques described above (or via the above described sensor-less,
engine performance and computer calculation based on pre-stored
data indicative of the performance level for the catalyst alone or
in combination with a more direct, confirmatory sensing as with a
methane bypass sensor). Such degradation monitoring sensing is thus
carried out by sensing means such as that described immediately
above.
[0085] FIG. 2A shows one example of a sequence of steps that can be
carried out under the present invention involving the ECU 7 (or
added dedicated control unit in communication with ECU 7) for
generation of increased CO (either by way of an added level of CO
content from that normally used, or an extended duration of supply
as to that which would normally be provided for desired engine
performance, or a combination of an added level and an added
duration of supply from the norm). This supplementation can be
achieved, for example via CO supplementation in the exhaust flow
for the purposes of lean CNG catalyst desulphation (e.g., a
catalyst treatment apparatus featuring CO supplementation apparatus
or CO supplementation means S working together, via reception and
output means of the supplemental apparatus S such as electronic
open and close valve triggering and mode position confirmation
means (not shown) in the valves, with an associated CO
supplementation programmed portion of the ECU (or some other
control means)). One embodiment of the invention features CO
supplementation apparatus S that is in fuel supply communication
with a fuel source, and has a fuel passageway and a controllable
valve structure (as by control unit signal reception and
transmission coordination with the reception and output means of
the valve structure), which valve structure is suited for an
in-feed of supplemental fuel to one or more combustion areas
upstream from catalyst device 40.
[0086] FIG. 2A shows a sequence of steps, involving the ECU and
supplementation apparatus S, for generation of increased CO in the
exhaust flow for the purposes of lean CNG catalyst desulphation. As
seen upon initiation of the desulfation
monitoring-with-supplementation (if needed) program, a flag is set
to zero, and there is initiated a sensed level of catalyst
degradation (e.g., a sensed lower activity level in the catalyst
indicative of catalyst degradation) using, for example, any of the
above described sensing methods, with a methane bypass sensing
means preferred for some examples. A comparison is then made
relative to the sensed level "X1" relative to a predetermined
triggering threshold for the CO supplementation program. For
example, the sensed value "X1" (with "X1" being any informative
representation of the level of degradation of the catalyst (such as
a methane conversion percentage for a sensed temperature of the
catalyst; which, if below a predetermined level, is deemed to be a
catalyst that has been SO.sub.2 poisoned as to require regeneration
via the CO supplementation process of the present invention)). If
the sensed value X1 is deemed to fall at or below a triggering
threshold level, the CO supplementation is carried out as shown in
FIG. 2A. If, however, the sensed value X1 is determined not to be
less than or equal to the trigger value Tr, the program returns to
a periodic sensing routine controlled by the control unit (e.g.,
ECU 7). Although not shown, a reverse triggering relationship
determination can be made under examples of the invention as when
Tr is, for instance, based on a methane escape level (rather than
an amount reduced or converted) which upon exceeding a slip
threshold level triggers CO supplementation (X1 equals the sensed
methane slip amount which, when greater than Tr (as the minimal
value that can be released without CO activation) starts CO
supplementation).
[0087] As further shown in FIG. 2A, if the X1 reduction level
across the catalyst is found to be at or below the trigger value
"Tr", CO supplementation is initiated by the CO supplementation
means under control of the ECU such as by supplying added CNG to
one or more of the combustion chambers (C1 to C4) so as to provide
greater CO content in the exhaust reaching the catalyst device 40,
while still retaining an overall lean run state in that exhaust
reaching monitored catalyst device 40. Alternatively, or in
addition thereto, there can be extended the time period of normal
fuel supply to the engine with the duration time period for fuel
supply being extended beyond that which is normally relied upon
during normal running or there can be a greater pressure, higher
flow rate as that used under normal operation. That is, the
supplementation in this case is provided with more of an added time
duration supply or a greater mass flow rate for a common period as
normally used to achieve the desired higher CO contact with the
catalyst being regenerated. The supplementation in examples of the
invention provides a CO content at the catalyst of 3.0% to 4.0%
(e.g., 3.5%) in the exhaust reaching the catalyst with the time
period of such oversupply being preset to achieve a desired level
of desulfation at the catalyst.
[0088] Following the supplementation (as in a programmed added CNG
fuel supplementation period at a predetermined flow rate to the
noted one or more combustion chambers), the catalyst device 40 is
again sensed for level of activity (which, in reverse, is
indicative as well as the level of degradation) and the current
sensed value "X2" is again compared against the threshold value Tr
to see if the last reactivation or regeneration treatment worked.
Upon confirmation that the desulfation process has worked, the
program is returned to the scheduled ECU monitored (time repeating)
sensing mode to monitor to see if the catalyst again moves to a
sulfate poisoned state requiring the CO supplementation activity
under the present invention. If, despite, the CO supplementation,
the again sensed value X2 remains below or at the trigger threshold
value, repeated CO supplementing is carried out (either in the same
fashion as previously carried out or via a ramped up treatment
involving an added extension of time at a prior supply level or an
increase in the overall supply as in a bump up in CO content from a
normal running nominal amount to, for example, 3% to 4% for a
desired time period or a combination of each). The number of
repeated attempts of CO supplementation is monitored (F=F+1) and if
the current value F reaches a threshold value "Y", there is deemed
to be a situation where the catalyst device 40 is not recoverable,
at least at the current time, and an "alarm" signal is sent out
such that the ECU can keep abreast of the performance or current
condition of catalyst device 40.
[0089] Thus, as an example of a method of reactivation of a
degraded lean burn CNG engine oxidation catalyst device 40, the
sensing means (e.g., 42 and/or (41 and 42)) is interpreted by the
ECU 7 (or a more specific, dedicated control unit such as one in
communication with ECU 7), wherein the ECU (or noted more dedicated
control unit) determines whether or not a preset value of sulfur
degradation in the catalyst has been reached. If that level is
deemed to not have been met (i.e., the catalyst is deemed not to
have been sufficiently degraded by sulfur such that restoration is
deemed not required at the present time), the program returns to
pre-sensing status (e.g., a timed periodic check of the
status).
[0090] Thus under the method of the present invention, if the level
of sulfur degradation of the catalyst is deemed to meet a
triggering threshold value, the CO supplementation means S is
activated by the applicable control unit (e.g., ECU 7) such that an
added supply of CO is provided to the exhaust passing over the
catalyst material of catalyst device 40 while there is still
retained an overall or general lean exhaust atmosphere over that
catalyst material of catalyst device 40. In one mode of
supplementation under the present invention, the CO supplementation
process includes a control unit triggering of an opening of
preferably less than the total number of CNG supply valves (e.g.,
only combustion chambers C1 and C4 relative to the overall
combustion chambers (C1, C2, C3, C4)) such that the limited number
of combustion chambers are supplied with an extra amount of fuel
(resulting in a supply of CO that is more than that suited or
applied in standard engine running performance). In this way, a
desired amount of supplemental CO is provided to the catalyst. This
lessening or limiting of the usage of fuel supply to the combustion
chambers is made in an effort to preclude moving the overall
exhaust output into an overall rich state, that might occur, for
instance, if all four combustion chambers were to be provided with
an excess amount of fuel such as the CNG fuel via line 50 and the
respective fuel supply valve(s) 5. For example, a "nominal" amount
of CO presence featured in standard running programming (e.g., 4300
PPM, or less than 1.0% (1%=10,000 PPM)) is supplemented such that
there is greater than that nominal amount as in a greater amount of
1.0% to <7.5%, and more preferably 2.0% to 6.0% CO in the
exhaust, and more preferably a range of 2.5 to 4.0% CO by volume in
the exhaust gas passing through the catalyst, and still more
preferably, in many uses of the present invention, a level of 3.0%
to 4.0% as in 3.5% (35,000 PPM). A range of CO supplementation that
is in the region exceeding 7.5% can result in a toggling from an
overall lean state to an overall rich state, with the latter
situation being undesirable under the present invention (e.g., an
increase in the more harmful hydrogen sulfide generation). The 3%
to 4% level range described above provides for rapid
desulfation/reactivation in many invention environments, while
safely maintaining an overall lean state at the catalyst under a
variety of arrangements for the combustion device system of the
present invention.
[0091] FIG. 2B shows a variation in the sequence of steps involving
the ECU for generation of increased CO in the exhaust flow for the
purposes of catalyst (e.g., lean CNG exhaust catalyst) desulfation.
In FIG. 2B there is carried out similar steps as in FIG. 2A
relative to determination of value X1. Following a sensing of value
X1 there is initially determined whether X1 is at or below a higher
threshold trigger value T.sub.H if X1 is not at or below T.sub.H,
the sensing cycle controlled by the ECU determines that the
degradation level of catalyst 40 is not yet problematic and can be
maintained without CO supplementation. If it is deemed that the
sensed value X1 is less than or equal to T.sub.H, a further
determination is made as to whether X1 falls within a range between
a lower (or poorer performance) threshold value T.sub.L and
T.sub.H. If X1 is deemed to fall within the illustrated T.sub.L to
T.sub.H range, a CO supplementation process is initiated by the ECU
at Level 1 (e.g., an added fuel supply to the one or more
combustion chambers of a combustion device and/or a retention of a
prior set fuel level supply for an added given amount of time,
despite a normal running mode suggesting for a lowering in the
supply amount for a given combustion device normal running mode at
the review time point). If instead the value X1 does not fall
within the noted range (and is thus below T.sub.L), there is
initiated a CO supplementation process at Level 2. A Level 1
process can entail a lesser amount of CO supplementation generation
as by, for example, a shorter timeframe input of CNG into the
cylinder(s), a lesser CNG input flow rate to the predetermined
cylinder(s); and/or a lower number of combustion chambers involved
than that featured in a Level 2 CO supplementation process
described below (or any combination of the three noted approaches
for Level 1). For example, a Level 1 CO supplementation can entail
a 1.6%, by volume, CO content in the exhaust reaching the catalyst,
while a Level 2 CO supplementation can entail a 3.2% by volume CO
content in the exhaust reaching the catalyst. Thus, there can be
utilized a higher threshold value that is directed at efficient
engine running performance well within any regulatory standard
under consideration and a more aggressive approach when it is
sensed that the level of degradation could result in a below
regulation level if not addressed properly.
[0092] Thus, if Level 2 is implemented, the ECU can trigger a
greater CO supplementation in an effort to regenerate what is
considered to be a more degraded (SO.sub.2 poisoned) catalyst 40
(as compared to Level 1). The enhanced CO supplementation can
include, for example, (and as compared to Level 1), i) a greater
timeframe input of CNG into the cylinder(s), ii) a greater CNG
input flow rate to the predetermined cylinder(s), iii) a higher
number of combustion chambers involved, or iv) an added time period
extension of a preexisting normal feed amount to all cylinders
during a time period when normal engine control dictates a
reduction is in supply amount for normal running as compared to
that featured in the Level 1 CO supplementation process described
above (or any combination of the i) to iv) noted approaches for
Level 2). The resultant outcome under Level 2 operation is an
overall greater supply and/or duration of supplemental CO to the
catalyst 40 as compared to a Level 1 implementation. Under this
approach the amount of CNG (or other supplementation CO fuel) used
for supplementation of CO can be more finely controlled as to
better fit the status and avoid overuse of CNG (or other
supplementation CO fuel utilized) while still retaining an overall
lean state. In other words, the two stage application can provide a
more nuanced approach that helps avoid too much CO content in the
exhaust to help avoid an overall lean to rich switch, and yet still
provide for a maximized or more efficiently high level of sulfur
removal when needed.
[0093] Thus, under the method of the present invention, upon adding
additional CNG (or an alternate extra CO external source, such as
one derived from an alternate engine fuel source as in a flex-fuel
option or an independent one assigned to provide CO
supplementation) to the one or more combustion chambers, there is
generated added CO (and if an HC fuel source is utilized there is
also added H.sub.2) in the exhaust stream reaching catalyst device
40. The lower light off temperature of the CO provides for an
exothermic temperature increase over the oxidation catalyst which
provides for a controlled localized regeneration of the catalyst as
the sulfur degrading the catalyst is removed.
EXAMPLES
[0094] To illustrate the improved performance of the present
invention through use of the present invention's CO supplementation
apparatus and method used for the purpose of desulfation of
catalysts subject to exhaust gas contamination, some examples and
comparisons are described below.
[0095] Testing Equipment Set UP
[0096] FIG. 3 shows a schematic illustration of test equipment
suited for use in analyzing samples representing the present
invention and comparative examples. That is, FIG. 3 shows a
schematic illustration of CNG engine simulation test equipment set
up for comparative and present invention analysis. As shown in FIG.
3 there is provided a variety of different gas sources that are
flow controlled via mass flow controllers or MFC's. The MFC's
provide gas blending to obtain the desired flow volume percentages
travelling through the test system and can be used to block off any
flow, which facilitates making the gas blend comparisons described
below.
[0097] As further shown in FIG. 3, there is provided in the test
equipment the option of H.sub.2O vapor delivery via the illustrated
vapor generator or vaporizer equipment VE. As described above,
water vapor can also degrade the performance of catalytic operation
and thus is factored into the testing to further present some
anticipated environments of use of the present invention.
[0098] FIG. 3 also illustrates an electric oven or heated chamber
that is used to heat samples and also exhaust leading to those
samples as to obtain desired environmental states for the catalyst
samples being tested.
[0099] The analytic components of the testing equipment, used for
generating the below described examples include a heated FID-Total
Hydrocarbon analyzer. That is, the present testing equipment
features an FID analyzer that measures the total HC via the FID's
carbon count. For monitoring of CO and CO.sub.2 concentration
levels, the analytic testing equipment further included
Non-Dispersive Infra-Red (NDIR) detectors. That is, each
constituent gas in a sample will absorb some infra-red at a
particular frequency. By shining an infra-red beam through a sample
cell (containing CO or CO.sub.2), and measuring the amount of
infra-red absorbed by the sample at the necessary wavelength, an
NDIR detector is able to measure the volumetric concentration of CO
or CO.sub.2 in the sample.
[0100] The monitoring of O.sub.2 concentration levels, with the
analytical testing components of the FIG. 3 test equipment, was by
way of the paramagnetic method. Paramagnetic technology features
two nitrogen-filled glass spheres that are mounted within a
magnetic field, on a rotating suspension, with a centrally-placed
mirror. Light shines on the mirror and is reflected onto a pair of
photocells. As oxygen is attracted into the magnetic field, it
displaces the glass spheres, causing suspension rotation which is
detected by the photocells. This generates a signal to a feedback
system, which passes a current through a wire mounted on the
suspension, creating a motor effect. This current is directly
proportional to the concentration of oxygen within the gas
mixture.
[0101] The analytic equipment of the present invention also
features a chemiluminescence--reference analyzer which measures
nitrogen dioxide (NO.sub.2) and oxides of nitrogen (NO.sub.x) based
on the reaction of nitric oxide (NO) with Ozone (O.sub.3): NO
molecules react with O.sub.3 to form excited NO.sub.2 molecules. If
the volumes of sample gas and excess ozone are carefully
controlled, the light level in the reaction chamber is proportional
to the concentration of NO.sub.2 in the gas sample.
[0102] FIG. 3 also shows bypass plumbing which was utilized to
analyze gas blends for conversion calculations. In addition to
providing greater flexibility as to the blend of gasses to reach
the catalyst, there are a variety of MFC controlled gas sources,
some or all of which can be utilized in the testing (e.g., methane
CH.sub.4 only or a blend of methane with other HC sources as in the
below described, methane CH.sub.4 (95%)/Ethane C.sub.2H.sub.6
(4%)/propane C.sub.3H.sub.8 (1%), HC gas mixture which is
representative of some NG running engine exhaust mixes).
[0103] Gas Blends Tested
[0104] The base gas blend components, flow rate and concentration
utilized as the base foundation in the Example testing of the
present invention are referenced in Table I below together with the
substrate dimensions and mixed gas flow rate (gas hourly space
velocity or GHSV) across the sample catalyst. Variations in the
base amounts shown in Table 1 under the present invention are
referenced in the discussion below.
TABLE-US-00001 TABLE 1 Concentrations NO 1000 ppm CO 4300 ppm
CH.sub.4 1000 ppm O.sub.2 4% CO.sub.2 13% H.sub.2O 10% H.sub.2 1433
ppm SO.sub.2 0 ppm GHSV 30.000 h.sup.-1 Drillcore 1'' .times.
3''
[0105] Table 1, illustrates the base reference gas flow with
modifications being controlled. For example, the Table 1 parameters
are applicable except where there is referenced below a parameter
variation (e.g., conversion of methane only to a mix of methane,
ethane and propane in place of methane only).
[0106] Catalyst Utilized
[0107] For each example test and comparison test a common catalyst
core size, dimension and cell density was utilized. That is, the
catalyst used for running the present invention examples and
comparison examples consisted of 1'' round by 3'' long
(2.54.times.7.62 cm) cordierite core, having a cell density of 400
cells per square inch (62 cells/cm.sup.2) and a cell wall thickness
of 6.5 mil (0.17 mm).
[0108] The cores were washcoated with PGM material supported on
gamma alumina based supports ("ABS"). Detailed slurry making and
washcoating procedures can be found in U.S. Pat. No. 7,041,622 B2
which is incorporated herein by reference for background discussion
purposes only.
[0109] Thus, under the testing procedure carried out for an example
of the present invention, the oxidation catalysts evaluated were
all Pd-based catalyst, with the active materials (i.e., Pd alone in
this testing series) dispersed on high surface area alumina ("ABS")
which was coated onto a cordierite substrate at a WC loading of 152
g/L (2.5 g/in.sup.3). Cores were subsequently removed and used for
testing as described above. Catalyst cores were 1'' (2.54 cm)
diameter by 3'' (7.62 cm) long.
[0110] Examples Testing Set-Up
[0111] The above described catalyst cores were placed in the test
set up schematically presented in FIG. 3. Before testing all
samples were initially aged at 800.degree. C. for 16 Hrs in a flow
of 90% air and 10% steam at a flow rate of 2.0.+-.0.1 L/minute. The
air flow rate was controlled by two mass flow controllers at 1.8
L/min and 0.2 L/min each for a total flow rate of 2.0.+-.0.1 L/min.
The mass flow controllers were calibrated with a Model 650 Digital
Flowmeter from Fisher Scientific and the flow rate was checked
before and after each aging. The water vapor content was controlled
by flowing air through a saturator held at 46.1.+-.1.5.degree.
C.
[0112] An oven temperature ramp of 5.degree. C./min was used. The
ramp went up to 845.degree. C. and was held for 18 hours to
compensate for oven and retort temperature difference, and for time
delay in reaching the desired temperature in the retort aging
chamber, respectively. The retort temperature was monitored by four
thermocouples, two closer to the chamber door and the other two
further into the chamber. A temperature difference of 20-40.degree.
C. between inside and outside thermal couples and 5-15.degree. C.
between each pair was typically observed.
[0113] To minimize variation between agings, a "dry" (without
samples) run was carried out to verify set-point parameters and
oven conditions before each aging.
Comparative Test Run--Example C1
[0114] FIG. 4 shows repeat light-off tests for a reference Pd CNG
catalyst evaluated in the absence of SO.sub.2. After the 2.sup.nd
light-off there is seen essentially no change in light-off
performance showing that the catalyst is completely stable in the
absence of SO.sub.2. The drop-off seen for the first light-off is
considered as a conventional adjustment that is associated with,
for example, burn off of contaminates and an added heat treatment
benefit, etc.
[0115] The comparative test run of C1 shown in FIG. 4 provides a
frame of reference relative to a CO=4300 ppm "nominal" content in
the exhaust flow, at a time when the catalyst has not been degraded
by sulfur poisoning.
[0116] FIG. 5 shows comparative test run C2 showing the effect of
adding 5 ppm SO.sub.2, starting with the 3.sup.rd light off after
the 1.sup.st and 2.sup.nd light offs in the absence of SO.sub.2. In
this test run, operating under a CO=4300 ppm nominal CO gas flow,
there is immediately seen a progressive and very large deactivation
of the catalyst until the performance stabilizes at a highly
deactivated state after the 5.sup.th light-off. Thus, upon being
degraded by sulfur poisoning the catalyst maintains the highly
deactivated state.
[0117] FIG. 6 shows a CNG test procedure used for investigating
SO.sub.2 influence as well as a review to determine what impact, if
any, a prolonged thermal treatment application has following sulfur
poisoning. As seen by FIG. 6, there was monitored temperature
fluctuations over time relative to two different types of gas
blends (one with standard lean 4% O.sub.2 (SL), and the other also
with standard lean 4% O.sub.2, but with SO.sub.2, at 5 ppm, added
into the standard lean 4% O.sub.2 flow (SLS)). The temperature
plotting shows the ramp up and down shorter duration spikes for
each run but for test run 7 wherein there was an extended
temperature application for 6 hours. The FIG. 6 temperature and gas
blend modification illustration was carried out relative to the
following sequence two light-offs (LO's) with an SL gas blend with
600.degree. C. short intervals shown in the graph. The two lean
LO's were followed under the testing procedure with three LO's
under the SLS gas blend, again showing shorter 600.degree. C.
temperature spikes. The gas blend was then carried back to SL and a
series of LO's were carried out inclusive of a prolonged heat
treatment (4 hrs. at 600.degree. C.). The extended duration heat
treatment was then removed for the final two LO's again showing
short duration 600.degree. C. peak temperature cycles.
[0118] FIG. 7 provides a conversion performance for a 9 run testing
sequence (comparative test run C3) carried out in accordance with
the 9 run test sequence protocol shown in FIG. 6 (with run 7 thus
carried out under the extended heat treatment mode of 600.degree.
C. for 4 hours). That is, FIG. 7 provides a comparison basis for
analyzing SO.sub.2 introduction followed by an extended duration
heat treatment, without the benefit of the present invention's CO
supplementation; and features a series of nine runs of the test
equipment wherein a common 4300 ppm "nominal" CO content was
present. The nine runs were all carried out under a lean burn
status relative to the above described Pd test catalyst.
[0119] The nine lean runs shown in FIG. 7 included two light-offs
without SO.sub.2, three SO.sub.2 poisoning light-offs (5 ppm
SO.sub.2) thereafter, followed by four light-offs without SO.sub.2.
The comparative example thus did not feature supplemental CO but
only a consistent "nominal" CO amount that is considered
illustrative of CO content in a non-CO-supplemented lean burn CNG
engine simulated running condition. As seen, even with the addition
of a thermal treatment at 600.degree. C. for 4 hours in an effort
to desulfate/reactivate the poisoned catalyst, the catalyst is not
able to recover its initial sulfur free light-off activity of the
catalyst. For example, as shown in FIG. 7, at 400.degree. C.
operating temperature the poisoned and subsequently thermally
treated catalyst has dropped from its "lean 2" pre-poisoned level
of activation of about 45% conversion of methane to a maximum post
thermal treatment state at lean 9 of about 23%, and for 500.degree.
C. there is a drop from a lean 2 state of about 92% down to a lean
9 state of about 72%; still further at 600.degree. C. there is a
drop from the lean 2 state of about 97% to the lean 9 state of
about 92%.
[0120] It can therefore be seen from FIG. 7 that even with a high
temperature and extended in time thermal treatment of this
deactivated catalyst (at 600.degree. C. for 4 hours) in the absence
of SO.sub.2, there is still not seen a recovery back to performance
levels initially seen in the absence of SO.sub.2. In other words, a
reactivation effort based on thermal treatment alone is considered
to be insufficient to return the catalyst to a suitably reactivated
state, particularly at typical operation temperatures.
Present Invention Examples
[0121] To illustrate the beneficial features of the present
invention, samples were tested using the enhancing CO
supplementation technique of the present invention and results are
shown in FIGS. 8-10. For example, in FIG. 8 there is seen nine
"lean run light off series" also with an overall lean 2 value of
about 9.2 at the catalyst sample prior to CO supplementation (and
after CO supplementation discontinuation).
[0122] As seen in FIG. 8, after two light-offs without SO.sub.2
(lean 1, lean 2), three SO.sub.2 at 5 ppm poisoning light-offs
followed (lean 3, lean 4, lean 5). Then there was carried out two
light-offs in the presence of 3.2% CO (lean 6, lean 7). Thereafter,
the CO supplementation was ceased and a nominal CO supply was
carried out (4300 ppm (lean 8, lean 9)) and the conversion
percentage determined. As seen by FIG. 8, the CO supplementation at
a level of 3.2% CO in runs 6 and 7 that took place following the
initial sulfur poisoning at 5 ppm SO.sub.2 in runs 3, 4 and 5,
resulted in a drastic improvement in light off temperatures and the
final recovery approaches that of the first light off lean 1. Again
the overall .lamda. value was retained in a lean state relative to
the tested catalyst sample environment. For example, during the CO
supplementation at 3.2% the overall lean state was maintained at
about 2.2.lamda., which is down from the initial about 9.2.lamda.
running state prior to supplementation, but well within a general
lean run state.
[0123] FIG. 8 also shows a sequenced, stepped increase in activity
following each CO supplementation run (lean 6, lean 7), with lean 6
showing a light off occurring at a much lower temperature, and a
greater than 50% conversion performance at 500.degree. C. (e.g.,
about 65%). Upon completion of the CO supplementation run of lean
7, there can be seen a significant recovery at the lower
temperatures as compared to the sulfur runs of 3 to 5, together
with a conversion % of about 85% at 500.degree. C. Post CO
supplementation runs, lean 8 and lean 9, are also shown not to
degrade that much with about a retained 80% at 500.degree. C. Still
further, at 400.degree. C., and following completion the CO
supplementation shown in lean run, the conversion level is about
the same as that of lean 2 (e.g., within 5%), with the final lean 9
being even closer (e.g., less than 5% differential). Accordingly it
can be seen from the FIG. 8 plotting that the presence of 3.2% CO
decreases the light off temperatures drastically and the final
recovery is about the same as the first light off.
[0124] As further seen from a comparison of the results of FIG. 8
with the results of FIG. 7, the use of high CO concentrations in
the exhaust is more efficient for catalyst recovery/regeneration
that just a simple thermal treatment such as that attempted in the
comparative testing above. The added CO has a special and unique
reactivation feature not seen by just using an overall heat or
thermal application treatment alone.
[0125] FIG. 9 further illustrates the significant benefits both in
a decrease in initial light off temperatures as well as overall
conversion performance by plotting nine "lean runs". The light off
runs in FIG. 9 were the same as the previous FIG. 8 runs, except
100% methane was replaced by a 95-4-1 mixture (95% methane, 4%
ethane, and 1% propane). As before, the presence of 3.2% CO
decreases the light off temperatures drastically, even more than a
methane only supply; and the final recovery is close to the first
light off. For example, as shown in FIG. 9, for the post CO
supplement lean 8 run at about 425.degree. C. there is about 55%
conversion which is well above the sulfur degraded run of about 17%
for lean 5. Also, at 400.degree. C. it can be seen that the lean 9
is within about 7% of lean 1 and within 15% of the maximum lean 2,
while the lean run 5, at this temperature of 400.degree. C., drops
to 13% conversion. There is achieved conversion of about 43% at
lower temperature of 300.degree. C. in the initial CO
supplementation (lean 6) and over 40% conversion at 200.degree. C.
for (lean 7). Still further, lean run 7 achieved about 85%
conversion at 300.degree. C. and about 97% at 500.degree. C.
[0126] Again, even after discontinuing the CO supplementation runs
of 6 and 7 at 3.2%, the runs of lean 8 and 9, without CO
Supplementation, still retained good performance as compared to the
lean runs 4 and 5. For example, lean runs 8 and 9 retained 60%
conversion performance at about 425.degree. C. and about 90%
conversion performance at 500.degree. C.
[0127] FIG. 10 shows an additional nine light off runs under the
above described lean 2 condition and with the same test conditions
as with the previous FIG. 9 runs, except the CO concentration was
decreased to 1.6% for light-offs/lean runs 6 and 7. The presence of
1.6% CO provided a desulfation effect, but to a lesser degree as
compared to 3.2% CO. Also, the .lamda. value for the 1.6% CO runs
about 3.9 which is well within the overall lean state desired under
the present invention. The light off temperatures of lean 6 and
lean 7 runs with 1.6% CO show improvements as compared to the
thermally degraded lean 4 and 5, but a shift to the right in the
temperature line as compared to the 3.2% runs. Moreover, at
500.degree. C. the lean run 7 with 1.6% CO still has about 85%
conversion, and the subsequent lean runs 8 and 9 show a retention
of conversion performance (in excess of about 80% at 500.degree.
C.) after the CO supplementation is discontinued.
[0128] Further, the testing shown in the present invention CO
supplementation process, illustrated in FIGS. 8 to 10 shows that
despite water (as represented by the supplied water vapor) being a
strong inhibitor on the catalytic activity of methane oxidation,
the additional CO in the exhaust is still able to improve the
catalytic performance despite the presence of 10% water (See Table
1 above).
[0129] FIG. 11 shows an example of a catalytic system 250 suited
for an exhaust passageway of a lean burn engine such as a lean burn
CNG fuel supply engine 100 having cylinders 200 (four shown with CO
supplementation of some or all of the four featured) as well as
manifold 386 leading to upstream oxidation catalyst 400 of the type
described in FIG. 1 together with one or more downstream exhaust
catalyst devices for further exhaust emission clean up. For
example, a representative of downstream catalyst 500 includes an
NO.sub.x removal catalyst such as a nitrogen storage catalyst NSC
or an SCR catalyst 600 or two SCR catalysts, two nitrogen storage
catalysts or a reverse order SCR (500) and NSC (600) or
alternatively an upstream or downstream particle filter (a
non-catalyzed or catalyzed particle filter such as those used to
address particle filters in gas (smaller particles) or diesel
(larger particles) running engines) and a corresponding NSC or SCR.
Also, the catalyst 400 can be moved further downstream with or
without catalysts 500 and/or 600, upstream or downstream thereof
(with many situations favoring a close coupled higher temperature
setting for catalyst 400). Suitable upstream and/or downstream
monitoring sensors such as those described above can be provided as
represented by sensors 110, 120, 130, 140, and 160 (with reference
number 170 representing an ammonia or ammonia precursor supplier,
as in urea supplier for an SCR catalyst that is particularly useful
in situations where 600 is an SCR catalyst utilizing, for example,
urea in NO.sub.x reduction. Various other catalyst and filter
combinations are featured under the present invention relative to
systems that run with the above described catalyst treatment
apparatus of the present invention having supplementation means S
for removing poison build up in a catalyst associated with the
supplementation means S.
[0130] While reference is made in the examples above to one or more
cylinders of a combustion engine, the catalytic treatment apparatus
CTA of the present invention is also suited for use in other
combustion devices as in a combustion chamber of a power plant used
to generate heat (e.g., for steam turbine running) and which is
fueled by a methane source fuel such as natural gas (having a
potential catalyst poisoning sulfur content). The scope of the
present invention is thus inclusive of the noted catalytic
treatment apparatus CTA and also systems making use of the
catalytic treatment apparatus, with the above described CNG engine
being one example of such a system, and the NG stationary power
plant providing an additional example of a system making use of the
catalytic treatment apparatus of the present invention.
[0131] For example, FIG. 12 shows power plant assembly 300
representing a further example of the present invention. That is,
as shown in FIG. 12 there is power plant assembly 300 comprising a
power boiler 302 having a combustion chamber 304 to which there is
provided a methane source fuel supply apparatus 306 (such as a
natural gas feed with flow controlled supply). An air feed is also
supplied via air intake 308, with the combination being subject to
combustion in the chamber 304, and the exhaust gas generated
exiting via exhaust passageway 311. The heat of combustion is used
to heat water travelling in water/high pressure stream line 310
which is circulated via pump 312. The high pressure steam generated
on the exit side from the combustion chamber is fed to steam
turbine 314 which powers electricity generator 316. The steam flow
exiting the turbine is fed to condenser 318 wherein a cool water
source 320 (e.g., a lake or ocean) is fed in heat exchange fashion
in the condenser to turn the circulation steam to water to be
re-fed to the combustion chamber.
[0132] FIG. 12 further reveals a version of the catalytic treatment
apparatus CTA with its supplementation apparatus S featuring a CO
source supplier 322 that is positioned for exhaust stream supply
upstream of the Pd based oxidation catalyst device 324 having
catalytic qualities like that described above for catalyst device
40 (albeit catalyst device 40 typically being on a smaller scale)
in the FIG. 1 embodiment. While other (standard and thus not shown)
sensing means are typically provided for a system power plant such
as that shown in FIG. 12, the CTA for the power plant system 300
under the present invention features sensor 326, which is similar
to the FIG. 1 referenced sensor 42 (e.g., a direct methane level
sensor which can determine the extent of methane bypass past
catalyst 324). There is also featured under the illustrated CTA a
control unit 328 in communication with sensor 326 as well as with a
flow amount controller 330 associated with the methane source fuel
supply apparatus 306 and the CO source supplier 322. As in the
earlier embodiment, the supplemental apparatus S of the present
embodiment makes use of components utilized for normal run
operation while also including modifications (e.g., the addition of
a stand alone CO source rather than relying on a normal run fuel
source for CO supplementation, the addition of receiver and
transmission units to valving, and/or
modifications/supplementations made to a preexisting control unit
or the addition of a stand alone control unit device dedicated to
the CTA only). The CO supplementation apparatus or means S is
designed to provide for a CO supplement effect in the exhaust
reaching catalyst 324.
[0133] As with the earlier described arrangement, the control unit
328 shown in the CTA is designed to provide a supplemental CO
content above that which is a nominal amount for proper combustion
conditions at the given time or period. This added CO content
functions in the manner described above to reactivate a sulfur
poisoned catalyst (e.g., a sulfur build up on the catalyst due to
the typical sulfur content in natural gas supply of 1 to 5 ppm) by
localized exotherm regions provided by the added CO content while
still running under an overall lean running state. The above
described relative supply amounts leading to the aforementioned
ranges of CO supplementation are applicable (as in 3.0 to 4.0% CO
content leading to the Pd based catalyst 324). The control unit
functions to supplement the CO content based on the readings of
sensor 326 which is designed to sense for when catalyst 324 has
been degraded by sulfur build-up, and to provide via the
supplementation apparatus S which in this embodiment includes
valving that is in communication with a fuel source 322 and also in
communication with the control unit to provide a greater than
normal CO supply in the exhaust stream. Thus, with the supplemental
apparatus S, the CO content in the exhaust flow is supplemented for
a sufficient time to achieve a desired level of reactivation in the
poisoned catalyst when sensor 326 indicates that the level of
methane slip has increased to a predetermined level as to trigger
desulfation).
[0134] Although this invention has been disclosed in the context of
certain preferred embodiments and examples, it will be understood
by those skilled in the art that the present invention extends
beyond the specifically disclosed embodiments to other alternative
embodiments and/or uses of the invention and obvious modifications
and equivalents thereof. In addition, while a number of variations
of the invention have been shown and described in detail, other
modifications, which are within the scope of this invention, will
be readily apparent to those of skill in the art based upon this
disclosure. It is also contemplated that various combinations or
sub-combinations of the specific features and aspects of the
embodiments may be made and still fall within the scope of the
invention. Accordingly, it should be understood that various
features and aspects of the disclosed embodiments can be combined
with or substituted for one another in order to form varying modes
of the disclosed invention. Also, the features presented in one
embodiment described above can be carried over to other disclosed
embodiments under the present invention, where appropriate, as in
the use of the feature of a stand-alone CO supplier in the FIG. 12
embodiment being utilized in the first embodiment and vice versa
(e.g., an NG increase in the FIG. 12 embodiment over what would be
utilized for normal run mode to generate for a period a larger CO
content in the exhaust flow in generally similar fashion as in the
FIG. 1 embodiment). Thus, it is intended that the scope of the
present invention herein disclosed should not be limited by the
particular disclosed embodiments described above, but should be
determined only by a fair reading of the claims.
* * * * *