U.S. patent application number 12/351148 was filed with the patent office on 2010-07-15 for pre-mix catalytic partial oxidation fuel reformer for staged and reheat gas turbine systems.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Joel Meier Haynes, Ke Liu, Rick Bruce Watson.
Application Number | 20100175379 12/351148 |
Document ID | / |
Family ID | 41528686 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100175379 |
Kind Code |
A1 |
Liu; Ke ; et al. |
July 15, 2010 |
PRE-MIX CATALYTIC PARTIAL OXIDATION FUEL REFORMER FOR STAGED AND
REHEAT GAS TURBINE SYSTEMS
Abstract
A gas turbine system includes a fuel reformer comprising: a fuel
inlet; an oxygen inlet; a pre-mixing zone configured to mix the
fuel and the oxygen in a pre-mixing device to form a gaseous
pre-mix; wherein the pre-mixing device comprises a flow
conditioning device configured to pre-condition the fuel stream,
wherein the flow conditioning device is disposed upstream of the
oxygen inlet; a diffuser disposed downstream of the flow
conditioning device; a catalytic partial oxidation zone disposed
downstream of the diffuser, wherein the catalytic partial oxidation
zone comprises a catalyst composition configured to react the fuel
and the oxygen to generate a syngas. The generated syngas is then
mixed with rest of the fuel to form a hydrogen-enriched fuel
mixture, which is then sent to the combustion chamber of a gas
turbine to reduce the NOx emission and extend the lean blow out
limit.
Inventors: |
Liu; Ke; (Rancho Santa
Margarita, CA) ; Haynes; Joel Meier; (Niskayuna,
NY) ; Watson; Rick Bruce; (Missouri City,
TX) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
41528686 |
Appl. No.: |
12/351148 |
Filed: |
January 9, 2009 |
Current U.S.
Class: |
60/723 ;
60/738 |
Current CPC
Class: |
F23R 3/286 20130101;
F05D 2220/75 20130101; F02C 3/30 20130101; F02C 7/22 20130101; F23R
3/40 20130101; F23C 2900/9901 20130101; Y02T 50/678 20130101; F23R
2900/00002 20130101; F02C 3/20 20130101; F23C 2900/03002 20130101;
F23C 13/06 20130101 |
Class at
Publication: |
60/723 ;
60/738 |
International
Class: |
F23R 3/40 20060101
F23R003/40 |
Goverment Interests
GOVERNMENT RIGHTS
[0001] This invention was made with Government support under
Government Contract No. DE-FG36-05G015023, awarded by the United
States Department of Energy. The Government has certain rights in
the invention.
Claims
1. A gas turbine system, comprising: a fuel inlet configured to
receive a fuel stream; an oxygen inlet configured to introduce a
first oxygen-containing gas; a fuel reformer system comprising: a
pre-mixing zone configured to mix a first portion of the fuel
stream and the oxygen-containing gas in a pre-mixing device to form
a gaseous pre-mix; a diffuser disposed downstream of and in fluid
communication with the pre-mixing zone, wherein the diffuser is
configured to provide a thermal shield between the pre-mixing zone
and a catalytic partial oxidation zone; a catalytic partial
oxidation zone disposed downstream of and in fluid communication
with the pre-mixing zone and configured to receive the gaseous
pre-mix, wherein the catalytic partial oxidation zone comprises a
catalyst composition configured to react the fuel and the oxygen to
generate a syngas from the gaseous pre-mix; and a dilution zone
disposed downstream of and in fluid communication with the
catalytic partial oxidation zone and configured to mix the syngas
into a second portion of the fuel stream to form a fuel mixture; a
gas turbine pre-mixer configured to mix a second oxygen-containing
gas from a gas turbine compressor with the fuel mixture; and a gas
turbine combustor configured to combust the fuel mixture.
2. The system of claim 1, wherein the pre-mixing zone comprises a
pre-mixing device comprising a plurality of swirler vanes
configured to provide a swirl movement to the fuel stream first
portion.
3. The system of claim 1, further comprising a steam inlet
configured to introduce steam to the pre-mixing device.
4. The system of claim 1, further comprising a heat exchanger
disposed downstream of and in fluid communication with the
catalytic partial oxidation zone, wherein the heat exchanger is
configured to simultaneously cool the syngas and pre-heat the first
portion of the fuel stream.
5. The system of claim 1, further comprising a water gas shift
reactor disposed downstream of and in fluid communication with the
catalytic partial oxidation zone, wherein the water gas shift
reactor is configured to increase a hydrogen content of the
syngas.
6. The system of claim 1, wherein the first oxygen-containing gas
is a portion of the second oxygen-containing gas.
7. The system of claim 6, further comprising a control valve to
control a volume flow rate of the first oxygen-containing gas
according to an oxygen to carbon ratio of the catalytic partial
oxidation zone.
8. The system of claim 1, further comprising a control valve to
control a volume flow rate of the first portion of the fuel
stream.
9. A method of operating a gas turbine system, comprising:
introducing a first fuel portion of a fuel stream into a pre-mixing
zone of a fuel reformer system; introducing a first
oxygen-containing gas to the first fuel portion in a flow
conditioning device to facilitate pre-mixing of the first fuel
portion and the first oxygen-containing gas to form a gaseous
pre-mix reacting the gaseous pre-mix to form a syngas through
catalytic partial oxidation; introducing the syngas into a second
fuel portion of the fuel stream to form a fuel mixture; mixing the
fuel mixture with a second oxygen-containing gas in a gas turbine
pre-mixer; and combusting the fuel mixture in a gas turbine
combustor.
10. The method of claim 9, further comprising introducing steam
into the pre-mixing zone.
11. The method of claim 10, wherein the steam is combined with the
first fuel portion.
12. The method of claim 11, wherein the combination of the steam
and the first fuel portion is combined with the first
oxygen-containing gas.
13. The method of claim 9, further comprising preheating the first
fuel portion to a temperature of about 300.degree. C. to about
500.degree. C.
14. The method of claim 9, further comprising cooling the syngas to
a temperature of about 250.degree. C. to about 450.degree. C.
15. The method of claim 9, further comprising increasing the
hydrogen content of the syngas through a water gas shift
reaction.
16. The method of claim 15, wherein the cooling occurs after the
catalytic partial oxidation and before the water gas shift
reaction.
17. A fuel reformer system, comprising: a fuel inlet configured to
receive a fuel stream; an oxygen inlet configured to introduce a
first oxygen-containing gas; a pre-mixing zone configured to mix a
first portion of the fuel stream and the oxygen-containing gas in a
pre-mixing device to form a gaseous pre-mix; a diffuser disposed
downstream of and in fluid communication with the pre-mixing zone,
wherein the diffuser is configured to provide a thermal shield
between the pre-mixing zone and a catalytic partial oxidation zone;
a catalytic partial oxidation zone disposed downstream of and in
fluid communication with the pre-mixing zone and configured to
receive the gaseous pre-mix, wherein the catalytic partial
oxidation zone comprises a catalyst composition configured to react
the fuel and the oxygen to generate a syngas from the gaseous
pre-mix; and a dilution zone disposed downstream of and in fluid
communication with the catalytic partial oxidation zone and
configured to mix the syngas into a second portion of the fuel
stream to form a fuel mixture.
Description
BACKGROUND OF THE INVENTION
[0002] The invention relates generally to a fuel reformer system
based on pre-mixed catalytic partial oxidation, and more
particularly to a gas turbine system employing the fuel reformer
system.
[0003] Fuel injection and mixing are critical to achieving
efficient and clean combustion in gas turbine engines. In the case
of gaseous fuels, it is desirable to obtain an optimal level of
mixing between air, fuel, and combustion products in a combustion
zone.
[0004] Exhaust gases from gas turbine engines contain substances
such as nitrogen oxides (NOx) that are harmful regulated emissions.
Hence, there has been increased demand for gas turbines that
operate in partially pre-mixed (PP) or lean, pre-mixed (LP) modes
of combustion in an effort to meet increasingly stringent emissions
goals. PP and LP combustion reduces harmful emissions of NOx
without loss of combustion efficiency.
[0005] However, combustion instabilities, also known as combustion
dynamics, are commonly encountered in development of low emissions
gas turbine engines. Combustion dynamics in the form of
fluctuations in pressure, heat-release rate, and other
perturbations in flow may lead to problems such as lean blow out,
structural vibration, excessive heat transfer to a chamber, and
consequently lead to failure of the system.
[0006] Reforming part of the fuel to hydrogen rich syngas, and then
mixing the syngas into the fuel before the turbine combustion
chamber is a solution to enhance the gas turbine turn capability by
improving the combustion dynamics. One method employs a rich
catalytic system to reform the fuel just prior to gas turbine
premixing and is further integrated into the gas turbine fuel
skid.
BRIEF DESCRIPTION OF THE INVENTION
[0007] Briefly, according to one embodiment, a gas turbine system
is provided. The gas turbine system includes a fuel reformer system
comprising: a fuel inlet configured to receive a fuel stream; an
oxygen inlet configured to introduce an oxygen-containing gas; a
pre-mixing zone configured to mix the fuel stream and the
oxygen-containing gas in a pre-mixing device to form a gaseous
pre-mix; wherein the pre-mixing device comprises a flow
conditioning device configured to pre-condition the fuel stream,
wherein the flow conditioning device is disposed upstream of the
oxygen inlet; a diffuser disposed downstream of and in fluid
communication with the flow conditioning device, wherein the
diffuser is configured to provide a thermal shield to the gaseous
pre-mix in the pre-mixing zone; a catalytic partial oxidation zone
disposed downstream of and in fluid communication with the diffuser
and configured to receive the gaseous pre-mix, wherein the
catalytic partial oxidation zone comprises a catalyst composition
configured to react the fuel and the oxygen to generate a syngas;
and a dilution zone disposed downstream of and in fluid
communication with the reaction zone and configured to mix the fuel
back into the syngas to form a hydrogen-enriched fuel mixture a gas
turbine pre-mixer configured to mix a oxygen-containing gas from a
gas turbine compressor with the hydrogen-enriched fuel mixture; and
a gas turbine combustor configured to combust the hydrogen-enriched
fuel mixture.
[0008] In another embodiment, a method of operating a gas turbine
system includes introducing a portion of a fuel stream into a
pre-mixing zone of a fuel reformer system; introducing an
oxygen-containing gas to the fuel stream in a flow conditioning
device to facilitate pre-mixing of the fuel stream and oxygen to
form a gaseous pre-mix; reacting the gaseous pre-mix in the
presence of a catalyst composition in a catalytic partial oxidation
zone to form a syngas through catalytic partial oxidation;
introducing the syngas stream into the fuel stream to form a
hydrogen-enriched fuel mixture; mixing the hydrogen-enriched fuel
mixture with an oxygen-containing gas in a gas turbine pre-mixer;
combusting the hydrogen-enriched fuel mixture in a gas turbine
combustor; and producing electrical power with a gas turbine in
operative communication with an electrical generator.
[0009] In yet another embodiment, a fuel reformer system comprises:
a fuel inlet configured to receive a fuel stream; an oxygen inlet
configured to introduce a first oxygen-containing gas; a pre-mixing
zone configured to mix a first portion of the fuel stream and the
oxygen-containing gas in a pre-mixing device to form a gaseous
pre-mix; a diffuser disposed downstream of and in fluid
communication with the pre-mixing zone, wherein the diffuser is
configured to provide a thermal shield between the pre-mixing zone
and a catalytic partial oxidation zone; a catalytic partial
oxidation zone disposed downstream of and in fluid communication
with the pre-mixing zone and configured to receive the gaseous
pre-mix, wherein the catalytic partial oxidation zone comprises a
catalyst composition configured to react the fuel and the oxygen to
generate a syngas from the gaseous pre-mix; and a dilution zone
disposed downstream of and in fluid communication with the
catalytic partial oxidation zone and configured to mix the syngas
into a second portion of the fuel stream to form a fuel
mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring now to the Figures, which are exemplary
embodiments, and wherein the like elements are numbered alike:
[0011] FIG. 1 is a diagrammatical illustration of an exemplary
embodiment of a gas turbine system having a pre-mix catalytic
partial oxidation fuel reformer system;
[0012] FIG. 2 is a diagrammatical illustration of an exemplary
embodiment of the pre-mix catalytic partial oxidation fuel reformer
system of FIG. 1;
[0013] FIG. 3 is a diagrammatical illustration of another exemplary
embodiment of the fuel reformer system of FIG. 1;
[0014] FIG. 4 is a schematic illustration of an exemplary
embodiment of a pre-mixing device from the fuel reformer system of
FIG. 3;
[0015] FIG. 5 is a cross-sectional view of another exemplary
configuration of the pre-mixing device from the fuel reformer
system of FIG. 3 comprising a plurality of counter swirling
vanes;
[0016] FIG. 6 is another cross-sectional view of the exemplary
embodiment of the pre-mixing device of FIG. 5;
[0017] FIG. 7 is a cross-sectional view of the fuel reformer system
of FIG. 3, specifically showing the catalytic partial oxidation
zone and the reaction zone; and
[0018] FIG. 8 is a cross-sectional view of an exemplary embodiment
of a gas turbine combustor of the gas turbine system of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0019] As described in detail below, embodiments of the present
disclosure provide a gas turbine system incorporating a fuel
reformer system and a method of providing the same. The gas turbine
system utilizes syngas formed by catalytic partial oxidation. The
syngas is generated by mixing and reacting a portion of the natural
gas or fuel with air to increase a concentration of hydrogen. The
syngas can then be mixed with the natural gas or fuel and sent to
the gas turbine combustor. Introduction of hydrogen into the
natural gas or fuel allows lowering of a lean blow out point and
enhances the combustion dynamics. Gas turbine turndown can be
reduced below 40% by the addition of hydrogen to the fuel as
compared to a system that does not introduce additional hydrogen to
the fuel.
[0020] Lowering of the lean blow out point permits the flow rate to
the gas turbine to be further turned down when demand for
electricity is low, thereby saving fuel and reducing emissions. The
term "lean blow out point" used herein refers to a point of loss of
combustion in a combustor. Variations in fuel composition and flow
disturbances result in a loss of combustion in sufficiently lean
flames. The term "combustion dynamics" used herein refers to
fluctuations in air pressure, temperature, heat release and
unsteady flow oscillations that affect operation of the gas
turbine. It is desirable to operate the gas turbine system with a
highly reactive fuel component, such as hydrogen, to help limit
loss of combustion. Moreover the fuel reformer system disclosed
herein is compact in size and of reduced complexity. Existing gas
turbine systems, therefore, can easily be retrofitted to include
the generator at a low cost and without significantly impacting the
size of the gas turbine system.
[0021] Turning now to FIG. 1, a block diagram illustrating an
exemplary embodiment of a gas turbine system 10 is shown. The gas
turbine system 10 includes a fuel reformer system 12 for doping the
hydrogen into the fuel of the gas turbine. A compressor 14 is in
fluid communication with both the fuel reformer system 12 and the
gas turbine pre-mixers 16. The compressor 14 is configured to
supply air to both the fuel reformer system 12 and the pre-mixers
16. A fuel stream 18 is also in fluid communication with the fuel
reformer system 12. As will be discussed in greater detail below,
the fuel and air combine and react in the fuel reformer system 12
to form the syngas, which can then be combined with more fuel and
sent to the gas turbine pre-mixers 16. The syngas and fuel is
further mixed with air from the compressor 14, and the entire
pre-mixed fuel is fed to a combustor 20. The pre-mixed fuel is
combusted in the combustor 20 and expanded in the gas turbine 22.
The turbine is driven by the combustion and expansion, and the
energy is converted to electricity, where it can be sent to a power
grid 24 to provide power, or can be stored and used at a later
time.
[0022] FIG. 2 further illustrates an exemplary embodiment of the
fuel reformer system 12 of FIG. 1. A fuel slipstream 30 is split
from the main fuel stream 18 is combined with a slipstream of
oxygen-containing gas 32 from the gas turbine compressor 14 and
sent to a premixing zone 34 of the fuel reformer system 12. As used
herein, the term "oxygen-containing gas" is generally used to refer
to any oxidant suitable for mixing with the fuel to form a
hydrogen-enriched fuel mixture. Exemplary oxygen-containing gases
can include, without limitation, air, pure oxygen (O.sub.2),
oxygen-enriched air, oxygen and steam containing combustion
exhaust, and the like.
[0023] In an optional embodiment, the fuel slipstream 30 can be
combined with steam 36 and fed through a heat exchanger 38
configured to pre-heat the fuel slipstream 30 prior to mixing with
the oxygen-containing gas slipstream 32 in the premixing zone 34.
The pre-heated fuel slipstream 30, with optional steam 36, can then
be premixed with the oxygen-containing gas 32 in the premixing zone
34. In another embodiment, the steam can be a component of the fuel
slipstream 30 or the oxygen-containing gas slipstream 32, rather
than being a separate supply stream as illustrated in FIG. 2.
[0024] The fuel and oxygen-containing gas are mixed to form a
gaseous premix, which is immediately fed into a catalytic partial
oxidation reactor 40. The gaseous premix undergoes a catalytic
partial oxidation reaction and a syngas 42 is formed. The syngas 42
can be cooled when it is diluted with the fuel stream 18 to form a
hydrogen-enriched fuel mixture, or it can be cooled with steam.
When the optional heat exchanger 38 is present in the fuel reformer
system 12, the syngas 42 can be cooled by passing through the heat
exchanger down to a temperature of about 250 degrees Celsius
(.degree. C.) to about 450.degree. C., specifically about
325.degree. C. to about 375.degree. C. Cooling the syngas 42 is
particularly advantageous when an optional water gas shift (WGS)
reactor 44 is present in the fuel reformer system 12. The WGS
reactor 44 can be disposed downstream of the catalytic partial
oxidation reactor 40, and in this case, downstream of the heat
exchanger 38. The WGS reactor 44 can be configured to further
increase a concentration of hydrogen in the syngas by reacting
steam with carbon monoxide in the syngas to form more hydrogen. The
hydrogen-enriched syngas 46 can then be recombined with the fuel
stream 18 to form a fuel mixture 48, which can be fed to the
combustor 20 of the gas turbine system 10.
[0025] FIG. 3 is another block diagram illustrating another
exemplary embodiment of the fuel reformer system 12 of FIG. 1. The
fuel reformer system 12 includes a pre-mixing zone 110, a selective
catalytic partial oxidation (SCPO) zone 112, a CPO zone 114, and a
dilution zone 116. The fuel stream 18, which can be pressurized
before entering the gas turbine system, can be preconditioned in a
pretreatment zone 118. In various embodiments, the fuel can be
pre-mixed with water or steam, can be preheated, can be
preconditioned by means of a fuel swirler, flow enhancer,
turbulence generator, or the like, disposed in the zone, can be
filtered to reduce the level of impurities, such as sulfur, in the
fuel, and other like preconditioning means in the pretreatment zone
118. A fuel bypass valve 120 can be disposed in fluid communication
between the fuel stream source 18 and the fuel pretreatment zone
118. The fuel bypass valve 120 can be configured to send a desired
portion 121 of the fuel stream to pretreatment and pre-mixing zones
of the syngas generator to be used in generation of hydrogen
content in the system. The remainder 124 of the fuel stream 18 can
be directed by the fuel bypass valve 120 to the dilution zone 116,
where the remainder of the fuel stream 124 can combine with the
syngas 126 generated in the CPO zone 114.
[0026] Similarly, air 128 from the compressor 14 can be directed by
an air bypass valve 122 disposed in fluid communication with the
compressor 14, the fuel reformer system 12, and the gas turbine
pre-mixers 16. A portion 130 of the air can be sent to the
pre-mixing zone 110 for mixture with the fuel. As will be described
in greater detail, the air 130 can be fed into the pre-mixing zone
110 via air injection orifices 132 disposed about the pre-mixing
zone 110. Optionally, the system can further include a boost
compressor 140 between and in fluid communication with the air
bypass valve 122 and the air injection orifices 132. The boost
compressor 140 is configured to increase the pressure of the air
stream 130 entering the pre-mixing zone 110 to further increase the
mixing dynamics of the fuel and the air in the zone. The remainder
134 of the compressor air not utilized by the fuel reformer system
12 is diverted by the bypass valve 122 to the gas turbine
pre-mixers 16, wherein the air 134 is pre-mixed with the fuel
mixture 136 before being fed to the combustor 20 in the gas turbine
system 10.
[0027] The fuel portion fed to the pre-mixing zone 110 is allowed
to mix with the air 130 from the compressor 14. The gaseous pre-mix
138 is fed over a selective catalytic partial oxidation catalyst in
the CPO zone. The catalyst is configured to convert the air and
fuel into hydrogen and carbon monoxide. The air and fuel are
allowed to react in the CPO zone 114 to generate a gaseous mixture
of syngas 126, comprising primarily the hydrogen and carbon
monoxide. In one embodiment, the syngas 126 includes hydrogen,
carbon monoxide, nitrogen, and water. The CPO zone 114 can have any
residence time suitable for forming the syngas from a particular
ratio of fuel and air. In one embodiment, the CPO zone 114 can have
a residence time of less than about 500 milliseconds (ms),
specifically less than about 200 ms. The term "residence time"
refers to a period of time during which the fuel and air react in
the CPO zone. In one embodiment, the air and fuel can be mixed in
the pre-mixing zone 110 in rich proportions. As used herein, the
term "rich proportions" refers to a stoichiometric ratio of the
number of oxygen atoms in the air to the number of carbon atoms in
the fuel of about 0.6 to about 1.6.
[0028] After the CPO zone 114, the syngas 126 travels to the
dilution zone 116, wherein the syngas 126 can be combined with the
fuel remainder stream 124. The hydrogen in the syngas 126 can be
diluted by the added fuel; and the warm, hydrogen-enriched fuel
mixture 136 can be fed to the gas turbine pre-mixers 16, wherein
the hydrogen-enriched fuel is further mixed with oxygen and
injected into a combustor of the gas turbine system.
[0029] As mentioned, the fuel reformer system 12 described herein
is a compact, low cost system. In one embodiment, the system 12 can
have a size equivalent to that of a single nozzle combustor in a
standard 90-nozzle gas turbine machine. In a specific embodiment,
the syngas generator system 12 can have an area equal to about 0.1
to about 0.9 of an area of the gas turbine combustor 20. The
compact size of the syngas generator system described herein makes
it suitable for being retrofitted onto existing gas turbine
systems. The retrofit system reforms the existing fuel supply for
the gas turbine. Not only, therefore, does the fuel reformer system
12 improve the combustion dynamics of the gas turbine system 10,
but it does so without the need to outlay the capital costs
associated with buying an entirely new gas turbine system. Another
advantage of the retrofit system is that it can be serviced without
interfering with the gas turbine operation. For example, the
retrofit fuel reformer system could be taken off line and serviced
(e.g., catalyst changed), and the fuel supply is allowed to bypass
the system, thereby preventing interruption to the gas turbine
operation.
[0030] FIG. 4 is a schematic illustration of an exemplary
embodiment 200 of a pre-mixing device, which can be employed in the
pre-mixing zone of a fuel reformer system in a gas turbine. In the
illustrated embodiment, the pre-mixing device 200 includes a fuel
inlet 202 configured to introduce a fuel stream into the pre-mixing
device 200. In addition, the pre-mixing device 200 includes an air
inlet 204 configured to introduce oxygen thereto. Further, a
pre-mixing device 206 is employed to pre-condition the fuel stream
prior to introduction of oxygen thereto. As seen in this
embodiment, the flow-conditioning device comprises the pretreatment
zone of the fuel reformer system and is disposed within the
pre-mixing zone itself. The pre-mixing device 206 can include a
plurality of swirler vanes configured to provide a swirl movement
to the fuel stream. Alternatively, or in addition, the pre-mixing
device 206 can include a nozzle configured to accelerate the fuel
stream to a desired velocity. In other embodiments, various types
of other flow conditioning devices for pre-conditioning the fuel
stream can be envisaged.
[0031] In operation, the fuel stream is pre-conditioned via the
plurality of swirler vanes of the pre-mixing device 206. Further,
oxygen can be introduced in a substantially transverse direction to
the direction of injection of the fuel stream via the air inlet
204. The air can be injected at a location 208 through a plurality
of holes or injection orifices disposed downstream of the plurality
of swirler vanes, through a plurality of holes disposed on each of
the plurality of swirler vanes, and/or through a center body or
walls of the pre-mixing device 200. A pressure drop across the
plurality of holes for introducing the air can be less than about
5%. In one embodiment, air can be injected at an angle that has a
component perpendicular to the direction of flow. Furthermore, the
injection holes can also introduce swirl around the axis of the
center body of the pre-mixing device 200. The pre-conditioned fuel
stream and air are mixed in a pre-mixing region 210 to form a
gaseous pre-mix that is further directed to CPO zone (not shown)
for catalytic partial oxidation through an exit 212. In the
illustrated embodiment, the pre-mixing region 210 is designed to
resist flame holding even in the presence of an ignition source by
minimizing recirculation zones.
[0032] In the pre-mixing device 200, the temperature of the fuel
stream can be about 100.degree. F. (38.degree. C.) to about
1,300.degree. F. (704.degree. C.) and the temperature of air can be
about 500.degree. F. (260.degree. C.) to about 1,400.degree. F.
(760.degree. C.). Further, the ratio of an effective area of the
air inlet 204 to an effective area of the flow-conditioning device
206 is about 0.1 to about 0.5. Pre-mixing device 206 can be
configured to introduce the fuel stream into the premixing region.
As used herein, the term `effective area` of the air inlet is
intended to refer to the volumetric flowrate of the air through the
inlet divided by the average velocity of the air.
[0033] FIG. 5 is a schematic illustration of another exemplary
embodiment of a pre-mixing device 300. FIG. 5 represents an
alternative design of the pre-mixing device. As illustrated, the
pre-mixing device 300 includes a fuel inlet 302 to introduce the
fuel stream 304 into the pre-mixing device 300. Further, the
pre-mixing device 300 includes a plurality of swirler vanes 306 to
provide a swirl movement to the fuel stream 304. Additionally, the
pre-mixing device 300 includes a plurality of counter flow swirl
vanes 308 disposed adjacent to the plurality of swirler vanes 306.
The direction of movement of the swirl and counter flow swirl vanes
306 and 308 is represented by reference numerals 310 and 312
respectively. In this exemplary embodiment, the fuel stream 304
flows from the inlet 302 upstream of the swirler vanes 306.
Further, oxygen 314 is introduced through a plurality of holes 316
disposed on the swirler vanes 306.
[0034] The total effective area for the plurality of holes 316 is
about 1/2 of the effective area of the swirler vanes 306 for the
design of the pre-mixing device 300. Further, the number of swirler
vanes 306 can be about 4 to about 15. Similarly, the number of
counter flow swirler vanes 308 can be about 4 to about 15.
Additionally, the turning angle for each of the swirler vanes 306
and 308 can be about 20 degrees to about 50 degrees. In one
embodiment, the turning angle of the counter flow swirler vanes 308
is relatively greater than the turning angle of the swirler vanes
306. As described earlier, the fuel stream 304 is pre-conditioned
through the swirler vanes 306 and 308, and oxygen 314 is pre-mixed
with the pre-conditioned fuel stream to form a gaseous pre-mix that
is directed to the CPO and CPO zones (see FIG. 1).
[0035] FIG. 6 is a schematic illustration of another
cross-sectional view of the pre-mixing device 300 of FIG. 5. In
this exemplary embodiment, the fuel stream 304 is introduced and is
pre-conditioned via the swirler vanes 306. Further, the pre-mixing
device 300 also includes counter flow swirl vanes 308 disposed
adjacent to the plurality of swirler vanes 306. As illustrated,
oxygen 314 is introduced through a wall 320 of the pre-mixing
device 300 and into swirler vanes 306. The oxygen 314 is mixed with
the pre-conditioned fuel stream 304 to form the gaseous pre-mix,
which is subsequently fed over the CPO catalyst 350 and
catalytically converted to syngas. It should be noted that the
mixing region could be either straight or converging. Further,
oxygen 314 can also be introduced through the center body with an
aerodynamic tip to prevent flow separation. In some embodiments,
the shape and design of the pre-mixing device 300 can be effective
in acting as a thermal shield for the CPO catalyst. As a thermal
shield, the pre-mixing device conical shape can help to keep a high
velocity of the gaseous pre-mix in the premixing zone to prevent
combustion from traveling upstream into the premixing zone.
[0036] The pre-mixing device designs described above advantageously
provide more uniform mixing of the reactants (fuel and oxygen)
before reaching the catalyst of the CPO zone. This permits the
gaseous pre-mix to be pre-heated to a higher temperature, thereby
improving the efficiency of the CPO reactor of the CPO zone. In one
embodiment, the gaseous pre-mix can be preheated to a temperature
of about 300.degree. C. to about 500.degree. C., specifically about
350.degree. C. to about 450.degree. C., and more specifically about
375.degree. C. to about 425.degree. C. (e.g., about 400.degree.
C.). In some embodiments the hot oxygen-containing gas slipstream
from the gas turbine compressor is enough to heat the fuel and
oxygen mixture in the premixing zone. In another embodiment, the
fuel slipstream can be preheated, for example, with a heat
exchanger (as shown in FIG. 2).
[0037] Turning now to FIG. 7, another schematic illustration of a
fuel reformer system 400 is shown. FIG. 7 shows an example 402 of
the pre-mixing devices disclosed above in fluid communication with
a catalyst zone 410. In this embodiment, a diffuser 404 is disposed
downstream of the pre-mixing device and upstream of the catalyst
zone 410. The diffuser 404 is configured to shield the gaseous
premix from the catalyst. The diffuser 404 is further configured to
keep the velocity of the gaseous premix exiting the premixing
device 402 higher than that of the catalyst zone 410. The flame
from the catalyst zone 410, therefore, is prevented from traveling
upstream into the pre-mixing device.
[0038] The catalyst zone 410 is in further fluid communication with
a CPO zone 420. Disposed downstream of the CPO zone 420, can be a
dilution zone (not shown). The gaseous pre-mix from the pre-mixing
zone 402 can be fed over a catalyst disposed in the catalyst zone
410. The catalyst can be configured to convert the air and fuel
into hydrogen and carbon monoxide. The catalyst zone 410 can be
arranged coaxially with the axis of the tubular CPO zone 420. The
CPO zone 420 can comprise a honeycomb structure of suitable
catalyst support material, upon which the catalyst is coated; or
the structure itself can comprise the catalyst. For example, the
CPO zone can comprise a catalyst coated ceramic honeycomb monolith
or a catalyst coated metallic honeycomb, or a ceramic honeycomb
monolith containing catalyst. The honeycomb structure of the CPO
zone can comprise a plurality of passages separated by
catalyst-coated walls; and is not limited to honeycomb structures.
The gaseous pre-mix can pass through these passages, over the
catalyst, thereby starting the reaction for conversion to syngas.
The catalyst can be any suitable material for promoting selective
partial oxidation. Examples of catalysts can include, without
limitation, platinum, palladium, rhodium, iridium, ruthenium,
chromium oxides, cobalt oxides, cesium, nickel, iron, alumina, or
combinations thereof, and other like catalysts suitable for
promoting partial oxidation.
[0039] The CPO zone 420 is configured to provide the residence time
necessary to produce the desired concentration of hydrogen from the
fuel. The gaseous pre-mix flows through the catalyst system of the
catalyst zone 410, and the pre-mix is converted thermally and/or
catalytically. The hydrocarbon fuel of the gaseous pre-mix is
partially oxidized by the air in the presence of the catalyst in
the CPO zone 420, to produce a reaction product gas comprising
hydrogen, carbon monoxide, water, carbon dioxide, and unburned
hydrocarbon fuel. The CPO zone 420 provides further time for the
partial oxidation reaction to continue before the formed syngas is
cooled and diluted in the dilution zone. The primary reactions that
occur over the catalyst in the catalyst zone 410, and further in
the CPO zone 420, are indicated in reactions 1-3 below:
CH.sub.4+1/2O.sub.2.dbd.CO+2H.sub.2; (1)
CH.sub.4+2O.sub.2.dbd.CO.sub.2+2H.sub.2O (3)
[0040] The reactions are shown with methane (CH.sub.4), the main
constituent of natural gas. In other embodiments, other types of
fuel can be employed in the fuel reformer system, and will depend
on the gas turbine system in which the syngas is being generated.
Other examples of fuels can include, without limitation, natural
gas, methanol, ethanol, ethane, liquid petroleum gas (LPG),
naphthas, typically virgin naphthas or cracked naphthas, such as,
e.g., light naphthas, full range naphthas or even heavy naphthas,
butane, propane, diesel fuel, kerosene, an aviation fuel, a coal
derived fuel, a bio-fuel, gas oil, crude oil, an oxygenated
hydrocarbon feedstock, refinery off gas, associated gas,
combinations thereof, and the like. Again, the syngas resulting
from the CPO reaction typically comprises hydrogen, carbon
monoxide, carbon dioxide, and steam. In one embodiment, the syngas
may also include a small amount of nitrogen (N.sub.2). In some
embodiments, the syngas can further comprise un-reacted fuel. The
oxidant used in the disclosed systems can comprise any suitable gas
containing oxygen, such as for example, air, oxygen-rich air or
oxygen-depleted air, and the like.
[0041] The reaction to syngas can further comprise conventional
steam reforming when steam is added to the fuel and oxygen, as
mentioned above. In such an instance, the natural gas is converted
to hydrogen following the reactions (4) and (5) as mentioned
below.
CH.sub.4+H.sub.2O CO+3H.sub.2 (4)
CO+H.sub.2O CO.sub.2+H.sub.2 (5)
[0042] The combustion and conversion of the substantially pre-mixed
reactants in the fuel reformer system leads to a compact CPO zone
420 that achieves near-equilibrium composition and negligible
formation of solid carbon in the CPO zone. The syngas formed in the
CPO zone 420 can then travel downstream to the dilution zone (as
shown in FIG. 3). The dilution zone is configured to cool down the
syngas after reaction and to dilute the syngas with the gas turbine
fuel. The hydrogen-enriched fuel mixture formed in the dilution
zone can have a hydrogen concentration of about 25 dry volume
percent (vol %) to 45 vol %, based on the total dry volume of the
fuel mixture. As mentioned above, in cases where higher
concentrations of hydrogen are desired, a WGS reactor can be
advantageously employed to boost the hydrogen content of the syngas
after the CPO zone.
[0043] Referring back now to FIG. 3, the hydrogen-enriched fuel
mixture is fed downstream from the fuel reformer system 12 to gas
turbine pre-mixers 16. The hydrogen-enriched fuel mixture can help
to lower the lean blow out point as well as to control the
combustion dynamics of a gas turbine. The fuel reformer system
provides a hydrogen-enriched fuel mixture, which can provide a way
to achieve a sustained lean, pre-mixed or partially pre-mixed flame
in the combustor of the gas turbine system, without lean blowout or
combustion dynamics. The fuel-syngas mixture therefore, is fed to
the pre-mixers of the gas turbine along with the rest of the fuel.
FIG. 8 is a schematic cross-sectional illustration of an exemplary
gas turbine combustor 500. The combustor 500 includes a combustor
housing 502 and a combustor liner 504 disposed within the housing
502. In operation, a fuel stream 506, which can include the
hydrogen-enriched mixture from the fuel reformer system, can be
introduced to the combustor and pre-mixed with more oxygen 508 from
the compressor via a pre-mixing device (such as those shown in any
of the previous figures). The pre-mixing device can be disposed
within the gas turbine pre-mixing region 510 within the housing
502. In the illustrated embodiment, the fuel stream 506 is
preconditioned through the pre-mixers. The fuel and oxygen are
combusted in the combustion chamber 512 at elevated temperature and
pressure. The combusted gas is compressed by the converging shape
of the combustor 500 and travels to the turbine (not shown) where
energy from the expansion of the compressed gas is used to drive a
turbine.
[0044] The turbine can be connected to an electric generator
configured to produce electricity from the gas turbine. In certain
embodiments, a pilot flame such as a fuel nozzle with a relatively
low degree of pre-mixing can be employed to initiate flame during
start-up and to ensure stable combustion in the combustion chamber
512. It should be noted that the combustion of substantially
pre-mixed fuel and oxygen when syngas is present can lead to
reduced NOx generation, improved flame stability, and increased
fuel efficiency.
[0045] Ranges disclosed herein are inclusive and combinable (e.g.,
ranges of "up to about 25 weight percent (wt %), or, more
specifically, about 5 wt % to about 20 wt %", is inclusive of the
endpoints and all intermediate values of the ranges of "about 5 wt
% to about 25 wt %," etc.). "Combination" is inclusive of blends,
mixtures, alloys, reaction products, and the like. Furthermore, the
terms "first," "second," and the like, herein do not denote any
order, quantity, or importance, but rather are used to distinguish
one element from another, and the terms "a" and "an" herein do not
denote a limitation of quantity, but rather denote the presence of
at least one of the referenced item. The modifier "about" used in
connection with a quantity is inclusive of the stated value and has
the meaning dictated by context, (e.g., includes the degree of
error associated with measurement of the particular quantity). The
suffix "(s)" as used herein is intended to include both the
singular and the plural of the term that it modifies, thereby
including one or more of that term (e.g., the colorant(s) includes
one or more colorants). Reference throughout the specification to
"one embodiment", "another embodiment", "an embodiment", and so
forth, means that a particular element (e.g., feature, structure,
and/or characteristic) described in connection with the embodiment
is included in at least one embodiment described herein, and may or
may not be present in other embodiments. In addition, it is to be
understood that the described elements may be combined in any
suitable manner in the various embodiments.
[0046] While the invention has been described with reference to a
preferred embodiment, it will be understood that various changes
may be made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from
essential scope thereof. Therefore, it is intended that the
invention not be limited to the particular embodiment disclosed as
the best mode contemplated for carrying out this invention, but
that the invention will include all embodiments falling within the
scope of the appended claims.
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