U.S. patent application number 13/421299 was filed with the patent office on 2012-09-13 for method and gas turbine combustion system for safely mixing h2-rich fuels with air.
This patent application is currently assigned to ALSTOM Technology Ltd. Invention is credited to Fernando Biagioli, Richard Carroni.
Application Number | 20120227411 13/421299 |
Document ID | / |
Family ID | 41534095 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227411 |
Kind Code |
A1 |
Carroni; Richard ; et
al. |
September 13, 2012 |
METHOD AND GAS TURBINE COMBUSTION SYSTEM FOR SAFELY MIXING H2-RICH
FUELS WITH AIR
Abstract
A method and apparatus are disclosed for mixing H2-rich fuels
with air in a gas turbine combustion system, wherein a first stream
of burner air and a second stream of a H2-rich fuel are provided.
All of the fuel is premixed with a portion of the burner air to
produce a pre-premixed fuel/air mixture. This pre-premixed fuel/air
mixture is injected into the main burner air stream.
Inventors: |
Carroni; Richard;
(Niederrohrdorf, CH) ; Biagioli; Fernando;
(Fislisbach, CH) |
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
41534095 |
Appl. No.: |
13/421299 |
Filed: |
March 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2010/062807 |
Sep 1, 2010 |
|
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|
13421299 |
|
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Current U.S.
Class: |
60/775 ; 60/737;
60/748; 60/776 |
Current CPC
Class: |
F23L 2900/07002
20130101; Y02E 20/34 20130101; F23C 2900/9901 20130101; F02C 3/30
20130101; F23R 3/286 20130101; Y02E 20/344 20130101; F23L 7/00
20130101 |
Class at
Publication: |
60/775 ; 60/776;
60/737; 60/748 |
International
Class: |
F02C 3/22 20060101
F02C003/22; F23R 3/28 20060101 F23R003/28; F23R 3/14 20060101
F23R003/14; F02C 3/30 20060101 F02C003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2009 |
EP |
09170508.7 |
Claims
1. A method for mixing H2-rich fuels with air in a gas turbine
combustion system, comprising: providing a first stream of burner
air and a second stream of a H2-rich fuel; premixing the fuel with
a portion of the burner air to produce a pre-premixed fuel/air
mixture; and injecting this pre-premixed fuel/air mixture into a
main burner air stream.
2. The method according to claim 1, wherein the premixing is done
in a manner for preventing flame anchoring at undesired locations,
including at least one of near an injection location and in a
burner.
3. The method according to claim 1, wherein an air excess factor of
.lamda.>1, is achieved in the premixing.
4. The method according to claim 1, comprising: separating air into
O2 and N2 with an air separation unit; and adding a portion of the
N2 from the air separation unit to at least one of the main burner
air and the pre-premixed fuel/air mixture.
5. The method according to claim 1, comprising: using a
pre-premixer formed as a channel with straight or slightly swirling
air flow to avoid at least one of recirculation and stagnation
regions.
6. The method according to claim 1, comprising: using a
pre-premixer having narrow channels whose hydraulic diameter is
less than a quenching distance.
7. The method according to claim 5, comprising: energizing boundary
layers of the air flow in the pre-premixer by using some film air,
in order to increase velocities in the at least one recirculation
and stagnation regions.
8. The method according to claim 7, comprising: accelerating the
air flow additionally via a jet-pump effect of injecting large
volumes of H2/N2 fuel.
9. The method according to claim 1, comprising: injecting water
mist into the H2-rich fuel for cooling due to a subsequent
evaporation of injected water.
10. The method according to claim 1, comprising: utilizing a main
swirler in a swirl-stabilized burner to further increase velocity
in a pre-premixer by taking advantage that local static pressure in
a central region of the burner is lower than a nominal burner
pressure.
11. The method according to claim 1, wherein an air excess factor
of .lamda.>1, is achieved in the premixing.
12. The method according to claim 1, comprising: using a
pre-premixer formed as a channel with straight or slightly swirling
air flow to avoid recirculation and/or stagnation regions.
13. A gas turbine combustion system, comprising: a combustion
chamber and at least one burner opening into the combustion chamber
for injecting a stream of burner air into the combustion chamber;
and at least one pre-premixer for providing a pre-premixed fuel/air
mixture; whereby the at least one burner and the at least one
pre-premixer are arranged relative to each other, such that the
pre-premixed fuel/air mixture will be injected into the stream of
burner air during operation.
14. A gas turbine combustion system according to claim 11, wherein
the at least one pre-premixer is formed as a channel with straight
or slightly swirling air flow.
15. A gas turbine combustion system according to claim 11, wherein
the at least one pre-premixer includes narrow channels whose
hydraulic diameter is less than a quenching distance.
16. A gas turbine combustion system according to claim 11, wherein
the at least one burner is a swirl-stabilized burner.
17. A gas turbine combustion system according to claim 11, wherein
the at least one burner is an AEV burner.
18. A gas turbine combustion system according to claim 11, wherein
the at least one burner is an SEV burner.
19. A gas turbine combustion system according to claim 11, wherein
the at least one pre-premixer is formed as a channel with straight
or slightly swirling air flow.
20. A gas turbine combustion system according to claim 11, wherein
the at least one burner is a swirl-stabilized burner.
Description
RELATED APPLICATION
[0001] This application claims priority as a continuation
application under 35 U.S.C. .sctn.120 to PCT/EP2010/062807, which
was filed as an International Application on Sep. 1, 2010,
designating the U.S., and which claims priority to European
Application 09170508.7 filed in Europe on Sep. 17, 2009. The entire
contents of these applications are hereby incorporated by reference
in their entireties.
FIELD
[0002] The present disclosure relates to gas turbines, and a method
for safely mixing H2-rich fuels with air in a gas turbine
combustion system.
BACKGROUND INFORMATION
[0003] Known combustors for hydrogen-rich fuels can rely upon very
high levels of dilution (with inert species, for example, N2 and/or
steam) of diffusion flames. See, for example, WO-A1-2008/135362 or
WO-A1-2008/155242. Derating (i.e., reducing flame temperatures) can
also be used. See, for example, EP-A1-0 731 255 or EP-A1-0 899 438.
Efforts are being made to develop lean-premix combustion systems
for hydrogen-rich fuels in order to further reduce emissions and to
minimize costly diluents. Such systems can involve a high degree of
premixing. Unfortunately, hydrogen-rich fuels can be so reactive
that significant modifications may be desired in order to safely
and cleanly burn these fuels. The modifications (for example,
increasing burner velocity, using very high fuel jet velocities),
however, can be incompatible with the specifications of modern gas
turbine burners (low burner pressure loss, low fuel pressure
loss).
[0004] Introducing H2-rich fuels into air in order to attain a good
air/fuel mixture prior to combustion can be exemplified by FIG. 1,
which shows laminar flame speeds for CH4 (a standard gas turbine
fuel) and for various H2/N2 mixtures. H2-rich laminar flame speeds
can differ from their CH4 counterparts in that:
[0005] The peak flame speed can be at least 6 times higher; the
flame speed in the entire range of usable fuel/air mixtures can be
higher than for CH4; and the peak flame speed can occur at the much
lower air excess factor (.lamda.) of approx. 0.6, rather than
approx. 1.0.
[0006] Turbulent burning velocity can largely determine the flame
location in a real burner. This parameter can exacerbate the
situation for H2-rich fuels, given that the turbulent burning
velocity is a function of pressure for H2 but not so for CH4.
[0007] When fuel is injected into hot air, the region near the
injection point can be characterized by very poor mixing. On a
local scale, .lamda. can vary between 0 and infinity.
[0008] Natural Gas:
[0009] The flammability limits can be narrow. On the rich side, a
flame cannot be sustained, even at relatively high .lamda.
(.apprxeq.0.7 in FIG. 1). The burning velocity (and hence laminar
flame speed) can be low, for example, near the rich extinction
limit. The risk of ignition in the injection area can be low, and
there can be insufficient anchoring in the event of flashback
(i.e., the flame is blown off).
[0010] H2-Rich Fuels:
[0011] The flammability limits can be wide, with very rich mixtures
(.lamda.<0.3) capable of sustaining a flame. The burning
velocities (and hence laminar flame speeds) can be high.
Unfortunately, the peak reactivity of H2-rich fuels can also be in
the rich region (for example, around .lamda.=0.5), which can mean
that the risk of ignition in the injection area can be high, and
the flame anchoring (once flame jump occurs) can be very strong.
Flashback thus can result in permanent flame anchoring, which can
lead to high emissions and possibly also to hardware
destruction.
[0012] Known methods of dealing with such high burning velocities,
and the drawbacks thereof, are listed below.
[0013] Utilizing Dilution:
[0014] At any given mixing quality, this action can reduce the
burning velocity (see dotted double arrow A in FIG. 1) but not
sufficiently. Furthermore, this action does not shift the
equivalence ratio at which peak burning velocities occur. Excessive
dilution can result in high fuel pressure losses and additional
costs. The diluent is not free. In the case of N2, its pressure
should be increased from that of the air separation unit to that of
the fuel. In the case of steam, there is a loss of efficiency
associated with extracting steam from the steam cycle.
[0015] Significantly increasing the burner air velocity. In order
to be effective, the burner velocity should be increased by a
suitable amount, thereby resulting in larger pressure losses across
the burner and hence reduction in gas turbine efficiency.
Furthermore, such high burner velocities can be incompatible with
the standard backup fuels (for example, Natural Gas). It is noted
that there will be regions of lower air velocity (for example,
boundary layers), which are often near those locations from which
fuel is injected.
[0016] Injecting fuel at higher velocities in order to avoid
flame-holding. Excessive jet velocities can cause high-pressure
losses in the fuel system, resulting in higher costs. Approaching
the sonic limit also poses stability problems.
[0017] None of these known methods, however, address the high
flammability of very rich fuel/air mixtures.
SUMMARY
[0018] A method is disclosed for mixing H2-rich fuels with air in a
gas turbine combustion system, comprising providing a first stream
of burner air and a second stream of a H2-rich fuel; premixing the
fuel with a portion of the burner air to produce a pre-premixed
fuel/air mixture; and injecting this pre-premixed fuel/air mixture
into a main burner air stream.
[0019] A gas turbine combustion system is disclosed comprising: a
combustion chamber and at least one burner opening into the
combustion chamber for injecting a stream of burner air into the
combustion chamber; and at least one pre-premixer for providing a
pre-premixed fuel/air mixture, whereby the at least one burner and
the at least one pre-premixer are arranged relative to each other,
such that the pre-premixed fuel/air mixture will be injected into
the stream of burner air during operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present disclosure is now to be explained more closely
by different embodiments and with reference to the attached
drawings.
[0021] FIG. 1 shows laminar flame speeds for CH4 (a known gas
turbine fuel) and for various H2/N2 mixtures at 1 atm and
20.degree. C.;
[0022] FIG. 2 illustrates a pre-premixing according to an exemplary
embodiment of the disclosure;
[0023] FIG. 3 shows an exemplary embodiment of a burner
encompassing a pre-premixing concept according to the disclosure;
and
[0024] FIG. 4 illustrates an exemplary embodiment of the disclosure
wherein a main swirler in a swirl-stabilized burner can be utilized
to further increase the velocity in a pre-premixer, by taking
advantage that a local static pressure in a central region of the
burner is lower than a nominal burner pressure.
DETAILED DESCRIPTION
[0025] An exemplary embodiment of the disclosure provides a method
for safely mixing H2-rich fuels with air in gas turbine combustion
systems (e.g., to provide safe mixing), which can effectively
permit the local fuel/air mixture to bypass the peak burning
velocity (i.e., .lamda.=0.6) prior to injection into the main
burner air stream (known as liner air).
[0026] A method according to an exemplary embodiment of the
disclosure includes: providing a first stream of burner air and a
second stream of a H2-rich fuel, premixing the fuel (e.g., all of
the fuel) with a portion of the burner air to produce a
pre-premixed fuel/air mixture, and injecting this pre-premixed
fuel/air mixture into the main burner air stream.
[0027] According to an exemplary embodiment of the disclosure, the
premixing can be done in a manner which can prevent flame anchoring
at undesired locations, especially near the injection location and
in the burner.
[0028] According to an exemplary embodiment of the disclosure, an
air excess factor of .lamda.>1, for example, .lamda.>1.3, can
be achieved in the premixing step.
[0029] According to an exemplary embodiment of the disclosure, air
can be separated into O2 and N2 by an air separation unit (ASU),
and a portion of the N2 from the air separation unit (ASU) can be
added to the main burner air and/or pre-premixed fuel/air
mixture.
[0030] According to an exemplary embodiment of the disclosure, a
pre-premixer can be in the form of a simple (for example, round)
channel with straight or slightly swirling air flow can be used to
avoid recirculation and/or stagnation regions.
[0031] According to an exemplary embodiment of the disclosure, a
pre-premixer including narrow channels whose hydraulic diameter is
less than the quenching distance, can be used.
[0032] According to an exemplary embodiment of the disclosure, the
boundary layers of the air flow in the pre-premixer can be
energized, for example, by using some film air, in order to
increase velocities in these regions.
[0033] According to an exemplary embodiment of the disclosure, the
air flow can be additionally accelerated via a "jet-pump" effect of
injecting large volumes of H2/N2 fuel.
[0034] According to an exemplary embodiment of the disclosure,
water mist can be injected into the H2-rich fuel to enhance the
safety of the method by the relative cooling due to the subsequent
evaporation of the injected water.
[0035] According to an exemplary embodiment of the disclosure, a
main swirler in a swirl-stabilized burner can be utilized to
further increase the velocity in the pre-premixer by taking
advantage that the local static pressure in the central region of
the burner can be lower than the nominal burner pressure.
[0036] A gas turbine combustion system for applying the method
according to exemplary embodiments of the disclosure can include a
combustion chamber and at least one burner opening into the
combustion chamber to inject a stream of burner air into the
combustion chamber, at least one pre-premixer for providing a
pre-premixed fuel/air mixture, whereby the at least one burner and
the at least one pre-premixer can be arranged relative to each
other, such that the pre-premixed fuel/air mixture can be injected
into the stream of burner air.
[0037] According to an exemplary embodiment of the gas turbine
combustion system the at least one pre-premixer can have the form
of a simple (for example, round), channel with straight or slightly
swirling air flow.
[0038] According to an exemplary embodiment of the gas turbine
combustion system, the at least one pre-premixer can include narrow
channels whose hydraulic diameter can be less than a quenching
distance.
[0039] According to an exemplary embodiment of the gas turbine
combustion system, the at least one burner can be a
swirl-stabilized burner.
[0040] According to an exemplary embodiment of the gas turbine
combustion system, the at least one burner can be a so-called EV
burner (in place of many: EP 0 321 809 B1) or a so-called AEV
burner (in place of many: EP 0 704 657).
[0041] According to an exemplary embodiment of the gas turbine
combustion system, the at least one burner can be a so-called SEV
burner (in place of many: EP 0 620 362 B1, pos. 5).
[0042] All of these documents mentioned herein relating to EV-,
AEV- and SEV-burners and all these developed improvements, patent
applications and patents, form an integrating component of this
patent application, and incorporated herein by reference in their
entireties.
[0043] The exemplary embodiments of the disclosure relate to
premixing the fuel with a portion of burner air (denoted as
"pre-premixing air") in a manner which can prevent flame anchoring,
and then injecting this fuel/air mixture (characterized by
.lamda.>1, for example, .lamda.>1.3) into the main burner air
stream (i.e., the liner air). This can be done in one or more
stages. FIG. 2 illustrates an exemplary embodiment of the concept
(which is called "pre-premixing"). P_pk2 and T_pk2 are the pressure
and temperature, respectively, at a compressor exit of the gas
turbine. P_fuel and T_fuel are the pressure and temperature,
respectively, of the fuel, T_mix is the temperature of the
pre-premixing mixture, while P_hood and T_hood are the pressure and
temperature, respectively, of the hood air (which is the air that
enters the burner). The pre-premixing method can involve elements
of the traditional solutions for H2-rich fuels (for example, high
air velocities, high dilution levels), but the negative effects can
be rather limited because these methods can apply to a portion of
the overall burner air (i.e., the pre-premixing air), rather than
the entire burner air flow.
[0044] Mass and energy balances show that about 25% and 45% of the
total burner air is needed such that the pre-premixed fuel/air has
a .lamda. of 0.6 and 1.0, respectively, for a 70/30 H2/N2 fuel (air
temperature 420.degree. C., fuel temperature 150.degree. C.,
T_ad=1750K).
[0045] In the event that the resulting liner cooling is
insufficient (because part of the compressor air was diverted to
the pre-premixer), it would be possible to add the remaining N2
from the ASU (air separation unit) to the liner air, the mixture
temperature of which would be significantly below the standard
liner air temperature of 400.degree. C. This stream of N2 would
only have to be compressed from the ASU pressure (approx. 5 bar for
a low-pressure device, or 15 bar for a high-pressure ASU) to the
P_pk2 pressure (i.e., at compressor exit).
[0046] The pre-premixing process is driven by a pressure loss
(.DELTA.P) that is larger than that across the burner. FIG.
2--based on a GT13E2 gas turbine of the applicant under full-load
conditions for an AEV-125 burner (AEV=Advanced
Environmental)--shows that this pressure loss can be proportional
to the sum of the liner and swirler pressure losses, .DELTA.P_liner
and .DELTA.P_swirler, amounting to .DELTA.P.apprxeq.2 to 3%.
[0047] Further safety benefits of the pre-premixing concept are
noted.
[0048] The relatively cold fuel is mixed with only a portion of the
entire burner air, meaning that the pre-premixed mixture
temperature T_mix is significantly lower (278.degree. C. and
310.degree. C. for .lamda.=0.6 and 1.0, respectively, compared to
350.degree. C. when the fuel is mixed with all the burner air
(based on 70/30 H2/N2 at 150.degree. C.). This reduces the
reactivity of the air/fuel mixture, thereby greatly assisting the
safe transition to .lamda..gtoreq.1).
[0049] The pre-premixing air stream is cooler than the hood air (by
around 20.degree. C.), because it is not used for liner cooling.
This can further reduce reactivity in the pre-premixer.
[0050] If N2 is used for a part of the pre-premixing air, then the
risk of ignition can be reduced due to lower O2; and lower
temperature; and the pre-premixed mixture can achieve greater
penetration depths in the burner (due to the higher fuel mass flow
rates relative to the air mass flow), thereby permitting better
mixing than when the non-pre-premixed fuel is injected into the
burner.
[0051] Several methods of achieving the desired pre-premixing are
described below. There are other methods of achieving the proposed
idea, which will be apparent to those skilled in the art.
[0052] The pre-premixer (16 in FIG. 4) can include a simple channel
(for example, round) with straight air flow. Aerodynamically simple
geometries can avoid recirculation and/or stagnation regions. The
boundary layers can be energized (for example, using some film air)
in order to increase velocities in these regions. Both jets in
cross-flow and co-flowing jets can be used. The latter can further
reduce risk of flame anchoring.
[0053] Lack of swirl in the pre-premixer means that the air
velocity can be around 50% higher than that in the burner (approx
120 m/s), using the given .DELTA.P.
[0054] The air flow can additionally be accelerated via the
"jet-pump" effect of injecting large volumes of H2/N2 fuel.
[0055] The pre-premixer can include small channels whose hydraulic
diameter is less than the quenching distance. Injection and
pre-mixing of the fuel in these small channels can prevent
homogeneous ignition from occurring during the mixing process and
prior to the attainment of higher .lamda.. The air velocity can be
small, because safety can now be promoted by quenching rather than
by convection. Small air velocities in narrow channels are
compatible with the available .DELTA.P.
[0056] An injection of water into H2-rich fuel and relative cooling
by subsequent evaporation would further enhance the safety of the
present methodology.
[0057] FIG. 3 is an example of a burner encompassing the new
pre-premixing concept described above. According to FIG. 3, in a
combustion system 10, a pre-premixed fuel/air mixture C is injected
through pre-premixers 11 and 12 into a burner 17 which opens into a
combustion chamber 13. Main air 22 is added through main burner air
inlets 14 and 15 near the exit of the pre-premixers 11, 12. The
pre-premixing concept can of course be adapted to known burners
such as the AEV and also the SEV (SEV=Sequential Environmental).
For example, see exemplary embodiments below. One or more
pre-premixers may be provided per burner.
Embodiment 1
[0058] The idea can be used for SEV (i.e. reheat) combustion as
well. In this case, the pre-premixer temperature benefit would be
even greater since the PK2 air used in the pre-premixer is colder
(e.g., 400.degree. C.-450.degree. C.) than the 1000.degree. C. of
the main burner air. A similar benefit would be seen in the
application to non-reheat lean-premix burners in recuperated
combustion systems.
Embodiment 2
[0059] Use less air in the pre-premixer. Whilst this gives
.lamda.<1, the local mixture temperature in the pre-premixer can
be significantly smaller. This can compensate for the higher flame
speeds associated with richer fuel/air mixtures. This can also
leave more air for liner cooling.
Embodiment 3
[0060] The pre-premixing concept can be applied to diffusion
burners too. Such a configuration would permit clean and safe
operation without derating (diffusion burners often have to run on
lower firing temperatures for NOx reasons) and without the need for
excessive dilution.
Embodiment 4
[0061] The main swirler in a swirl-stabilized burner can be
utilized to further increase the velocity in the pre-premixer,
simply by taking advantage of the fact that the local static
pressure in the central region of the burner is lower than the
nominal burner pressure (see dotted line B in FIG. 1). This is
demonstrated in FIG. 4. According to FIG. 4, a combustion system 20
includes a burner 17 with a pre-premixer 16. A pre-premixed
fuel/air mixture 21 generated within the pre-premixer 16 enters the
burner 17 in an axial direction (axis 19). Main air 22 enters the
burner 17 via a hood 18, thereby generating a swirl with a low
static pressure region 24. The resulting fully premixed fuel/air
mixture 23 exits the burner 17 to enter the subsequent combustion
chamber. In general, the main air flow (i.e., "hood" or liner air)
can enter the burner via axial, radial or "hybrid" swirlers.
[0062] Thus, it will be appreciated by those skilled in the art
that the present disclosure can be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The presently disclosed embodiments are therefore
considered in all respects to be illustrative and not restricted.
The scope of the disclosure is indicated by the appended claims
rather than the foregoing description and all changes that come
within the meaning and range and equivalence thereof are intended
to be embraced therein.
LIST OF REFERENCE NUMERALS
[0063] 10,20 Combustion system [0064] 11,12 Pre-premixer [0065] 13
Combustion chamber [0066] 14,15 Main burner air inlet [0067] 16
Pre-premixer [0068] 17 Burner [0069] 18 Hood [0070] 19 Axis [0071]
21,C Pre-premixed fuel/air mixture [0072] 22,D Main air [0073] 23
Fully premixed fuel/air mixture [0074] 24 Low static pressure
region
* * * * *