U.S. patent application number 10/010594 was filed with the patent office on 2003-06-05 for retrofittable air assisted fuel injection method to control gaseous and acoustic emissions.
This patent application is currently assigned to Honeywell International, Inc.. Invention is credited to Srinivasan, Ram.
Application Number | 20030101729 10/010594 |
Document ID | / |
Family ID | 21746446 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030101729 |
Kind Code |
A1 |
Srinivasan, Ram |
June 5, 2003 |
Retrofittable air assisted fuel injection method to control gaseous
and acoustic emissions
Abstract
In the operation of gas turbine engines, it is an ever
increasing goal to reduce the amount of harmful elements contained
within the emissions of the engine. It is also desirable to provide
a method and system that is capable of being utilized to retrofit
existing gas turbine engines. In particular, it is of primary
importance to reduce the amounts of nitrogen oxides contained
within the emissions. Many times, reduced emissions comes at the
cost of decreased flame operability. The present invention provides
airflow to the pilot fuel line of a combustor in order to reduce
the total harmful emissions, yet at the same time allow improved
flame stability.
Inventors: |
Srinivasan, Ram; (Chandler,
AZ) |
Correspondence
Address: |
Honeywell International, Inc.
Law Dept. AB2
P.O. Box 2245
Morristown
NJ
07962-9806
US
|
Assignee: |
Honeywell International,
Inc.
Morristown
NJ
|
Family ID: |
21746446 |
Appl. No.: |
10/010594 |
Filed: |
December 5, 2001 |
Current U.S.
Class: |
60/776 ;
60/737 |
Current CPC
Class: |
F23R 3/36 20130101; F23R
3/286 20130101 |
Class at
Publication: |
60/776 ;
60/737 |
International
Class: |
F23R 003/30 |
Claims
We claim:
1. A method of combusting hydrocarbon fuel, comprising: injecting
an air stream into an air assist valve resulting in an air assist
valve air stream; allowing said air assist valve air stream and
pilot fuel to flow through a pilot fuel tube resulting in a pilot
fuel stream; allowing fuel to flow from a premix fuel line to a
premixer resulting in a premix fuel stream; combining said pilot
fuel stream, premix fuel stream, and an air stream resulting in a
mixture stream; igniting said mixture stream; and wherein a
temperature and composition of said mixture stream are selected to
control simultaneously the amounts of NO.sub.x formed in a main
combustor and a stability of a flame in said main combustor,
thereby controlling a total amount of NO.sub.x emitted.
2. The method as in claim 1, wherein said pilot fuel is in liquid
form.
3. The method as in claim 1, wherein said pilot fuel is in gaseous
form.
4. The method as in claim 1, further comprising expanding the
mixture stream across a turbine thereby producing power.
5. The method as in claim 1, wherein between 0-50 percent of the
total fuel is supplied through said pilot fuel line.
6. The method as in claim 1, wherein between 50-100 percent of the
total fuel is supplied through said premix fuel line.
7. The method as in claim 1, wherein said air assist valve air
stream is less than 10 times said pilot fuel stream.
8. The method as in claim 1, wherein said NO.sub.x emitted is below
9 parts per million.
9. The method as in claim 1, wherein said air stream is bleed air
from a gas turbines engine core compressor and injected into said
air assist valve resulting in an air assist valve air stream.
10. A system for combusting a hydrocarbon fuel, comprising: a
combustor having an upstream end and a downstream end; and a premix
area connected to the upstream end of said combustor for receiving
and substantially premixing fuel and air prior to delivery of said
upstream end of said combustor, said premix area comprising; a
centerbody extending longitudinally through said premix area; at
least one premix fueling pathway positioned radially around said
centerbody which receives premix fuel; at least one fueling pathway
positioned radially within said centerbody, which receives air
assisted pilot fuel and allows said air assisted pilot fuel to exit
through a pilot fuel outlet pathway; an igniter located within said
centerbody; and at least one pilot air pathway positioned radially
within said centerbody and allows said air to exit through a pilot
air outlet pathway.
11. The system as in claim 10, further comprising an air assist
line in communication with a pilot fuel.
12. The system as in claim 11, wherein said air assist line has a
check valve to prevent fuel entering a source of said air assist
line.
13. The system as in claim 11, wherein said air assist line air
flow is between 0 and 60 lb/hr.
14. The system as in claim 11, wherein said air assist line is in
communication with a bleed air valve from a core compressor.
15. The system as in claim 11, further comprising an air assist
pump.
16. A system for combusting a hydrocarbon fuel, comprising: a
combustor having an upstream end and a downstream end; a pilot fuel
line in communication with an air assist line, wherein fuel from
said pilot fuel line is injected with air from said air assist line
and allowed to flow through a pilot flow tube to a premix area; a
check valve controllably communicating with said air assist air
stream; a premix fuel line connected to said premix area, radially
located around a centerbody; said premix area is connected to the
upstream end of said combustor for receiving and substantially
premixing fuel from said pilot fuel tube and said premix fuel tube,
said premix area comprising; said centerbody extending
longitudinally through said premix area; a fueling pathway
positioned radially within said centerbody, which receives air
assisted pilot fuel; a pilot air pathway positioned radially within
said centerbody; and an igniter located centrally within said
centerbody.
17. The system as in claim 16, wherein 0-50 percent of the fuel is
supplied through said pilot fuel line.
18. The system as in claim 16, wherein 50-100 percent of the fuel
is supplied through said premix fuel line.
19. The system as in claim 16, further comprising a combustor liner
in communication with a heat shield, said heat shield in
communication with a combustor cap, wherein said heat shield is
interposed between said combustor liner and said combustor cap.
20. The system as in claim 16, wherein said air assist line air
flow is between 0 and 60 lb/hr.
21. The system as in claim 16, wherein said air assist line is in
communication with a bleed air valve from the compressor.
22. The system as in claim 16, further comprising an air assist
pump.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/251,902 filed Dec. 6, 2000 and
titled "EMISSIONS IMPROVEMENT IN GAS TURBINE COMBUSTORS."
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to generally to
industrial and power generation systems, and more particularly to a
method and system for modifying industrial and power generation
systems with reduced emissions and improved flame operability.
[0003] The conventional gas turbine combustor, as used in a gas
turbine power generating system, requires a mixture of fuel and air
which is ignited and combusted uniformly. Generally, the fuel
injected from a fuel nozzle into the inner tube of the combustor is
mixed with air for combustion, fed under pressure from the air
duct, ignited by a spark plug and combusted. The gas that results
is lowered to a predetermined turbine inlet temperature by the
addition of cooling air and dilutent air, then injected through a
turbine nozzle into a gas turbine.
[0004] It is well known within the art that exhaust gases produced
by combusting hydrocarbon fuels can contribute to atmospheric
pollution. This occurrence is attributed to the development of
localized high temperature zone, which can exceed 2,000.degree. C.
Exhaust gases typically contain many undesirable pollutants such as
nitric oxide (NO) and nitrogen dioxide (NO.sub.2), which are
frequently grouped together as Nitrogen Oxides (NO.sub.x), unburned
hydrocarbons (UHC), carbon monoxide (CO), and particulates,
primarily carbon soot.
[0005] It is also known that the amount of undesirable pollutants
can be reduced and controlled by design modifications, clean-up of
exhaust gases and/or regulating the quality of fuel. The formation
of oxides of nitrogen involves the direct oxidation of nitrogen and
oxygen, and the rate of the chemical reaction producing this
by-product is an exponential function of temperature which is
particularly dependant on the temperature in the main combustion
zone. Therefore, a small reduction in temperature within the main
combustion zone can result in a large reduction in the quantity of
oxides of nitrogen.
[0006] Gas turbine engines emit higher levels of Oxides of Nitrogen
(NO.sub.x) at high power operation. This is caused by high peak
flame temperatures existing in the combustion chamber. In most gas
turbine dry low NO.sub.x combustors, emissions are reduced by
premixing fuel and air. The fuel and air must be premixed to a very
lean mixture to reduce the peak flame temperature. Typically, the
amount of airflow required to reduce the NO.sub.x levels below 25
parts per million (ppm) is greater than 30 times the amount of fuel
flow. Combustors operating with such lean mixtures operate very
close to lean extinction limits and tend to have poor operability.
Frequently, a richer, piloted region in the combustor is used to
improve the operability of dry low emission combustors. In these
systems, most of the NOx emissions are produced in the pilot
region.
[0007] U.S. Pat. No. 5,303,542 issued to Hoffa discloses a method
of reducing emissions that maintains flame temperature within
predetermined limits by increasing the combustor airflow during
periods of increased fuel flow and by increasing the burner area
when the airflow has reached an upper limit. Increases in burner
area are countered by decreasing airflow until the airflow reaches
a lower limit, at which time the procedure repeats itself. When the
fuel flow is decreased, the airflow is reduced until it reaches its
lower limit, at which time the burner area is decreased, allowing
the airflow to rise to its upper limit, at which time, the
procedure repeats itself.
[0008] Accordingly, what is needed is a method and system for
combusting hydrocarbon fuels that allows for improved operability
and stability of the flame, while still providing reduced
emissions.
SUMMARY OF THE INVENTION
[0009] In one aspect of the present invention, a method of
combusting hydrocarbon fuel is disclosed comprising injecting an
air stream into an air assist valve resulting in an air assist
valve air stream; allowing the air assist valve air stream and
pilot fuel to flow through a pilot fuel tube resulting in a pilot
fuel-air mixture stream; allowing fuel to flow from a premix fuel
line to a premixer resulting in a premix fuel stream; combining the
pilot fuel stream, premix fuel stream and an air stream resulting
in a mixture stream; and igniting the mixture stream. The
temperature and composition of the mixture stream are selected to
control simultaneously the amounts of NO.sub.x formed in the main
combustor and the stability of the flame in the main combustor,
thereby controlling the total amount of NO.sub.x emitted.
[0010] According to another aspect of the invention, a system for
combusting a hydrocarbon fuel is disclosed comprising a combustor
having an upstream end and a downstream end; a premix area
connected to the upstream end of the combustor for receiving and
substantially premixing fuel and air prior to delivery to the
upstream end of the combustor. The premix area is comprised of a
centerbody extending longitudinally through the premix area, at
least one fueling pathway positioned radially within the
centerbody, which receives air assisted pilot fuel and allows the
air assisted pilot fuel to exit through a pilot fuel outlet
pathway, at least one premix fueling pathway positioned radially
within the centerbody which receives premix fuel, and at least one
pilot air pathway positioned radially within the centerbody and
allows air to exit through a pilot air outlet pathway. This system
may also include an air assist line in communication with the pilot
fuel. The air assist line may also have a check valve to prevent
fuel entering the source of the air assist line. The air assist
line may be in communication with a bleed air valve from the core
compressor.
[0011] According to an embodiment, a system for combusting a
hydrocarbon fuel is disclosed comprising a combustor having an
upstream end and a downstream end; a pilot fuel line in
communication with an air assist line, wherein fuel from the pilot
fuel line is injected with air from the air assist line and allowed
to flow through a pilot flow tube to a premix area. A check valve
is controllably in communication with the air assist air stream. A
premix fuel line is connected to the premix area and radially
located around a centerbody. The premix area is connected to the
upstream end of a combustor and receives and premixes fuel from the
pilot fuel tube and premix fuel tube. The premix area is comprised
of a centerbody extending longitudinally through the premix area; a
fueling pathway is positioned radially within the centerbody and
receives air assisted pilot fuel. A pilot air pathway is positioned
radially within the centerbody. The system also comprises an
igniter located centrally within the centerbody.
[0012] The fuel supplied to the combustor may be varied between the
premix fuel line and the pilot fuel tube. According to an
embodiment, about 0-50 percent of the fuel is supplied through the
pilot fuel line and about 50-100 percent of the fuel is supplied
through the premix fuel line. Preferably, less than twenty percent
(20%) of the fuel may be supplied through the pilot fuel line and
greater than eighty percent (80%) supplied through the premix fuel
line.
[0013] The system may also have a combustor liner in communication
with a heat shield. The heat shield may also be in communication
with a combustor cap, wherein the heat shield is interposed between
the combustor liner and combustor cap.
[0014] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following drawings, description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross-section of a natural gas combustor that
uses one embodiment of the present invention;
[0016] FIG. 2 is a cut-away view of the natural gas combustor of
FIG. 1;
[0017] FIG. 3 is a perspective view of the natural gas combustor of
FIG. 1;
[0018] FIG. 4 is a schematic diagram showing the aerodynamic effect
of air assist; and
[0019] FIG. 5 is a plot of test data showing improved emissions
achieved with the use of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The following detailed description is of the best currently
contemplated modes of carrying out the invention. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention,
since the scope of the invention is best defined by the appended
claims.
[0021] The present invention generally provides an easily adaptable
method and system that is capable of retrofitting industrial and
power generation systems to reduce emissions while providing
improved operability. The present invention allows for minimized
air flow to achieve reduced No.sub.x emissions without increasing
CO emissions.
[0022] While the prior art typically utilizes a mixture of fuel and
air to a lean mixture to reduce the peak flame temperature, this
results in lean premixed combustors operating very close to the
lean extinction limits and tend to have poor operability.
Frequently, a richer, piloted region in the combustor is used to
improve operability, but this often comes at the cost of increased
emissions. The present invention allow for reduced emissions and
improved operability.
[0023] For the purposes of promoting an understanding of the
principles of the invention, reference is made to the embodiments
illustrated in the drawings and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations and further modifications in the illustrated device,
and such further applications of the principles of the invention as
illustrated therein being contemplated as would normally occur to
one skilled in the art to which the invention relates.
[0024] The system may be an add-on feature to current generation
combustors allowing for generation combustors to be retrofitted in
a manner that will reduce emissions. The system may utilize an air
assist injected into the pilot fuel line. An embodiment according
to the present invention is depicted in FIG. 1. Air is injected
through an air assist 10. The air assist valve air stream is less
than 10 times the pilot fuel stream which can flow through a pilot
fuel line 14. The air assist valve air stream may be injected by
several methods. These may include, without limitation, the use of
bleed air from the gas turbine engine core compressor and/or the
use of an air assist pump. An air assist pump may be required, such
as when bleed air from the core compressor is used. The need for an
air assist pump depends upon the required fuel pressure, and the
pressure loss in the recuperator (which is bypassed by the bleed
air). As would be understood by those of skill in the art, an
external air pump could be used to supply all the air-assist 10
valve air stream without using any core compressor bleed air. The
air injection can be turned on when emission reduction is needed
and turned off at other operating conditions.
[0025] A pilot fuel tube 12 can require a tee to the existing pilot
fuel line 14. The air assist line 10 can be attached to the tee.
According to an alternate embodiment, a small mixing chamber with
connections from pilot fuel and air assist source is used. The air
assist line may have a check valve to prevent fuel entering the
source of air assist 10. Air assisted fuel can be led through the
pilot fuel tube 12 to an upstream end of a combustor 27. Another
fuel line, a premix fuel line 20, may allow fuel to flow to an area
within a premix area 22, but outside of a centerbody 23. The premix
area 22 can be contained within the upstream end of the combustor
27. The centerbody 23 may extend longitudinally through or within
the premix area 22.
[0026] A combustor cap may contain premixer area 22 and centerbody
23 at the upstream end of the combustor 27. A pilot air outlet
pathway 21 may be positioned radially within the centerbody 23 and
receive pilot air, and may allow pilot air to exit through the
pilot air outlet pathway 21.
[0027] A fueling pathway 24 can receive fuel from the pilot fuel
tube 12 and allow air to exit through the pilot fuel outlet 25. An
igniter 18 can create a flame and burn the product from the pilot
air outlet pathway 21 and the pilot fuel outlet pathway 25. The
resulting mixture stream can enter the combustor 27 which may be
encased by a combustor liner 28, and surrounded by a heat shield
30.
[0028] FIG. 2 depicts a cut-away view of the natural gas combustor
of FIG. 1. As shown, the combustor liner 28 allows for the receipt
of the mixture stream and radially surrounds the heat shield 30.
The premix area 22 can be contained in the upstream end of the
combustor and is upstream from the combustor liner 28. The
centerbody 23 may also be located in the upstream end of the
combustor and can contain the pilot air pathway 16 which can
surround the fueling pathway 24. Fuel from the pilot fuel tube 12
may be introduced into the premix area 22 through the fueling
pathway 24 and allowed to exit through the pilot fuel outlet
pathway 21. Fuel from the premix fuel line 20 may be introduced
into the premix area 22, but not within the centerbody 23. The
igniter, not shown, may placably fit within the igniter pathway 19
contained within the centerbody 23.
[0029] FIG. 3 depicts a perspective view of the natural gas
combustor of FIG. 1. As shown, the combustor line 28 may be
radially surrounded by the heat shield 30. The heat shield can be
in communication with the premix area 22, which is surrounded by
the combustor cap 26. The premix fuel line 20 can be in
communication with the premix area 22. The pilot fuel line 14 can
be in communication with the premix area 22.
[0030] FIG. 4 depicts the effect of the present invention on flame
location and shape. As shown, the mixture stream may be ignited by
the igniter 18, and the NOx production zone that results as in the
present invention creates a smaller and leaner zone, Air assist NOx
production Zone 32. Previously, a larger and richer NOx production
zone resulted, as shown by the non-air assist NOx Production Zone
34. The Air assist NOx production zone is also located farther away
from the pilot fuel injectors, which can be used to reduce acoustic
emissions.
EXAMPLES
[0031] FIG. 5 depicts the effect of air assist as measured in a
Parallon 75 microturbine power generation system using the
configuration depicted in FIG. 1. Gaseous emissions were measured
at full load conditions. The combustor was operated with twenty
percent (20%) of the fuel supplied through the pilot and the
remaining eighty percent (80%) through the premixer. Metered air
assist flow was varied from about zero to 40 lb/hr flow rate. As
depicted, the NO.sub.x emissions at 0 pph air assist flow was
measured to be about 25 ppm. As the air assist flow was increased
to about 40 pph, the NO.sub.x emissions were reduced to about 6
ppm, without increasing Carbon Monoxide (CO) emissions. Further
reduction in NOx emissions have been observed by reducing the pilot
fuel flow split and/or by increasing the air assist flow.
[0032] It should be understood, of course, that the foregoing
relates to preferred embodiments of the invention and that
modifications may be made without departing from the spirit and
scope of the invention as set forth in the following claims.
* * * * *