U.S. patent application number 09/953022 was filed with the patent office on 2002-06-20 for method and apparatus for compressing gaseous fuel in a turbine engine.
This patent application is currently assigned to Capstone Turbine Corporation. Invention is credited to Mackay, Robin.
Application Number | 20020073713 09/953022 |
Document ID | / |
Family ID | 23666716 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020073713 |
Kind Code |
A1 |
Mackay, Robin |
June 20, 2002 |
Method and apparatus for compressing gaseous fuel in a turbine
engine
Abstract
A gas turbine engine includes a rotatable impeller having a
plurality of vanes with inlet and outlet ends. A plurality of
diffuser channels are spaced apart radially beyond the outlet ends.
A movable source of gaseous fuel is positioned adjacent the inlet
ends of the vanes. The movable source of gaseous fuel is movable as
a function of the rotational speed of the impeller, whereby the
flow of gaseous fuel injected from the movable source is ejected
from the outlet ends of the vanes into a selected one of the
plurality of diffuser channels to facilitate combustion.
Inventors: |
Mackay, Robin; (Rancho Palos
Verdes, CA) |
Correspondence
Address: |
Rachele Wittwer
IRELL & MANELLA LLP
Suite 900
1800 Avenue of the Stars
Los Angeles
CA
90067
US
|
Assignee: |
Capstone Turbine
Corporation
|
Family ID: |
23666716 |
Appl. No.: |
09/953022 |
Filed: |
September 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09953022 |
Sep 13, 2001 |
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09772537 |
Jan 29, 2001 |
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09772537 |
Jan 29, 2001 |
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09420494 |
Oct 19, 1999 |
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Current U.S.
Class: |
60/776 ;
60/734 |
Current CPC
Class: |
F02C 7/2365 20130101;
F02C 3/22 20130101 |
Class at
Publication: |
60/776 ;
60/734 |
International
Class: |
F02C 007/22 |
Claims
What is claimed is:
1. A gas turbine engine comprising: a rotatable impeller having a
plurality of vanes with inlet and outlet ends; a plurality of
diffuser channels spaced apart radially beyond said outlet ends; a
movable source of gaseous fuel positioned adjacent said inlet ends
of said vanes for injecting gaseous fuel into the inlet ends so
that the fuel will be compressed with air in the impeller and
ejected into a selected one of said plurality of diffuser channels;
wherein said movable source of gaseous fuel is movable as a
function of the rotational speed of the impeller, whereby the flow
of gaseous fuel injected from said movable source is always
directed into said selected one of the plurality of diffuser
channels to facilitate combustion.
2. The gas turbine engine of claim 1, wherein said movable source
of gaseous fuel comprises a movable source of natural gas.
3. The gas turbine engine of claim 1, further comprising a cylinder
having a movable piston connected to said movable source, said
cylinder being in fluid communication with said outlet ends to
receive compressed impeller exhaust to move said movable piston,
thereby adjusting the position of the movable source based upon
exhaust pressure of the rotating impeller.
4. The gas turbine engine of claim 1, further comprising a
servomotor operatively connected with said movable source for
moving said movable source.
5. A method of compressing gaseous fuel in a gas turbine engine
comprising: a) rotating an impeller about an impeller axis of the
gas turbine engine, wherein the impeller includes inlet and outlet
portions at opposing ends of a plurality of vanes; b) injecting
gaseous fuel from a movable source of gaseous fuel into said inlet
portions such that the fuel travels along said vanes and through
the respective outlet portions to a selected one of a plurality of
diffuser channels spaced apart radially beyond said outlet
portions; and c) adjusting the position of said movable source with
respect to the impeller axis based upon the rotational speed of the
impeller to ensure that the injected gaseous fuel enters said
selected one of the diffuser channels as the rotational speed of
the impeller is varied.
6. The method of claim 5, wherein said adjusting step comprises
rotating the movable source about said impeller axis.
7. The method of claim 5, wherein said adjusting step comprises
receiving pressurized air from the impeller in a cylinder having a
piston connected to the movable source, thereby moving the movable
source in response to exhaust pressure changes of the impeller.
8. The method of claim 5, wherein said injecting step comprises
injecting natural gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and apparatus for
compressing gaseous fuel in the rotatable impeller of a gas turbine
engine.
BACKGROUND ART
[0002] A typical gas turbine engine includes a power section, a
gear box, and various accessories such as a starter, fuel control,
lubrication system, etc. The power section includes a centrifugal
compressor, an axial turbine, and a combustor. The compressor and
turbine sections of the engine can rotate at speeds as high as
100,000 rpms. Air is compressed in the compressor to about 10.6
atmospheres, for example, before it goes to the combustor. The
combustor is split into two zones. At full load, the primary
combustion chamber operates at fairly close to stoichiometric, the
ideal fuel/air ratio. All of the fuel, and approximately 1/4 of the
air, start to burn in this zone. The remaining 3/4 of the air
enters the secondary combustion zone through holes in the burner
liner. This air provides a relatively cool blanket between the
burning gases and the liner before it mixes. This serves to keep
the liner cool. It also dilutes the temperature of the hot gases
down to the point where the turbine nozzles and wheels will have a
long life.
[0003] Accordingly, in the combustor, the fuel is burned, which
heats the air, which then expands through the turbine wheels. The
turbine wheels drive the compressors and, through the reduction
gear box, the generator.
[0004] It is sometimes desirable to use natural gas rather than
diesel fuel in a gas turbine engine because natural gas is
generally less expensive, requires no storage tank, burns cleaner,
produces significantly less NO.sub.x, and provides higher
efficiency and more power than diesel fuel.
[0005] A major problem with the use of natural gas is that it must
be compressed enough to enter the combustor, and known gas
compressors are very expensive and require significant energy to
run. A typical compressor for a two turbine installation costs
between $40,000 and $65,000 and requires 25 to 50 kilowatts to run
it, depending upon the input pressure. Most of the compressors
available are screw-type or reciprocating compressors. They are
generally equipped with gas coolers, oil separators, and
accumulators.
[0006] Due to the high cost of add-on gas compressors, it is
desirable to provide a method and apparatus for compressing the gas
in a manner which eliminates the add-on gas compressor, while
maintaining the required concentration of natural gas in the
mixture which is injected into the primary zone of the
combustor.
DISCLOSURE OF INVENTION
[0007] The present invention overcomes the above-referenced
shortcomings of prior art gas compressors by providing a gas
compressor which is integral with the gas turbine engine. The
gaseous fuel is injected into the rotatable impeller (i.e., the
compressor) of the engine, and is ejected from the impeller into a
selected one of a plurality of diffuser channels positioned
peripherally about the impeller. The gas is then directed from the
selected diffuser channel(s) to the primary zone of the combustor.
The source of gaseous fuel is movable in order to adjust the
position at which the gaseous fuel is injected into the impeller so
that the fuel is always directed into the selected diffuser
channel(s).
[0008] More specifically, the present invention provides a gas
turbine engine including a rotatable impeller having a plurality of
vanes with inlet and outlet ends. A plurality of diffuser channels
are spaced apart radially beyond the outlet ends. A movable source
of gaseous fuel is positioned adjacent the inlet ends of the vanes
for injecting gas into the impeller at a position from which the
impeller ejects an air/gas mixture from the outlet ends into a
selected one of a plurality of diffuser channels. The movable
source of gaseous fuel is movable as a function of the rotational
speed of the impeller, whereby the flow of gaseous fuel injected
from the movable source is always directed into the selected
diffuser channel to facilitate combustion. The fuel from the
selected diffuser channel is directed to the primary zone of the
combustor so that the appropriate concentration of fuel is
maintained for burning in the combustor.
[0009] This invention is useful for a variety of gaseous fuel,
including natural gas, vaporized propane, vaporized butane,
etc.
[0010] A further aspect of the invention provides a method of
compressing gaseous fuel in a gas turbine engine comprising: a)
rotating an impeller about an impeller axis of the gas turbine
engine, wherein the impeller includes inlet and outlet portions at
opposing ends of a plurality of vanes; b) injecting gaseous fuel
from a movable source of gaseous fuel into the inlet portions such
that the fuel travels along the vanes and through the respective
outlet portions to a selected one of a plurality of diffuser
channels spaced apart radially beyond the outlet portions; and c)
adjusting the position of the movable source with respect to the
impeller axis based upon the rotational speed of the impeller to
ensure that the injected gaseous fuel enters the selected one of
the diffuser channels as the rotational speed of the impeller is
varied. The gaseous fuel is then directed from the selected
diffuser channel to the primary zone of the combustor for
burning.
[0011] The adjustment of the movable source may be accomplished by
capturing pressurized air exhausted from the impeller and using the
compressed air to move a piston connected to the movable source, or
electronically by a servomotor.
[0012] Accordingly, an object of the present invention is to
provide a method and apparatus for compressing gaseous fuel for use
in a gas turbine engine in a manner in which the add-on gas
compressor is eliminated.
[0013] The above object and other objects, features, and advantages
of the present invention are readily apparent from the following
detailed description of the best modes for carrying out the
invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 shows a partial vertical cross-sectional view of a
compressor for use with the present invention;
[0015] FIG. 2 shows a cross-sectional view of the compressor of
FIG. 1 rotated 90.degree.;
[0016] FIG. 3 shows a schematic plan view of a compress in
accordance with the present invention; and
[0017] FIG. 4 shows a schematically arranged side view of a
compressor assembly in accordance with an alternative embodiment of
the invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0018] Referring to FIGS. 1 and 2, a compressor 10 is shown for use
with the present invention. The compressor 10 includes an impeller
12 which is rotatable about an impeller axis 14, and a compressor
body 16 which forms a plurality of diffuser channels 18, 20, 22
spaced apart radially beyond the periphery 24 of the impeller
12.
[0019] The impeller 12 includes a plurality of impeller vane 26,
each of which includes inlet and outlet ends 28, 30,
respectively.
[0020] If the impeller 12 were not turning but still had air
flowing through it, the air entering at point A would discharge at
point B and enter diffuser channel C. However, the impeller 12
would be rotating in operation, and as it turns slowly the exit
compressor discharge will be at point D and the air will enter
diffuser channel E (reference number 22). As it turns faster, the
diffuser channel through which the air enters will move further
around. At any given speed and temperature, all of the air entering
the compressor at point A will go into one or two specific diffuser
channels. If a diffuser channel is in the correct position, the air
should enter just that one diffuser channel.
[0021] The subject of this invention is to direct gaseous fuel into
the inlet end 28 of the impeller and to direct the resulting
air/fuel mixture, once it has been compressed by the impeller 12,
into the selected diffuser channel 18, 20, 22 so that the
compressed air/fuel mixture may be properly directed to the primary
zone of the combustor for burning,
[0022] If a pipe is added at point A. which discharges natural gas,
this gas would be entrained into the air and compressed along with
the air and discharged into a specific diffuser channel 18, 20, 22.
If the diffuser has thirteen channels, {fraction (1/13)}th of the
air would be in that channel, less the amount of air displaced by
the natural gas. If the overall air/fuel ratio is roughly 135:1,
the air/fuel ratio in the selected diffuser channel would be
approximately 10:1. Thus, for a lean premix combustor, more air
will have to be added to the mixture. This air can be added either
before or after the recuperator. This mixture would then be ducted
directly to the primary zone of the combustor. The air from the
other twelve diffuser passages would go through the recuperator and
then be used as dilution air in the secondary zone of the
combustor.
[0023] The diffuser channel 18, 20, 22 through which the air/fuel
mixture exits will be determined by the velocity and temperature of
the mixture and the speed of rotation of the compressor. To some
extent, this is self-compensating. The faster the compressor turns,
the faster the speed of the fluid going through it. However, this
is probably inadequate to ensure that all of the fuel/air mixture
goes into the same diffuser channel. One solution is to rotate the
diffuser to a new and appropriate position as the speed of the
compressor changes. This would pose a challenge for the ducting
plus a significant mechanical complication.
[0024] A better solution is to mount the natural gas inlet nozzle
on a ring that rotates as the speed of the compressor changes. This
could be done with a servomotor which determines its position from
the frequency of the generator, which is directly related to the
speed of the compressor. A less expensive solution is to have a
small piston in a cylinder. Compressor discharge air is fed into
the cylinder and the piston rotates the ring. As the compressor
speeds up, the compressor discharge pressure increases, thus
rotating the ring and the position through which the natural gas
enters. Then, the fuel/air mixture always exits into the same
diffuser channel. A position sensor matched against the generator
frequency could provide a check on whether or not the pneumatic
actuation system was working. Additionally, ambient temperature and
compressor compensation may be needed, depending upon the
application.
[0025] Because the fuel/air mixture does not pass through the
recuperator, it will not experience the pressure drop in the
recuperator which the remaining gas experiences. This will permit
it to flow more easily into the combustor. This may be crucial as
the molecular weight of the fuel/air mixture is less than that of
air and the compressor discharge pressure of the fuel/air mixture
may be slightly lower than that of the diffuser channels
discharging air alone.
[0026] A secondary consideration is that if the fuel/air mixture
does not go through the recuperator, the efficiency of the gas
turbine will be lower as only {fraction (12/13)}ths of the air will
be recuperated. However, there is some compensation as the
temperature rise of the air which does go through the recuperator
will be higher because of the reduced mass flow. In addition, lower
temperature combustion air could also lead to lower NO.sub.x,
output. Furthermore, the passages through the recuperator are well
defined and discrete, therefore it might be possible to route the
fuel/air mixture through the recuperator and keep it
segregated.
[0027] Embodiments of the invention are illustrated schematically
in FIGS. 3 and 4. Referring to FIG. 3, the compressor assembly 10
includes a fuel ring 32 with a movable source 34 of natural gas 36
connected to the ring 32. If the compressor 10 was stationary but
still had air flowing through it, then air entering through inlet
passage A would discharge out through the two passages located a
A'. There are two outlet passages because a splitter blade starts
part-way through the passage. The outlet positions are offset from
the inlet because the blades are curved. Correspondingly, air
entering through inlet passage B would discharge out through the
two passages located at B', and so on.
[0028] However, the compressor will be spinning. Therefore, air
entering at inlet A will turn with the compressor rotation and
might exit at outlet positions I', H',G', or F'.
[0029] Assume that the compressor is turning at a speed in which
the air entering through inlet passage A when inlet passage A is at
the top is discharged at outlet positions G'. If natural gas at
very low pressure is injected correctly in front of inlet passage
A, it will mix with the air entering at inlet passage A and the
resulting mixture should be compressed and discharged at outlet
positions G as well. As the compressor turns, inlet passage A moves
away from the natural gas nozzle which now discharges into inlet
passage B as it is now at the top. However, it still discharges at
outlet positions G' as that location is fixed. Thus, a series of
inlet passages rotate in front of the fuel nozzle but the fuel/air
mixture discharges at outlet positions G'.
[0030] With a multi-passage diffuser, the inlet to one diffuser
passage is located at outlet positions G'. The fuel/air mixture now
goes through a discrete passage in the multi-passage diffuser and
is taken to the primary zone of the combustor 33. If necessary, it
may then be diluted with air from the other passages.
[0031] When the compressor speed changes, the amount of rotation
changes and the natural gas/air mixture no longer discharges
through the same diffuser passage.
[0032] The invention contemplates rotating the fuel nozzle 34 as
the compressor speed changes. The bell mouth shroud on the
compressor inlet can be sectioned into an inner shroud 48 and an
outer shroud 50 (as described below with reference to FIG. 4) with
the fuel ring 32 containing the fuel nozzle mounted in between.
This ring 32 can then be rotated backward with respect to the
compressor rotation as the speed of the compressor increases. Then
the natural gas/air mixture will always discharge into the same
diffuser passage regardless of compressor speed.
[0033] The fuel ring can be mounted in a variety of ways including
anti-friction bearings, etc. It can be actuated using a cylinder 40
which is charged by captured discharge from the compressor at 42,
which causes movement of the piston 44. The piston 44 is connected
to the rotatable ring 32 and movable therewith, thereby allowing
adjustment of the position of the source 34 of natural gas 36. The
captured discharge at 42 will have a higher pressure with increased
speed of rotation, therefore pressure in the cylinder 40 will
increase and the piston 44 will move a greater amount at higher
speeds, thus rotating the ring 32 and source 34 as the speed
changes.
[0034] An alternative embodiment is shown in FIG. 4 wherein the
ring 32 is adjusted by a servomotor 46, which is operatively
connected to the ring 32, which is positioned between the outer
shroud 48 and inner shroud 50. The speed of the impeller 12 is
sensed, and the servomotor 46 adjusts the rotational position of
the ring 32 and movable source 34 based upon the sensed speed.
[0035] The concept would be improved if the impeller did not have
splitter blades which reduce the area into which the fuel/air
mixture discharges.
[0036] This concept offers several advantages. The hardware is much
simpler and lower cost than a separate compressor. It is far more
efficient than any of the fuel/gas compressors currently known. It
can probably even be used with low BTU gases without significant
energy consumption. It is much more compact than a separate gas
compressor, and the required maintenance should be minimal.
[0037] While the best modes for carrying out the invention have
been described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention within the scope of the
appended claims.
* * * * *