U.S. patent application number 10/355145 was filed with the patent office on 2004-08-05 for method for catalytic combustion in a gas- turbine engine, and applications thereof.
This patent application is currently assigned to Capstone Turbine Corporation. Invention is credited to Hamrin, Douglas A., Pont, Guillermo, Rouse, Gregory C..
Application Number | 20040148942 10/355145 |
Document ID | / |
Family ID | 32770476 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040148942 |
Kind Code |
A1 |
Pont, Guillermo ; et
al. |
August 5, 2004 |
Method for catalytic combustion in a gas- turbine engine, and
applications thereof
Abstract
The present invention provides a method for sustained catalytic
combustion of low BTU fuels in a gas-turbine engine, and
applications thereof. The method comprises ingesting fuel and
combustion air into a catalytic reactor to produce thermal energy
and converting the thermal energy to mechanical energy with a
turbine. The fuel and the combustion air are mixed to form a
fuel-air mixture. The ingested combustion air is used to oxidize
the ingested fuel. Fuels having a higher heating value in a range
of between 1000 and 5 BTU/scf are mixed with the combustion air and
oxidized using the catalytic reactor.
Inventors: |
Pont, Guillermo; (Los
Angeles, CA) ; Hamrin, Douglas A.; (Studio City,
CA) ; Rouse, Gregory C.; (Westlake Village,
CA) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Capstone Turbine
Corporation
|
Family ID: |
32770476 |
Appl. No.: |
10/355145 |
Filed: |
January 31, 2003 |
Current U.S.
Class: |
60/777 ;
60/723 |
Current CPC
Class: |
Y02E 20/348 20130101;
F23L 15/04 20130101; Y02T 50/60 20130101; F23R 3/40 20130101; Y02E
20/34 20130101; F02C 9/28 20130101; F23N 1/02 20130101; F23R
2900/00002 20130101; F23N 5/003 20130101; F23N 2223/04 20200101;
F23N 2223/08 20200101; Y02T 50/677 20130101; F23N 2241/20
20200101 |
Class at
Publication: |
060/777 ;
060/723 |
International
Class: |
F23R 003/40 |
Claims
What is claimed is:
1. A method for catalytic combustion, comprising: ingesting fuel
and combustion air in a catalytic reactor, the amount of the
ingested combustion air being sufficient to substantially fully
oxidize the ingested fuel; oxidizing substantially all of the
ingested fuel with the catalytic reactor to produce thermal energy;
and converting at least a portion of the thermal energy to
mechanical energy with a turbine.
2. The method of claim 1, further comprising: prior to said
ingesting step, mixing the ingested fuel and the ingested
combustion air to form a fuel-air mixture having a
substantially-predetermined fuel-air ratio.
3. The method of claim 2, wherein said mixing step comprises mixing
fuel having a higher heating value of less than 750 BTU/scf.
4. The method of claim 2, wherein said mixing step comprises mixing
fuel having a higher heating value of less than 100 BTU/scf.
5. The method of claim 2, wherein said mixing step comprises mixing
fuel having a higher heating value of less than 30 BTU/scf.
6. The method of claim 2, further comprising: increasing the
pressure of the fuel-air mixture.
7. The method of claim 2, further comprising: prior to said mixing
step, increasing the pressure of the fuel.
8. The method of claim 2, further comprising: prior to said
oxidizing step, transferring energy to the fuel-air mixture to
increase the temperature of the fuel-air mixture.
9. The method of claim 8, wherein said transferring step comprises
transferring thermal energy from turbine exhaust gasses to the
fuel-air mixture.
10. The method of claim 9, wherein said transferring step further
comprises heating the turbine exhaust gasses with a pre-heater
disposed downstream of the turbine.
11. The method of claim 9, wherein said transferring step further
comprises heating the turbine exhaust gasses with an electrical
heating element disposed downstream of the turbine.
12. The method of claim 9, wherein said transferring step further
comprises oxidizing a fuel injected into the turbine exhaust gasses
to heat the turbine exhaust gasses.
13. The method of claim 1, further comprising: prior to said
ingesting step, mixing the ingested fuel and the ingested
combustion air so as to prevent no more than an insubstantial
amount of fuel from entering a bleed air flow streamline.
14. The method of claim 13, further comprising: reducing unburned
fuel in bleed air extracted from the bleed air flow streamline
prior to exhausting the bleed air to the environment.
15. The method of claim 14, wherein said reducing step comprises:
oxidizing unburned fuel with a catalyst.
16. The method of claim 14, wherein said reducing step comprises:
recirculating bleed air so that it mixes with the ingested fuel and
the ingested combustion air.
17. The method of claim 2, further comprising: adjusting a rate of
fuel supply to control the fuel-air ratio.
18. The method of claim 2, further comprising: adjusting a rate of
combustion air supply to control the fuel-air ratio.
19. The system of claim 2, further comprising: adjusting a rate of
fuel supply to control the operating temperature of the catalytic
reactor.
20. The system of claim 2, further comprising: adjusting turbine
speed to control the operating temperature of the catalytic
reactor.
21. The method of claim 2, further comprising: obtaining data
related to the functionality of the catalytic reactor; and storing
the data in a memory.
22. The method of claim 21, wherein the data includes information
about the total operating time of the catalytic reactor.
23. The method of claim 21, wherein the data includes information
about a temperature rise time following a change in the fuel-air
mixture being oxidized by the catalytic reactor.
24. The method of claim 23, further comprising: performing a
diagnostic test to obtain the data.
25. The method of claim 21, wherein the data includes information
about unburned hydrocarbon levels in exhaust gasses from the
catalytic reactor.
26. A method for catalytic combustion, comprising: mixing fuel and
combustion air to form a fuel-air mixture having a
substantially-predetermined fuel-air ratio, the amount of
combustion air mixed with the fuel being sufficient to
substantially fully oxidize the fuel; transferring energy to the
fuel-air mixture to increase the temperature of the fuel-air
mixture; ingesting at least a portion of the fuel-air mixture in a
catalytic reactor; oxidizing substantially all of the ingested
fuel-air mixture with the catalytic reactor to produce thermal
energy; and converting at least a portion of the thermal energy to
mechanical energy with a variable speed turbine.
27. The method of claim 26, wherein said mixing step comprises
mixing fuel having a higher heating value of less than 750
BTU/scf.
28. The method of claim 26, wherein said mixing step comprises
mixing fuel having a higher heating value of less than 100
BTU/scf.
29. The method of claim 26, wherein said mixing step comprises
mixing fuel having a higher heating value of less than 30
BTU/scf.
30. The method of claim 26, further comprising: prior to said
mixing step, increasing the pressure of the fuel.
31. The method of claim 26, wherein said transferring step
comprises transferring thermal energy from turbine exhaust gasses
to the fuel-air mixture.
32. The method of claim 31, wherein said transferring step further
comprises heating the turbine exhaust gasses with a pre-heater
disposed downstream of the turbine.
33. The method of claim 26, wherein said mixing step comprises:
mixing the fuel and the combustion air so as to prevent no more
than an insubstantial amount of fuel from entering a bleed air flow
streamline.
34. The method of claim 33, further comprising: reducing unburned
fuel in bleed air extracted from the bleed air flow streamline
prior to exhausting the bleed air to the environment.
35. The method of claim 34, wherein said reducing step comprises:
oxidizing unburned fuel with a catalyst.
36. The method of claim 26, further comprising: adjusting the rate
of fuel supply to control the fuel-air ratio.
37. The method of claim 26, further comprising: adjusting the rate
of combustion air supply to control the fuel-air ratio.
38. The system of claim 26, further comprising: adjusting the rate
of fuel supply to control an operating temperature of the catalytic
reactor.
39. The system of claim 26, further comprising: adjusting turbine
speed to control an operating temperature of the catalytic
reactor.
40. The method of claim 26, further comprising: performing a
diagnostic test to obtain data about the functionality of the
catalytic reactor; and storing the data in a memory.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for sustained
catalytic combustion of low BTU fuels in a gas-turbine engine, and
applications thereof.
BACKGROUND OF THE INVENTION
[0002] A gas-turbine engine converts fuel and air into thermal and
mechanical energy. In the electric power industry, for example,
this mechanical energy is used to power an electric generator and
produce electricity.
[0003] Conventional gas-turbine engines have limitations. Among
others, these limitations include an inability to operate using low
BTU fuels and the production of unwanted emissions. Complex fuel
delivery systems, combustion systems, and emission control systems
have been developed for the conventional gas-turbine engines in an
attempt to overcome these limitations. These systems are expensive,
and they do not completely compensate for the limitations.
[0004] What is needed is a gas-turbine engine that does not have
all of the limitations of the conventional gas-turbine engines.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention provides a method for sustained
catalytic combustion of fuels in a gas-turbine engine, and
applications thereof. The method comprises ingesting fuel and
combustion air into a catalytic reactor to produce thermal energy
and converting the thermal energy to mechanical energy with a
turbine.
[0006] In accordance with the invention, fuel and combustion air
are mixed to form a fuel-air mixture. The amount of combustion air
mixed with the fuel is sufficient to substantially fully oxidize
the fuel. Energy is transferred to the fuel-air mixture to increase
a temperature of the mixture prior to ingestion and oxidation by
the catalytic reactor. This is done so that the fuel-air mixture is
above a minimum operating temperature of the catalytic reactor when
it is ingested. The catalytic reactor oxidizes substantially all of
the ingested fuel and produces thermal energy. Exhaust gasses from
the catalytic reactor expand across a turbine. This causes the
turbine to rotate and thereby convert thermal energy to mechanical
energy.
[0007] As noted above, fuel and combustion air are mixed together
to form a fuel-air mixture that is ingested and oxidized by the
catalytic reactor. In an embodiment, a fuel having a higher heating
value in a range of between 1000 and 100 BTU/scf is mixed with
combustion air. In another embodiment, a fuel having a higher
heating value in a range of between 100 and 15 BTU/scf is mixed
with combustion air. In still another embodiment, a fuel having a
higher heating value in a range of between 30 and 5 BTU/scf is
mixed with combustion air. These ranges are by way of example only.
In other embodiments, fuels having different higher heating values
are mixed with combustion air. As used herein, the term "heating
value" means the amount of energy released when a fuel is burned
completely in a steady-flow process and the products are returned
to the state of the reactants. The actual "heating value" obtained
is dependent on the phase of the H.sub.2O (water/steam) in the
combustion products. If the H.sub.2O is in liquid form, the heating
value obtained is called "higher heating value" (HHV). If the
H.sub.2O is in vapor form, the heating value obtained is called
"lower heating value" (LHV).
[0008] In certain embodiments of the invention, fuel may be
injected into the low-pressure inlet of a compressor, rather than
downstream of the compressor. This eliminates the need for complex
or high-pressure fuel delivery systems having fuel gas compression.
A fuel mixer mixes the fuel with combustion air to form the
fuel-air mixture. It is a feature of the present invention that the
fuel can be mixed with combustion air so as to minimize the amount
of fuel present in any bleed air drawn from the compressor. In
certain embodiments, the concentration of any unburned fuel in the
bleed air is reduced prior to being exhausted to the environment.
This is achieved, for example, by oxidizing any unburned fuel with
a catalyst.
[0009] It is a feature of the invention that the energy for
increasing the temperature of the fuel-air mixture may be
transferred thermal energy, for example, from hot turbine exhaust
gasses, from an electrical heating element, or from a flame. A
recuperator fluidly coupled to the turbine may be used, for
example, for transferring heat from hot exhaust gasses to the
fuel-air mixture prior to oxidation by the catalytic reactor.
[0010] It is also a feature of the present invention that a desired
operating temperature can be obtained by adjusting fuel
concentration and/or rate of oxidation. This is achieved, for
example, by controlling a fuel supply rate to maintain a desired
fuel concentration, by controlling a combustion air supply rate to
maintain the desired fuel concentration, and/or by adjusting
turbine speed to control a rate of oxidation.
[0011] In certain embodiments, data related to the functionality of
the catalytic reactor is stored and used for diagnostics. This
stored data can include, for example, information about the total
operating time of the catalytic reactor, information about
temperature rise time following a change in the fuel-air mixture
being oxidized by the catalytic reactor, and/or information about
changes in unburned hydrocarbon levels. A diagnostic test can be
performed to obtain the data.
[0012] Further embodiments, features, and advantages of the present
invention, as well as the structure and operation of the various
embodiments of the present invention are described in detail below
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention is described with reference to the
accompanying figures. In the figures, like reference numbers
indicate identical or functionally similar elements. Additionally,
the left-most digit or digits of a reference number identify the
figure in which the reference number first appears. The
accompanying figures, which are incorporated herein and form part
of the specification, illustrate the present invention and,
together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
relevant art to make and use the invention.
[0014] FIG. 1 is a block diagram of a catalytic combustion system
employed with the invention.
[0015] FIG. 2 is a block diagram of a gas-turbine engine.
[0016] FIG. 3 is a more detailed block diagram of a catalytic
combustion system.
[0017] FIG. 4 illustrates a gas-turbine engine.
[0018] FIGS. 5A-B illustrate a cross-section of a compressor and a
mixing zone.
[0019] FIG. 6 illustrates a catalytic reactor.
[0020] FIG. 7 illustrates a recuperator and a pre-heater.
[0021] FIG. 8 is a schematic diagram of a fuel-air control
system.
[0022] FIG. 9 is a flowchart of a method for starting up the
combustion system.
[0023] FIG. 10 is a flowchart of a method for controlling the fuel
delivery rate of the combustion system during start-up.
[0024] FIG. 11 is a graph illustrating a start-up sequence for the
combustion system.
[0025] FIG. 12 is a flowchart of a method for normal fuel control
in a moderate BTU combustion system having a fuel control
value.
[0026] FIG. 13 is a flowchart of a method for normal fuel control
in a low BTU combustion system having an air control value.
[0027] FIG. 14 is a flowchart of a method for normal fuel control
in an ultra low BTU combustion system having no fuel control valve
and no an air control value.
[0028] FIG. 15 is a block diagram illustrating how to calculate
fuel concentration for a combustion system without a fuel
value.
[0029] FIG. 16 is a graph illustrating temperature rise as a
function of time nd power level for the combustion system.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Introduction
[0031] The present invention provides a method for sustained
catalytic combustion of low BTU fuels using a gas-turbine engine or
a combustion system that includes a catalytic reactor. Engines and
systems according to the present invention have many features and
advantages including, but not limited to, variable speed operation,
ease of installation and operation, low maintenance requirements,
ability to burn a wide range of low BTU fuels, low emissions, and
capability of sustained catalytic combustion over a wide range of
operating power levels.
[0032] As noted above, it is a feature of engines and systems
according to the present invention that they are capable of
sustained catalytic combustion over a wide range of operating power
levels. For sustained catalytic combustion, the operating
temperature of a gas-turbine engine should preferably remain within
a limited band of operating temperatures over a wide range of
operating lower levels. A typical band of catalytic reactor
operating temperatures is approximately between 800.degree. F. and
1100.degree. F. However, for conventional gas-turbine engines,
operating temperature is a function of power level. Thus, when
conventional gas-turbine engines operate at part load, they
typically reduce their operating temperature while maintaining a
constant engine speed. This reduction of operating temperature
causes the operating temperature of the conventional gas-turbine
engines to fall outside the limited band of catalytic reactor
operating temperatures. Unlike known constant-speed gas-turbine
engines, gas-turbine engines according to the invention adjust
their engine speed with power level to maintain a nearly constant
operating temperature over a wide range of operating power
levels.
[0033] In addition to adjusting engine speed with power level to
maintain a early constant operating temperature, gas-turbine
engines and systems according to the present invention have
recuperators and pre-heaters that help maintain the minimum
operating temperature needed for sustained catalytic combustion,
even during periods of fuel interruption. Recuperators and
pre-heaters are not typically used with known fixed speed
gas-turbine engines having relatively high compression ratios
exceeding about 8:1.
[0034] It is a further feature of engines and systems according to
the present invention that fuel can be injected into these engines
and systems at the compressor inlet. Thus, there is no need for
complex or high-pressure fuel delivery systems having fuel gas
compression. In fact, in some embodiments, no fuel-metering valve
is needed, as controlling the speed of the gas-turbine engine can
control the fuel flow to the engine.
[0035] These and other features and advantages of the present
invention will now be described in detail with reference to the
accompanying drawings.
EXAMPLE ENGINES AND SYSTEMS ACCORDING TO THE INVENTION
[0036] FIG. 1 is a block diagram of a catalytic combustion system
100 according to the invention. System 100 includes a gas-turbine
engine 102, a motor-generator 104, and an electrical power
controller 106. As illustrated in FIG. 1, gas-turbine engine 102
includes a catalytic reactor 108.
[0037] Gas-turbine engine 102 consumes fuel and combustion air to
produce mechanical energy. Gas-turbine engine 102 is capable of
sustained catalytic combustion over a wide range of operating power
levels. Unlike known constant-speed gas-turbine engines, the engine
speed of gas-turbine engine 102 is varied with power level to
maintain a narrow band of operating temperatures or a nearly
constant operating temperature. This narrow band of operating
temperatures or nearly constant operating temperature condition
allows catalytic reactor 108 to continue operating regardless of
the operating power level of gas-turbine engine 102. The features
and operation of gas-turbine engine 102 as well as catalytic
reactor 108 are further described below with reference to FIG. 2
and FIG. 3.
[0038] Motor-generator 104 is mechanically coupled to gas-turbine
engine 102. Motor-generator 104 is used both to motor gas-turbine
engine 102, and thereby start or control/adjust the speed of
gas-turbine engine 102, and to convert the mechanical energy of
gas-turbine engine 102 to electrical energy. Motor-generator 104
may have a permanent magnet rotor (not shown), as would be known to
persons skilled in the relevant art. One example of a known type of
motor-generator applicable to the system of the present invention
is shown in commonly owned U.S. Pat. No. 5,903,116, which is
incorporated herein by reference in its entirety. The features and
operation of gas-turbine engine 102 are further described below
with reference to FIG. 3.
[0039] Power controller 106 is electrically coupled to
motor-generator 104. Power controller 106 serves many functions.
For example, power controller 106 couples the electric output of
motor-generator 104 to a load. This load may be either a
stand-alone load (not shown) or a utility grid (not shown). Power
controller 106 is also used to start-up gas-turbine engine 102.
Other functions performed by power controller 106 include, for
example, controlling the flow of power to and from motor-generator
104, transforming and conditioning the electrical power generated
by motor-generator 104, and controlling operating transients
experienced by system 100. The features and operation of power
controller 106 are further described below with reference to FIG.
3.
[0040] Among other features and advantages, gas-turbine engine 102
has low maintenance requirements, it can burn a wide range of low
BTU fuels, and it has low emissions. In certain embodiments of this
invention, the gas-turbine engine 102 is capable of oxidizing a
fuel having a higher heating value in a range of between 1000 and
100 BTU/scf. In other embodiments, the gas-turbine engine 102 is
capable of oxidizing a fuel having a higher heating value in a
range of between 100 and 15 BTU/scf. In still other embodiments,
the gas-turbine engine 102 is capable of oxidizing a fuel having a
higher heating value in a range of between 30 and 5 BTU/scf. These
ranges are by way of example only, as other embodiments of the
present invention are capable of oxidizing fuels having different
higher heating values.
[0041] FIG. 2 is a block diagram of gas-turbine engine 102.
Gas-turbine engine 102 includes a compressor 202, a recuperator
204, catalytic reactor 108, a turbine 206, and a pre-heater 208.
Compressor 202 and turbine 206 are coupled to a shaft 210. Shaft
210 is supported by bearings 212. Fuel flow may be controlled by
valves 203 and/or 205. In one embodiment, no valve is required to
control fuel or air flow. Bleed air may be used to operate and/or
cool bearings 212.
[0042] The components of gas-turbine engine 102 are as follows. The
compressor 202 is a one-stage, centrifugal flow compressor. The
recuperator 204 is a metallic, counter flow, primary surface type
heat exchanger. The catalytic reactor 108 is a high-temperature,
low emissions catalytic reactor. The turbine 206 is a one-stage
radial inflow turbine. The pre-heater 208 is an electric heater or
a gas flame or another source of heat. The bearings 212 are air
bearings that operate free of contact with the shaft 210. These
components are by way of example only and are not intended to limit
the invention. Other components can be used in place of these
components without deviating from the invention.
[0043] The operation of gas-turbine engine 102 will now be
described with reference to the components illustrated in FIG.
2.
[0044] During operation, fuel and air are mixed together to form a
fuel-air mixture having a desired fuel-air ratio. The pressure of
the fuel-air mixture is increased to a desired pressure by
compressor 202. The temperature of the fuel-air mixture is
increased to at least the minimum operating temperature of
catalytic reactor 108 using recuperator 204. Recuperator 204
transfers thermal energy from exhaust gasses of gas-turbine engine
102 to the fuel-air mixture, thereby increasing the temperature of
the fuel-air mixture. Catalytic reactor 108 substantially oxidizes
the fuel present in the fuel-air mixture and produces heated
exhaust gasses. The exhaust gasses from catalytic reactor 108
expand across turbine 206 and cause turbine 206 to rotate. The
exhaust gasses exiting turbine 206 pass through recuperator 204 and
are exhausted from gas-turbine engine 102.
[0045] During periods of operation, when the exhaust gasses exiting
turbine 206 are below a desired temperature such as, for example,
during the start-up of the gas-turbine engine 102, pre-heater 208
is used to increase the temperature of the exhaust gasses before
they enter recuperator 204. In addition, valves 216 and 218 can be
aligned to recirculate the exhaust gasses during start-up to the
inlet of compressor 202. Either the entire exhaust gas flow or some
portion thereof can be recirculated. Recirculating the exhaust
gasses reduces pre-heater energy input by providing preheated
combustion air recovered during start-up that would otherwise be
vented to the atmosphere. Once the temperature of the air entering
catalytic reactor 108 reaches a minimum operating temperature
(e.g., the temperature at which catalytic reactor 108 would begin
effectively oxidizing any entering fuel-air mixture), valves 216
and 218 can be realigned to vent some or all of the recirculated
exhaust gasses to the atmosphere.
[0046] Fuel and air (combustion air) are mixed together to form a
fuel-air mixture which is introduced into the inlet of compressor
202. An advantage of this arrangement is that there is no
requirement for a complex, high-pressure fuel delivery system. The
amount of combustion air mixed together with the fuel is sufficient
to completely oxidize the fuel. A fuel valve is typically used to
control the fuel-air ratio in embodiments designed to use fuels
having higher heating values in the range of between 1000 and 100
BTU/scf. An air valve is typically used to control the fuel-air
ratio in embodiments designed to use fuels having higher heating
values in the range of between 100 and 15 BTU/scf. In embodiments
designed to use fuels having higher heating values in the range of
between 30 and 5 BTU/scf, no valve is needed to control the
fuel-air ratio. In these embodiments, the speed of gas-turbine
engine 102 controls fuel flow.
[0047] In other embodiments, only combustion air is introduced into
the inlet of compressor 202. In these embodiments, the
high-pressure fuel is injected into the compressed combustion air
exiting compressor 202. The pressure of the fuel injected into the
compressed air must be greater than the pressure of the compressed
air. An advantage of these embodiments is that no fuel will be
present in any bleed air tapped from the compressor 202. In some
embodiments, fuel is injected into the high-pressure exit 251 of
the recuperator 204.
[0048] Recuperator 204 is used to transfer thermal energy from the
exhaust gasses of gas-turbine engine 102 to the fuel-air mixture
prior to the fuel-air mixture entering catalytic reactor 108. The
transferred thermal energy raises the temperature of the fuel-air
mixture above the minimum operating or start-up temperature of the
catalytic reactor 108.
[0049] Catalytic reactor 108 oxidizes or bums the fuel-air mixture
and produces exhaust gasses to drive turbine 206. The operating
temperature of catalytic reactor 108 varies depending on the
material and catalytic substrate used to construct catalytic
reactor 108. Catalytic reactor 108 is able to oxidize/burn various
fuels including mixtures and dilute mixtures including one or more
of the fuels listed below in Table 1. As described herein,
catalytic reactor 108 is preferably a high-temperature catalytic
reactor that produces little or no NO.sub.X or CO gasses. Such
catalytic reactors are available, for example, from Sud-Chemie
Prototech, Inc., 32 Fremont Street, Needham, Mass. 02494.
1TABLE 1 Gas LEL V/V % HEL V/V % Ignition Temp .degree. F. Methane
5.0 15 990 Propane 2.1 9.5 840 Butane 1.9 8.5 550 Natural Gas 3.8
17 900 Carbon Monoxide 12.5 74 1128 Ethane 3.0 12.5 880 Hydrogen
4.0 75 930
[0050] Turbine 206 is designed to operate in a range of between
45,000 rpm and 96,000 rpm. The speed of turbine 206 is a function
of the output power level of gas-turbine engine 102. Turbine 206
produces sufficient mechanical power to drive, for example, a 30
kw, a 60 kw, a 100 kw, or a 200 kw electric generator. These values
are by way of example only. Other embodiments have turbines capable
of driving other generators.
[0051] As noted above, pre-heater 208 maybe an electric heater, a
gas flame, or another suitable heat source. Pre-heater 208 can be
placed in the flow stream, upstream of the catalytic reactor 108 at
251, downstream of the catalytic reactor 108 at 253, or downstream
of turbine 206 at 255 to directly heat the working fluid.
Alternatively, pre-heater 208 can be coupled to a component,
through which the exhaust gasses flow, to indirectly heat the
exhaust gasses. In one embodiment, pre-heater 208 is an electric
band heater 702 (see FIG. 7) wrapped around recuperator 204. This
embodiment takes advantage of the heat transfer area of recuperator
204 to heat the exhaust gasses and fuel-air mixture. In addition,
this embodiment has the advantage that it does not impose an
additional pressure drop that can be imposed by an electric heating
element or a fuel injector when these items are placed in the
exhaust flow stream to heat the exhaust gasses. In another
embodiment, pre-heater 208 may be embedded in recuperator 204. In a
further embodiment, catalytic reactor 108 is directly heated using,
for example, an electric heater.
[0052] As described herein, a pre-heater 208 located downstream of
the catalytic reactor 108 at 253 or 255 has the advantage that any
hot streaks from the pre-heater do not pass through the catalytic
reactor. Pre-heater hot steaks therefore will not have detrimental
effects on the catalyst of catalytic reactor 108. These embodiments
of pre-heater 208 can, if fired, utilize gaseous or liquid
fuels.
[0053] As illustrated in FIG. 2, compressor 202 and turbine 206 are
coupled to a single shaft 210. Shaft 210 is supported by bearings
212. Bearings 212 include a radial bearing and a bilateral thrust
bearing. These bearings are preferably air bearings that may be
operated and/or cooled by bleed air from compressor 202. Air
bearings do not require conventional oil lubrication, and thus have
lower maintenance requirements and higher reliability than other
types of bearings. Other bearings, including conventional oiled
bearings, can be used.
[0054] FIG. 3 is a more detailed block diagram of catalytic
combustion system 100 according to the invention. Each of the
subsystems of catalytic combustion system 100 discussed above with
respect to FIG. 1, namely gas-turbine engine 102, motor-generator
104, and power controller 106, is shown in FIG. 3.
[0055] As illustrated in FIG. 3, the components of gas-turbine
engine 102 include compressor 202, recuperator 204, catalytic
reactor 108, turbine 206, pre-heater 208, a fuel mixer 302, and a
fuel-air controller 304. With the exception of the fuel mixer 302
and fuel-air controller 304, each of these components and its
operation is described above with reference to FIG. 2.
[0056] Fuel mixer 302 is a static mixer design as illustrated in
more detail in FIGS. 5A-B. Combustion air enters fuel mixer 302 at
a rate determined, for example, by the operating speed of
gas-turbine engine 102. Fuel is injected into fuel mixer 302 and
mixed with the incoming combustion air to produce a fuel-air
mixture. The mass flow rate of the combustion air and the mass flow
rate of the fuel determine the fuel-air ratio of the fuel-air
mixture. As noted herein, in other embodiments, the fuel is
injected at other locations such as, for example, after compressor
202.
[0057] Fuel mixer 302 is preferably designed so that the fuel-air
mixture exiting a mixing zone is below an explosive limit of the
fuel and so that the peak fuel concentration that comes into
contact with any potential ignition sources within gas-turbine
engine 102 (e.g., generator windings, bearings, or compressor
shroud) is below a flammability limit of the fuel. Fuel mixer 302
is also preferably designed to have a geometry that prevents more
than an insubstantial amount of fuel (e.g., 10-100 PPM) from
entering a flow streamline used for extracting bleed air (See FIG.
5B).
[0058] Fuel-air controller 304 is coupled to fuel mixer 302.
Fuel-air controller 304 controls either the mass flow rate of the
fuel, the mass flow rate of the combustion air, or both. Fuel-air
controller 304 typically opens and closes a fuel valve 203 and or
207 to adjust and vary the fuel-air ratio in embodiments designed
to use fuels having higher heating values in the range of between
1000 and 100 BTU/scf. Fuel-air controller 304 typically opens and
closes an air valve 205 to adjust and vary the fuel-air ratio in
embodiments designed to use fuels having higher heating values in
the range of between 100 and 15 BTU/scf. In embodiments designed to
use fuels having higher heating values in the range of between 30
and 5 BTU/scf, the fuel or air valve may not be needed to control
the fuel-air ratio.
[0059] Fuel-air controller 304 receives an input from a temperature
controller 328. This input allows the fuel-air controller 304 to
make automatic adjustments to the fuel-air ratio based on the
operating temperature of the gas-turbine engine 102.
[0060] Still referring to FIG. 3, power controller 106 comprises a
bi-directional generator converter 306, a bi-directional load
converter 308, and a DC bus 310. Bi-directional generator converter
306 is coupled to the motor-generator 104 and DC bus 310.
Bi-directional load converter 308 is coupled to DC bus 310 and to a
load 332. Bi-directional generator converter 306 and the
bi-direction load converter 308 together control the flow of
electrical power between motor-generator 104 and load 332.
[0061] Power controller 106 also includes a battery 312 and a
bi-directional battery converter 314. Battery 312 is coupled to
battery converter 314. Bi-directional battery converter 314 is
coupled to DC bus 310. Bi-directional battery converter 314
controls the flow of electrical power between battery 312 and DC
bus 310.
[0062] Power controller 106 includes a speed controller 316. Speed
controller 316 is coupled to bi-directional generator controller
306. Speed controller 316 is used to operate bi-directional
generator converter 306 and adjust and vary the speed of
motor-generator 104, for example, during start-up of system 100 or
during changes in the operating power level of system 100. Speed
controller 316 receives an input speed control signal 318 (e.g.,
speed set point signal) and/or an input power control signal 320
(e.g., power set point signal).
[0063] Power controller 106 includes a brake resistor 322. Brake
resistor 322 is coupled to DC bus 310. Brake resistor 322 is used
to dissipate excess power generated by motor-generator 104 and to
control the voltage of DC bus 310 during certain operating
transients (e.g., when any excess power generated by
motor-generator 104 cannot be absorbed and stored by battery 312).
In operation, when the voltage on DC bus 310 rises above a
predetermined voltage level, brake resistor 322 is turned on and is
used to absorb and dissipate energy.
[0064] The energy dissipated by brake resistor 322 may be
transferred to the exhaust gasses of gas-turbine engine 102 (e.g.,
the brake resistor is used in a manner similar to that of
pre-heater 208). This is particularly useful in stand-alone power
supply applications. Conversely, pre-heater 208 can be used to
fulfill the function of brake resistor 322. When rapid load
reduction is required by system 100, the load can be transferred to
pre-heater 208. In this situation, a portion of the electrical
energy generated by motor-generator 104 is converted to thermal
energy and recovered by system 100 using recuperator 204. This
embodiment of the invention allows the catalytic reactor 108 to be
kept at operating temperature while load is being taken off the
system 100. In a variation of this embodiment, gas-turbine engine
102 is run at a constant speed, and brake resistor 322 and/or
pre-heater 208 is used to dissipate excess power from system 100
during partial loads. In this embodiment, recuperator 204 is used
to recover at least some of the energy dissipated by brake resistor
322 or pre-heater 208, thereby reducing the amount of fuel (input
energy) required at partial loads. This embodiment is also
particularly useful for standalone operation of system 100 because
it can instantaneously adjust power supplied to load 332.
[0065] Power controller 106 includes a voltage controller 324.
Voltage controller 324 is coupled to bi-directional generator
controller 306, bi-directional load controller 308, bi-directional
battery converter 314, and/or brake resistor 322, if these elements
are present. Voltage controller 324 is used to operate these
components of system 100 and thereby control the voltage level of
DC bus 310. Voltage controller 324 receives an input voltage
control signal 326 (e.g., voltage set point signal).
[0066] Power controller 106 also includes a temperature controller
328 that controls the operating temperature of gas-turbine engine
102. Temperature controller 328 is coupled to fuel-air controller
304 and pre-heater 208. Temperature controller 328 receives an
input temperature signal for the exhaust gasses exiting turbine
206. Temperature controller 328 also receives an input temperature
control signal 330 (e.g., temperature set point signal).
Temperature controller 328 turns-on and turns-off pre-heater 208
and controls, for example, the opening and closing of a fuel valve
203 and/or a fuel valve 207 and/or an air valve 205, if
present.
[0067] A more detailed description of an appropriate power
controller 106 is disclosed in commonly owned U.S. Pat. No.
6,487,096 B1. The disclosure of U.S. Pat. No. 6,487,096 B1 is
incorporated herein in its entirety by reference as though set
forth in full hereafter.
[0068] Catalytic combustion system 100 illustrated in FIG. 3 has
three substantially decoupled control loops. These three control
loops control (1) the operating temperature of gas-turbine engine
102, (2) the rotary speed of gas-turbine engine 102 and motor
generator 104, and (3) the operating voltage of DC bus 310. These
three control loops will now be described with reference to the
components of system 100 illustrated in FIG. 3.
[0069] A first control loop controls the operating temperature of
gas-turbine engine 102. This control loop is implemented, in part,
by temperature controller 328. Temperature controller 328 regulates
a temperature related to the desired operating temperature of
catalytic reactor 108 to a set point (e.g., temperature control
signal 330). This is achieved, for example, by varying fuel flow to
catalytic reactor 108. Temperature controller 328 receives a
temperature control signal 330, or set point T, and a measured
temperature from a temperature sensor (not shown) connected, for
example, to an exhaust gas outlet of turbine 206. Temperature
controller 328 generates and transmits a fuel control signal to
fuel-air controller 304. The fuel control signal controls the
amount of fuel supplied to catalytic reactor 108 by fuel mixer 302.
The fuel is controlled to an amount intended to result in a desired
operating temperature in catalytic reactor 108. A temperature
sensor (not shown) may directly measure the temperature of
catalytic reactor 108 or may measure a temperature of an element or
area from which the temperature of catalytic reactor 108 can be
inferred. The speed of the temperature control loop is about 100
ms.
[0070] A second control loop, controlled in part by speed
controller 316, controls the speed of shaft 210. Shaft 210 is
common to turbine 206, compressor 202, and motor-generator 104.
Speed is varied by varying the torque applied by motor-generator
104 to common shaft 210. The torque applied by motor-generator 104
to common shaft 210 depends upon power or current drawn from or
pumped into windings of motor-generator 104. Bi-directional
generator converter 306 is controlled by speed controller 316 to
transmit power or current into or out of motor-generator 104. A
sensor (not shown) in motor-generator 104 or gas-turbine engine 102
senses the rotary speed on common shaft 210 and transmits that
rotary speed signal to speed controller 316. Speed controller 316
receives the rotary speed and compares it to speed control signal
318. Speed controller 316 generates and transmits to bi-directional
generator converter 306 a control signal which controls the
operation of bi-directional generator converter 306 and the
transfer of power or current between motor-generator 104 and DC bus
310. Speed control signal 318 may be formed or derived from power
control signal 320. The speed of the speed control loop is about 20
ms.
[0071] A third control loop, controlled in part by voltage
controller 324, controls bus voltage on DC bus 310 to a set point
(e.g., voltage control signal 326). This control is achieved by
transferring power between motor-generator 104 and any of load 332,
battery 312, brake resistor 324, and pre-heater 208. A sensor (not
shown) measures voltage on DC bus 310 and transmits a measured
voltage signal to voltage controller 324. Voltage controller 324
receives the measured voltage signal and compares it to a voltage
set point V (e.g., voltage control signal 326). Voltage controller
324 generates and transmits signals to bi-directional generator
converter 306, bi-directional load converter 308, brake resistor
322, and bi-directional battery converter 314, thereby controlling
the transmission of power from motor-generator 104 to load 332,
brake resistor 322, and battery 312, respectively. This control of
power flow controls the voltage of DC bus 310. The speed of the
power control loop is about 500 ms.
[0072] FIG. 4 illustrates a cut-away sectional view of a
gas-turbine engine 102. Illustrated in FIG. 4 are example
embodiments of compressor 202, recuperator 204, catalytic reactor
108, and pre-heater 208. In the embodiment illustrated in FIG. 4,
pre-heater 208 is an electric pre-heater that is located in the
flow stream of the turbine exhaust gasses upstream of the
recuperator heat exchanger surface.
[0073] FIGS. 5A-B illustrate an example fuel mixer 302 and an
example compressor 202 having a hub line 506. The example fuel
mixer 302 includes fuel lines 502 coupled to injectors 504. Fuel is
injected into fuel mixer 302 using fuel lines 502 and injectors 504
to form a fuel-air mixture. Four injector-fuel line assemblies are
shown, however, one or more may be used in practice to assure good
mixing. The zone downstream of injectors 504 is the mixing zone
503. Adequate mixing of fuel and air is accomplished when mixing
zone 503, injector geometry 504, injector location, and injector
quantity provide sufficient turbulence. Mixing may also be enhanced
by structures (not shown) located within or adjacent to the mixing
zone that promote turbulence.
[0074] As illustrated by FIG. 5B, injector 504 is preferably placed
into the combustion air flow stream at a pre-selected depth so that
no fuel is present in the air flow stream traveling along hub 506
of compressor 202. This placement minimizes or eliminates the
presence of unburned fuel in any bleed air drawn from the
compressor 202. The depth that injector 504 is placed into the
combustion air flow stream is adjustable.
[0075] In addition to adjusting the depth of injector 504 into the
combustion air flow stream of fuel mixer 302, the following two
approaches can be implemented to reduce or eliminate any unburned
fuel in gas-turbine engine 102. These two approaches are only
illustrative, and they are not intended to limit the invention.
[0076] First, since most of the unburned fuel will likely go into a
secondary air flow used for bearing cooling and thrust balancing,
and eventually end up in a cavity in the center housing region of
gas-turbine engine 102, this cavity can be evacuated. Evacuation
can be achieved by installing a bleed circuit from this cavity to a
location outside the gas-turbine engine 102. Typically, the
pressure in the cavity will be higher than ambient pressure
establishing the desired bleed flow. The gas that is bled off from
the cavity may be re-introduced at the inlet of gas-turbine engine
102 for complete oxidation.
[0077] Second, a low activation temperature catalyst (not shown)
can be added to the surfaces of the low-pressure/turbine exhaust
side of recuperator 204 to reduce or eliminate unburned fuel. This
catalyst would oxidize any unburned fuel downstream of turbine 206.
In addition, it would help heat the gas on the high-pressure side
of recuperator 204 and improve the efficiency of gas-turbine engine
102.
[0078] As noted herein, injecting the fuel into the inlet of
compressor 202 ensures that the fuel is well mixed with the
combustion air prior to reaching catalytic reactor 108. In the case
of liquid fuels, the recuperator ensures the fuel is vaporized
prior to reaching catalytic reactor 108. For safety reasons, the
fuel-air mixture formed should not be flammable. This will ensure
that any unwanted sparks caused, for example, by a compressor rub
will not ignite the fuel-air mixture.
[0079] Fuel may be injected at the discharge of compressor 202. In
such embodiments, a compressor discharge cavity (not shown) and
recuperator 204 ensure the fuel and the combustion air are well
mixed prior to reaching catalytic reactor 108. As noted above,
recuperator 204 helps ensure the liquid fuel is vaporized prior to
reaching catalytic reactor 108.
[0080] Injecting high-pressure liquid fuel downstream of compressor
202 at location 249 is preferable to injecting gaseous fuels
downstream of compressor 202. This is due to the fact that pumping
a liquid fuel to a high pressure generally takes less power than
compressing a gaseous fuel to a high pressure. Both can be
accomplished, however.
[0081] The catalytic combustion system 100 offers many fuel-use
advantages compared to conventional gas-turbine engines. For
example, one advantage is that the catalytic combustion system 100
is capable of using any liquid fuel that can be adequately
vaporized. The catalytic combustion system 100 is also more
tolerant to the use of automotive type or pulse width modulation
(PWM) type fuel injectors than conventional gas-turbine
engines.
[0082] FIG. 6 illustrates catalytic reactor 108. Catalytic reactor
108 has many corrugated metal sheets 602. These metal sheets are
coated with a catalytic coating 604. Catalytic reactor 108 is
designed to have a relatively large surface area for oxidizing the
fuel-air mixture. As noted above, catalytic reactors suitable for
use in combustion system 100 are available, for example, from
Sud-Chemie Prototech, Inc., 32 Fremont Street, Needham, Mass.
02494.
[0083] FIG. 7 illustrates recuperator 204 and electric band heater
702. Electric band heater 702 is one means for implementing the
function of pre-heater 204. Electric band heater 702 is wrapped
around recuperator 204 to take advantage of the heat transfer area
of recuperator 204 and to heat the exhaust gasses and fuel-air
mixture passing through recuperator 204. As noted above, this
embodiment has the advantage that it does not impose an additional
pressure drop that can be imposed by an electric heating element or
a fuel injector when these items are placed in the exhaust flow
stream to heat the exhaust gasses.
[0084] FIG. 8 is a schematic diagram of a fuel-air control system
800 according to the invention. Fuel-air control system 800
includes fuel-air controller 304, a manual isolation valve 802, a
fuel strainer 804, a pressure regulator 806, a pilot shut-off valve
808, a gas temperature sensor 809, a fuel flow control valve 810,
and a fuel shut-off valve 812. Pressure regulator 806 provides a
stable pressure upstream of fuel flow control valve 810. Fuel flow
control valve 810 adjusts fuel flow to the engine. Fuel shut off
valve 812 isolates the fuel supply from the engine at shut down or
in an emergency. Each of valves 806, 810 and 812 is operated by
fuel-air controller 304.
[0085] As described herein, fuel-air controller 304 makes automatic
adjustments to the fuel-air ratio entering catalytic reactor 108.
Fuel-air controller 304 receives as inputs a temperature parameter
from gas temperature sensor 809, engine parameters 814 from
gas-turbine engine 102 (e.g., including turbine exhaust temperature
or catalytic reactor inlet temperature), and control parameters 816
from other control systems of catalytic combustion system 100. In
the embodiment illustrated in FIG. 8, the fuel-air ratio is
adjusted by adjusting fuel flow injected into the inlet of
compressor 202 using fuel flow control valve 810.
EXAMPLE METHOD EMBODIMENTS OF THE INVENTION
[0086] In the description that follows, example method embodiments
of the invention are presented. These example methods embodiments
can be used with the example engines and systems described
herein.
[0087] FIG. 9 is a flowchart illustrating the steps of a method 900
for starting up a catalytic combustion system. Starting up a
catalytic combustion system is different than starting up a known
non-catalytic combustion system. This is because a catalytic
combustion system will not oxidize a fuel-air mixture until a
minimum temperature is achieved within the catalyst.
[0088] Method 900 starts at step 902. In step 902, the speed of a
gas-turbine engine is accelerated to a speed S.sub.1. Speed S.sub.1
represents a minimum speed at which the engine can be operated for
a set period of time without damaging the engine. For example, in
an engine having air bearings, the speed S.sub.1 may represent the
minimum speed needed for the air bearings to function.
[0089] In step 904, a pre-heater is turned on to add thermal energy
to gasses being circulated through the gas-turbine engine. These
circulating gasses constitute combustion air.
[0090] In step 906, a temperature control is set to a temperature
T.sub.1. Temperature T.sub.1 is the minimum temperature needed
within a catalyst to start efficient oxidation of a fuel-air
mixture. Temperature T.sub.1 may be a related temperature such as,
for example, turbine exhaust temperature that can be related to the
minimum temperature needed within a catalyst to start efficient
oxidation of a fuel-air mixture.
[0091] In step 908, the operating temperature of the gas-turbine
engine is checked to determine whether it has reached the
temperature T.sub.1 set in step 906. If the operating temperature
has reached temperature T.sub.1, control passes to step 912.
Otherwise, control passes to step 910.
[0092] In step 910, the gas-turbine engine is run at speed S.sub.1,
and the pre-heater is left on to continue adding thermal energy to
circulating gasses. After a selected period of time, control is
passed from step 910 back to step 908.
[0093] In step 912, the pre-heater is turned off. The pre-heater is
turned off because it is no longer needed to raise the temperature
of any circulating gasses to temperature T.sub.1.
[0094] In step 914, fuel is added to the circulating gasses to form
a fuel-air mixture. There is a time delay from when the pre-heater
is turned-off to when the fuel is added to form a fuel-air mixture.
This time delay is used to ensure the pre-heater will not act as an
auto ignition source for the fuel-air mixture.
[0095] In step 916, control is passed from a catalytic combustion
start-up method 900 to a start-up fuel control method.
[0096] FIG. 10 is a flowchart illustrating the steps of a method
1000 for controlling the fuel delivery rate in a catalytic
combustion system during start-up. Method 1000 is used to protect
the catalytic combustion system against any harmful effects caused
by ramping up the fuel delivery rate too quickly.
[0097] Method 1000 starts at step 1002. In step 1002, the
temperature control is set to a temperature T.sub.2. Temperature
T.sub.2 is the temperature at which the speed of the gas-turbine
engine can be accelerated to a minimum speed for normal sustained
operation.
[0098] In step 1004, the operating temperature of the gas-turbine
engine is checked to determine whether it has reached the
temperature T.sub.2 set in step 1002. If the operating temperature
has reached temperature T.sub.2, control passes to step 1010.
Otherwise, control passes to step 1006.
[0099] In step 1006, the gas-turbine engine is run at speed
S.sub.1, and the fuel delivery rate is maintained at a start-up
rate. This start-up fuel delivery rate is not a function of
gas-turbine engine operating temperature. After a set period of
time, control is passed from step 1006 either to optional step 1008
or to step 1004.
[0100] In step 1008, the fuel delivery rate is optionally
controlled as a function of engine operating temperature. If step
1008 is employed, the start-up fuel delivery rate is increased in
step 1008 as a function of operating temperature in order to reduce
the start-up time of the catalytic combustion system. After a set
period of time, control is passed from step 1008 to 1004.
[0101] In step 1010, the speed of the gas-turbine engine is
increased to a speed S.sub.2. The speed S.sub.2 is the minimum
speed necessary for normal sustained operation of the gas-turbine
engine.
[0102] In step 1012, fuel delivery control is changed so that the
fuel delivery rate is controlled as a function of gas-turbine
engine speed. Thus, as the speed of the gas turbine engine
increases due to an increase in demanded power, the fuel delivery
rate increases to maintain a constant or nearly constant operating
temperature. Conversely, as the speed of the gas turbine engine
decreases due to a decrease in demanded power, the fuel delivery
rate decreases to maintain a constant or nearly constant operating
temperature.
[0103] In step 1014, control passes from method 1000 to a method
for normal fuel control. A normal fuel control method is needed
after start-up to change the control gains to those needed to
accommodate the response time of the catalytic reactor and to
incorporate any delays needed to account for normal operating
system response times.
[0104] FIG. 11 is a graph illustrating an example start-up sequence
for a catalytic combustion system according to the invention. FIG.
11 illustrates the operation of method 900 and method 1000.
[0105] At time 0 seconds, the gas-turbine engine is accelerated
from a speed of 0 rpm to a speed of 25,000 rpm (i.e., speed
S.sub.1). The pre-heater is turned on, and it starts adding thermal
energy to the system (circulating gasses).
[0106] At approximately 725 seconds, the operating temperature of
the system (turbine exhaust temperature (TET)) has reached
800.degree. F. (temperature T.sub.1), and the pre-heater is turned
off. When the pre-heater is turned off, the operating temperature
of the engine initially drops, but then quickly recovers and
continues to rise as heat is released by the oxidation of fuel.
[0107] At approximately 925 seconds, the operating temperature of
the system (TET) has reached 1000.degree. F. (temperature T.sub.2),
and the gas-turbine engine is starting to accelerate from a speed
of 25,000 rpm to a speed of 45,000 rpm (i.e., speed S.sub.2). The
means of controlling fuel delivery rate is changed so that the rate
of fuel delivery is controlled as a function of gas-turbine engine
speed. Thus, as the engine accelerates, so does the fuel delivery
rate. In turn, the operating temperature of the gas-turbine engine
also rises.
[0108] At 1000 seconds, both the engine speed and the engine
operating temperature have reached their respective set points
(i.e., 45,000 rpm and 1100.degree. F. Other set points are used in
other embodiments. Thus, these values are not to be used to limit
the invention.
[0109] FIG. 12 is a flowchart illustrating the steps of a method
1200 for normal fuel control in a moderate BTU fuel catalytic
combustion system according to the invention. Moderate BTU fuel
mixtures typically contain between 1000 and 100 BTU/scf. (See
commonly owned U.S. patent application Ser. No. 10/303,051, filed
Nov. 25, 2002, which is incorporated herein by reference in its
entirety, for a description of a non-catalytic combustion system
capable of utilizing moderate BTU fuel mixtures.)
[0110] Method 1200 starts at step 1202. In step 1202, the operating
temperature of the gas-turbine engine is checked to determine
whether it is greater than a set point temperature, TSPT. If the
operating temperature is greater than T.sub.SPT, control passes to
step 1214. Otherwise, control passes to step 1204. A dead-band is
typically employed around the set point temperature T.sub.SPT to
stabilize any controls used to implement the method 1200.
[0111] In step 1204, the position of the fuel valve supplying fuel
to the gas-turbine engine is checked to determine whether it is
greater than 99% open. If the fuel valve is greater than 99% open,
control passes to step 1208. Otherwise, control passes to step
1206.
[0112] In step 1206, the fuel valve is opened by a selected amount
in an attempt to raise the operating temperature of the catalytic
combustion system. Opening the fuel valve increases the rate at
which fuel is delivered to the catalytic reactor, and it increases
the amount of thermal energy produced by the catalytic reactor.
[0113] In step 1208, the operating speed of the gas-turbine engine
is checked to determine whether it is greater than a minimum set
point speed, S.sub.MIN. If the operating speed is greater than
S.sub.MIN, control passes to step 1212. Otherwise, control passes
to step 1210.
[0114] In step 1210, the gas-turbine engine is turned off or shut
down. Control is passed to step 1210 only if the thermal content of
the fuel being used is too low for proper operation of the
gas-turbine engine.
[0115] In step 1212, the speed of the gas turbine engine is lowered
in an attempt to raise the operating temperature of the gas-turbine
engine. In step 1212, the speed is never lowered below the speed
S.sub.MIN. After the engine speed is lowered, control is returned
to step 1202.
[0116] In step 1214, the position of the fuel valve supplying fuel
to the gas-turbine engine is checked to determine whether it is
less than 1% open. If the fuel valve is less than 1% open, control
passes to step 1218. Otherwise, control passes to step 1216.
[0117] In step 1216, the fuel valve is closed by a selected amount
in an attempt to lower the operating temperature of the catalytic
combustion system. Closing the fuel valve decreases the rate at
which fuel is delivered to the catalytic reactor, and it decreases
the amount of thermal energy produced by the catalytic reactor.
[0118] In step 1218, the operating speed of the gas-turbine engine
is checked to determine whether it is less than a maximum set point
speed, S.sub.MAX. If the operating speed is less than S.sub.MAX,
control passes to step 1222. Otherwise, control passes to step
1220.
[0119] In step 1220, the fuel is turned off or the engine is
throttled. Control is passed to step 1220 only if the thermal
content of the fuel being used is too high for proper operation of
the gas-turbine engine.
[0120] In step 1222, the speed of the gas turbine engine is raised
in an attempt to lower the operating temperature of the gas-turbine
engine. In step 1222, the speed is never raised above the speed
S.sub.MAX. After the engine speed is raised, control is returned to
step 1202.
[0121] FIG. 13 is a flowchart illustrating the steps of a method
1300 for normal fuel control in a low BTU fuel catalytic combustion
system. Low BTU fuels have a higher heating value of between 100
and 30 BTU/scf. Low BTU fuel mixtures contain, for example, 15000
ppm CH.sub.4 (1.5% CH.sub.4) or 2.5% CO/2.5% H.sub.2. The remaining
content is air. In such embodiments, the fuel concentration is so
low that fresh air flow rather than fuel flow into the engine
should to be controlled.
[0122] Method 1300 starts at step 1302. In step 1302, the operating
temperature of the gas-turbine engine is checked to determine
whether it is greater than a set point temperature, T.sub.SPT. If
the operating temperature is greater than T.sub.SPT, control passes
to step 1314. Otherwise, control passes to step 1304.
[0123] In step 1304, the position of the air valve 205 supplying
air to the gas-turbine engine is checked to determine whether it is
less than 1% open. If the air valve is less than 1% open, control
passes to step 1308. Otherwise, control passes to step 1306.
[0124] In step 1306, the air valve is closed by a selected amount
in an attempt to increase the operating temperature of the
gas-turbine engine. Closing the air valve increases the fuel-air
ratio of the fuel-air mixture being oxidized by the catalytic
reactor, and it increases the amount of thermal energy being
produced by the catalytic reactor.
[0125] In step 1308, the operating speed of the gas-turbine engine
is checked to determine whether it is greater than a minimum set
point speed, S.sub.MIN. If the operating speed is greater than
S.sub.MIN, control passes to step 1312. Otherwise, control passes
to step 1310.
[0126] In step 1310, the gas-turbine engine is turned off or shut
down. Control is passed to step 1310 only if the thermal content of
the fuel being used is too low for proper operation of the
gas-turbine engine.
[0127] In step 1312, the speed of the gas turbine engine is lowered
in an attempt to raise the operating temperature of the gas-turbine
engine. In step 1312, the speed is never lowered below the speed
S.sub.MIN. After the engine speed is lowered, control is returned
to step 1302.
[0128] In step 1314, the position of the air valve supplying air to
the gas-turbine engine is checked to determine whether it is
greater than 99% open. If the air valve is greater than 99% open,
control passes to step 1318. Otherwise, control passes to step
1316.
[0129] In step 1316, the air valve is opened by a selected amount
in an attempt to lower the operating temperature of the catalytic
combustion system. Opening the air valve dilutes the fuel in the
fuel-air mixture and reduces the fuel-air ratio of the mixture
being injected into the gas-turbine engine.
[0130] In step 1318, the operating speed of the gas-turbine engine
is checked to determine whether it is less than a maximum set point
speed, S.sub.MAX. If the operating speed is lower than S.sub.MAX,
control passes to step 1322. Otherwise, control passes to step
1320.
[0131] In step 1320, the fuel is turned off or the engine is
throttled. Control is passed to step 1320 only if the thermal
content of the fuel being used is too high for proper operation of
the gas-turbine engine.
[0132] In step 1322, the speed of the gas turbine engine is raised
in an attempt to lower the operating temperature of the gas-turbine
engine. By increasing the flow of air through the catalytic
combustion system without significantly increasing the rate of fuel
flow, the operating temperature will decrease. In step 1322, the
speed is never raised above the speed S.sub.MAX. After the engine
speed is raised, control is returned to step 1302.
[0133] As described herein, the method 1300 is particularly useful
for low BTU fuel-air mixture that can be introduced at the gas
turbine engine compressor inlet upstream of the air filter and
filtered using a production air induction system. In these
embodiments, the fuel content in the air flow can vary and thus
should be measured or monitored in a manner similar to the one
described below.
[0134] The present invention can also be used in an ultra low BTU
fuel source environment. In some applications such as, for example,
a dairy barn, the methane content of the air inside the building
may be high enough to sustain engine operation (e.g., the air
inside the building has a BTU content on the order of 5-30
BTU/scf). In this case, fresh air from outside of the building may
have to be ducted to the air control system. The air control system
will have components similar to those found in a fuel control
system (e.g., fuel control system 800) except that the control
software will be modified to open the air valve when less fuel is
needed and to close the air valve when more fuel is needed. In
order to prevent engine over-speed, there should be a shutoff valve
in the piping system used to deliver the fuel-air mixture to the
gas-turbine engine.
[0135] FIG. 14 is a flowchart illustrating the steps of a method
1400 for normal fuel control in an ultra low BTU catalytic
combustion system. Method 1400 is intended for use in a combustion
system without a fuel control valve and without an air control
valve.
[0136] Method 1400 starts at step 1402. In step 1402, the operating
temperature of the gas-turbine engine is checked to determine
whether it is greater than a set point temperature, T.sub.SPT. If
the operating temperature is greater than T.sub.SPT, control passes
to step 1410. Otherwise, control passes to step 1404.
[0137] In step 1404, the operating speed of the gas-turbine engine
is checked to determine whether it is greater than a minimum set
point speed, S.sub.MIN. If the operating speed is greater than
S.sub.MIN, control passes to step 1408. Otherwise, control passes
to step 1406.
[0138] In step 1406, the gas-turbine engine is turned off or shut
down. Control is passed to step 1406 only if the thermal content of
the fuel being used is too low for proper operation of the
gas-turbine engine.
[0139] In step 1408, the speed of the gas turbine engine is lowered
in an attempt to raise the operating temperature of the gas-turbine
engine. In step 1408, the speed is never lowered below the speed
S.sub.MIN. After the engine speed is lowered, control is returned
to step 1402.
[0140] In step 1410, the operating speed of the gas-turbine engine
is checked to determine whether it is less than a maximum set point
speed, S.sub.MAX. If the operating speed is lower than S.sub.MAX,
control passes to step 1414. Otherwise, control passes to step
1412.
[0141] In step 1412, the fuel is turned off or the engine is
throttled. Control is passed to step 1412 only if the thermal
content of the fuel being used is too high for proper operation of
the gas-turbine engine.
[0142] In step 1414, the speed of the gas turbine engine is raised
in an attempt to lower the operating temperature of the gas-turbine
engine. In step 1408, the speed is never raised above the speed
S.sub.MAX. After the engine speed is raised, control is returned to
step 1402.
[0143] Method 1400 can be thought of as a method for controlling
air flow into the gas-turbine engine without using an air control
valve. Air flow is controlled using a fixed orifice. In certain
ultra low BTU applications (e.g., when the fuel is an air-methane
mixture and the methane concentration is between 1.0 and 1.35%), it
is possible to operate the fuel system of a catalytic combustion
system according to the invention without a control valve. The
engine is controlled in these embodiments using parameters such as
engine speed and engine operating temperature (e.g., turbine
exhaust temperature). Eliminating the flow control valve reduces
the cost of the fuel system, and it simplifies the required
hardware.
[0144] As described herein, in certain embodiments of the
invention, the fuel content in the fuel-air mixture can vary and
thus should be measured or monitored. FIG. 15 is a block diagram
illustrating how to calculate fuel concentration for a low BTU fuel
combustion system having an air flow control valve. This method can
be adjusted, however, and used for other BTU fuel combustion
systems having a fuel flow control valve rather than an air flow
control valve.
[0145] As illustrated in FIG. 15, the total air flow through an
engine (W.sub.TOTAL) is a function of the air flow (W.sub.AD) from
an air flow control valve and the air flow (W.sub.A) and the fuel
flow (W.sub.F) that make up the low BTU fuel mixture supplied to
the engine (W.sub.A+W.sub.F). The total air flow (W.sub.TOTAL) is a
function of the rotational speed (N) of the engine and the
operating temperature of the engine (e.g., turbine exhaust
temperature (TET)). This function (EQ. 1) can be determined
experimentally by recording W.sub.TOTAL for various values of N and
TET.
W.sub.TOTAL=W.sub.AD+(W.sub.F+W.sub.A)=f(N,TET) EQ. 1
[0146] The operating temperature of the engine (e.g., turbine
exhaust temperature (TET)) is also a function of the rotational
speed (N) of the engine and the fuel-air ratio (F/A) being oxidized
by the engine. By measuring the operating temperature of the engine
(e.g., TET) for various fuel-air ratios and various engine speeds,
a plot can be created that gives the fuel-air ratio being oxidized
by the engine as a function of N and TET. This function (EQ. 2) can
be determined experimentally by recording TET for various values of
N and F/A.
F/A=W.sub.F/(W.sub.AD+W.sub.A)=f(N,TET) EQ. 2
[0147] By rearranging and combining EQ. 1 and EQ. 2, it can be seen
that the amount of fuel present in the low BTU fuel is:
W.sub.F=(W.sub.TOTAL.multidot.F/A)/(1-(F/A)) EQ. 3
[0148] Because W.sub.TOTAL and F/A are functions of engine speed
(N) and engine operating temperature (e.g., TET), which can be
determined experimentally and recorded in the form of maps or
graphs, the fuel flow (W.sub.F) during engine operation can be
determined using EQ. 3 and the maps or graphs created for
W.sub.TOTAL and F/A.
[0149] The functionality of the catalyst in the catalytic reactor
108 is checked or tested on a periodic basis (e.g., on a weekly
basis). The functionality of the catalyst can be used to determine
when the catalyst has reached the end of its useful operating life.
Data obtained during this periodic check or test is stored in a
memory so that is can be used for subsequent analysis and
diagnostic evaluations. The check or test involves determining the
time needed to return to an expected operating temperature
following a change in fuel delivery rate or a change in output
power level.
[0150] FIG. 16 is a graph illustrating temperature rise as a
function of time and power level for a combustion system.
[0151] An old catalytic reactor is replaced with a new catalytic
reactor whenever the old catalytic reactor has reached the end of
its useful operating life. A catalytic reactor can be said to have
reached the end of its useful operating life, for example, if it
has operated for a specified number of hours, if the gas-turbine
engine can no longer operate at full speed using a particular
fuel-air ratio, or if unburned hydrocarbon levels exceed a
specified threshold level.
[0152] The functionality of the catalyst is characterized by a
functionality value. For example, a functionality value relating to
a heat-up rate of the combustion system (temperature rise time) is
used to characterize the functionality of the catalyst. This
functionality value can be derived using the following test. First,
operate the combustion system so that it is supplying a known power
level to a utility grid (e.g., 10 kW). Next, reduce the operating
temperature set point of the combustion system by a selected amount
(e.g., 50.degree. F.). Open the fuel valve to a particular percent
open setting (e.g., 40% open). Measure the time it takes the
combustion system to return to the normal operating temperature
(e.g., TET) set point. An older catalyst or a catalyst reaching the
end of its useful operating life will take longer to get to the
normal operating temperature set point. The measured time it takes
the combustion system to return to the normal operating temperature
(e.g., TET) set point can be stored and used to trend the
functionality of the combustion system over time using, for
example, exponential or linear averaging.
[0153] A reaction detection algorithm is used to eliminate any need
for a catalyst temperature sensor and to improve the robustness of
controller software algorithms. The reaction detection algorithm is
incorporated into the logic of temperature controller 328. The
reaction detection algorithm is used to operate pre-heater 208.
CONCLUSION
[0154] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. It will be
understood by those skilled in the art that various changes in form
and details can be made therein without departing from the spirit
and scope of the invention as defined in the appended claims. Thus,
the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *