Technical Field
[0001] This invention relates to a gas turbine and more particularly to a method of operating
a gas turbine, which includes a catalytic combustor.
Background Art
[0002] An axial flow rotary machine, such as an industrial gas turbine for a co-generation
system or a gas turbine engine for an aircraft, includes a compressor section, a combustion
section, and a turbine section. As the working medium gases travel along the flow
path, the gases are compressed in the compressor section, thereby causing the temperature
and pressure of the gases to rise. The hot, pressurized gases are burned with fuel
in the combustion section to add energy to the gases, which expand through the turbine
section and produce useful work and/or thrust.
[0003] The burning of fuel, however, causes the gas turbine to emit undesirable oxides of
nitrogen (NO
x). Regulations limiting the amount of NO
x emissions produced by gas turbines has motivated the development of certain technologies
such as diluent injection in the combustion section, lean premixed Dry Low NO
x (DLN) combustion and catalytic combustion. A conventional catalytic combustor typically
includes a precombustion zone, a premixing zone, a catalyst zone and a combustion
zone. The catalyst zone includes a catalytic reactor, which includes a catalyst. A
typical precombustion zone includes a preburner, which increases the temperature of
the working medium gases in order to initiate and maintain the catalytic reaction
between such gases and the catalyst. In this case, however, the preburner is the leading
producer of NO
x, especially during start-up and low load operations when the preburner is required.
Disclosure of Invention
[0004] An object of the present invention includes eliminating the pre-combustion zone of
a catalytic combustor in a gas turbine, thereby reducing the pollutants created by
a gas turbine during operation, especially during start-up and low load operation.
[0005] Accordingly the present invention includes a method for operating a gas turbine,
which contains a catalytic combustor, wherein such method comprises heating a catalyst
within the catalytic combustor to a predetermined temperature thereby activating catalytic
combustion of a fuel-air mixture. Such method includes electrically heating the catalyst
when the temperature of the catalyst falls below the predetermined temperature, namely
upon starting the gas turbine and/or partial load conditions during operation. Electrically
heating the catalyst reduces the intake air temperature required to initiate combustion,
thereby reducing and/or eliminating the requirement of preheating the intake air.
Eliminating the preburner, therefore, improves the simplicity and control of operating
the gas turbine. A method of electrically heating the catalyst includes connecting
a generator to the gas turbine, thereby generating electricity which is directed to
a portion of the catalyst when the catalyst falls below the predetermined temperature.
Re-directing electricity to the catalyst and back into the gas turbine provides efficient
operation of the gas turbine.
[0006] An additional or alternate embodiment of a method for electrically heating the catalyst
includes providing a portion of the catalyst with electricity from an auxiliary power
supply.
[0007] The present invention further includes a gas turbine as specified in claim 6. Preferably,
such gas turbine consists essentially of the elements (a), (b), (c), and (d).
[0008] The present invention also includes a catalytic combustor consisting essentially
of a premixing zone, a catalyst zone having a catalyst therein, a combustion zone,
and means for electrically heating a portion of the catalyst to a predetermined temperature.
The catalyst zone is disposed between the premixing zone and the combustion zone.
Inclusion of the means for heating a portion of the catalyst eliminates the requirement
of a pre-combustion zone, thereby removing such zone and the cause of a significant
portion of the pollutants created when operating a gas turbine.
[0009] The foregoing and other objects, features and advantages of the present invention
will become more apparent in light of the following detailed description of exemplary
embodiments thereof as illustrated in the accompanying drawings.
Brief Description of Drawings
[0010]
Fig. 1 is an illustration of an electric power generating system which includes an
industrial gas turbine engine and generator.
Fig. 2 is a schematic diagram of a gas turbine of the present invention equipped with
an electrically heated catalytic combustor.
Best Mode for Carrying out the Invention
[0011] Although the present invention is described in relation to an industrial gas turbine,
the present invention can also apply to any gas turbine engine application.
[0012] Referring to Fig. 1, the electric power generating system
10 includes an industrial gas turbine
12 that drives a generator
14. The generator
14 can be used to drive local electrical needs or connected to a power grid network.
The industrial gas turbine
12, however, is not limited to driving an electrical generator
14. The gas turbine can also be used to drive other types of loads.
[0013] Referring to Fig. 2, the industrial gas turbine
12 is axially located along axis (R
x) and includes a compressor section
16, a combustion section
18, a turbine section
20 and a shaft
22. The combustion section
18 is a catalytic combustor, which includes a premixing zone
24, a catalyst zone
26, and a combustion zone
28. Intake air enters the compressor section
16, and fuel enters the premixing zone
24 of the combustion section
18 through fuel supply lines
30,
32 and mixes with the intake air, thereby creating a combustible fuel-air mixture. The
fuel-air mixture enters the catalyst zone
26 where combustion of the mixture is initiated and continues to completion in the combustion
section
28, thereby adding energy to the working medium gas. The turbine section
20 includes a turbine, indicated by lines
42, which rotates as the heated gas expands through this section. The turbine
42 is connected to one end of the shaft
22, which transmits power to the compressor
54 and the generator
14. When the turbine
42 rotates, the shaft
22 also rotates, thereby enabling the generator
14 to produce electricity, which travels along lines
44.
[0014] The catalyst zone
26 includes a catalytic reactor
40 and a temperature sensor
36. The catalytic reactor
40 contains a ceramic or metal honeycomb catalyst matrix, which may be wash-coated with
alumina, stabilized alumina or a similar catalyst substrate. The wash-coated catalyst
substrate is impregnated with an active catalyst material, such as one or more of
the precious metals or a combination of precious metals that are capable of withstanding
the combustion temperature of the catalytic reactor. Certain types of precious metals
that are catalytically active and capable of withstanding elevated temperatures include
platinum, palladium, and rhodium.
[0015] Upon sensing that the temperature of the catalytic reactor
40 is less than a predetermined temperature, the temperature sensor
36 delivers a signal along line
52 to the controller
38. The controller
38, in turn, delivers electric current via lines
50 to the catalytic reactor
40, thereby elevating the temperature of at least a portion of the catalytic reactor
40 to the predetermined temperature. It is preferable to elevate the temperature of
the portion of the catalytic reactor
40 nearest the premixing zone
24, which is referred to as the inlet portion, in order to initiate catalytic combustion
as early as possible within the catalytic reactor
40. The predetermined temperature is dependent upon the type of catalyst, the type of
fuel and the fuel-air composition. The predetermined temperature, however, is a temperature
at or above the catalyst light-off temperature, wherein the catalyst light-off temperature
is a temperature sufficient to initiate and maintain catalytic combustion. Maintaining
at least a portion of the catalytic reactor
40 at the predetermined temperature ensures that the fuel-air mixture will combust within
the combustion zone
18. The heat generated by the combustion, in turn, increases the temperature of the
catalytic reactor
40, thereby sustaining catalytic combustion.
[0016] The temperature sensor
36 senses the temperature of the catalytic reactor
40 and sends a signal to controller
38 along line
52. Upon sensing that the catalytic reactor
40 has attained the predetermined temperature, the controller discontinues or reduces
(i.e., modulates) the amount of electricity delivered to the catalytic reactor
40 as necessary to maintain the catalyst temperature at or above the predetermined temperature.
If the catalyst matrix of the catalytic reactor
40 is constructed of ceramic, then the electric current will have to be applied to an
electrically conducting material within or on the ceramic. If the catalyst matrix
is constructed of metal, then the electric current will be applied directly to the
support structure.
[0017] The controller
38 is capable of receiving electricity from both the generator
14, along lines
44 and
46, and an auxiliary power supply
34 (e.g., auxiliary generator) along lines
48. At start-up and at low load conditions, the generator
14 may not produce a sufficient amount of electricity to heat the catalytic reactor
40 to the predetermined temperature due to the lack of rotational shaft speed. The auxiliary
power supply
34, therefore, provides the controller
38, along lines
48 with additional electricity during such operating conditions. The controller
38, in turn, furnishes the catalytic reactor
40 with the necessary power to maintain the catalytic reactor
40 at the predetermined temperature until the generator
14 independently produces a sufficient amount of electricity to maintain the temperature
of the catalytic reactor
40 above the predetermined temperature. Re-directing the electricity generated by the
generator
14 to the catalytic reactor
40 provides for an efficient co-generation system
10.
1. A method for operating a gas turbine, the gas turbine extending axially and having
an upstream end and a downstream end, a compressor section, a catalytic combustor
section and a turbine section, the compressor section being relatively toward the
upstream end, the turbine section being relatively toward the downstream end, the
catalytic combustor section disposed between the compressor section and the turbine
section, the catalytic combustor section having a premixing zone, a catalyst zone
and a combustion zone, the premixing zone being relatively toward the compressor section,
the combustion zone being relatively toward the turbine section, the catalyst zone
disposed between the premixing zone and the combustion zone and having a catalyst
therein, comprising the steps of:
(a) introducing intake air into the compressor section;
(b) allowing the intake air to enter the mixing zone of the catalytic combustor section;
(c) introducing fuel into the mixing zone and creating a fuel-air mixture which enters
the catalyst zone; and
(d) heating at least a portion of the catalyst to a predetermined temperature, thereby
initiating catalytic combustion of the fuel-air mixture.
2. The method of claim 1 further comprising the step of heating the portion of the catalyst
to said predetermined temperature when the temperature of the catalyst falls below
the predetermined temperature.
3. The method of claim 1 or 2, wherein the step of heating the portion of the catalyst
comprises electrically heating the portion.
4. The method of claim 3 wherein the step of electrically heating a portion of the catalyst
comprises the steps of connecting a turbine, within the turbine section, to a shaft;
rotating the turbine and the shaft; generating electricity from the rotating shaft;
and directing at least a portion of the generated electricity to the portion of the
catalyst.
5. The method of claim 3 or 4 wherein the step of electrically heating a portion of the
catalyst comprises applying electricity to the portion from an auxiliary power supply.
6. A gas turbine extending axially and having an upstream end and a downstream end, comprising:
(a) a compressor section being relatively toward the upstream end;
(b) a turbine section being relatively toward the downstream end;
(c) a catalytic combustor section disposed between said compressor section and said
turbine section, said catalytic combustor section consisting essentially of a premixing
zone, a catalyst zone and a combustion zone, said premixing zone being relatively
toward said compressor section, said combustion zone being relatively toward said
turbine section, said catalyst zone disposed between said premixing zone and said
combustion zone, said catalyst zone comprising a catalyst therein; and
(d) means for heating at least a portion of said catalyst to a predetermined temperature.
7. The gas turbine of claim 6 wherein said means for heating comprises:
(a) a turbine within said turbine section;
(b) a shaft connected to said turbine;
(c) a generator connected to said shaft, said generator generating electricity when
said turbine rotates; and
(d) a controller which directs electricity from said generator to said portion of
said catalyst when the temperature of said catalyst is less than said predetermined
temperature.
8. The gas turbine of claim 6 or 7 wherein said means for heating comprises an auxiliary
electrical power supply and a controller which directs electricity from said auxiliary
electrical power supply to said portion of said catalyst when the temperature of said
catalyst is less than said predetermined temperature.
9. The gas turbine of any of claims 6 to 8 wherein said catalyst is a material from the
group consisting essentially of platinum, palladium and rhodium.