BACKGROUND
This disclosure relates, in general, to methods for stabilizing refractory
carbides in a high temperature combustion-gas environment.
Current gas turbine performance, whether for land, sea or air uses, is limited
by the allowable hot-section material temperature and the cooling penalty required to
maintain the integrity of those materials. In conventional turbine systems, for
Jfe instance, compressor discharge air may be used as a coolant for hot gas path
components. The "hot gas path" of these turbine systems includes components such
as the combustor liners and flame holding segments, stationary vanes and rotating
blades of a high-pressure turbine stage, and the shrouds around the rotating blades.
Composite and monolithic materials have been under development for many years to
provide higher temperature capabilities of these hot gas path components, leading to
higher firing temperatures and engine efficiencies. Refractory carbides, such as
refractory metal carbides (MCs) and ceramic matrix composites (CMCs) are such
materials. Refractory carbides have extremely high melting points. Ceramic matrix
composites (CMCs) consist commonly of continuous SiC reinforcing fibers within a
matrix of SiC-Si, which is made using a molten silicon infiltration process. The
desirable properties of CMCs include high thermal conductivity, high matrix cracking
stress, high inter-laminar strengths, and good environmental stability. Though CMCs
^W offer higher temperature capability, up to at least 2800°F, they are still limited by
environmental factors that require specialized coatings and cooling. In particular, for
temperatures above 2200°F, uncoated CMCs suffer from excessive oxidation and
recession. Currently, CMCs utilize an environmental bond coat (EBC) based on
mullite and Ba-Sr-aluminosilicate ceramic chemistries. The EBC prevents the CMC
material from loss due to recession, though with associated concerns over damage or
loss of the coating.
All conventional gas turbine engines employ separate combustion systems
and turbines that must be in close proximity with the combustors. The design and
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operability of the combustor, whether of diffusion, premixed, or combined modes, gas
or liquid fuels, has great influence on the thermal management of the turbine. In
addition, the thermal management of the combustor system itself can significantly
contribute to the resulting gas temperature profile and pattern factors, combustion
instabilities, and emissions. With the technology shift to lower emissions and zero
emissions engines, new combustion strategies demand innovations in combustor and
turbine structure. Additionally, there is a need for systems and methods for
operations which allow for increased temperature operation while maintaining
integrity and performance of the turbine components.
^ SUMMARY
This disclosure is generally directed to a system and method of stabilizing
hot gas path components with a high carbon activity gas. More particularly, the
disclosure is in the field of gas turbine power generation systems.
In one embodiment, the disclosure relates to a method for stabilizing a
refractory carbide hot gas path component. In this method, fuel is combusted in a
combustor. A high carbon activity gas is delivered to at least a portion of a component
of a hot gas path that is thermally coupled to the hot gas path. At least a portion of a
hot gas path component comprises refractory carbide.
In one embodiment, the disclosure relates to a turbine power generation
^ ^ system. The system comprises a number of hot gas path components that are
^* thermally coupled to a hot gas path. At least a portion of at least one of the hot gas
path components comprises refractory carbide or ceramic matrix composite (CMC).
A combustor is configured to combust a mixture of air with a fuel to produce an
exhaust gas stream. A turbine is configured to convert energy of this exhaust stream
into useful mechanical energy. A high carbon activity gas is delivered by a conduit to
at least one of the hot gas path components.
In one embodiment, the disclosure relates to a cooling system for a hot gas
path component. This system includes a hot gas path component and a first conduit
that delivers a high carbon activity gas to at least a portion of the hot gas path
3
component. This high carbon activity gas forms a film of cover gas on a surface of at
least one hot gas path component. For purposes of this disclosure, "a surface" can
refer to any surface of a hot gas path component, including internal or external
surfaces.
The above described and other features are exemplified by the following
detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present system will
^ ^ become better understood when the following detailed description is read with
reference to the accompanying drawings in which like characters represent like parts
throughout the drawings, wherein:
FIG. 1 is a process flow diagram of a turbine power generating system,
which is adapted to utilize a high carbon activity gas as a turbine component
stabilization source according to one embodiment.
FIG. 2 is a process flow diagram of a turbine power generating system,
which is adapted to utilize a high carbon activity gas including sequestered carbon
dioxide as a turbine component stabilization source according to one embodiment.
FIG. 3 illustrates a schematic diagram of an example of an aviation high-
A} pressure gas turbine and combustor in one embodiment.
DETAILED DESCRIPTION
Each embodiment presented below facilitates the explanation of certain
aspects of die disclosure, and should not be interpreted as limiting the scope of the
disclosure. Moreover, approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative representation
that could permissibly vary without resulting in a change in the basic function to
which it is related. Accordingly, a value modified by a term or terms, such as
"about," is not limited to the precise value specified. In some instances, the
4
approximating language may correspond to the precision of an instrument for
measuring the value.
In the following specification and claims, the singular forms "a", "an" and
"the" include plural referents unless the context clearly dictates otherwise. As used
herein, the terms "may" and "may be" indicate a possibility of an occurrence within a
set of circumstances; a possession of a specified property, characteristic or function;
and/or qualify another verb by expressing one or more of an ability, capability, or
possibility associated with the qualified verb. Accordingly, usage of "may" and "may
be" indicates that a modified term is apparently appropriate, capable, or suitable for
^J an indicated capacity, function, or usage, while taking into account that in some
circumstances, the modified term may sometimes not be appropriate, capable, or
suitable.
This disclosure utilizes a refractory carbide material and system to create a
hot gas path component that is capable of withstanding at least about 3000°F
according to one example. In this disclosure, the oxidation and volatilization of
turbine hot gas path components are suppressed by introducing a continuously
renewed, chemically stabilizing film of high carbon activity gases on a surface of the
hot gas path components. These gases provide stabilization of the refractory carbide,
whether that is on the exterior surfaces or on the interior surfaces. Here, the high
carbon activity gas is provided to at least a portion of a surface of a hot gas path
component, and specifically a portion that is comprised of a refractory carbide, to
wr protect it from post-combustion gases. This protective layer functions to minimize
recession of the carbide.
The disclosure allows for refractory carbides to be used at extremely high
temperatures, which in one example is >3000°F. Other temperature ranges are also
accommodated with the refractory carbides. Carbides for use in the hot gas path
components will possess high melting points and will have structural stability and
strength at high temperatures. Examples of such refractory carbides include, but are
not limited to, TiC, ZrC, HfC, TaC, SiC, NbC and B4C. For purposes of this
disclosure, the terms "refractory carbide", "refractory metal carbide" and "ceramic
5
matrix composite" may be used interchangeably with the terms applicable to both the
matrix and reinforcing component. While silicon carbide-based CMCs are described
in the examples herein, the person of skill will realize that other refractory carbide
composites, as well as monoliths, that possess similar properties may be used. Oxides
would not be suitable for use in the methods and systems described herein.
Carbon activity is a thermodynamic ratio of carbon partial pressure in an
environment as compared to the standard state carbon activity of 1.0 in graphite.
High carbon activity gases, therefore, are those in which the partial pressure of carbon
in a gas is higher than the activity of carbon in the refractory carbide at the
^ ^ component's surface. For purposes of this disclosure, the actual value for the carbon
activity is between about 0.1 and about 1.0.
The person of skill will appreciate that, while the description below is
illustrative of a gas turbine system, any system utilizing refractory carbide
components that can be oxidized and recessed during a firing process could utilize
embodiments of this disclosure. Jet engines, land-based turbines, or rocket nozzles,
afterburners or motors are exemplary of such alternative systems. The methods and
systems of the disclosure are useful for power generating turbines, aero-derivative
engines, and marine propulsion engines.
FIG. 1 illustrates a turbine power generating system 100 utilizing a high
carbon activity gas 25 that stabilizes the hot gas path components of the turbine. The
W§ turbine power generating system includes an air compressor 12, a combustor 66, a
turbine 14, and an electrical generator 16. The compressor 12, the turbine 14, and the
electrical generator 16 may be linked by two shafts 18 and 20. It should be noted that
the shafts 18 and 20 may also be the same shaft. The shaft(s) allows the mechanical
energy produced by the turbine 14 to be utilized by the generator 16 and the
compressor 12.
The air 10 entering at an inlet of the air compressor 12 is compressed. The
compressed air 54 leaving an outlet of the air compressor 12 may then be supplied to
6
a combustor 66; various combustor embodiments that may be utilized are described in
detail below.
In certain embodiments, it may be advantageous to have complete coverage
of the hot gas path component, while in other embodiments, lesser coverage may be
desired. The availability of different combustor systems and a control valve on the
mixing chamber allows for control of the high carbon activity gas injection rates.
Current turbine film cooling relies entirely on the use of rows of discrete
film holes oriented at shallow angles to the surface. The effective design and location
t^ of these film rows can lead to full coverage protective gas layers. In combustors
today, it is common to use multihole, full coverage film cooling, or other forms of
complete slot type film cooling to achieve the objective. Hence, the technology does
exist to introduce the high carbon activity protective layer over a full hot gas path
component. Challenges do still exist in providing sufficient coverage in extreme
geometry regions such as airfoil trailing edges, blade tips, and interfacial slots
between components, as well as highly turbulent flow streams. For such regions,
engineered versions of transpiration cooling similar to that obtained for a porous wall
can be used.
The allocation of gases and film coverage can be tailored to various degrees
and locations to benefit optimized work extraction and engine efficiency. The method
can be used to augment combustion in a system, for example by using a high carbon
£ft activity gas protected vane and/or blade downstream of a conventional combustor, or
as the combustor only, or as combustor and vane system, or as a distributed
combustion system through several components.
A variety of further embodiments of the combustion system may be used for
purposes of this disclosure. Aviation engines typically use annular combustors, while
land-based power turbine engines use can-annular combustors. Advanced aircraft
engine combustor-turbine systems may already experience a certain level of burning
around the nozzle guide vanes. Airfoil film cooling can react with unburaed fuel to
create film heating near the surfaces of the hot gas path. Some combustion systems
7
seek the merging of the combustor and the turbine inlet guide vane into a single
system. Such a combined combustor and turbine inlet guide nozzle injects fuel on the
surface of the nozzle. The fuel cools the nozzle, and combustion occurs downstream
of the nozzle. For example, staged combustors may introduce a primary combustion
zone upstream and a secondary combustion zone just ahead of, or into, the turbine
inlet vanes. Trapped vortex combustion (TVC) is a form of staged combustion that
employs a recirculation wall cavity as the pilot burner. The TVC device creates a
flame stabilization zone providing continuous sources of ignition by mixing hot
products and burning gases with the incoming fuel.
^ P A conventional combustor followed by a CMC3000 vane (CMC with
protective film) may be used in which the CMC is protected by the high carbon
activity gas, thereby eliminating all compressor discharge air from the vane. This
system allows a higher firing temperature, or current firing temperatures with lower
flame temperatures (lower emissions). The high activity carbon gas augments the
combustor system to provide a more staged system, as described in the example
below.
In one non-limiting example, the conventional combustor and turbine inlet
guide vane may be replaced by a CMC Coanda nozzle, such as described in U.S.
Patent Publication Numbers US 20080134685 and US 20080078181. This new
system achieves both functions of a combustor and an inlet guide vane while being
made of CMC. Briefly, in this combustor, fuel is injected in a controlled pattern
^ F tangential to a curvilinear wall with the Coanda effect causing the jets to stick to the
surface. In applications using gaseous fuel, CH4, for instance, may be both the main
fuel injection and the protective gas for the CMC. In applications using liquid fuel,
such as jet fuel, the hydrocarbon fuel would be atomized inside the CMC components,
then used as injected gaseous fuel to form the CMC protective layer. In both
applications, combustion may occur both through the aero flow passage and
downstream of the nozzle.
Those that are skilled in the art will know that in some cases it may be
desirable to preheat the compressed air 54 in a recuperator before feeding the
8
compressed air 54 to the combustor 66. The fuel 24 is also supplied to the combustor
66. The flow of the fuel may be controlled by a flow control valve. The fuel may be
injected into the combustor 66 by an injection nozzle. For high pressure gas turbine
applications, it is also advantageous to utilize multiple combustion chambers, or cans,
circumferentially situated about the rotational axis of turbine to combust the fuel 24
and the compressed air 54.
Inside the combustor 66, the fuel 24 and the compressed air 54 are mixed
and ignited by an igniter to produce an exothermic reaction. After combustion, the
hot, expanding gases 56 resulting from the combustion are directed to an inlet nozzle
^ r of the turbine 14. When expanded through the turbine 14, the hot gases create turbine
shaft power. The turbine power, in turn, drives the air compressor 12. Turbine
exhaust gas 26 exits the turbine.
In some embodiments, the turbine exhaust gas 26 may be fed to a steam
generator 30. In recuperated systems, the turbine exhaust gas 26 may first be fed
through the recuperator to heat the combustion air before the exhaust gas is
transmitted to additional heat recovery stages. The turbine exhaust gas 26 fed to the
steam generator 30 is used to heat water 28 and produce steam 32. The steam 32 is fed
to the steam generator 36, which may be a steam turbine powered generator, to
produce additional electric power 38.
In order to allow the combustor 66 to fire at higher temperatures, high
^ft carbon activity gas 25 is supplied via a first conduit 68 to the hot gas path to cool
and/or protect the hot gas path components of the turbine system 100. In some
embodiments, a regulator 74, such as a valve or a gland seal, may be present to
selectively control the amount of the high carbon activity gas distributed to the hot gas
path.
The high carbon activity gas may be the same fuel 24 as discussed earlier,
but may alternatively come from a separate source. Fluid hydrocarbon fuels such as,
but not limited to, methane, naphtha, butane, gasoline, jet fuel, biofuel or natural gas
would be appropriate for this use. In some embodiments, the high carbon activity gas
9
is delivered to the hot gas path components as a spray or in a gasified form. As used
herein, the term "hot gas path components" generally refers to hardware components
which are exposed to the hot gases produced by the combustor 66. These hot gas path
components may be stationary or rotating. Examples of such hot gas path
components include, but are not limited to, a combustor (including a combustor
component, for instance, a combustor liner or a flame holding segment), a shroud, a
vane or a blade of a turbine, a rocket, a ram jet or a scram jet.
The high carbon activity gas 25 may be delivered anywhere in the turbine
system 100 that allows for sufficient cooling and/or protection of a hot gas path
^ ^ component. As a non-limiting example, the figure shows the high carbon activity gas
25 being delivered directly to the turbine 14. Alternatively, the high carbon activity
gas 25 may be delivered to the combustor 66 or the shaft 20 where it may be
distributed throughout the turbine 14. The high carbon activity gas 25 could, in some
embodiments, be mixed with air from the compressor 12 to form a coolant. In other
embodiments, the high carbon activity gas 25 could protect a portion of the turbine 14
while compressor extraction air cools another portion (whether metal or CMC).
In some embodiments, the rotating blades in the turbine may be replaced.
Here, the high carbon activity gas would be used in CMC blades, completely
eliminating the chargeable air from the blades. The resulting rotational combustor
system would produce a well-mixed high temperature gas for subsequent turbine
stages. Use of fuels as the high carbon activity gas will lead to subsequent further
^r combustion, unlike the use of CO2 or other non-reacting gas alone. The high carbon
activity gases may, in some cases, react with certain phases of the refractory carbide;
however, in many cases these gases will mix and react downstream or away from the
refractory carbide surface.
The turbine power may also drive an electrical generator 16. The electrical
generator 16 uses the mechanical energy to produce electric power 22. The present
invention could also be configured without the electrical generator 16. Turbine power
would be transmitted and applied directly, as in the case of a mechanically driven
application.
10
Under certain conditions, it may be desirable to mix the high carbon activity
gas with carbon dioxide prior to delivery to the hot gas path. FIG. 2 illustrates a
turbine power generating system utilizing a high carbon activity gas 25 mixed with
carbon dioxide. In this embodiment, high carbon activity gas 25 is carried through a
first conduit 68 to a mixing chamber 72. Carbon dioxide is supplied from a source via
a second conduit 46 to the mixing chamber 72. The mixing chamber 72 need not be a
separate component as illustrated in the figure, but may be a confluence of the second
conduit 46 and the first conduit 68, as long as carbon dioxide can be mixed together
with the high carbon activity gas 25.
^ ^ In some embodiments, a valve (not shown)may be present to selectively
control the amount of the carbon dioxide and the amount of high carbon activity gas
that is to be mixed and distributed to the hot gas path. This valve allows for varying
the concentration of the high carbon activity gas and/or carbon dioxide delivered to
the hot gas path components.
In some embodiments, the carbon dioxide may be removed from the cooled
exhaust gas 42 and optionally stored in a reservoir 44, as shown. Carbon dioxide may
be removed from the exhaust gas 42 using many different processes. For example,
membrane separators or carbon dioxide scrubbers may be used to filter or otherwise
separate carbon dioxide from the exhaust gas stream. Because the present method and
system may be employed with any carbon dioxide sequestration process, further
^_ discussion of carbon dioxide sequestration methods is not provided herein.
Several advantages may be realized by adding sequestered carbon dioxide in
high carbon activity gas 25. In some instances, the gas turbine engine would no longer
need to use compressor bypass air for cooling. As such, all compressor air may then
be fed to the combustor. This allows (1) a smaller compressor to be used to reduce
"parasitic" energy losses incurred when turning the compressor, and/or (2) more air to
be fed to the combustor to produce more powerful combustion. Both of these changes
would improve output and efficiency. Also, in some instances, adding sequestered
carbon dioxide may increase the total mass flow of the turbine. This further increases
the output of the gas turbine engine. This increase in power would help offset the
11
energy cost of moving the carbon dioxide. Even though the carbon dioxide must be
compressed prior to its introduction into the hot gas path, a system such as the one
described that allows for a use of the sequestered carbon dioxide may be desirable
under the proper conditions.
FIG. 3 illustrates a schematic diagram of an example of a conventional
aviation high-pressure gas turbine and combustor in one embodiment.
The chemical activity of carbon required to stabilize refractory carbides,
such as SiC for a currently utilized CMC system, is established by injecting a
protective hydrocarbon gas to the hot gas path component, forming a protective layer
on a surface of the component. This hydrocarbon layer must do three things in order
to effectively protect the hot gas path component. The first is to exclude water vapor.
Without being held to any one theory, it is believed that this action is accomplished by
limiting the diffusion of water vapor through the protective layer. Additionally, it is
believed that the layer reacts with available H2O to reduce the H2O effective vapor
pressure at the surface of the metal carbide component. The second function of the
protective layer is to reduce the partial pressure of O2 in order to limit the rate of
direct oxidation of the metal carbide. If and when an oxide species finds its way into
the protective layer, either from the combustion gas or as an addition, it must be
reduced to limit the rate of oxidation at very high temperature. The O2 potential
needed for this is a function of both the refractory carbide of interest as well as
.^ temperature. Once these two functions are accomplished, the third purpose of the
^ F film is to maintain the carbon activity at a high enough level to minimize the
evaporation of the refractory carbide and thus stabilize it. Finally, as the high carbon
activity gas will typically be supplied at a much lower temperature than the
combustion gases, it may provide cooling to the hot gas path component, both as
internal cooling and film cooling, allowing much higher firing temperatures.
However, it is not necessarily the case that the refractory carbide be kept at a lower
temperature than the combustion gases, provided that the MC is fully stabilized.
A system that utilizes nitrogen as a cover gas may exclude water vapor
successfully. However, nitrogen in practice could not be made with low enough
12
oxygen content to prevent direct oxidation, which is an issue at temperatures greater
than 2500°F. The SiC«2 can dissociate and evaporate given the increase in SiO vapor
pressure, and the viscosity of the SiC>2 glass which forms on the CMC decreases to the
point that the once-protective oxide would be removed. Furthermore, not all MC
oxides are protective. These may evaporate or spall once formed. In these cases the
oxygen content of the cover gas must be kept low enough to limit substantial direct
oxidation even with the exclusion of water vapor.
In one example, combusted gas product (CO2) is re-introduced to the hot
section components after mixing with a hydrocarbon, e.g. methane or jet fuel, to
^ F adjust the carbon potential in the gas. For a SiC based CMC material without
coatings, the CO2 can oxidize SiC according to Eq. 1 a.):
la.) SiC + CC-2 • Si02 + 2C
With the Law of Mass Action however, at high carbon activity or low CO2 pressure,
the reaction of Eq. 1 a.) is driven to the left and SiC is stable. These conditions put
limits on the acceptable ranges for both carbon activity and C02 partial pressure.
If Si02 does form, it reacts with H2O vapor according to Eq. 1 b.) below resulting in
recession and consumption of the CMC:
1 b.) Si02 + 2H20 • Si(OH)4
^ ^ Combining Eq la.) and 1 b.) and representing the carbon-containing species as CH4
for example, gives the overall Eq 2.:
2.) SiC + 4H20 • Si(OH)4 + CH4
This shows that water in the air, or the post-combustion gases, leads to evaporation of
the SiC and production of methane (CH4). If a protective layer on the surface of the
refractory carbide is high in carbon chemical activity, such as with CH4 content, then
this reaction can be driven to the left, suppressing the consumption of the SiC.
Likewise, the direct sublimation of SiC proceeds according to Eq. 3.):
13
3.) SiC (s) • SiC (g) • Si (g) + C
in which gaseous Si is produced with carbon. Again, the provision of a high carbon
chemical activity can drive this reaction to the left, directly suppressing the
evaporation of the SiC.
According to this chemical stability scenario, if the refractory carbide can be
completely and efficiently covered by a layer of high carbon activity gas, then the
refractory carbide will withstand high temperatures such as 3000°F temperatures
^ ^ without loss or degradation of material. Further, a refractory carbide system with
^ ^ injection of a high carbon activity gas, with full coverage of the surface by these
gases, allows full protection of the surfaces even with combustion of the fuel in the
mainstream flow rather than only downstream. This system will result in
hydrocarbon stabilization of the refractory carbide components.
Refractory carbide components currently require environmental barrier
coatings (EBCs) to avoid oxidation and recession. However, in this present system,
no environmental coatings are required, thereby eliminating one source of possible
system failure or degradation. Using stand alone carbide components without EBC
has many benefits. 1.) EBCs are prime reliant, i.e. the life of the component is limited
by the life of the EBC. Use of high carbon activity gas in place of EBCs extends life
to that inherent of the mechanical durability of the carbide component and not the life
^ ^ of the EBC. 2.) Manufacturing and materials costs are greatly reduced by eliminating
EBCs. EBCs require multiple deposition steps to produce all the layers comprising
the coating. These processes add not only materials and labor costs but also the need
for investing in high-cost manufacturing equipment. 3.) EBCs add significant weight
to a coated component. For aviation applications in particular, improved performance
and reduced fuel consumption would result in the use of cover gases in lieu of EBCs.
The use of an uncoated refractory carbide component with a continuously renewed
vapor chemical protective film presents an opportunity for a 3000°F capable material
that may be protected using a hydrocarbon vapor source (e.g., fuel). Provision of such
turbine components could lead to completely new engine architectures in which both
14
non-chargeable and chargeable air cooling flows are nearly eliminated with
consequent increases in engine efficiency and specific fuel consumption (SFC) of
several points.
It is to be understood that the above description is intended to be illustrative,
and not restrictive. For example, the above-described embodiments (and/or aspects
thereof) may be used in combination with each other. In addition, many
modifications may be made to adapt a particular situation or material to the teachings
of the various embodiments without departing from their scope. While the invention
has been described in detail in connection with only a limited number of
W* embodiments, it should be readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to incorporate any
number of variations, alterations, substitutions or equivalent arrangements not
heretofore described, but which are commensurate with the spirit and scope of the
invention. Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may include only some
of the described embodiments. Accordingly, the invention is not to be seen as limited
by the foregoing description, but is only limited by the scope of the appended claims.

WE CLAIM:
1. A method for stabilizing a refractory carbide hot gas path component
comprising:
combusting a tuel in a combustor; and
delivering a high carbon activity gas to at least a portion of a hot gas path
component thermally coupled to a hot gas path,
wherein at least a portion of the hot gas path component comprises refractory
^ 1 ^ carbide.
2. The method of claim 1, further comprising selectively confroUing a flow of the
high carbon activity gas to the hot gas path.
3. The method of claim 1, wherein the hot gas path component is selected from a
combustor, a vane, a blade, a rocket, a ramjet, a scram jet and a shroud.
4. The method of claim 1, wherein the hot gas path component comprises a
portion of a turbine system.
5. The method of claim 4, wherein the turbine system comprises:
the combustor configured to combust air with the fuel to produce an exhaust
gas stream;
a turbine configured to convert energy of the exhaust stream into useful
mechanical energy; and
^ ^ a first conduit configured to deliver the high carbon activity gas to the hot gas
path.
6. The method of claim 5, wherein the turbine system further includes at least
one of:
a compressor configured to compress air;
a valve configured to selectively control an amount of the high carbon activity
gas distributed to the hot gas path;
a generator configured to convert mechanical energy produced by the turbine
into electrical energy; and
16
a shaft linking the compressor, the turbine, and the generator to allow
mechanical energy produced by the turbine to be utilized by the generator and
the compressor.
7. The method of claim 5, wherein the delivering the high carbon activity gas
forms a film of cover gas on a surface of the hot gas path component.
8. The method of claim 1, wherein the high carbon activity gas comprises at least
one hydrocarbon fuel.
9. The method of claim 8, wherein the high carbon activity gas further comprises
carbon dioxide.
^ ^ 10. The method of claim 9, comprising sequestering the carbon dioxide from an
exhaust stream of the turbine system in a reservoir.
11. The method of claim 1, wherein said refractory carbide comprises a ceramic
matrix composite.
12. A turbine power generation system, comprising:
a plurality of hot gas path components comprising a combustor and a turbine,
said combustor configured to combust a mixture of air with a fiiel to
produce an exhaust gas stream, and said turbine configured to convert
energy of said exhaust stream into useful mechanical energy; and
wherein said plurality of hot gas path components is thermally coupled to a
hot gas path; and
a first conduit configured to deliver a high carbon activity gas to at least one
hot gas path component of said plurality of hot gas path components;
^ p wherein a refractory carbide comprises at least a portion of said plurality of
hot gas path components.
13. The turbine power generation system according to claim 12, further
comprising a valve configured to selectively control an amoimt of said high
carbon activity gas delivered to said hot gas path.
14. The turbine power generation system according to claim 12, wherein said
combustor comprises a Coanda nozzle.
15. The turbine power generation system according to claim 12, further
comprising at least one of:
a compressor configured to compress air;
17
a generator configured to convert mechanical energy produced by said turbine
into electrical energy; and
a shaft linking said compressor, said turbine, and said generator to allow
mechanical energy produced by said turbine to be utilized by said generator
and said compressor.
16. The turbine power generation system according to claim 12, wherein said
refractory carbide comprises a ceramic matrix composite.
17. A cooling system for a hot gas path component, said system comprising:
a hot gas path component; and
a first conduit configured to deliver a high carbon activity gas to said hot gas
^ ^ path component,
wherein said high carbon activity gas forms a film of cover gas on a surface of
said hot gas path component.
18. The cooling system according to claim 17, wherein said hot gas path
component is selected from a combustor, a vane, a blade, a rocket, a ramjet, a
scram jet and a shroud.