Systems relating to geothermal energy and the operation of gas turbine engines   

BACKGROUND OF THE INVENTION

This present application relates generally to gas turbine engines and apparatus, systems and methods related thereto. More specifically, but not by way of limitation, the present application relates to apparatus, systems and methods for enhancing gas turbine energy performance by use of, among other things, geothermal energy.

With rising energy cost and increasing demand, the objective of improving the efficiency of gas turbine engines and more effectively exploiting renewable energy sources, such as geothermal energy, is a significant one. Toward this aim, as described below, cost-effective systems may be developed to use the relatively constant temperature found beneath the surface of the earth to improve gas turbine engine operation, particularly as it relates to hot and cold day operation.

As one of ordinary skill in the art will appreciate, the performance of gas turbine engines may be negatively affected when ambient temperatures are either too hot or too cold. For example, when the inlet air temperature is too hot, the gas turbine heat rate increases and output power deceases, which, of course, decreases the efficiency of the engine. On the other hand, when ambient temperatures fall below a certain level, icing may occur. This may occur at the inlet to the compressor, for example, on the inlet to the filter house, or the inlet guide vanes or other similarly situated components. The icing may damage equipment or cause it to operate ineffectively. For example, icing may prevent the IGV from operating correctly, which may negatively impact the efficiency of the turbine engine.

Convention systems have been proposed for resolving these issues. For example, for hot day operation, some conventional systems propose the use of a mechanical chiller system to cool the air entering the compressor. This option is undesirable because the energy required to operate the chiller significantly impacts the overall efficiency of the gas turbine engine as well as the high equipment cost associated with the chiller. Another conventional system is an inlet fogging system, which includes injecting water vapor into the air entering the compressor. The evaporation of the injected vapor decreases the temperature of the air flow. However, the proper function of this type of system is still at least somewhat dependent on ambient conditions and requires the installation of costly hardware and control systems. Further, the addition of water to the engine flow path in this manner may cause more rapid degradation and erosion of parts within the flow path and, as such, generally increases maintenance costs.

For cold day operation, conventional systems generally include drawing energy from the engine exhaust to raise the temperature of the air entering the compressor. Again, though, such systems require an installation of costly hardware and control systems. Further, to the extent that the energy in the exhaust may be used for other purposes, such as, for example, as the heat source in the steam turbine of a combined cycle plant, the diverting of a portion of the exhaust energy generally decreases the overall efficiency of the power plant.

As a result, there remains a need for improved apparatus, systems and methods for cost-effectively alleviating performance issues in gas turbine engines that occur during hot and cold day operation.

The present application thus describes a geothermal heat exchange system for use in a gas turbine power plant that includes an inlet plenum that directs a flow of air to a compressor that compresses a flow of air that is then mixed with a fuel and combusted in a combustor such that the resulting flow of hot gas is directed through a turbine, the geothermal heat exchange system comprising means for exchanging heat between a ground and the flow of air moving through the inlet plenum.

The present application further describes a geothermal heat exchange system for use in a gas turbine power plant that includes an inlet plenum that directs a flow of air to a compressor that compresses a flow of air that is then mixed with a fuel and combusted in a combustor such that the resulting flow of hot gas is directed through a turbine, the geothermal heat exchange system comprising a plurality of heat pipes that are configured to exchange heat between a location within a ground at a predetermined depth and the flow of air moving through the inlet plenum; wherein the heat pipe comprises a two-phase heat transfer device that includes a sealed tube made of a material with high thermal conductivity both a hot end and a cold end; and the sealed tube is evacuated and backfilled with a small quantity of a working fluid.

These and other features of the present application will become apparent upon review of the following detailed, description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a gas turbine engine typical of the types of turbine engines that may be used in power plants in which embodiments of the present invention may be used;

FIG. 2 illustrates a schematic plan of a gas turbine engine, the representation of which will be used to illustrate power plants according to embodiments of the present invention;

FIG. 3 is a schematic plan illustrating the configuration of a gas turbine power plant according to an exemplary embodiment of the present application;

FIG. 4 is a schematic plan illustrating a front view (i.e., into the mouth of the inlet plenum) of the configuration of heat pipes in the inlet plenum according to an exemplary embodiment of the present application; and

FIG. 5 is a schematic plan illustrating the configuration of a gas turbine power plant according to an alternative embodiment of the present application.

DETAILED DESCRIPTION

Illustrative embodiments of the invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

To describe clearly the invention of the current application, it may be necessary to select terminology that refers to and describes certain machine components or parts of a turbine engine. Whenever possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. However, it is meant that any such terminology be given a broad meaning and not narrowly construed such that the meaning intended herein and the scope of the appended claims is unreasonably restricted. Those of ordinary skill in the art will appreciate that often certain components may be referred to with several different names. In addition, what may be described herein as a single part may include and be referenced in another context as consisting of several component parts, or, what may be described herein as including multiple component parts may be fashioned into and, in some cases, referred to as a single part. As such, in understanding the scope of the invention described herein, attention should not only be paid to the terminology and description provided, but also to the structure, configuration, function, and/or usage of the component as provided herein.

In addition, several descriptive terms may be used herein. The meaning for these terms shall include the following definitions. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to a flow of working fluid through the turbine. As such, the term “downstream” means the direction of the flow, and the term “upstream” means in the opposite direction of the flow through the turbine engine. Related to these terms, the terms “aft” and/or “trailing edge” refer to the downstream direction, the downstream end and/or in the direction of the downstream end of the component being described. And, the terms “forward” or “leading edge” refer to the upstream direction, the upstream end and/or in the direction of the upstream end of the component being described. The term “radial” refers to movement or position perpendicular to an axis. It is often required to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “inboard” or “radially inward” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “outboard” or “radially outward” of the second component. The term “axial” refers to movement or position parallel to an axis. And, the term “circumferential” refers to movement or position around an axis.

Referring now to the figures, FIG. 1 is an illustration of a convention gas turbine engine 50. In general, gas turbine engines operate by extracting energy from a pressurized flow of hot gas that is produced by the combustion of a fuel in a stream of compressed air. As illustrated in FIG. 1, gas turbine engine 50 may be configured with an axial compressor 52 that is generally mechanically coupled by a common shaft or rotor to a downstream turbine section or turbine 54, and a combustor 56 positioned between the compressor 52 and the turbine 54.

The compressor 52 may include a plurality of stages, with each stage having a row of compressor rotor blades followed by a row of compressor stator blades. Particularly, a stage generally includes a row of compressor rotor blades, which rotate about a central shaft, followed by a row of compressor stator blades, which remain stationary during operation. The compressor stator blades generally are circumferentially spaced one from the other and fixed about the axis of rotation. The compressor rotor blades are attached to the shaft such that, when the shaft rotates during operation, the compressor rotor blades rotate about it. As one of ordinary skill in the art will appreciate, the compressor rotor blades are configured such that, when spun about the shaft, they impart kinetic energy to the air or fluid flowing through the compressor 52. The turbine 54 also may include a plurality of stages. A turbine stage may include a plurality of turbine buckets or turbine rotor blades, which rotate about the shaft during operation, and a plurality of nozzles or turbine stator blades, which remain stationary during operation. The turbine stator blades generally are circumferentially spaced one from the other and fixed about the axis of rotation. Whereas, the turbine rotor blades may be mounted on a turbine wheel for rotation about the shaft.

In use, the rotation of compressor rotor blades 60 within the axial compressor 52 compresses a flow of air. In the combustor 56, energy is released when the compressed air is mixed with a fuel and ignited. The resulting flow of pressurized hot gases from the combustor 56, which generally is referred to as the working fluid of the engine, is then expanded through the turbine rotor blades. The flow of working fluid induces the rotation of the turbine rotor blades about the shaft. Thereby, the energy of the fuel is transformed into the kinetic energy of the flow of working fluid, which is then transformed into the mechanical energy of the rotating blades and, via the connection between the rotor blades and the shaft, the rotating shaft. The mechanical energy of the shaft may then be used to drive the rotation of the compressor rotor blades, such that the necessary supply of compressed air is produced, and also, for example, to drive a generator (not shown) to produce electricity.

FIG. 2 illustrates a schematic plan of a gas turbine engine 100, the representation of which will be used to illustrate power plants according to embodiments of the present invention. As shown, the gas turbine engine 100 may include a compressor 52, a combustor 56, and a turbine 54. At the upstream end of the compressor 52, an inlet plenum 112 may be located. The inlet plenum 112 essentially provides a channel through which a supply of air is directed into the compressor 52. It will be appreciated that the configuration of the inlet plenum 112 may comprise many different configurations. As illustrated, the inlet plenum may be configured to have a relatively wide mouth that decreases in cross-sectional area into a channel that directs a supply of air to the inlet of the compressor 52. Of course, in some gas turbine engine applications, a significantly smaller structure may be used to provide an inlet for the air entering the compressor 52. As such, as used herein, inlet plenum 112 is meant to describe any structure, large or small, that is positioned upstream of one of the stages of the compressor 52 through which at least a portion of the air entering the compressor 52 passes. As one of ordinary skill in the art will appreciate, the inlet plenum 112 may include certain components, such as filters, silencers, etc., that improve the function of it. However, because these components are not essential or preclusive to the function of a power plant according to the present invention, they have been omitted from the figures. As will be seen, the flexibility of embodiments of the present invention allows that it may be incorporated in a variety of ways into substantially any type of inlet plenum 112 structure or directly into the compressor 52 itself.

FIG. 3 is a schematic plan illustrating the configuration of a gas turbine power plant 130 according to an embodiment of the present application. Similar to the system shown in FIG. 2, the gas turbine power plant 130 may include a compressor 52, a combustor 56, a turbine 54, and an inlet plenum 112. According to the present invention, the gas turbine power plant 130 also may include a heat exchange device that provides for the exchange of energy between the flow of air in the inlet plenum 112 or through the compressor 52 and the earth or ground 134. As used herein, “ground” is meant to include any type of geothermal medium. In some embodiments, ground refers to the earth at a predetermined level underground, as shown in FIG. 3. As will be appreciated, the temperature of the ground beneath the surface of the earth remains fairly constant regardless of the season. This is particularly true at depths between approximately 25 and 500 feet beneath the surface of the ground. In some embodiments, shallower depths also may be used; for example, depths between approximately 10 and 50 feet beneath the surface of the ground may be appropriate for certain applications.

These relatively constant subsurface temperatures mean that the ground temperature within these given depth ranges remains relatively cool year round even in warm climate locations. For example, the ground temperature of Atlanta, Ga. remains a fairly constant 62° F. throughout the year. At the other end of the spectrum, in relatively cold climate locations, the ground temperature remains relatively warm even in the coldest months of the year. For example, the ground temperature of New York, N.Y. remains a fairly constant 52° F. throughout the year. As stated, “ground” also may refer to other types of geothermal mediums, such as a subsurface location in a body of water, such as a lake or a river or the ocean.

As shown in FIG. 3, in one preferred embodiment, the heat exchange device may be one or more elongated heat transfer structures 136, such as one or more pipes, that extend from a position within the ground (which, for example, may be a position in the ground below the earth\'s surface, a subsurface location in a lake, or other such position) to a position within the inlet plenum 112. The heat transfer structures 136 may be configured to efficiently transfer heat from a hot side (which, depending on the application as well as current ambient and ground temperature conditions, may be either the ground or the inlet plenum) to a cold side (which, depending on the application as well as current ambient and ground temperature conditions, may be either the ground or the inlet plenum). At the hot side and the cold side, the structure 136 generally will include an outer surface that conducts heat well, such as a metallic surface. In addition, one end of the structure 136, which, as shown may be a pipe, may be placed within the ground at a desired depth such that it contacts the surrounding earthen material or water and heat transfer between the surrounding material and the structure 136 is as desired. The other end of the structure or pipe 136 may be placed in the inlet plenum 112 such that the air flowing through the inlet plenum 112 flows over and around it so heat transfer occurring between the structure 136 and the air flow occurs at a desired rate.

In some embodiments, the elongated structure 136 of FIG. 3 may comprise a conventional heat pipe. A heat pipe is a two-phase heat transfer device with a high effective thermal conductivity. A heat pipe generally consists of a sealed pipe or tube made of a material with high thermal conductivity such as steel, copper or aluminum at both hot and cold ends. It can be cylindrical or planar, and, as discussed below, the inner surface may be lined with a capillary wicking material. In construction, the heat pipe is evacuated and backfilled with a small quantity of a working fluid such as water, acetone, nitrogen, methanol, ammonia, or sodium. Other types of inorganic materials also may be used. Heat is absorbed in the evaporator region by vaporizing the working fluid. The vapor transports heat to the condenser region where the vapor condenses, releasing heat to a cooling medium.

In some embodiments, the heat pipe of the current invention may be a looped heat pipe, i.e., a heat pipe with a wick structure that exerts capillary pressure on the liquid phase of the working fluid. The wick structure may include any material capable of exerting sufficient capillary pressure on the condensed liquid to wick it back to the heated end. In some embodiments, the wick structure may be one of the common wick structures used in conventional heat pipe applications, which include a groove wick structure (i.e., a series of grooves the run lengthwise along the inner surface of the heat pipe), a wire mesh wick structure, a powder metal wick structure, and a fiber/spring wick structure. The heat pipe may not need a wick structure if gravity or some other source of acceleration is sufficient to overcome surface tension and cause the condensed liquid to flow back to the heated end.

As shown in FIG. 3, in some embodiments, the heat pipes 136 of the present invention may be aligned vertically. In this arrangement and in the absence of a wicking structure, geothermal energy from the ground 134 may be used to heat the flow of air into the compressor 52 (i.e., the warmer ground end of the heat pipe 136 evaporates a working fluid that condenses at the cold end of the heat pipe in the inlet plenum 132 thereby heating the air flowing around it). This arrangement may be used when the ground temperature exceeds the air temperature, which may be effective during cold day operation in preventing ice formation on engine components.

According to an alternative embodiment of the present application, a wick structure, as described above, may be employed so that the vertically aligned heat pipes of FIG. 3 still may be used when the ground temperature is less than ambient air temperature. In this case, engine operators may desire to cool the ambient air being supplied to the compressor. Instead of gravity returning the condensed fluid to the cold side of the heat pipe, the capillary pressure provided by the wick structure overcomes gravity, wicking the condensed fluid upward from the colder ground side to the warmer side inside the plenum. Once inside the plenum, the heat pipe absorbs heat from the passing air flow via the evaporation of the wicked fluid. Cooling the air in this manner, as discussed, generally increases the efficiency of the gas turbine power plant and may be used when the ambient temperature is high to improve engine performance.

The advantages of using heat pipes for any necessary cooling or heating several. First, heat pipes are completely passive heat transfer systems, having no moving parts to wear out. Second, heat pipes require no energy to operate. Third, heat pipes are relatively inexpensive. Fourth, heat pipes are flexible in size, shape and effective operating temperature ranges.

In operation, when ambient temperatures go below a desirable level, heat pipes having the configuration shown in FIG. 3 may be activated to pump heat from underground to heat the air passing through the inlet plenum 112. This, for example, may be used to prevent unwanted ice from forming on the inlet filter house or inlet guide vanes. On the other hand, when ambient temperatures go above a desirable level, heat pipes having the configuration shown in FIG. 3 may be activated to pump heat from the air passing through the inlet plenum 112 into the ground. This, for example, may be used on hot days to increase the efficiency of the engine.

As shown in FIGS. 3 and 4, in some embodiments, the heat pipes may have a plurality of branches. The branches 138 generally increase the surface area for heat exchange with the earth.

FIG. 4 illustrates a front view of the inlet plenum 112 (i.e., into the mouth of the inlet plenum 112) and demonstrates an exemplary configuration of heat transfer structure 136 (in this case, heat pipes) within the inlet plenum according to an embodiment of the present application. As shown, the heat pipes may be arranged vertically and extend from the interior of the inlet plenum 112 to a desired depth within the ground 134. A plurality of heat pipes may be evenly distributed across the inlet plenum 112. In certain applications, more or less heat pipes may be used.

Referring now to FIG. 5, an alternative embodiment of a gas turbine power plant according to the present application is shown, a gas turbine power plant 150. In this case, a secondary heat transfer structure 152 is configured to exchange heat between the inlet plenum 112 and the exhaust of the turbine 54. A heat recovery steam generator 154 may be present in this type of power plant, as shown. A portion of the turbine exhaust may be diverted from the main flow via an exhaust by pass 155 and directed through a heat transfer unit 156. Within the heat transfer unit 156, the exhaust may heat the secondary heat transfer structure 152. The secondary heat transfer structure 152, as shown, may connect to the heat transfer structure 136, where the heat from the exhaust may be pumped into the inlet plenum 112. This configuration provides an additional heating element to the power plant, which, as one of ordinary skill in the art will appreciate, may be necessary for certain applications. The secondary heat transfer structure 152 may comprise heat pipes consistent with the description above.

As stated, in preferred embodiments, the heat transfer structure 136 and the secondary heat transfer structure 152 comprise heat pipes. In other embodiments according to the present invention, the heat transfer structure 136 and the secondary heat transfer structure 152 may comprise other conventional heat transfer structures or systems. For example, a heat sink made from solid pipes of conductive metals may be used in place of the heat pipes. While the two-phase heat transfer associated with heat pipes may be more efficient mode of heat transfer, the single phase conductive heat transfer associated with certain solid materials may be sufficient for some applications. In other embodiments, a heat transfer fluid may be circulated via a pump through a circuit so that the fluid exchange heat between the ground 134 and the inlet plenum 112. In still other embodiments, a thermosiphon may be used. As one of ordinary skill in the art will appreciate, a thermosiphon is a mechanism similar to a heat pipe in which thermal energy is transferred by fluid buoyancy rather than evaporation and condensation.

As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present application. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.