Method and control system for controlling compressor output of a gas turbine engine

A method and control system for controlling compressor output for a gas turbine engine is disclosed. The power output of a gas turbine engine can vary and be below desired output levels due to operating conditions such as ambient temperature and elevation. These operating conditions can lead to lower output of the gas compressor of the turbine engine and lower operating temperatures within or proximate to a turbine of the gas turbine engine and lead to less power output. Additional fuel can be added to increase power to the gas producer shaft and increase turbine temperature of the gas turbine engine. A power transfer device can be used to remove or add power to the gas producer shaft to balance the gas producer mechanical limits and turbine thermal limits at maximum levels and lead to higher power output.

TECHNICAL FIELD

The present disclosure generally pertains to gas turbine engines. More particularly this application is directed toward a method and control system for controlling compressor output of a gas turbine engine.

BACKGROUND

Gas turbine engines can maximize output power and efficiency at a given ambient temperature by designing the gas producer shaft speed and at maximum power turbine temperature limits to be met simultaneously. This is known as the match temperature. In a typical turbine engine this situation occurs at a single ambient temperature. However, if power can be independently input or withdrawn from the gas producer shaft it is possible to stay optimized at all ambient temperature, increasing the maximum power capability.

U.S. Pat. No. 7,188,475 to McGinley et al. describes a two spool gas turbine engine used to drive variable speed loads, such as an electric generator, or the fan/propeller of an aircraft engine. The gas turbine engine is designed to withstand transient speed and temperature conditions which are encountered when sudden changes to the load on the generator, fan, or propeller occur. By adding a relatively small motor/generator to the gas generator spool of the gas turbine engine, the compressor speed and airflow can be quickly adjusted to compensate for external load changes. This reduces the severity and duration of the transient conditions, resulting in decreased operation and reliability problems such as overspeed, compressor surge, and high turbine temperature. The motor/generator may also be used as an engine starting device.

The present disclosure is directed toward overcoming one or more of the problems discovered by the inventors.

SUMMARY

A method for controlling compressor output of a two shaft gas turbine engine is disclosed herein. The method includes determining a gas producer shaft speed and a temperature of the turbine. The method further includes in response to the gas producer shaft speed being below a gas producer shaft speed threshold and the temperature of the turbine being within a predetermined range of a turbine temperature threshold, increasing the amount of fuel to be combusted within the combustion chamber and by applying additional power to the gas producer shaft with the power transfer device. The method further includes in response to the gas producer shaft speed being within a predetermined range of the gas producer shaft speed threshold and the measured turbine temperature being below the turbine temperature threshold increasing the amount of fuel to be combusted within the combustion chamber and by removing power from the gas producer shaft with the power transfer device.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the accompanying drawings, is intended as a description of various embodiments and is not intended to represent the only embodiments in which the disclosure may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that embodiments of the disclosure can be practiced without these specific details. In some instances, well-known structures and components are shown in simplified form for brevity of description.

FIG. 1is a schematic illustration of an exemplary gas turbine engine. Some of the surfaces have been left out or exaggerated for clarity and ease of explanation. Also, the disclosure may reference a forward and an aft direction. Generally, all references to “forward” and “aft” are associated with the flow direction of primary air (i.e., air used in the combustion process), unless specified otherwise. For example, forward is “upstream” relative to primary air flow, and aft is “downstream” relative to primary air flow.

In addition, the disclosure may generally reference a center axis95of rotation of the gas turbine engine, which may be generally defined by the longitudinal axis of its gas producer shaft120(sometimes referred to as a gas producer rotor) and power turbine shaft130(supported by a plurality of bearing assemblies150). The center axis95may be common to or shared with various other engine concentric components. All references to radial, axial, and circumferential directions and measures refer to center axis95, unless specified otherwise, and terms such as “inner” and “outer” generally indicate a lesser or greater radial distance from, wherein a radial96may be in any direction perpendicular and radiating outward from center axis95.

Where the drawing includes multiple instances of the same feature, for example bearing assemblies150, the reference number is only shown in connection with one instance of the feature to improve the clarity and readability of the drawing. This is also true in other drawings which include multiple instances of the same feature.

A gas turbine engine100can be referred to as a two shaft gas turbine engine and include a gas producer shaft120and a power turbine shaft130. The gas producer shaft120and power turbine shaft130can be independent and rotate at different speeds.

The gas turbine engine100includes an inlet110, a gas producer or compressor200, a combustor300, a turbine400, an exhaust500, and a power output coupling50.

The compressor200includes one or more compressor rotor assemblies220, inlet guide vanes255, and one or more compressor variable guide vanes250and fixed guide vanes251(sometimes referred to as stators or stationary vanes). The variable guide vanes250or the fixed guide vanes251axially follow each of the compressor disk assemblies220. In some embodiments, the guide vanes250within the first few compressor stages are variable guide vanes. The variable guide vanes250may each be rotated about their own axis to control gas flow.

The inlet guide vanes255axially can precede the variable guide vanes250. The inlet guide vanes255may be rotated to modify or control the inlet flow area of the compressor200by an actuation system260. In some embodiments, the inlet guide vanes255are variable guide vanes and may be rotated about their own axis.

The actuation system260can include an actuator261, actuator arm262, and a linkage system263. The actuator261can move actuator arm262that moves or translates the components of the linkage system263. The linkage system263can include linkage arms264. A linkage arm264may be connected to each inlet guide vane255and each variable guide vane250. When the actuator arm262is moved it causes each linkage arm264to be moved and rotate each inlet guide vane255and each variable guide vane250. The actuator261, actuator arm262, and linkage arms264may be coupled together and configured to rotate each variable guide vane the same amount. In an embodiment the action system260is in electrical communication with a program logic controller800. The program logic controller800can send commands to the actuation system260such that the actuation system260changes the position of the inlet guide vanes255and the variable guide vanes250.

The combustor300includes one or more fuel injectors600(sometimes referred to as injectors) and includes one or more combustion chambers390. The turbine400includes one or more turbine rotor assemblies420and one or more nozzle assemblies450. The exhaust500includes an exhaust diffuser510and an exhaust collector520.

One or more of the rotating components are coupled to each other and driven by the gas producer shaft120or the power turbine shaft130. The power turbine shaft130can be axially separated from the gas producer shaft120and be located downstream from the gas producer shaft120.

As illustrated, the combustor300may include a combustion chamber390or “liner”. Depending on its configuration, the combustor300may include one or more of the above components. For example, the combustor300may include a plurality of injectors600annularly distributed around the center axis95.

In operation, air10enters the gas turbine engine100via its inlet110as a “working fluid”, and is compressed by the compressor200. In the compressor200, the working fluid is compressed by the series of compressor rotor assemblies220. In particular, the air10is compressed in numbered “stages”, the stages being associated with each compressor rotor assembly220. For example, “4th stage air” may be associated with the 4th compressor rotor assembly220in the downstream or “aft” direction. While only five stages are illustrated here, the compressor200may include many more stages or fewer stages.

Similar to the compressor rotor assemblies220, the turbine rotor assemblies420and nozzle assemblies450can be positioned in numbered “stages”. The stages can be associated with the position of each turbine rotor assembly420and nozzle assembly450in the order that they received combusted air. For example, 3rdstage combusted air may be associated with a third stage nozzle assembly of the nozzle assemblies450. Alternatively, the stages can be associated with the position of each turbine rotor assembly420and nozzle assembly450in the order that they are received by the power turbine shaft130. For example, the nozzle assemblies450can include a first power turbine stage nozzle assembly that represents the first nozzle assembly450located proximate to the power turbine shaft130.

Once compressed air10leaves the compressor200, it enters the combustor300, where it is diffused and fuel is added. Air10and fuel are injected into the combustion chamber390via injector600and ignited. After the combustion reaction, energy is then extracted from the combusted fuel/air mixture via the turbine400by each stage of the series of turbine rotor assemblies420. The initial stages (for example stages one and two) of the turbine400drive the gas producer shaft120, thus driving the compressor200. The combusted air progresses within the turbine400and the last stage or stages (for example stage three and four) of the turbine400drives the power turbine shaft130, thus generating power to the power output coupling50. This portion of the turbine400can be referred to as a power turbine. In an embodiment the gas producer shaft120and power turbine shaft130are separated proximate a 3rdstage of the turbine400.

Exhaust gas90may then be diffused in exhaust diffuser510and collected, redirected, and exit the system via an exhaust collector520. Exhaust gas90may also be further processed (e.g., to reduce harmful emissions, and/or to recover heat from the exhaust gas90).

The gas turbine engine100can include a power transfer device700and a gearbox750. In an embodiment the power transfer device700and gearbox750are located proximate to the forward end of the gas turbine engine100. The gearbox750can be connected to the gas producer shaft120. The power transfer device700can be an electric motor and generator that can be connected to the gas producer shaft120. In other examples the power transfer device700can represent a brake to absorb power and a turbo expander to provide power to the gas producer shaft120. The power transfer device700can add or subtract power from the gas producer shaft120. The power transfer device700can be connected to the gearbox750and may transmit power to the gearbox750. In other examples the power transfer device700is part of the gearbox750and the gearbox750can import and export power from the gas producer shaft120.

The gas turbine engine100can include a programmable logic controller (PLC)800. The programmable logic controller800can be used to control components of the gas turbine engine100, engine load, and other off package devices. Power transfer device conduit705can extend between the PLC800and the power transfer device700. The PLC800can be in signal communication with the power transfer device700via the power transfer device conduit705.

The PLC800can be connected to a speed sensor816and a temperature sensor818. The speed sensor816can be located adjacent to the gas producer shaft120. The speed sensor816can be configured to capture speed information related to gas producer shaft120as it rotates about the center axis95during operation, also referred to as gas producer shaft speed (referred to as “NGP”).

The gas turbine engine100can include speed sensor conduit817that can extend from the speed sensor816to the PLC800. The speed sensor conduit817can provide signal communication between the speed sensor816and the PLC800. The PLC800can determine the NGP based on the captured speed information from the speed sensor816.

The temperature sensor818can be located within the turbine400. In the embodiment, the temperature sensor818is located within the 4thstage of the nozzle assemblies450. In other examples the temperature sensor818can be located within the 3rdstage or 4th stage of the turbine rotor assemblies420and nozzle assemblies450. In an example the temperature sensor818is located within the power turbine section of the turbine400. In another example the temperature sensor is located downstream of the gas producer shaft120. The temperature sensor818can be configured to capture information related to the temperature within the turbine at a specific location and this temperature can be referred to as T5. Typically T5can be measured and used to model T3, turbine rotor inlet temp. In a standard engine the T3/T5ratio can be fairly constant. T3is usually the thermal limit of the gas turbine engine100.

The gas turbine engine100can include temperature sensor conduit819that can extend from the temperature sensor818to the PLC800. The temperature sensor conduit819can provide signal communication between the temperature sensor818and the PLC800. The PLC800can determine T5based on the captured temperature information from the temperature sensor818.

The gas turbine engine100can include fuel injector conduit610that extends from the fuel injector600to the PLC800. The fuel injector conduit610can provide signal communication between the fuel injector600and the PLC800. The PLC800can provide signals to the fuel injector600to instruct the fuel injector to increase or decrease the amount of fuel being injected by the fuel injector600.

In an example the PLC800can communicate with the power transfer device700, fuel injectors600, and sensors816,818, wirelessly.

In an embodiment the power transfer device700and PLC800make up a control system.

One or more of the above components (or their subcomponents) may be made from stainless steel and/or durable, high temperature materials known as “superalloys”. A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys may include materials such as HASTELLOY, INCONEL, WASPALOY, RENE alloys, HAYNES alloys, INCOLOY, MP98T, TMS alloys, and CMSX single crystal alloys.

FIG. 2is a functional block diagram of an embodiment of the programmable logic controller fromFIG. 1. The PLC800may be in digital communication with the power transfer device700, fuel injector600, speed sensor816and temperature sensor818. The PLC800may have a controller804operatively connected to a database814via a link822connected to an input/output (I/O) circuit812. It should be noted that, while not shown, additional databases814may be linked to the controller804in a known manner. Furthermore, these databases814may be external to the PLC800.

In one embodiment the controller804includes a program memory806, the processor808(may be called a microcontroller or a microprocessor), a random-access memory (RAM)810, and the input/output (I/O) circuit812, all of which are interconnected via an address/data bus821. It should be appreciated that although only one microprocessor808is shown, the controller804may include multiple microprocessors808. Similarly, the memory of the controller804may include multiple RAMs810and multiple program memories806. Although the I/O circuit812is shown as a single block, it should be appreciated that the I/O circuit812may include a number of different types of I/O circuits. The RAM(s)810and the program memories806may be implemented as semiconductor memories, magnetically readable memories, nonvolatile memories, and/or optically readable memories, for example.

The program memory806and RAM810can be a non-transitory computer-readable medium having stored thereon computer-executable code (e.g., disclosed software or subroutines) and/or data. In one embodiment, the program memory also includes long-term or permanent memory, such as flash memory and/or ROM. The program memory806and/or the RAM810may store various applications (i.e., machine readable instructions) for execution by the microprocessor808. For example, an operating system830may generally control the operation of the PLC800and provide a user interface to the PLC800to implement the processes described herein. The program memory806and/or the RAM810may also store a variety of software832for accessing specific functions of the PLC800.

By way of example, and without limitation, the software832may include, among other things: obtaining the digital signal associated with speed information provided by speed sensor816, generating a NGP value, comparing the NGP value to a gas producer shaft speed threshold (NGPmax), also referred to as NGP topped, sending digital signals to the power transfer device700in response to the NGP being lower than the NGPmax, obtaining the digital signal associated with temperature information provided by the temperature sensor818, generating a T5value, comparing the T5value to a turbine temperature threshold (T5max), also referred to as T topped, sending digital signals to the power transfer device700in response to the T5being lower than the T5max, sending digital signals to the fuel injector600to increase the amount of fuel being injected into the combustion chamber390if the NGP is less than the NGPmax and/or the T5is less than the T5max.

The software832may include subroutines to execute any of the operations described herein. In an example the software832can be firmware. The software832may include other subroutines, for example, interfacing with other hardware in the PLC800, etc. The program memory806and/or the RAM810may further store data related to the configuration and/or operation of the PLC800, and/or related to the operation of one or more software832. For example, data may be data gathered from the speed sensor816and temperature sensor818, data determined and/or calculated by the processor808, etc. In addition to the controller804, the PLC800may include other hardware resources. The PLC800may also include various types of input/output hardware such as the visual display826and input device(s)828(e.g., keypad, keyboard, etc.). It may be advantageous for the PLC800to communicate with a broader network (not shown) through any of a number of known networking devices and techniques (e.g., through a computer network such as an intranet, the Internet, etc.).

INDUSTRIAL APPLICABILITY

The present disclosure generally applies to increasing the power generation of gas turbine engines100. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine100, but rather may be applied to stationary or motive gas turbine engines, or any variant thereof. Gas turbine engines, and thus their components, may be suited for any number of industrial applications, such as, but not limited to, various aspects of the oil and natural gas industry (including include transmission, gathering, storage, withdrawal, and lifting of oil and natural gas), power generation industry, cogeneration, aerospace and transportation industry, to name a few examples.

Gas turbine engines100can be designed and calibrated to operate at/near a gas producer shaft speed threshold (NGPmax), such as at 100% maximum design speed, and a turbine temperature threshold (T5max). Gas turbine engines100are designed to prevent operating above the NGPmax and T5max values, but can lose out on power output if operated below either the NGPmax and T5max values. By adjusting the position of the inlet guide vanes255and the variable guide vanes250, adding or subtracting power from the gas producer using the power transfer device700, and adding fuel to the combustor300, the NGP and T5values can be brought up and closer to NGPmax and T5max values, additional power output can be captured via the power turbine shaft130.

The turbine temperature threshold (T5max) is to limit the temperature experienced within the gas turbine engine100proximate to area of the combustion chamber390and the first stage of the nozzle assemblies450, also referred to as the “hot section”. If the hot section is exposed to temperatures above the design limits the gas turbine engine100can experience detrimental effects such as increased wear. Temperature, sometimes referred to as T3, within the hot section, can be very high during engine operation. The T3value is typically inferred by T5which is at a different, cooler location. The ratio between T3and T5values can be predicted and can be used to infer temperature values within the gas turbine engine100in areas such as the hot section. Using the maximum design temperature (T3max) for the hot section and the ratio between T3and T5the turbine temperature threshold (T5max) can be determined.

These gas turbine engines100are typically designed for a particular ambient temperature (for example 59 degrees Fahrenheit) and elevation. Operating different from these design conditions can promote the gas turbine engine100to operate below the gas producer shaft speed threshold (NGPmax) and/or the turbine temperature threshold (T5max) and thus limit the power output of the gas turbine engine100.

Typically, the gas producer shaft120derives its power from the first few stages of the turbine rotors420and nozzle assemblies150. In a disclosed embodiment, a power transfer device700can be used to increase or decrease NGP to improve the power output of the gas turbine engine100.

FIG. 3is a flowchart of a method for controlling the speed of a gas producer shaft of the gas turbine engine fromFIG. 1. The following description of the flowchart also makes reference to elements depicted inFIG. 2.

The method/process900begins at block905and includes the PLC800checking if more power is desired from the gas turbine engine100. If more power is desired, the process continues to block910. If more power is not desired the process proceed to block930and maintains the operating parameters for the duration of the process interval.

At block910, the PLC800determining a gas producer shaft speed (NGP) and a turbine temperature (T5). The PLC800can receive the gas produced shaft speed information captured by the speed sensor816and determine the NGP. The PLC800can receive the turbine temperature information captured by the temperature sensor818and determine the T5value.

At block920, the PLC800compares the NGP value to the NGPmax value and the T5to the T5max value. If NGP is approximately equal to NGPmax and the T5value is approximately equal to T5max then the PLC800proceeds to block930. In other words, if the NGP is within a predetermined range of the NGPmax and the T5value is within a predetermined range of the T5max then the PLC800proceeds to block930.

If NGP is not approximately equal to the NGPmax and/or the T5value is not approximately equal to the T5max then proceed to block940. In other words, if NGP is not within a predetermined range of NGPmax and/or the T5value is not within a predetermined range of T5max then proceed to block940.

At block930, the PLC800maintains the operating parameters and does not send out digital signals to the fuel injectors600and power transfer device700to make additional adjustments. The process900is then repeated starting back at block910.

At block940, the PLC800compares the NGP value to the NGPmax value and the T5to the T5max value. If NGP is below NGPmax and the T5value is below T5max then the PLC800proceeds to block950. If NGP is not below NGPmax or the T5value is not below T5max then the PLC800proceeds to block960.

At block950, the PLC800sends digital signals to the fuel injector600to increase the fuel injection amount. The fuel injector600then injects additional fuel to be combusted within the combustion chamber390of the gas turbine engine100. In an example the PLC800communicates to the fuel injector to increase the fuel amount until NGP is approximately at/within a predetermined range of NGPmax and/or T5is approximately at/ a predetermined range of T5max.

At block960, the PLC800compares the NGP value to the NGPmax value and the T5to the T5max value. If NGP is within a predetermined range of NGPmax and the T5value is below T5max then the PLC800proceeds to block970. In an example if NGP is within a predetermined range of NGPmax and the inlet guide vanes255and variable guide vanes250are in a maximum position and the T5value is below T5max, then the PLC800proceeds to block970. If NGP is not within the predetermined range of NGPmax then the PLC800proceeds to block980.

At block970, the PLC800sends digital signals to the power transfer device700to remove power from the gas producer shaft120. The power transfer device700then removes power from the gas producer shaft120. The PLC800then proceeds to block950where additional fuel is added. The additional fuel added leads to an increase of power to the gas producer shaft120to balance the power removed from the gas producer shaft120by the power transfer device700(block970) to maintain NGP within the predetermined range of NGPmax. value. In an example the additional fuel added also leads to an increased T5value to bring T5to within a predetermined range of T5max. The PLC800then proceeds to return to block910to repeat the process900.

At block980, the PLC800compares the NGP value to the NGPmax value and the T5to the T5max value. If NGP is below NGPmax and the T5value is within a predetermined range of T5max then the PLC800proceeds to block990. In an example if T5is within a predetermined range of T5max and the inlet guide vanes255and variable guide vanes250are not in a maximum position, and the NGP value is below NGPmax, then the PLC800proceeds to block990.

At block990, the PLC800sends digital signals to the power transfer device700to increase power to the gas producer shaft120. The power transfer device700then applies additional power to the gas producer shaft120. The additional power to the gas producer shaft120leads to additional cooling effects provided by the compressor200.

The PLC800then proceeds to block950where additional fuel is added. The additional fuel added leads to an increase of temperature to balance the cooling effects provided by the additional air from the increase in power to the gas producer shaft120(Block990) and maintains the T5value within a predetermined range of T5max. The additional fuel added and additional power provided by the power transfer device700also leads to an increased NGP. In an example the increased NGP is to bring NGP within a predetermined range of NGPmax. The PLC800then proceeds to return to block910to repeat the process900.

In an embodiment, the process ofFIG. 3can be implemented at intervals of 100 milliseconds.

The steps of a method or algorithm or the functions of a module, unit or block described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. Furthermore, those of skill in the art will appreciate that the various illustrative logical blocks, modules, units, and method steps described in connection with the above described figures and the embodiments disclosed herein can often be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, units, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled persons can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure. In addition, the grouping of functions within a module, block, unit or step is for ease of description. Specific functions or steps can be moved from one module, block or unit to another without departing from the disclosure.

Although this disclosure has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed disclosure. Accordingly, the preceding detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses of the disclosure. In particular, the described embodiments are not limited to use in conjunction with a particular type of gas turbine engine. For example, the described embodiments may be applied to stationary or motive gas turbine engines, or any variant thereof. Furthermore, there is no intention to be bound by any theory presented in any preceding section. It is also understood that the illustrations may include exaggerated dimensions and graphical representation to better illustrate the referenced items shown, and are not consider limiting unless expressly stated as such.