Patent Application
20190010821
The disclosure relates generally to turbomachines, and more particularly, to controlling turbine clearances for operational performance and system protection in a gas turbine.
Turbomachines, such as gas turbines, include one or more rows of airfoils, including stationary airfoils referred to as stator vanes and rotating airfoils referred to as rotor blades or buckets. A gas turbine may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Typically, an axial compressor has a series of stages with each stage comprising a row of rotor blades followed by a row of stationary stator vanes. Accordingly, each stage generally comprises a pair of rotor blades and stator vanes. Typically, the rotor blades increase the kinetic energy of a fluid that enters the axial compressor through an inlet and the stator vanes convert the increased kinetic energy of the fluid into static pressure through diffusion. Accordingly, both sets of airfoils play a vital role in increasing the pressure of the fluid.
Gas turbine efficiency may be closely tied to control of the fluid paths through the airfoils in the turbine section. Gaps between a stage of airfoils and the casing adjacent the airfoils may create a secondary flow path that decreases turbine efficiency. As atmospheric and/or operating temperatures increase, expansion of casings or other components may expand these gaps and lower efficiency. Gas turbines have implemented a variety of systems for actively controlling blade tip clearance between the blade tips and adjacent casing. One such system uses cooling air or another cooling system to reduce the temperature of the casing, causing it to contract and reduce the gap size. These clearance control systems may require a measurement of the gap in order to correctly control the gap width. If the gap is allowed to become too large, operating efficiency is reduced. If the gap is too small, it may cause a stall or a collision event. Various configurations of sensors for directly or indirectly measuring the gap, such as clearance probes, have been implemented. These additional sensors within the fluid path or mechanics of the gas turbine are subject to wear and failure and may not last the operational life or maintenance cycles of the gas turbine.
A first aspect of this disclosure provides a gas turbine system using a virtual clearance measurement. The gas turbine includes a stage of airfoils and a casing adjacent the stage of airfoils that define a clearance distance between the stage of airfoils and the casing. A clearance control mechanism controllably adjusts the clearance distance based upon a clearance control signal. A clearance controller provides the clearance control signal to the clearance control mechanism. The clearance controller receives a clearance value as an input to a closed loop controller that generates the clearance control signal. A virtual clearance function generates the clearance value from at least one system measurement of the gas turbine system.
A second aspect of the disclosure provides a method for controlling airfoil clearance using a virtual clearance measurement. The method comprises measuring an exhaust temperature from a gas turbine. The gas turbine includes a stage of airfoils and a casing adjacent the stage of airfoils that define a clearance distance between the stage of airfoils and the casing. A clearance value is calculated using a virtual clearance function to transform at least one combustor performance value and an exhaust temperature value into the clearance value. A clearance control signal is generated and output to a clearance control mechanism. The clearance control signal is based on a closed loop controller and the clearance value. The clearance distance between the stage of airfoils and the casing is modified in response to the clearance control value using the clearance control mechanism.
A third aspect of the disclosure a method of generating and using a virtual clearance function. A combustor performance parameter is selected for a unit design for a gas turbine. The gas turbine includes a stage of airfoils and a casing adjacent the stage of airfoils that define a clearance distance between the stage of airfoils and the casing. A performance model is selected for the unit design for the gas turbine. The performance model includes the selected combustor performance parameter, an exhaust temperature parameter, and a clearance parameter correlating to the clearance distance in a range of operating conditions. A virtual clearance function is calculated that includes a transfer function from one of the selected combustor performance parameter or the exhaust temperature parameter to the clearance parameter. The virtual clearance function is used to generate a clearance control signal to a clearance control mechanism based on measurement of the selected combustor performance parameter and the exhaust temperature parameter in the gas turbine. The clearance distance between the stage of airfoils and the casing is modified in response to the clearance control value using the clearance control mechanism.
The illustrative aspects of the present disclosure are arranged to solve the problems herein described and/or other problems not discussed.
These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:
It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
In some embodiments, aspects of the disclosure may be implemented through an existing control system for managing a gas turbine, other turbomachine, power generation facility, or portion thereof. Aspects of the disclosure may be implemented for any gas turbine that includes an existing airfoil clearance control mechanism or may be modified to include an airfoil clearance control mechanism, such as a case temperature management blower or a mechanical, hydraulic, or pneumatic actuator for adjusting the spacing between the blade tip and the adjacent casing. In some embodiments, existing clearance control mechanisms may include a feedback control loop and receive a clearance control signal to adjust shroud clearance to a desired gap clearance. Clearance distance may be measured as the distance from a distal surface of an airfoil, including any attached distal shroud, to the nearest surface of the case, representing the narrowest choke point of fluid flow through the space between the distal surface of the airfoil and the case. In some embodiments, an existing clearance controller provides closed loop control of the clearance control mechanism based on receiving a clearance measurement as an input to the controller. A gas turbine control system or integrated plant management system including gas turbine control may provide continuous, periodic, or event-based clearance measurements to the clearance controller to adjust the measured clearance distance versus the desired clearance distance. In some embodiments, the clearance controller may receive a measured clearance distance directly from a sensor system, such as a clearance probe. Whether from the control system or directly from a sensor system, the measured clearance distance is a clearance value that may be replaced by a virtual clearance measurement according to some embodiments.
Referring to
In some embodiments, control system 110 may include a virtual clearance measurement subsystem 111 that utilizes selected system measurements 112 from a plurality of system measurements that control system 110 utilizes for other system operations and management functions. For example, control system 110 may measure a plurality of system parameters 118 to manage operation of the gas turbine system based on air flow rate 160, fuel flow rate 162, turbine speed 164, and temperature, e.g., ambient temperature 166, firing temperature 168, exhaust temperature 170, etc. Control system 110 may monitor and adjust system parameters 118 and other parameters to control the air flow rate 166, fuel flow rate 162, and turbine speed 164 to achieve desired operating conditions for gas turbine 130. For example, system parameters 118 may include air flow rate 160, fuel flow rate 162, turbine speed 164, ambient temperature 166, firing temperature 168, and exhaust temperature 170. Virtual clearance measurement subsystem 111 may use selected system measurements 112 and a virtual clearance function 114 to generate a virtual clearance measurement value 116 without directly measuring the clearance distance in gas turbine 130. For example, system measurements 112 may include a combination of gas turbine exhaust temperature 170 and a combustor performance value, such as fuel flow rate 162 or firing temperature 168. Virtual clearance function 114 may include a transfer function for converting one of system measurements 112 into virtual clearance measurement value 116. In some embodiments, these transfer functions are represented graphically and are further explained with regard to
Control system 110 may communicate with or includes a clearance controller 120 that may include a closed loop controller 122 for dynamically managing the clearance of a clearance control mechanism 150 associated with gas turbine 130. Closed loop controller 122 may include a control loop including a plurality of inputs to generate a clearance control signal 126 to clearance control mechanism 150. In some embodiments, closed loop controller 122 may use a desired clearance set point 124 as the target parameter for closed loop control and may receive a clearance measurement value that provides the real-time control input to which closed loop controller 122 responds and corrects. For example, clearance controller 120 may have an input parameter for clearance measurement. In some embodiments, clearance measurement values may be received from control system 110, such as virtual clearance measurement value 116. In some embodiments, a difference between desired clearance set point 124 and virtual clearance measurement value 116 may be injected into a control loop of closed loop controller 122 to modify clearance control signal 126 to clearance control mechanism 150 and adjust the clearance distance in gas turbine 130. In some embodiments, clearance control signal 126 is not a distance value for the clearance distance but a related control parameter, such as temperature for a thermal clearance control mechanism.
Gas turbine 130 may include any kind of conventional turbomachine including a compressor 132, combustor 134, and a turbine section 136. Turbine section 136 may include a plurality of stages, including a first stage along the fluid flow path through turbine section 136. For example, turbine section 136 may include an example stage 138 including airfoil blades 140, 142 with clearance distance 144, 146 to casing 148. The portion of casing 148 adjacent and closest to stage 138 of airfoil blades 140, 142 defines clearance distance 144, 146 between the stage 138 of airfoil blades 140, 142 and casing 148. Gas turbine 130 may further comprise clearance control mechanism 150. For example, clearance control mechanism 150 may include a case temperature management blower or a mechanical, hydraulic, or pneumatic actuator for adjusting clearance distance 144, 146 between airfoil blades 140, 142 and the adjacent casing 148. Clearance control mechanism 150 adjusts clearance distance 144, 146 in response to clearance control signal 126. In one embodiment, clearance control mechanism 150 may include an actuator and a feedback loop for adjustably controlling clearance distances 144, 146 between the maximum and minimum distances available based on the geometry and adjustment capabilities of the system. In some embodiments, clearance control mechanism 150 may be used to minimize clearance distances 144, 146 to reduce fluid leak and increase system efficiency during steady-state operation of gas turbine 130. In some embodiments, gas turbine 130 may be equipped with a plurality of sensors for measuring various operating system parameters, such as system parameters 118, and providing those measurements to control system 110. For example, one or more sensors in or proximate to compressor 132 may provide air flow rate 160 values and ambient temperature 166 values to control system 110 via compressor measurement signals 152. One or more sensors proximate to combustor 134 or a related fuel system may provide fuel flow rate 162 values and firing temperature 168 values to control system 110 via combustor measurement signals 154. One or more sensors in turbine section 136 may provide turbine speed 164 values and exhaust temperature 170 values to control system 110 via turbine measurement signals 156.
Note that the value ranges and curves shown in
Referring to
The foregoing drawings show some of the operational processing associated according to several embodiments of this disclosure. It should be noted that in some alternative implementations, the acts described may occur out of the order described or may in fact be executed substantially concurrently or in the reverse order, depending upon the act involved.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201741023637 | Jul 2017 | IN | national |
