Patent Application
20100287948
The invention relates generally to gas turbines and more specifically to a method and equipment for controlling speed and acceleration of the gas turbine during unloaded maintenance operations.
The economy of gas turbine operation dictates that gas turbines be available to produce power to the maximum extent possible. However, it is known that planned and unplanned outages for gas turbine preventive maintenance and repair are required over the life of the equipment. It is advantageous to be able to expeditiously shutdown the gas turbine, establish the conditions required to perform the maintenance, and then return to operation quickly after the maintenance is complete. One example of an operation requiring a shutdown, cooldown, startup and heatup of a gas turbine is a turbine water wash of a hot gas path.
In order to burn heavy fuels (crude and residual oil) turbine washes are required. These washes occur every 3 to 17 days depending on the composition of the fuel and other operating and environmental conditions. The traditional wash cycle provides for injection of a wash solution into a combustor and through the hot gas path of the gas turbine. The wash cycle includes a wash, a soak, a rinse, a drain and a dry operation. The wash cycle may last about 1-2 hours. However, the total time conventionally required to shutdown and cooldown the gas turbine, perform the wash cycle, and then return the gas turbine to base load may take up to about 45 hours. In large part, the overall length from shutdown of the gas turbine to a return to base load is limited by allowing a non-forced cooldown to about 150 degrees F. in order to avoid thermal stresses and reduced life for the turbine rotor, the compressor rotor and the casings.
It is extremely costly for the power plant operator to have gas turbines out of service for the turbine wash cycle about 45 hours every 3 to 17 days Further, the operation of the wash cycle requires significant manpower over an extended period of time to support the wash cycle operation and the gas turbine transitioning. These personnel are not normally on duty around the clock.
Accordingly, it is desirable to provide a method and equipment for reducing the outage time for gas turbine operations of shutting down, cooling down, starting up and returning to service, while at the same time limiting thermal stresses on gas turbine components and preventing excessive fatigue or damage to components from transients. More precise control over acceleration and speed of the gas turbine during unloaded rotation may facilitate such outage improvements and limit damage to components.
Briefly in accordance with one aspect of the present invention, a gas turbine speed and acceleration control system for unloaded rotation is provided. The speed control system includes a starter motor with an output shaft, a torque converter operably connected between the output shaft of the starter motor and a shaft of a gas turbine, a working fluid within an enclosed body of the torque converter, and a working fluid drain system and a working fluid fill system for the torque converter, wherein a draining and a refilling of the working fluid in the body of the torque converter controls a speed and acceleration of the gas turbine during unloaded rotation.
According to a second aspect of the present invention, a method is provided for controlling acceleration and speed of a gas turbine during unloaded rotation with torque converter control. The method includes operating a starter motor through a torque converter to drive a rotor of the turbine. Working fluid level is controlled within the torque converter for setting acceleration of the turbine during a first speed range. The method further includes controlling a means for mechanically adjusting coupling between a rotation of the output shaft of the starter motor and a rotation of the gas turbine shaft of the torque converter for setting acceleration of the turbine during a second speed range.
A third aspect of the present invention provides a gas turbine including a gas turbine shaft and a compressor and a speed control system for unloaded rotation of the gas turbine. The speed control system includes a starter motor, a torque converter operably connected between an output shaft of the starter motor and a shaft of a gas turbine, and a working fluid drain and fill system for the torque converter adapted for draining and refilling the torque converter to control speed and acceleration of the gas turbine during one mode of operation. Further included is means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft for speed and acceleration control of the gas turbine.
These and other features, aspects, and advantages of the present invention 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:
The following embodiments of the present invention have many advantages, including providing speed and acceleration control during unloaded rotation of the gas turbine through new use of a starter motor and torque converter. Enhanced speed and acceleration control during unloaded gas turbine rotation may assist in significantly reducing current outage time for power gas turbines during operations that require a shutdown and cooldown and subsequent startup and heatup of a gas turbine or individual parts thereof. Such speed and acceleration control may allow decreased duration of the outages, including forced cooling of the system that was heretofore avoided. Such speed and acceleration control over the unloaded gas turbine rotation may assist in maintaining the life of the compressor and turbine rotor, casings, starting means, and exhaust system by limiting speed and acceleration induced stresses that could otherwise add to thermal stresses associated with heatup and cooldown operations.
U.S. patent application Ser. No. 12/767,134 by Draper et al., entitled “AVAILABILITY IMPROVEMENTS TO HEAVY FUEL FIRED GAS TURBINES”, filed on Apr. 26, 2010 and assigned to General Electric Co. provides an inventive method for a gas turbine shutdown, cooldown and return to operation turbine. The method and equipment are provided to reduce the overall cycle time for the maintenance, yet mitigate the life penalties, thereby providing greater power production while maintaining (or potentially extending) rotor life. The method includes small hold times during the turbine shutdown and startup and slower turbine ramp rates during cooldown and startup, which more than offset thermal stresses from a forced cooldown, considerably shortening the overall operation. The method of Draper et al. (Ser. No. 12/767,134) is employed for performing a turbine wash cycle from an operating condition at baseload through a return to baseload operation. However, the method may be more broadly employed for a variety of operations necessitating cooldowns to maintenance conditions and restoration to turbine operation. It should also be understood that parts of the method may be employed without performance of the full method.
The present invention facilitates speed and acceleration control during operations, such as those described in Draper et al. (Ser. No. 12/767,134) requiring unloaded gas turbine rotation. Such speed and acceleration control may minimize thermal stress on limiting gas turbine components and extend life of these components and at the same allow operations to be performed more expeditiously.
The present invention provides a gas turbine speed and acceleration control system for unloaded rotation. The system includes a starter motor with an output shaft and a torque converter operably connected between the output shaft of the starter motor and a gas turbine shaft. A working fluid is provided within an enclosed body of the torque converter. A working fluid drain system and a working fluid fill system for the torque converter, is provided such that a draining and a refilling of the working fluid in the body of the torque converter controls a speed and acceleration of the gas turbine. In a further aspect of the invention, coupling between the input and output of the torque converter may be adjusted with discrete vane settings that may be alternated to control a speed and acceleration of the unloaded gas turbine.
The torque converter is rotatingly connected through the body to the output shaft of the starter motor and includes means for spinning the working fluid within the body. The torque converter is also rotatingly connected through the body to the gas turbine shaft and includes means for rotating the gas turbine shaft by extracting work from the spinning of the working fluid within the body. The torque converter further includes means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft by adjusting vanes within the fluid flow path.
In a first embodiment of the torque converter, the means for spinning the working fluid within the body includes a first set of vanes rotatingly connected to the output shaft of the starter motor. For the first embodiment, the means for rotating the gas turbine shaft by extracting work from the spinning of the working fluid within the body includes a second set of vanes rotatingly connected to the gas turbine shaft. The means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft may include a linkage changing an orientation of the vanes of either of the first set of vanes and the second set of vanes according to discrete settings of the vanes.
In a second embodiment of the torque converter, an impeller or pump wheel that is rotatingly connected to the output shaft of the starter motor spins the working fluid within the body. The means for rotating the gas turbine shaft by extracting work from the spinning of the working fluid within the body includes one or more turbine wheels rotatingly connected to the gas turbine shaft and a set of guide vanes interposed between a discharge of the impeller and the turbine wheel such that the orientation of the guide vanes variably couples the spinning fluid with the turbine wheels. The means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft includes changing an orientation of the guide vanes according to discrete settings.
The means for mechanically adjusting coupling may include discrete linkage settings corresponding to orientation of the adjustable vanes or the movable guide vanes and establishing discrete output speed settings of the gas turbine shaft. For the embodiments of the torque converter, three discrete linkage settings establishing three discrete speeds for the gas turbine shaft may be provided. The linkage settings may be controlled by an output from a turbine control system.
A first operating mode may be provided for a speed control system. The first operating mode may include a first setting of the means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft and a filling of the working fluid level within the body for accelerating the gas turbine. The gas turbine speed control for the first operating mode also includes a draining of the working fluid level within the body for slowing the acceleration of the gas turbine shaft to the first speed. Refilling the working fluid level restores coupling between the input and output and promotes acceleration. Alternating filling and draining of the working fluid level may be employed to control acceleration up to the first speed associated with the first setting of the means for mechanically adjusting coupling.
A second operating mode of the speed control system includes the body of the torque converter remaining full with the working fluid. An alternate positioning between the first setting and the second setting of the discrete settings of the means for mechanically adjusting coupling provides for controlling accelerating the gas turbine to a second speed.
For a third operating mode of speed control, the body of the torque converter remains full with the working fluid. A third setting of the means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft provides for accelerating the gas turbine in combination with firing for return to power operation.
The gas turbine speed control system may further include a speed sensor for the gas turbine and a speed and an acceleration measurement for the gas turbine, which may be derived from the speed sensor. A gas turbine control signal may be provided to the drain system and a control signal to the fill system of the torque converter to control speed and acceleration of the gas turbine. The control signal may operate individual drain and fill valves. Alternately, an actuator for a spool valve may be provided to control both drain and fill operations. A control signal may also be provided to the means for mechanically adjusting coupling between the rotation of the output shaft of starter motor and the rotation of the gas turbine shaft of the torque converter to control speed and acceleration of the gas turbine. The means being the linkage to the adjustable vanes of the first embodiment and the guide vanes of the second embodiment.
A turbine control system may receive speed sensor inputs for the gas turbine shaft to determine speed and acceleration. The turbine control system or subsystems thereof may include a speed and acceleration schedule for gas turbine rotor for various defined unloaded rotation operations. The speed and acceleration schedule may be established to limit thermal stress to gas turbine components. The turbine control system or subsystems thereof may include known types of feedback control systems to provide drain/fill signals and alternating speed setting signals to the torque converter to drive the unloaded gas turbine rotor according to the embedded speed and acceleration schedule.
A turbine control system (1090) may provide vane control signals (1094) to the vane control device (1070) according to a desired schedule for accelerating the turbine rotor in a manner to reduce stress to turbine components. The first speed setting (lowest setting) will turn the rotor to approximately 11% speed at steady state. The second speed setting (middle setting) will turn the rotor to approximately 22% speed. The third speed setting (highest setting) will accelerate the gas turbine rotor during startup to assist the fired turbine in accelerating to full speed no-load (FSNL).
A fill control (1081) may supply working fluid for filling the torque converter (1020) through fill line (1050). A drain control (1082) may drain working fluid from the torque converter (1020) through drain line (1055). Turbine speed and acceleration may be monitored by turbine speed sensor (1085) to a turbine control system (1090). Control signal (1095) for fill control (1081) and control signal (1096) for drain control (1082) may be provided by turbine control system (1090).
Gas turbine rotor speed may be monitored by turbine speed sensor (1085) supply speed signal (1093) to a turbine control system (1090) for use in speed and acceleration calculations. The turbine control system (1090) may provide vane control signals (1194) to the guide vane actuator (1170) according to an embedded schedule (1197) for speed and acceleration of the turbine rotor in a manner to reduce stress to turbine components. The first speed setting (lowest setting) will turn the rotor to approximately 11% speed at steady state. The second speed setting (middle setting) will turn the rotor to approximately 22% speed. The third speed setting (highest setting) will accelerate the gas turbine rotor during startup to assist the fired turbine in accelerating to full speed no-load (FSNL).
A fill/drain control (1181) may supply working fluid for filling the torque converter (1120) through fill line (1050) and drain line (1155). Control signal (1195) for fill/drain control may be provided by turbine control system (1090).
A method is provided for using the torque converter powered by the starter motor to slow the acceleration of the gas turbine rotor and control speed. A two-step control strategy is provided for control of acceleration and speed according to a speed and acceleration schedule within the turbine control system. A first control mode may be applied from zero speed to the first speed setting (approximately 11%). The torque converter power may be modulated in this range, according to a speed and acceleration schedule in the turbine control system, by draining and refilling the working fluid in the system. The torque converter may start filled, when the speed and acceleration of the turbine shaft meets a specific level, the torque converter will drain. To raise acceleration and speed, the torque converter will re-fill.
Once the first speed setting on the torque converter is reached, a brief hold may occur. The torque converter control methodology will change between the first speed (approximately 11% speed) and second speed (approximately 22% speed). Acceleration between the first speed and the second speed for torque converter may be controlled by shifting the vane positions between the first speed setting and the second speed setting, where the second speed setting will raise the acceleration and the first speed setting will lower the acceleration.
A further aspect adds additional speed points between zero speed (ratchet) after shutdown, and 22% speed (currently used for forced cool down). Speed control may be enhanced by modulating the working fluid level in the torque converter for speed and acceleration control between 0 and 11% speed (the first vane setting), and shifting vane settings for speed and acceleration control between 11% and 22% (the second vane setting).
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.
This application is related and draws priority to U.S. Provisional Patent Application Ser. No. 61/178,013 entitled “AVAILABILITY IMPROVEMENTS TO HEAVY FUEL FIRED GAS TURBINES”, filed on May 13, 2009 and assigned to General Electric Co, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61178013 | May 2009 | US |
