Methods and systems for controlling gas turbine clearance

Abstract

A method and system for controlling the clearance in a gas turbine. The current clearance between a turbine blade and a casing of the gas turbine is determined. Then, a determination is made as to whether the current clearance is within a predetermined clearance threshold and a control action is taken if the current clearance is outside of the predetermined clearance threshold.

1 . A method for controlling the clearance in a gas turbine, comprising:
 calculating a current clearance between a turbine blade and a casing of the gas turbine;   determining whether the current clearance is within a predetermined clearance threshold; and   taking a control action if the current clearance is outside of the predetermined clearance threshold.   
   
   
       2 . The method of  claim 1 , wherein calculating the current clearance comprises:
 determining a current operating condition and a current operating temperature of the gas turbine;   calculating a mechanical growth and a thermal growth of the gas turbine based on the current operating condition and the current operating temperature; and   adjusting a predefined initial clearance of the gas turbine based on the calculated mechanical growth and the calculated thermal growth.   
   
   
       3 . The method of  claim 2 , wherein the mechanical growth and the thermal growth of the gas turbine comprises one or more of a mechanical growth and a thermal growth of a shaft of the gas turbine, a mechanical growth and a thermal growth of a turbine blade of the gas turbine, the thermal growth of a shroud of the gas turbine, and the thermal growth of a casing of the gas turbine. 
   
   
       4 . The method of  claim 1 , wherein the clearance of the gas turbine is controlled for at least the first two stages of the gas turbine. 
   
   
       5 . The method of  claim 1 , wherein the clearance of the gas turbine is controlled for one or more of a start operating condition, a purge operating condition, a shut down operating condition, a load operating condition, a no load operating condition, a base load operating condition, and a cool down operating condition. 
   
   
       6 . The method of  claim 1 , wherein the predetermined clearance threshold is equal to or less than approximately 0.08 inches. 
   
   
       7 . The method of  claim 1 , wherein the control action comprises one or more of shutting off the gas turbine, setting off an alarm, transmitting an alarm message, or altering the clearance of the gas turbine. 
   
   
       8 . The method of  claim 7 , wherein altering the clearance of the gas turbine comprises regulating a thermal growth of an inner turbine shell of the gas turbine. 
   
   
       9 . The method of  claim 8 , wherein the thermal growth of the inner turbine shell is regulated by controlling a temperature of a gas that is circulated through one or more cavities within the inner turbine shell. 
   
   
       10 . The method of  claim 1 , further comprising:
 determining whether the gas turbine may be ignited based on the current clearance of the gas turbine.   
   
   
       11 . A system for controlling the clearance in a gas turbine, comprising:
 a compressor configured to circulate a gas through the clearance control system and through one or more cavities located in a casing of the gas turbine, wherein a thermal growth of the casing is controlled by the gas circulating through the casing;   a heater configured to heat the gas circulated by the compressor prior to the gas being circulated through the casing; and   a control unit configured to determine a current clearance of the gas turbine and determine a desired temperature of the gas being circulated through the casing in order to control the thermal growth of the casing and the clearance of the gas turbine, wherein the control unit is further configured to control the heating of the gas by the heater.   
   
   
       12 . The system of  claim 11 , further comprising:
 a cooler configured to cool the gas supplied to the compressor;   wherein the control unit is further configured to control the cooling of the gas by the cooler.   
   
   
       13 . The system of  claim 11 , wherein the control unit determines the current clearance of the gas turbine by taking the steps of:
 determining a current operating condition and a current operating temperature of the gas turbine;   calculating a mechanical growth and a thermal growth of the gas turbine based on the current operating condition and the current operating temperature; and   adjusting a predefined initial clearance of the gas turbine based on the calculated mechanical growth and the calculated thermal growth.   
   
   
       14 . The system of  claim 12 , wherein the mechanical growth and the thermal growth of the gas turbine comprises one or more of a mechanical growth and a thermal growth of a shaft of the gas turbine, a mechanical growth and a thermal growth of a turbine blade of the gas turbine, the thermal growth of a shroud of the gas turbine, and the thermal growth of a casing of the gas turbine. 
   
   
       15 . The system of  claim 12 , wherein the clearance of the gas turbine is controlled for at least the first two stages of the gas turbine. 
   
   
       16 . The system of  claim 12 , wherein the clearance of the gas turbine is controlled for one or more of a start operating condition, a purge operating condition, a shut down operating condition, a load operating condition, a no load operating condition, a base load operating condition, and a cool down operating condition. 
   
   
       17 . The system of  claim 12 , wherein the control unit is further configured to determine whether the current clearance of the gas turbine is within a predetermined clearance threshold. 
   
   
       18 . The system of  claim 12 , wherein the control unit is further configured to take a control action if the current clearance is outside of the predetermined clearance threshold. 
   
   
       19 . The system of  claim 20 , wherein the control action comprises one or more of shutting off the gas turbine, setting off an alarm, or transmitting an alarm message. 
   
   
       20 . The system of  claim 1 , wherein the control unit is further configured to determine whether the gas turbine may be ignited based on the current clearance of the gas turbine.