Method and apparatus for controlling moisture separator reheater

Abstract

A system and a method are provided that may be used to control the temperature of steam being reheated by a moisture separator reheater (MSR). One embodiment provides a system including a steam turbine, a moisture separator reheater coupled to the steam turbine, and a controller programmed to control a temperature of steam leaving the moisture separator reheater based at least in part on sensor feedback. The controller is programmed to facilitate substantially smooth linear temperature ramping.

1 . A method for operating a turbine system, comprising:
 supplying first main steam from a main steam source to a high pressure steam turbine to enable the high pressure steam turbine to rotate a shaft in the turbine system using the main steam;   supplying exhaust steam from the high pressure steam turbine to a moisture separator reheater to enable the moisture separator reheater to produce thermally enhanced steam by reheating the exhaust steam using second main steam received from the main steam source;   supplying the thermally enhanced steam from the moisture separator reheater to a low pressure steam turbine to enable the low pressure steam turbine to rotate the shaft using the thermally enhanced steam;   determining, using one or more sensors, a measured temperature of the thermally enhanced steam output from the moisture separator reheater; and   controlling supply of the second main steam from the main steam source to the moisture separator reheater based at least in part on the measured temperature to facilitate substantially linearly ramping temperature of the thermally enhanced steam.   
     
     
         2 . The method of  claim 1 , wherein controlling the supply of the second main steam comprises adjusting target temperature of the thermally enhanced steam proportionally with changes in loading percentage of the turbine system while performing a loading operation, an unloading operation, or both. 
     
     
         3 . The method of  claim 1 , wherein controlling the supply of the second main steam comprises:
 determining, using a control system, a target valve position of a valve fluidly coupled between the main steam source and the moisture separator reheater; and   instructing, using the control system, the valve to adjust valve position based at least in part on the target valve position to facilitate controlling the temperature of thermally enhanced steam.   
     
     
         4 . The method of  claim 3 , wherein determining the target valve position comprises:
 determining, using the control system, a first temperature reference setpoint that ramps substantially linearly based on load percentage of the turbine system; and   determining the target valve position based at least in part on the first temperature reference setpoint and the measured temperature of the thermally enhanced steam.   
     
     
         5 . The method of  claim 4 , wherein determining the target valve position comprises:
 determining a maximum ramp rate of the temperature of thermally enhanced steam;   determining the target valve position based at least in part on difference between the first temperature reference setpoint and the measured temperature when the first temperature reference setpoint does not differs from the measured temperature by more than the maximum ramp rate; and   when the first temperature reference setpoint differs from the measured temperature by more than the maximum ramp rate:
 determining a second temperature reference setpoint based at least in part on the maximum ramp rate; and 
 determining the target valve position based at least in part on difference between the measured temperature and the second temperature reference setpoint. 
   
     
     
         6 . The method of  claim 1 , comprising determining, using a control system, a loading model that describes relationship between turbine load percentage and target temperature of the thermally enhanced steam;
 wherein controlling the supply of the second main steam comprises:
 determining, using the control system, a temperature reference setpoint based at least in part on the loading model and a current load percentage of the turbine system; and 
 instructing, using the control system, a valve fluidly coupled between the main steam source and the moisture separator reheater to control the supply of the second main steam to the moisture separator reheator based at least in part on the temperature reference setpoint. 
   
     
     
         7 . The method of  claim 6 , wherein determining the loading model comprises:
 determining a loading line to be used to determine the temperature reference setpoint while the turbine system performs a loading operation, wherein the temperature reference increases proportionally with increases in the load percentage of the turbine system; and   determining an unloading line to be used to determine the temperature reference setpoint while the turbine system performs an unloading operation, wherein the temperature reference decreases proportionally with decreases in the load percentage of the turbine system.   
     
     
         8 . The method of  claim 6 , wherein determining the temperature reference comprises:
 determining the temperature reference setpoint as a first temperature corresponding with the current load percentage in the loading model when the first temperature differs from the measured temperature by less than a maximum ramp rate; and   determining the temperature reference setpoint as a second temperature by adjusting the measured temperature based at least in part on the maximum ramp rate when the first temperature differs from the measured temperature by more than the maximum ramp rate.   
     
     
         9 . A tangible, non-transitory, computer-readable medium that stores instructions executable by one or more processors of a control system to control operation of a turbine system, wherein the instructions comprise instructions to:
 instruct, using the one or more processors, a first valve fluidly coupled between a high pressure steam turbine and a main steam source to enable supply of main steam from the main steam source to the high pressure steam turbine to facilitate rotating a shaft in the turbine system using the main steam;   instruct, using the one or more processors, a second valve fluidly coupled between the moisture separator reheater and a low pressure turbine to enable supply of thermally enhanced steam from the moisture separator reheater to the low pressure steam turbine to facilitate rotating the shaft using the thermally enhanced steam;   determine, using the one or more processors, measured temperature of the thermally enhanced steam based at least in part on sensor data received from one or more sensors; and   instruct, using the one or more processors, a third valve fluidly coupled between the main steam source and the moisture separator reheater to adjust a first valve position to facilitate substantially linearly ramping temperature of the thermally enhanced steam by controlling amount of the main steam available to heat the exhaust steam in the moisture separator reheater.   
     
     
         10 . The computer-readable medium of  claim 9 , comprising instructions to instruct, using the one or more processors, a fourth valve fluidly between the high pressure turbine and the moisture separator reheater to adjust a second valve position to facilitate substantially linearly ramping the temperature of the thermally enhanced steam by controlling amount of the exhaust steam available to heat the exhaust steam in the moisture separator reheater. 
     
     
         11 . The computer-readable medium of  claim 9 , wherein the instructions to instruct the third valve to adjust the first valve position comprise instructions to:
 determine a first target temperature of the thermally enhanced steam that changes proportionally with changes in loading percentage of the turbine system during loading operations, unloading operations, or both; and   instruct the third valve to adjust the first valve position from a current valve position to a target valve position based at least in part on the first target temperature and the measured temperature of the thermally enhanced steam.   
     
     
         12 . The computer-readable medium of  claim 11 , wherein the instructions to instruct the third valve to adjust the first valve position comprise instructions to:
 determine a proportional term based at least in part on a proportional gain and a difference between the measured temperature and the first target temperature of the thermally enhanced steam;   determine an integral term based at least in in part on an integral gain and an integral of the difference between the measured temperature and the first target temperature of the thermally enhanced steam;   determine a derivative term based at least in part on a derivative gain and a derivative of the difference between the measured temperature and the first target temperature of the thermally enhanced steam; and   instruct the third valve to adjust the first valve position based at least in part on a sum of the proportional term, the integral term, and the derivative term.   
     
     
         13 . The computer-readable medium of  claim 11 , wherein the instructions to instruct the third valve to adjust the first valve position comprise instructions to:
 instruct the third valve to adjust the first valve position based at least in part on a first difference between the measured temperature and the first target temperature of the thermally enhanced steam when the first target temperature does not differ from the measured temperature by more than a temperature threshold; and   when the first target temperature differs from the measured temperature by more than the temperature threshold:
 determine a second target temperature of the thermally enhanced steam by adding the temperature threshold to the measured temperature when the first target temperature is greater than the measured temperature; 
 determine the second target temperature by subtracting the temperature threshold from the measured temperature when the first target temperature is less than the measured temperature; and 
 instruct the third valve to adjust the first valve position based at least in part on a second difference between the measured temperature and the second target temperature of the thermally enhanced steam. 
   
     
     
         14 . The computer-readable medium of  claim 9 , wherein the instructions to instruct the third valve to adjust the first valve position comprise instructions to:
 adjust the first valve position toward a fully open position when a target temperature of the thermally enhanced steam is greater than the measured temperature of the thermally enhanced steam; and   adjust the first valve position toward a fully closed position when the target temperature is less than the measured temperature of the thermally enhanced steam.   
     
     
         15 . The computer-readable medium of  claim 9 , comprising instructions to determine, using the one or more processors, a loading model that describes relationships between loading percentage of the turbine system and target temperature of the thermally enhanced steam, wherein the loading model comprises:
 a loading line that describes a first relationship used when the turbine system performs a loading operation to linearly increase the target temperature as the loading percentage of the turbine system increases; and   an unloading line that describes a second relationship used when the turbine system performs an unloading operation to linearly decrease the target temperature as the loading percentage of the turbine system decreases.   
     
     
         16 . A turbine system comprising:
 a moisture separator reheater comprising a first heat exchanger, wherein:
 the first heat exchanger is configured to receive first main steam from a main steam source; 
 the moisture separator reheater is configured to receive exhaust steam output from a first steam turbine after second main steam received from the main steam source is used to actuate a shaft in the turbine system; and 
 the moisture separator reheater is configured to output thermally enhance steam to be used by a second steam turbine to actuate the shaft by flowing the exhaust gas around the first heat exchanger; 
   a temperature sensor coupled to an output of the moisture separator reheater, wherein the temperature sensor is configured to determine a measured temperature of the thermally enhanced steam; and   a first valve fluidly coupled to the first heat exchanger, wherein the first valve is configured to adjust supply of the first main steam to the first heat exchanger based at least in part on the measured temperature to facilitate substantially linearly ramping temperature of the thermally enhanced steam.   
     
     
         17 . The turbine system of  claim 16 , comprising a second valve fluidly coupled between the first steam turbine and a second heat exchanger in the moisture separator reheater, wherein:
 the second heat exchanger is configured to receive extraction steam from the first turbine;   the moisture separator reheater is configured to flow the exhaust gas around the second heat exchanger to facilitate producing the thermally enhanced steam; and   the second valve is configured to adjust supply of the extraction steam to the second heat exchanger based at least in part on the measured temperature to facilitate substantially linearly ramping the temperature of the thermally enhanced steam.   
     
     
         18 . The turbine system of  claim 16 , comprising a controller communicatively coupled to the temperature sensor and the first valve, wherein the controller is configured to:
 determine the measured temperature of the thermally enhanced steam based at least in part on sensor data received from the temperature sensor;   determine a first target temperature of the thermally enhanced steam based at least in part on a loading percentage of the turbine system, wherein the first target temperature changes proportionally with changes in the loading percentage while the turbine system is performing a loading operation or an unloading operation; and   instruct the first valve to adjust valve position based at least in part on a current valve position and difference between the first target temperature and the measured temperature of the thermally enhanced steam when the first target temperature and the measured temperature differ by less than a rate change threshold.   
     
     
         19 . The turbine system of  claim 18 , wherein, when the first target temperature and the measured temperature differ by more than the rate change threshold, the controller is configured to:
 determine a second target temperature threshold by adjusting the measured temperature of the thermally enhanced steam based at least in part on the rate change threshold; and   instruct the valve to adjust the valve position based at least in part on the current valve position and difference between the second target temperature and the measured temperature of the thermally enhanced steam.   
     
     
         20 . The turbine system of  claim 16 , wherein:
 the first steam turbine comprises a high pressure steam turbine configured to facilitate rotating the shaft by flowing the main steam over a first one or more turbine blades coupled to the shaft; and   the second steam turbine comprises a low pressure steam turbine configured to facilitate rotating the shaft by flowing the thermally enhanced steam over a second one or more turbine blades coupled to the shaft.