Combined Cycle Plant Steam Temperature Control for Minimum Output Reduction
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Solution Overview
Problem
Combined cycle plants face challenges in reducing their minimum output while maintaining operational efficiency, particularly in managing steam temperature to prolong turbine rotor lifespan and prevent unnecessary output decreases.
Innovation Solution
A method and control device that adjust the steam temperature decrease rate and timing to be within predetermined ranges, using a nozzle to spray water into the steam line, allowing for a controlled reduction in steam temperature before gas turbine output decreases, thus setting a lower operating minimum output and extending turbine lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the plant output is decreased rapidly, then the response time to target output is shortened, but the steam temperature decreases too quickly causing thermal stress in turbine rotor
Solution Approach 1:
The control device performs preliminary cooling of steam before the gas turbine output is reduced. By activating the steam temperature regulator (spray water valve) in advance to decrease steam temperature, the system prepares the steam turbine for upcoming load reduction, allowing faster response while preventing excessive temperature drops that would cause thermal stress.
Solution Approach 2:
The control device dynamically adjusts the steam temperature regulator based on real-time conditions. It calculates the difference between current and target output, determines appropriate temperature decrease rates, and continuously modifies the spray water valve opening degree to optimize both response speed and turbine rotor protection throughout the load reduction process.
2Reliability
If the steam temperature is maintained constant during output reduction, then turbine rotor lifespan is preserved, but the operating minimum output cannot be reduced below a predetermined level
Solution Approach 1:
The system performs preliminary steam temperature reduction before the gas turbine output decreases. By lowering the steam temperature in advance through the spray water valve, the steam turbine can operate at reduced temperatures and pressures, enabling the plant to achieve lower minimum output levels while still protecting the turbine rotor from excessive thermal stress.
Solution Approach 2:
The control device changes the steam temperature parameter dynamically during operation. By adjusting the steam temperature to decrease at controlled rates based on the magnitude of output reduction, the system enables operation at lower minimum output levels while maintaining turbine rotor safety through controlled thermal conditions.
3Reliability
If water is sprayed into steam to reduce temperature, then steam temperature can be controlled within safe limits, but the operating efficiency of the system decreases
Solution Approach 1:
The steam temperature regulator operates periodically or intermittently rather than continuously. The spray water valve is activated only when needed during output reduction to control steam temperature, and deactivated when not required, minimizing energy loss from continuous water injection while maintaining steam temperature within safe limits during critical periods.
Solution Approach 2:
The system changes operational parameters by adjusting spray water flow rates based on actual needs. By controlling the amount of water sprayed into the steam according to the required temperature reduction and operational conditions, the system achieves effective temperature control while minimizing the negative impact on operating efficiency through optimized water injection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the operating minimum output of combined cycle plants, preventing excessive steam turbine output decreases and prolonging turbine rotor lifespan by controlling temperature changes.
Implementation Method 1
using a nozzle to spray water into the steam line, allowing for a controlled reduction in steam temperature
Data Source
Figure 1
Figure 2
Figure 3(a)~3(f)
AI summary
A control device (100) comprises: a reception unit (101) which receives a load schedule (LS) indicating a future load of a combined cycle plant; a steam temperature control unit (103) which controls the temperature of steam that flows into a steam turbine (30); and a fuel control unit (104) which controls a flow rate of fuel supplied to a gas turbine 10. The steam temperature control unit (103) outputs a command to a steam temperature adjusting device (26, 28) prior to a load decrease time at which the load is to be reduced according to the load schedule (LS), the command indicating a manipulated variable which causes the steam temperature to decrease.