Steam Turbine Startup Control via Predictive and Current Constraint Switching
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Solution Overview
Problem
Existing steam turbine power plants face challenges in safely starting operations due to unpredictable thermal stresses and differential thermal expansion, which can lead to damage from sudden temperature changes and malfunctions in measuring instruments, making it difficult to maintain startup constraints within safe limits.
Innovation Solution
The steam turbine power plant calculates both predictive and current values of startup constraints, using these to determine first and second control input variables, with the first being preferred but switching to the second if the first is not available, to control thermal stresses and differential thermal expansion within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If predictive calculation is used to control startup constraints, then startup safety can be maintained under normal conditions, but the system becomes vulnerable to measurement failures and prediction inaccuracies
Solution Approach 1:
The system performs preliminary predictive calculations of thermal stresses and differential thermal expansion before startup to determine safe operating parameters. This advance preparation allows the control system to establish target values for steam temperature and flow rate that will keep the turbine within safe thermal limits during startup, addressing the reliability aspect while the fallback mechanism handles prediction accuracy issues
Solution Approach 2:
The invention implements a fallback mechanism that prepares alternative control strategies in advance. When predictive calculation fails or loses accuracy due to measurement issues, the system switches to alternative methods such as using historical data, simplified models, or conservative startup procedures. This beforehand cushioning ensures that startup safety is maintained even when prediction accuracy deteriorates
2Productivity
If steam temperature and flow rate are increased rapidly during startup, then productivity is improved, but thermal stress and differential thermal expansion exceed safe limits
Solution Approach 1:
The control system dynamically adjusts steam temperature and flow rate during startup based on real-time thermal stress calculations. Rather than using fixed ramp rates, the system continuously modifies the heating profile to match the actual thermal state of the turbine, allowing faster startup when thermal margins permit while preventing excessive thermal stress when approaching safety limits
Solution Approach 2:
The invention changes the control parameters from fixed startup procedures to dynamically calculated target values for steam temperature and flow rate. By continuously updating these parameters based on predictive thermal stress calculations, the system optimizes the balance between startup speed and thermal stress management, improving productivity without compromising the strength of turbine components
3Ease of operation
If differential thermal expansion is not controlled, then startup simplicity is maintained, but contact between rotor and casing occurs causing damage
Solution Approach 1:
The system implements feedback control by continuously monitoring differential thermal expansion between the rotor and casing during startup. The predictive calculation model uses this feedback to adjust steam temperature and flow rate commands in real-time, ensuring that thermal expansion remains within safe limits. This automated feedback mechanism maintains startup simplicity while preventing rotor-casing contact that would occur with uncontrolled thermal expansion
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 ensures safe startup of the steam turbine power plant even when prediction accuracy is compromised, preventing thermal stress and differential thermal expansion from exceeding limits and allowing for smooth control switching.
Implementation Method 1
steam abruptly increases in both temperature and flow rate. A consequential sudden increase in a surface temperature of the turbine rotor relative to an internal temperature thereof augments a radial temperature gradient and thus increases a thermal stress
Implementation Method 2
differential thermal expansion due to a difference in heat capacity occurs between the turbine rotor and casing of the turbine
Data Source
AI summary
Disclosed is a steam turbine power plant adapted to start operating safely even if prediction accuracy of its startup constraints cannot be obtained. The system calculates predictive values and current values of startup constraints of a steam turbine from process variables of plant physical quantities, next calculates in parallel both a first control input variable for a heat medium flow controller based on predictive values, and a second control input variable for a main steam control valve based on the current values, and while preferentially selecting the first control input variable, if the first control input variable is not calculated, selects the second control input variable instead. After the selection of at least one of the first and second control input variables, the system outputs an appropriate command value to the heat medium flow controller and the main steam control valve according to the kind of selected control input variable.