Steam Turbine Startup Control via Predictive Thermal Stress Limits
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Solution Overview
Problem
Steam turbine power plants face challenges in reducing startup time and managing thermal stress and differential thermal expansion, leading to potential damage and reduced energy efficiency due to limited control over steam flow rates and excessive thermal stress.
Innovation Solution
A system comprising heat source equipment, a steam generator, an electric generator, heat medium and low-temperature flow controllers, and a prediction device that predicts startup constraints and adjusts control input variables to maintain thermal stress and differential thermal expansion within safe limits, allowing for flexible steam generation and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the steam flow rate is increased to reduce startup time, then the productivity is improved, but the thermal stress and differential thermal expansion increase causing potential damage
Solution Approach 1:
The control system performs predictive calculations of thermal stress and differential thermal expansion before steam is supplied to the turbine. Based on these predictions, the controller pre-adjusts the steam flow rate to ensure that even with increased flow for faster startup, the thermal stress and differential thermal expansion remain within safe limits. This preliminary prediction and adjustment action enables faster startup without compromising reliability.
2Reliability
If the steam flow rate is controlled by a control valve to regulate thermal stress, then the reliability is improved, but the energy efficiency deteriorates due to surplus steam being given away via bypass valve
Solution Approach 1:
Instead of using a control valve to throttle steam flow (which creates energy loss through the bypass valve), the system changes the approach by controlling the steam flow rate through predictive calculation and controller adjustment of the steam supply. The controller determines an appropriate steam flow rate based on predicted thermal stress and differential thermal expansion, allowing the steam turbine to receive the needed steam without requiring energy-wasting bypass operations. This parameter-based control method maintains reliability while improving energy efficiency.
3Productivity
If the control range of startup constraints is extended to allow faster startup, then the productivity is improved, but the risk of exceeding maximum permissible thermal stress increases
Solution Approach 1:
The control system continuously monitors the actual thermal stress and differential thermal expansion during startup and compares these values against the predicted values and maximum permissible limits. Based on this feedback, the controller dynamically adjusts the steam flow rate to maintain operation within safe constraints while maximizing startup speed. This feedback mechanism enables the system to operate at the boundaries of the extended control range without exceeding safety limits, thus improving productivity while managing risk.
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
Enables rapid startup and reduced energy loss by controlling steam flow and temperature, extending the control range of thermal stresses and other startup constraints, thereby enhancing the operational efficiency and accuracy of steam turbine power plants.
Implementation Method 1
heat source equipment for heating a low-temperature flow by applying a heat medium to generate a high-temperature flow
Implementation Method 2
steam generator for generating steam using the high-temperature flow generated by the heat source equipment
Implementation Method 3
differential thermal expansion due to a difference in heat capacity occurs between the rotor and casing of the turbine
Implementation Method 4
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
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Disclosed is a steam turbine power plant adapted to start operating very efficiently in an extended control range of its startup constraints such as a thermal stress. The steam turbine power plant includes heat source equipment 1 that heats a low-temperature flow by applying a heat medium and thus generates a high-temperature flow, a steam generator 2 that generates steam using the high-temperature flow generated by the heat source equipment 1, a steam turbine 3 driven by the steam generated by the steam generator 2, an electric generator 4 that converts rotational motive power of the steam turbine 3 into electric power, a heat medium controller 12 that controls a supply rate of the heat medium supplied to the heat source equipment 1, a low-temperature flow controller 14 that controls a supply rate of the low-temperature flow supplied to the heat source equipment 1, a prediction device 22 that predicts startup constraints of the steam turbine 3 from control input variables of the controllers 12, 14 when the steam turbine 3 is started, and a control input variables setter 23 that controls the controllers 12, 14 so as to prevent data predictions by the prediction device 22 from exceeding limit values of the startup constraints.