Combined Cycle Power Plant Steam Extraction Control
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Solution Overview
Problem
Combined cycle power plants face inefficiencies due to variations in ambient temperatures affecting HRSG exhaust gas temperatures, leading to excessive low pressure steam extraction and reduced thermal efficiency when trying to maintain higher exit gas temperatures as required by local regulations.
Innovation Solution
A control system modulates the amount of low pressure steam extraction from the steam turbine engine to the HRSG using a heating element and proportional valve, ensuring the HRSG exhaust gas temperature meets setpoints across varying ambient conditions, thereby optimizing steam usage and thermal efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low pressure steam extraction is increased to maintain higher HRSG exit gas temperatures, then HRSG exit gas temperature requirement is met, but thermal efficiency is reduced due to excessive steam extraction
Solution Approach 1:
The control system continuously monitors HRSG exit gas temperature and adjusts the steam extraction valve position based on the difference between actual and setpoint temperatures. When temperature is above setpoint, the valve closes to reduce extraction; when below, the valve opens to increase extraction, creating a closed-loop feedback control that prevents excessive steam extraction and maintains thermal efficiency.
Solution Approach 2:
The system dynamically adjusts the steam extraction rate based on real-time ambient temperature conditions and HRSG operating parameters. The proportional valve modulates the extraction amount continuously rather than operating at fixed positions, allowing optimal steam extraction at each operating point to maintain thermal efficiency while meeting temperature requirements.
2Loss of energy
If steam extraction is reduced to minimize thermal efficiency loss, then thermal efficiency is improved, but HRSG exit gas temperature falls below minimum requirements
Solution Approach 1:
The feedback control system ensures minimum temperature requirements are met while maximizing thermal efficiency by continuously adjusting steam extraction based on the actual temperature deviation. The controller prevents temperature from falling below the setpoint while minimizing unnecessary steam extraction, achieving both temperature compliance and efficiency optimization simultaneously.
3Adaptability or versatility
If ambient temperature varies, then power plant operates under different conditions, but control complexity increases to maintain optimal performance
Solution Approach 1:
The control system uses feedback from temperature sensors and ambient conditions to automatically adjust steam extraction, eliminating the need for complex manual control mechanisms. The proportional valve and controller work together to handle varying ambient temperatures through automated regulation, reducing operational complexity while maintaining adaptability.
Solution Approach 2:
The system changes the steam extraction parameter dynamically based on ambient temperature and HRSG operating conditions. By adjusting the extraction rate as a variable parameter rather than using fixed settings, the control system adapts to different ambient conditions with relatively simple control logic, avoiding the need for complex multi-mode control systems.
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
The solution maintains minimum required HRSG exhaust gas temperatures while minimizing excessive steam extraction, enhancing thermal efficiency of the combined cycle power plant by adjusting steam output based on ambient and setpoint temperatures.
Implementation Method 1
a heating element fluidly interposed between the steam turbine engine and the HRSG to heat fluid output from the steam turbine engine
Implementation Method 2
a heat recovery steam generator (HRSG) to produce steam from high energy fluids produced from the generation of power in the gas turbine engine
Data Source
AI summary
A combined cycle power plant in which a gas turbine engine generates power, a heat recovery steam generator (HRSG) produces steam from high energy fluids produced from the generation of power in the gas turbine engine and a steam turbine engine generates additional power from the steam produced in the HRSG. The combined cycle power plant includes a heating element fluidly interposed between the steam turbine engine and the HRSG to heat fluid output from the steam turbine engine, which is to be fed to the HRSG and a control system to control an amount the fluid output from the steam turbine engine is heated by the heating element based on differences between HRSG and ambient temperatures.