MPC Steam Header Blending for Combined Cycle Efficiency
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Solution Overview
Problem
In combined cycle power plants, the pressure and temperature of steam generated by heat recovery steam generators (HRSGs) often do not match the conditions at the steam turbine header, leading to undue stress on the steam turbine and efficiency losses due to bypassed steam, which is not used to generate electricity and is wasted as heat.
Innovation Solution
The implementation of model predictive control (MPC) logic to dynamically adjust setpoints for the gas turbine and HRSG sections, minimizing the amount of bypass steam by predicting and optimizing steam properties to match the conditions at the steam turbine header, thereby controlling the operation of bypass and isolation valves to ensure steam quality meets the required parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If steam from HRSG is introduced into the steam turbine, then electricity generation efficiency is improved, but steam turbine stress increases when steam properties do not match
Solution Approach 1:
The system dynamically adjusts steam generation parameters (pressure, temperature) by modifying gas turbine load setpoints and HRSG steam ramp setpoints to match steam turbine header conditions. This ensures steam properties align with turbine requirements, eliminating stress while maintaining efficiency.
Solution Approach 2:
The control system continuously monitors steam properties at the turbine header and uses this feedback to adjust HRSG steam generation and gas turbine loading. This closed-loop control ensures steam parameters remain matched to turbine requirements, preventing stress accumulation.
2Reliability
If steam bypass valves are used to prevent mismatched steam from entering the turbine, then steam turbine protection is improved, but energy efficiency deteriorates due to wasted heat
Solution Approach 1:
The system predicts future steam properties and adjusts gas turbine loading and HRSG steam generation in advance to prevent mismatches before they occur. This proactive control eliminates the need for bypass valves, ensuring all generated steam can be utilized by the turbine without energy waste.
Solution Approach 2:
The system converts the potential harmful effect of steam mismatches into a benefit by using predictive control to pre-adjust operating parameters. This prevents bypass valve activation, transforming what would be wasted heat into useful work by ensuring all steam reaches the turbine.
3Manufacturing precision
If dynamic setpoint adjustment is implemented, then steam property matching is improved, but control system complexity increases
Solution Approach 1:
The system implements dynamic setpoint adjustment where gas turbine load setpoints and HRSG steam ramp setpoints are continuously modified based on predicted steam properties. This dynamic control enables precise steam property matching while adapting to changing plant conditions in real-time.
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 minimizes the production of excess bypass steam, reduces efficiency losses, and prevents stress on the steam turbine and condenser, while ensuring that steam quality matches the turbine's operational conditions, thereby enhancing overall plant efficiency and reducing waste heat.
Implementation Method 1
exhaust gas produced by the gas turbine is captured by a heat recovery steam generator (HRSG), which generates steam from heat energy in the exhaust gas
Data Source
AI summary
Methods and apparatus to optimize ramp rates in combined cycle power plants are disclosed herein. An example method disclosed herein includes predicting a first setpoint for a gas turbine in a combined cycle power plant over a prediction horizon and predicting a second setpoint for a steam generator over the prediction horizon. The example method includes identifying a first steam property of steam generated by the steam generator in the combined cycle power plant based on the second setpoint. The example method includes comparing the first steam property to a second steam property of steam associated with a steam turbine in the combined cycle power plant and dynamically adjusting at least one of the first setpoint or the second setpoint based on the comparison.