Gas Turbine Transient Control via Predictive Temperature Bias
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Solution Overview
Problem
Gas turbine engines experience fluctuations in air-to-fuel ratio during fast-ramping conditions due to lag in measured engine exhaust temperature, leading to high emissions of nitrogen oxides and combustion instabilities.
Innovation Solution
A predictive control system that adjusts engine control settings by determining a temperature bias based on the ramp rate and time lag in exhaust temperature measurements, using a processor to correct air-to-fuel ratio and guide vane positions, thereby maintaining stable combustion dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fast ramping capability is implemented to meet power generation demands, then productivity and response speed improve, but combustion stability and emissions control deteriorate due to temperature measurement lag
Solution Approach 1:
The control system performs preliminary action by predicting the exhaust temperature based on the measured temperature and ramp rate before the actual temperature is measured. This predictive approach allows the control system to adjust fuel-air ratio in advance, compensating for the measurement lag and maintaining combustion stability during fast ramping conditions.
Solution Approach 2:
The system implements feedback control by continuously monitoring the measured exhaust temperature, comparing it with the predicted temperature, and adjusting the fuel-air ratio based on the difference. This closed-loop feedback mechanism ensures that combustion stability is maintained despite the inherent lag in temperature measurement during rapid transients.
2Reliability
If fast ramping is used to maintain grid power generation, then power generation reliability improves, but nitrogen oxide emissions increase due to air-to-fuel ratio fluctuations
Solution Approach 1:
By predicting the exhaust temperature ahead of time based on the ramp rate, the control system can pre-adjust the fuel-air ratio to optimal levels before the temperature deviation occurs. This preliminary adjustment prevents the air-to-fuel ratio fluctuations that would otherwise lead to increased nitrogen oxide emissions during fast ramping.
Solution Approach 2:
The feedback mechanism continuously monitors the temperature difference between measured and predicted values, and automatically adjusts the fuel-air ratio to maintain optimal combustion conditions. This real-time feedback control ensures that emissions remain within acceptable limits even during rapid power generation changes.
3Device complexity
If measured exhaust temperature is used directly for control, then measurement simplicity is maintained, but control accuracy deteriorates due to time lag during transients
Solution Approach 1:
The system introduces an intermediary element - a predictive model - that acts as a mediator between the measured temperature and the control decisions. This model uses the measured temperature and ramp rate to generate a predicted temperature that accounts for the measurement lag, thereby improving control accuracy without significantly increasing system complexity.
Solution Approach 2:
The control system changes the temperature parameter from the directly measured value to a predicted value that incorporates the ramp rate information. This parameter transformation effectively compensates for the time lag, providing more accurate temperature information for control purposes while maintaining relatively simple system architecture.
Data Source
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Figure 3
AI summary
A control system and method for a gas turbine engine are provided. A controller (40) is responsive to at least one parameter to control an air-to-fuel ratio. The parameter may be a measured engine exhaust temperature from a temperature sensor (42). During a transient, such as a ramping condition of the engine, a measured value of such parameter may have a time lag affecting one or more control settings during the transient condition. The controller is programmed to predictively determine a bias for the measured value of the parameter to correct such control settings and avoid combustion instabilities and high emissions during such transient conditions.