Gas Turbine Transient Control Algorithm for Combustion Stability
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Solution Overview
Problem
Conventional DLN combustion systems for gas turbines face challenges in managing transient events, leading to under-fired conditions, combustion dynamics, and potential flame loss due to lag in turbine exhaust thermocouple measurements, which can result in hardware damage and high emissions during ultra-low emissions operations.
Innovation Solution
A transient event-based control algorithm that adjusts gas fuel splits immediately to prevent combustion dynamics and loss of flame, and employs a long-term response by stepping up the emissions model gain to maintain NOx emissions within limits, using a combination of immediate and long-term responses based on detected transient events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DLN control algorithms rely solely on turbine exhaust temperature and compressor pressure ratio to determine operating conditions, then the control system is simple and easy to operate, but the system responds slowly to transient events causing under-fired conditions and combustion dynamics
Solution Approach 1:
The control system performs preliminary actions by detecting transient events (water wash, load changes) before they cause under-fired conditions. When a transient event is detected, the system proactively adjusts fuel splits and emissions model gain in advance, preventing combustion dynamics and flame loss rather than reacting after the problem occurs.
Solution Approach 2:
The system dynamically adjusts control parameters based on detected transient conditions. During transients, the emissions model gain is increased and fuel splits are modified in real-time, allowing the control system to adapt its response characteristics to match the changing operating conditions, thereby maintaining combustion stability throughout the transient event.
2Object-generated harmful factors
If the emissions model gain is increased to maintain NOx emissions within limits during transient events, then emissions control is improved, but the control algorithm complexity increases
Solution Approach 1:
The system applies local quality by selectively modifying only the emissions model gain parameter during transient events, rather than changing the entire control algorithm structure. This targeted adjustment maintains emissions control effectiveness while minimizing the increase in overall system complexity, as only specific parameters are adjusted rather than the complete control logic.
3Reliability
If fuel splits are adjusted immediately to prevent combustion dynamics during transients, then combustion stability is improved, but the mismatch between actual and reference exhaust temperature increases
Solution Approach 1:
The system performs preliminary fuel split adjustments when transients are detected, preventing combustion dynamics before they occur. By acting in advance and proactively modifying fuel distribution, the system maintains combustion stability during the transient event, accepting temporary temperature measurement discrepancies as a necessary trade-off for preventing hardware damage and flame loss.
Data Source
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AI summary
A method of managing transient events regularly seen during gas turbine 10 operation that may cause undesirable operation and hardware damage. During certain transient operations, a lag may be seen between reference exhaust temperature and actual turbine exhaust temperature. This lag can result in an under-fired condition within the combustion system of variable magnitude and duration. Either fuel split schedules or a control algorithm can be positioned during these transients to prevent combustion dynamics or loss of flame. Combustion dynamics are known to cause damage that may require hardware replacement. Once the transient has completed, normal control operation is resumed.