Sequential Combustion Gas Turbine Control for NOx Emission Limits
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Solution Overview
Problem
Gas turbines with sequential combustion face challenges in controlling NOx emissions and component stress due to leakage-induced measurement errors in turbine outlet temperatures, leading to increased fuel flow and emissions.
Innovation Solution
A method involving continuous measurement and averaging of turbine outlet temperatures, with adjustments based on predetermined thresholds and emission levels, to maintain targeted NOx limits and reduce component stress, utilizing a closed-loop control system with semiautomatic logic adaptations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the controller increases fuel flow to compensate for perceived low TAT1 measurements, then the measured TAT1 appears to be maintained at design temperature, but the actual TAT1 and TIT1 increase leading to higher NOx emissions
Solution Approach 1:
A cold leakage detection module is introduced as an intermediary between the TAT1 measurement and the fuel flow control. This module detects cold leakage flows that affect temperature measurements and generates compensatory control signals to correct the measurements before they reach the fuel flow controller, preventing erroneous fuel increases that would raise NOx emissions
Solution Approach 2:
The system implements a feedback loop where TAT1 measurements are continuously monitored, compared against expected values, and used to adjust fuel flow. The cold leakage detection adds a feedback mechanism that identifies measurement errors caused by cold leakage and feeds correction signals back to the control system, preventing the chain of errors that leads to increased NOx emissions
2Reliability
If multiple TAT1 measurement points are used and averaged, then measurement reliability should improve, but cold leakage flows cause some measurements to be erroneous, affecting the average
Solution Approach 1:
The system applies different evaluation criteria to different local TAT1 measurement points. Instead of simple averaging, the cold leakage detection module identifies which measurement points are affected by cold leakage and applies weighted evaluation or exclusion to those specific points, maintaining overall system reliability while preserving precision
3Adaptability or versatility
If the gas turbine operates with sequential combustion and variable compressor inlet guide vanes, then operational flexibility is improved, but control complexity increases making it difficult to maintain NOx emission targets
Solution Approach 1:
The cold leakage detection and correction functionality is extracted as a separate, dedicated module within the control system. This modular approach handles the complexity of cold leakage compensation independently, allowing the main sequential combustion control to maintain its operational flexibility without being burdened by the additional control complexity
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
Effectively prevents exceeding NOx emission limits and reduces component stress by accurately controlling turbine outlet temperatures and fuel flow, ensuring efficient operation and extended machine life.
Implementation Method 1
continuously measuring locally at various points the turbine outlet temperature TAT1 of the high-pressure turbine
Implementation Method 2
controlling the operation of the first combustor depending on said average TAT1 temperature
Data Source
Figure 1
AI summary
The invention relates to a method for controlling the operation of a gas turbine (10) with sequential combustion, which gas turbine (10) comprises a compressor (12) with variable inlet guide vanes (VIGV), a first combustor (13), a high-pressure turbine (14) downstream of said first combustor (13), a second combustor (16) downstream of said high-pressure turbine (14), and a low-pressure turbine (17) downstream of said second combustor (16) A prevention of exceeding targeted NOx emission limits as well as a prevention of component stress increase is achieved by adjusting an average TAT1 temperature (TAT1 AVG), if at least one local TAT1 measurement value is increasing above a predetermined threshold value during base load operation.