Combustion Tuning Guidelines: Understanding and Mitigating Dynamic Instabilities in Modern Gas Turbine Combustors

DLN combustors used in modern utility Combustion Turbines (CTs) must operate within tight tolerances of equivalence ratio, fuel/air mixing and turbulence in order to deliver single digit NOx emission performance, while maintaining combustion stability and design power output. As lean NOx emissions from large CTs are driven to increasingly lower levels, even small changes in combustion conditions or manufacturing tolerances can lead to the onset of combustion instabilities and acoustic combustion noise. If left unattended, dynamic oscillations in ultra-low NOx premix combustors can produce resonant acoustics that can in turn cause adverse impacts on performance, including the ability to deliver capacity, or the premature failure of critical system components and emergency shut-downs. For example, it is widely accepted that extreme changes in ambient temperature, or minor changes in fuel composition and temperature, or the use of power augmentation techniques under certain conditions, can lead to combustion instabilities. EPRI is leading a multi-task program to map the operating regime for stable combustion in modern DLN combustors; identify key operating conditions that most influence the onset of combustion instabilities; and develop DLN tuning guidelines based on users’ experience and vendors’ monitoring and control systems. The overall objective of these projects is to maximize the operational flexibility of modern CTs based on implementation of active monitoring and control guidelines aimed at anticipating, preventing, and effectively responding to the onset of combustion-induced dynamic instabilities and CT noise. This paper briefly discusses the dynamics of combustion instabilities in premix DLN combustors; presents the preliminary results from detailed parametric analysis of a large database; and our findings on DLN tuning approaches such as modulating fuel flows and changing inlet guide vanes, that can be used effectively to control combustion instabilities.