Combustion Dynamics Monitoring Considerations For Systems With Autotuning

Gas turbine autotuning systems are surfacing as a popular OEM and third party solution to minimize manual tuning for emissions compliance, combustion dynamics, and performance optimization. While these systems provide many valuable benefits, they also introduce new challenges. This paper presents a review of autotuning systems, including the general approaches, benefits, challenges, and best practices for combustion dynamics monitoring. The primary benefit of autotuning is that it provides a mostly automated solution to address operability/emissions challenges which arise due to changes in ambient conditions, fuel composition, and machine aging. The operability and emissions challenges include compliant NOx and CO, acceptable combustion dynamics levels, acceptable operability (i.e., turndown and lean blowout avoidance), and in some cases optimized performance. The overarching potential benefit of autotuning systems is their ability to address all of these issues simultaneously and continuously. The paper first presents a brief outline of the general tuning considerations for autotuning systems, with some examples from real plant data to illustrate the tuning sensitivities. It next reviews the major challenges that autotuning can introduce to combustion dynamics monitoring, such as combustor fault pattern recognition and greater consequences of instrumentation faults. Finally, the paper recommends best practices for monitoring combustion dynamics in systems with autotuning. These recommendations include what to do (and what not to do) to continue health monitoring with advanced pattern recognition software, and how to recognize the signatures of combustion dynamics instrumentation faults. This paper is directed at gas turbine operators. It presents familiar plant data to help this audience understand the core working principles of an autotuning system. This understanding is an important basis for determining when a combustion dynamics event is attributable to the operations of the autotuning system, an instrumentation fault, or combustion system hardware degradation. With this understanding established, this paper also presents a list of capabilities and best practices that should be incorporated into combustion dynamics monitoring strategies for units that use autotuning.