Opto-Acoustical Flame Monitoring of CCGT: Searching for Humming Precursors

Modern gas turbines are prone to trigger and sustain pressure oscillations induced by heat release in their combustor; these oscillations, called humming, can cause severe damage on the machine structure, or, on a less detrimental level, can limit gas turbine performance from load point of view or NOx emissions, increasing their concentration in flue gas. Thermoacoustic oscillation problem, although deeply investigated during the last 15 years, is far from being solved, so that both theoretical and experimental approaches are being used in order to improve basic knowledge of this phenomenon. With this aim an optoelectronic detector based system has been developed to be installed on a 270MW gas turbine to detect radiative energy release fluctuations due to thermoacoustic oscillations. This optoelectronic device has been used in combination with standard piezoelectric sensors with the target to get a better insight of the humming phenomenon. A data analysis method based on well established data processing techniques has been applied to data gathered from the field. The ensemble of data processing techniques seems to offer a method to evaluate the actual risk of thermoacoustic instabilities. This is the very first application of the proposed tool, and a long way has to be run before it is assessed as a prognostic device. Nevertheless in the h.o. of the authors, this first application encourages the continuation of developing the tool extending the base of monitored plants.