Online Combustion Dynamics Monitoring System (CDMS) for Combustion Turbines: Experience and Examples of How CDMS Supports Operations and Prevents Damages

The development of advanced premix burners in combustion turbines has paved the way for dry low NO_x combustion. The very lean mixtures of air and fuel in these burners lead to lower flame temperatures, drastically reducing the thermal production of nitric oxides. Careful tuning can reduce NO_x emissions to single digit levels. The downside is that the introduction of lean premix combustion has made flames more susceptible to instabilities. Excess air is added to such an extent that the mixture approaches the lean-blow-out limit. Changing ambient conditions or a deviation from the mean calorific value of the fuel can lead to acoustic oscillations or pressure pulsations, known as “humming”. Low frequency pulsations or “chugging” can also occur. Besides flame flash back, also lean blow out of the flames is possible. Acoustic oscillations of the combustion chamber can excite natural frequencies of hot gas path components leading to mechanical vibrations. The vibrations can become large enough for the safety system to trip the machine and can cause severe damages (see figure 1). The need to monitor combustion dynamics and avoid possible damages caused by high dynamics has gained increased attention over the last years. This paper will cover some background and theory on this phenomenon and will then focus on how to detect, monitor and avoid damages caused by increased combustion dynamics. More and more users install combustion dynamics monitoring systems (CDMS) to monitor the combustion dynamics on-line. Examples will be given of how users of KEMA’s combustion dynamics monitoring system FlameBeat® have changed their operations and prevented damages based on the information presented by the CDMS.