The paper describes the application of different flame sensors for the monitoring and optimization of industrial burners. Direct information from the flame was obtained using pressure transducers and radiation sensors. Their fast response and non-intrusive character make such instruments particulary suitable for the monitoring of industrial flames, as a key step to develop advanced control strategies. The tests were performed in a gas-fired furnace (60 kWt), for a wide range of burner settings (air-staging ratios, swirl numbers of the two air streams) leading to very different flames: high/low NOx, stable/unstable... In a first stage, flame data were compared to flue gas compositions and burner settings in order to identify relationships among actual combustion conditions and the response of the sensors (both in the time and frequency domains). The results demonstrate that the flame condition can be adequately monitored using some selected parameters derived from the pressure and radiation signals, and that both statistical (averages, standard deviations) or frequency (bands of the power spectra) analysis can be alternatively used to monitor, almost in real-time, the state of the flame. In a second stage, a minimization algorithm was applied to optimize the performance of the burner according to different cost functions. The tests reported demonstrate that this approach can be used successfully in combustion processes. Its implementation in real burners can, however, pose some difficulties, such as long response times or the risk of flame pulsations or blow-off. The use of flame sensors can be helpful in avoiding or reducing those problems.
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