High Temporal Resolution Pyrometry and Velocimetry Based on Acoustic Frequency Division Multiplexing

Real-time and accurate flue gas temperature and velocity measurement is crucial for the safety, efficiency, and low emission of a power plant operation. This article describes a new technique for measuring flue gas temperature and velocity based on acoustic frequency division multiplexing (FDM) in a simultaneous way. The FDM method provides a technique that allows the simultaneous utilization of multiple acoustic signals that leads to a greatly reduced measurement cycle time required; therefore, the measurement system’s temporal resolution is significantly improved. With this new FDM method, the composite signal formed of two channels’ is decomposed by using a Butterworth filter for the extraction of the amplitude and phase information of signals passing each of the individual channels. From the derived frequency signals, the time of flight (TOF) on each acoustic path can be obtained. Demonstrated through both a theoretical analysis and experimental results, by applying the new technique, the measurement period can be reduced to 0.083 times (or say less than 10%) of that by using a traditional method. At the same time, the experimental results indicate that the new technique also improves the accuracy of the measurements. The sensitivity of the FDM method is 3.3, and 2.6 times higher than that of the HWA and traditional methods for velocity, and 1.6 and 1.4 times higher for temperature measurement. Moreover, its optimal robustness and precision are verified by several combined experiments with and without wind with background noise.