Experimental Research On Reconstruction Of Velocity Field In Furnace Using Acoustic Measurement

The combustion of pulverized-coal in large-scale boilers of power station is a complex physical and chemical reaction, which is occurred under the condition of large space, frequent fluctuation and having conspicuous three-dimension character. The monitoring of combustion status is very important to safety, economy and cleaning of boilers in operation. The measurement of combustion gas velocity is a complex and important issue in combustion area. When the combustion gas status in furnace is known, the optimized control of combustion and well-organized production can be achieved. Acoustic measurement is one of techniques that can provide information about flue gas velocity in large-scale boilers of a coal-fired power station. The propagation time of acoustic signals through furnace is influenced by gas velocity. Therefore, based on the measurement of all propagation time, the combustion gas velocity field can be reconstructed by reconstruction algorithm of velocity field.In the thesis, the research in large-scale boiler combustion diagnosis and control in the world is introduced. After analyzing the common methods for combustion gas velocity measurement in the furnace, the thesis points out that the acoustic measurement is of practical significance when applied to reconstruct combustion gas velocity field. The basic acoustic theory and principle used in reconstruction of cross-section velocity field are also presented. Since signal processing is essential in acoustic measurement, we use FIR(finite impulse response)filter ,which is designed by Parls-McClellan algorithm,combined with wavelet frame theory to process signals.After experiment on a model boiler furnace, we compare the experimental result of cross-section velocity field with the actual velocity field measured by thermo-anemometer, and it turns out that the compared reconstructed results can reflect the distribution status of furnace cross-section velocity field, and be consistent with the practical flow distribution.In conclusion, as a new technology of furnace velocity measurement, using acoustics in reconstruction of furnace combustion gas velocity field is of great significance to improve the precision of velocity field measurement. It is also the foundation of furnace velocity field visualization, and can help unit operators to diagnose combustion and analyze accident better. As a result, the security and economy of boiler are improved.