Study Of Real-time Monitoring On Furnace Temperature Field Based On Acoustic Theory

In large coal-fired power plant, to operate safely and efficiently, to lower pollution, and to realize the essence of the combustion, the distribution and visualization of the furnace temperature field is important in practical value and scientific meaning. However, the processing of combustion in power plant furnace is instantaneous, random and in hard environment, and the scale of furnace is large. At present, there is not an effective monitoring measurement on furnace temperature field has been established. Based on acoustic theory, the real-time monitoring technique on furnace temperature field by acoustic method has been proposed. Further theory and experiment study has been developed. It offers theory and technique instruction to engineering application.The wave equation and speed equation of sound propagation in furnace are deducted. The model between sound speed and media temperature is established. According to Fermat's theory and variational calculation, the mathematical model of sound path in dissymmetrical temperature field is established. Furthermore, the sound path equation is solved. The possible measurement error in acoustic pyrometry is analyzed. By the analysis of sound field in furnace, there is standing wave field when the wave is of low frequency, and there is diffusion field when the wave is of high frequency. The critical frequency is Schroeder Frequency.Based on two-channel measurement model, the time delay estimation algorithm based on cross correlation is given. More accurate result can be gotten by filtered in frequency field. The right statistic analysis method should be selected among the different type of signal and noise. The time delay estimation based on high-order cumulant is given. The acquired background noise in furnace is added to signal with exponential distribution. One hundred Monte Carlo simulation tests of TDE are done based on the ML cross-correlation method and high-order cumulant method respectively under different signal noise ratio (SNR). The result shows that the influence of correlated Gaussian noise can be restrained from the non-Gaussian signal based on the third-order cumulant method even under poor SNR. Aimed at reverberation that could be appeared in furnace, the cepstrum method and envelope analysis is given.The reconstruction algorithm of temperature field based on series expansion is given. The linear equation of weights matrix, image matrix, and projection matrix is established. Aimed at the inverse problem model of temperature field reconstruction, the algebraic reconstruction equation is given. Regularization of the ill-posed problem has been done. The reconstructions of some typical flame distribution in furnace are simulated by computer. The algorithm can offer accurate temperature at any spot of the furnace cross section. Some random noise is added to the simulated measurement data, and the result show that the algorithm is robust. Aimed at the typical symmetrical temperature distribution in furnace, the algorithm by presumed a single path temperature function firstly, then been gridded and interpolated is proposed. The reconstruction result showed that it is accurate and feasible.According to theory analysis and experiment measurement, the backgroundnoise in furnace is mainly due to the combustion noise with low middle frequency at the range of 250~1000Hz. The overall sound pressure level is about 110~120dB. The possibility density function is nearly Gaussian distribution. Some important component of acoustic pyrometer designed. An eight-channeled acoustic pyrometer is developed. The experiments under normal temperature condition are done respectively in lab and in 300MW boiler in one power plant.