Research On Furnace Temperature Field Reconstruction Technique Based On Acoustic Theory

The temperature of the furnace as an operating parameter of large coal-fired boilers, is very important to control and diagnosis the boiler. The acoustic thermometry has the properties of non-intrusive measurement, wide measurement range, high accuracy and good real-time performance. And the reconstruction of temperature field by acoustic method has been studied in the article based on the former research.Combining the cross-correlation time delay estimation method with the Hilbert transform aiming to obtain envelope is proposed to calculate the time of flight (TOF) in the furnace.50MW furnace as the research object, through analysis of the background noise and the attenuation characteristics of acoustic signal in the furnace, it is determined to choose the linear sweep signal as the acoustic signal. With the experiment in the furnace, the result indicates the method with extracting the envelope effectively improves the precision of the TOF.In order to obtain accurate temperature distribution, simulation of temperature reconstruction has been analyzed. In the case of unimodal symmetric model and unimodal skewed model, the author reconstructs the temperature field using the reconstruction algorithms of least square method and temperature field reconstruction algorithm based on parabola model respectively. The results show that two algorithms can reconstruct the temperature field well with enough data. In addition, the author analyzes the influence to temperature field reconstruction precision caused by the positions of the sensors’ measurement precision, the TOF’s measurement precision and the sensors’ number and distribution based on MATLAB platform. The result tells that, the reconstruction precision is more sensitive to the TOF’s measurement precision than the measurement precision of the sensors’ positions. What’s more, when the number of sensors is small, the reconstructed temperature field is poor; It can be appropriate to reduce the number of sensors if the requirement is to get the temperature distribution of the flame center.For the sake of verifying the feasibility of the acoustic thermometry, the acoustic temperature measurement system has been established. And the author has carried out experiments under the condition of laboratory and power plant furnace. The experiment in the laboratory shows that the system can get accurate TOF. In the process of experiment in boiler, due to the limited number of fire holes, the reconstructed temperature field can not reflect the temperature distribution precisely, but it can show the range of the temperature in the furnace. Although the temperature distribution obtained in the experiment can’t be verified at present, but it lays the foundation for the realization of acoustic measurement with more propagation paths.