Research Of Temperature Field Reconstruction Of Boiler Furnace Based On Acoustic Method

The measurement of temperature field in boiler furnace is of great practical significance.The basic requirement of boiler is to establish and maintain a stable combustion flame.It is particularly important to determine the temperature distribution inside the furnace.However,the traditional temperature detection method is difficult to apply to the measurement of temperature field in furnace because of its limitation.The temperature field reconstruction based on acoustic method has many advantages,such as non-contact,large measuring space,wide measuring range,continuous real-time measurement,maintenance etc.These advantages can effectively compensate for the lack of traditional temperature measurement methods.When the acoustic thermometry method is applied to the furnace temperature detection,the acoustic sensors need to be installed at the opening of the furnace,so the number of acoustic sensors is relatively small,this thesis focuses on the reconstruction error of 2D and 3D temperature field reconstruction with fewer sensors and analyzes the factors that affect the reconstruction accuracy.The finite element method analyzes the effect of neglecting the acoustic wave bending on the reconstruction.The main work of this thesis can be summarized as follows:(1)Aiming at the common problems existing in most acoustic temperature reconstruction algorithms at present,it must satisfy that the number of effective acoustic wave paths is larger than the number of grids,the reconstruction temperature points are few.Tikhonov regularization method is used to solve the temperature field reconstruction problem.The temperature points calculated by Tikhonov regularization method are far more than the number of paths,which can avoid the error introduced by the result interpolation.(2)When the number of grids is less than the number of effective paths,the reconstruction equation of the temperature field is overdetermined equation.It is found through simulation experiments that the LSM,SVD and Tikhonov regularization algorithms can get relatively small error results under these conditions.However,due to the small number of temperature points,the reconstruction result needs to be interpolated.After interpolation,the temperature field reconstruction error increases significantly.(3)When the number of meshes is larger than the number of effective paths,the reconstruction of the temperature field is underdetermined,which can not be solved by the conventional method.In this thesis,an improved Tikhonov regularization method is used to reconstruct the 2D temperature field model,the root mean square error of the reconstruction results of all the temperature fields is less than 2.7%.The results show that the regularization parameters,the number of grids,the number of sensors and the temperature difference in the region have an important influence on the reconstruction results.(4)In this thesis,the Tikhonov regularization method is used to reconstruct the 3D temperature field.Three typical temperature field models are used in the experiments.The root mean square errors of the reconstruction results are all within 8%.The influence of sensor number,distribution mode and meshing on the reconstructed 3D temperature field is analyzed.(5)Considering the bending effect of sound waves propagating in non-isothermal field,a 2D transient model of acoustic wave propagation is established by finite element tool COMSOL.The acoustic propagation time in isothermal and non-isothermal fields is analyzed.The effect of neglecting the bending effect on the temperature field reconstruction is also studied.