Research On Gas-solid Two-phase Flow Imaging Based On ECT Technology

Two-phase flow widely exists in national economic industries such as electric power,environmental protection,chemical industry,metallurgy,nuclear energy and other national economic industries,especially in the metallurgy,electric power and other departments need to understand the distribution of dust inside the fluidized bed,which is of great significance for the measurement and safety monitoring of the production process.Electrical capacitance tomography(ECT)technology uses the sensor array placed around the measured pipeline and container to obtain the projection data of the measured non-conductive object field(i.e.capacitance measurement value)under different observation angles.Through image reconstruction algorithm the medium(dielectric constant)distribution of the measured object field is reconstructed.It has the advantages of fast response,low cost,non-invasion,wide application range,safety and no radiation,among which two-phase flow detection is a typical application.This paper mainly focuses on the related problems of gas-solid two-phase flow imaging based on ECT technology.The main work of the paper is as follows:First,it is found that the post-processing of the reconstructed image by filtering can improve the imaging effect,reduce the number of iterations,and shorten the reconstruction time,based on the analysis of the Landweber iterative imaging algorithm.In this paper,an adaptive threshold filtering method is proposed,which takes into account the reconstruction effect and reconstruction speed,and can be applied to two-phase flow reconstruction imaging.Second,the off-line iterative on-line reconstruction algorithm is improved.Firstly,the selection of iterative step size ? and the substitution of the first-order iterative method with the second-order iterative method are introduced.Secondly,the sensitivity matrix is optimized by updating the sensitivity matrix to eliminate the target artifacts;Thirdly,the optimal mesh number of image reconstruction is selected based on the condition number of the sensitivity matrix,and the selection method of the best iterative times k of the off-line part of the algorithm is detailedly analyzed in addition,and the best iterative times are given for different flow patterns.Finally,the rationality of the off-line iterative on-line reconstruction method under the second-order iterative method is analyzed by comparing the simulation data of several flow patterns.Third,the series model is used as the normalized capacitance model for sensor calibration.Combined with the sensor calibration method and the sensor wear detection method,the influence of the wall wear amount under different solid phase concentrations on the capacitance measurement value is analyzed.In the case of wall wear amount of 2mm,the simulation analysis of the changes in different detection concentrations shows that the accuracy of capacitance detection can be effectively improved by tracking data on the zero capacitance of the system under the case of low solid/gas ratio content.