Implementation Of EMT System For High Solid Ratio Gas-Liquid-Solid Three-Phase Fluidized Bed Measurement

The gas-liquid-solid three-phase fluidized bed is an important reaction plant in the petrochemical and biological engineering.The online measurement of the phase media in the fluidized bed is of great significance to the optimization of the fluidization process and the fluidized bed itself.Being non-invasive,high real-time and non-radiation,Electromagnetic tomography(EMT)can be employed to measure the conductivity or permeability distribution,which provides an effective method for mapping the distribution of high-permeability solid phase in fluidized bed.In this thesis,the design and implementation of an electromagnetic tomography system for mapping of the magnetic permeability distribution,i.e.the high permeability catalysts particles in the gas-liquid-solid fluidization,are presented.The system employs the linear tunneling magneto resistance(TMR)sensors which is of high sensitivity and accuracy,as the substitution of the receiver coils.The main works are summarized as follows:1.Coils are employed as receivers in the developed EMT systems.The induction voltage of the receiver coil depends on the excitation frequency and coil geometry.In addition,the capacitive coupling between the coils will affect the accuracy of the measurement signal.The characteristics of TMR sensor and receiver coil have been investigated.A TMR-coil sensor array is designed and optimized.The experimental results show that the output of the TMR sensor is independent of the excitation frequency and is of high sensitivity to the magnetic field,which helps to improve the EMT system performance.2.Most of the developed EMT systems focus on the reconstruction of conductivity distribution.To investigate the magnetic catalyst distributions,the EMT sensitivity matrix for magnetic permeability measurement was calculated in 2D and 3D models by using the simulated perturbation method.The reconstructed permeability distributions in the field of interest were obtained by using multiple image reconstruction algorithms in the simulation platform.The reconstructed images verified the feasibility of TMR sensor's application in EMT system.3.The EMT system is developed based on FPGA.Sinusoidal excitation signals of different frequencies can be generated to meet the different application requirements.The front-end filter and amplification circuit for small voltage signal is constructed.The programmable amplifier circuit is designed to improve the dynamic range of measurement system.Multiple excitation and measurement strategies can be realized with the system.An orthogonal sequence demodulation algorithm is implemented in FPGA to calculate the amplitude and phase angle of the measurement signals.The preliminary test results show that the system is stable and accurate.4.The static image reconstruction experiments were carried out using the EMT system in gas-solid two-phase and gas-liquid-solid three-phase media.Having been tested with different solid concentrations,the EMT system can obtain the solid distributions,verifying the feasibility of EMT's application in high solid ratio gas-liquid-solid three-phase fluidized bed.In addition,the effect of independent measurement number on the quality of reconstructed images is preliminarily discussed.