Electrical Tomography Imaging Method For Gas-Liquid-solid Three Phase Fluidized Bed Measurement

In the fluidization process,the interaction,flow structure and mechanism of multiphase medium are very complicated.Due to the lack of effective online measurement methods,the design,the design,optimization and control of fluidized bed are significantly affected.It is usually difficult to obtain the distributions of different medium and determine the three-phase flow in real time by using the existing detection techniques.Electrical tomography techniques have the advantages of fast response,low cost in long-time running,non-invasive and no radiation,which provide a feasible solution to the on-line monitoring of fluidized bed.In the gas-liquid-solid three-phase fluidization processes,the liquid phase behaves as the heat carrier,which makes the solid phase turn into fluidization state and improve the reaction performance.In this thesis,the use of electrical tomographic imaging techniques for the online mapping of the medium distributions has been investigated,aiming at the requirements in the gas-liquid-solid three-phase fluidized bed detection.The research works are summarized as below:(1)A differential electrical capacitance tomography(ECT)sensor and measurement system have been designed and implemented to achieve high sensitivity and accomplish the detection of plant-scale fluidized bed.Experimental results show that the average signal to noise ratio(SNR)of all channels has been increased from 52 dB to 68 dB,which suggests a significant improvement in the system performance.(2)A complex permeability sensor that based on the solenoid coil is developed to estimate the equivalent permeability of gas/solid and gas/liquid mixtures and its changes,which are verified by the numerical simulations and experiment results.The mixtures of Al2O3 and ferrite powder of different volume ratio are measured,showing that the maximum relative error is 5.35% as compared with the results obtained from Maxwell model.In this way,it is not necessarily to make the particles/powders into special geometry prior to permeability measurement,which is meaningful for the development of electromagnetic induction tomography(EMIT)system.(3)The Tunnel Magnetoresistive(TMR)sensor is of small size and high sensitivity.The use of different TMR sensor arrays in EMT,i.e.as the substitution of receiver coils,has been numerically studied.The simulation results suggest that EMT sensor containing more TMR sensor can improve the image reconstruction quality.In addition,it is suggested that the TMR sensors that embedded within the imaging area can provide better image performance than the boundary sensor whenever the intrusive sensor can be accepted.(4)In addition,an ECT/EMT dual-modality measurement system based on FPGA is designed.Most of the modules have been tested.The preliminary tests on the A/D and signal source demonstrate that the system structure is feasible,which guarantee the functionality of ECT/EMT system.Finally,the research works are summarized and the suggestions on the improvements of ECT/EMT system are presented.