| Gas-liquid-solid three-phase fluidized bed has been widely employed in the petroleum,chemical,pharmaceutical,environmental protection and many other industries.Therefore,the accurate online measurements of flow parameters,i.e.the flow pattern,phase fraction and velocity,are of utmost importance for the safety and efficiency of industrial processes.Due to the complex flow characteristics of multi-phase flow,the existing online flow measurement methods usually fail to satisfy all the requirements of gas-liquid-solid three-phase flow detection.Electrical tomography(ET)techniques have the capability of non-invasive,non-radioactive and ultra-fast tomographic imaging,which has significant advantages in the field of multi-phase flow measurement.The fusion of two or more tomographic modalities is expected to achieve the online investigation of phase holdups and distributions of gas-liquid-solid three phases.In this thesis,the design and implementation of a fast electrical capacitance tomography(ECT)and electromagnetic tomography(EMT)system has been presented,which aims at the gas-liquid-solid three-phase flow parameters detection.The main works are summarized as follows:1.A multi-frequency digital phase sensitive demodulation method with extended dynamic range has been proposed and the its experimental circuits has been designed.The experimental results show that,the dynamic range of proposed digital phase sensitive demodulation method can be extended to 4 times of the original circuit with the maximum error lower than 4.8%,without adding any variable gain amplifier circuits.2.In order to measure the permeability of particle/powder materials,a 4-tap solenoid sensor is designed,and a digital measurement system based on field programmable gate arrays(FPGA)is proposed.The permeability measurement can be directly made by the proposed system,without the need to prefabricate the measured particle/powder materials into a specific mechanical structure/shape.Its advantages include fast measurement,wide frequency band and satisfied data repeatability.Meanwhile,it can be used as a pre-calibration component for the EMT measurements,which is of practical significance to the determination of the phase fraction of high permeability/conductivity solid phases.3.A parallel ECT/EMT tomography measurement system based on the multiple FPGAs has been designed,implemented and tested.It can perform the data conversions at the closest place to the transducer circuits,reducing the scale of analog signal processing circuits and improving the overall signal-to-noise ratio(SNR)level.The multi-modality excitation signal sources are integrated in the system and can be alternated to the suitable modality,i.e.ECT,ERT and EMT.Under the control of a Micro Blaze 32-bit processer,the electrical tomography system can accomplish different excitation and measurement strategies by referring to the configuration data stored in the EEPROM or FLASH memory.Preliminary tests show that the system can accomplish various measurement tasks,including the different sensor modalities and measurement channels.The SNR can be better than 60 d B.The system has good repeatability and scalability.4.In addition,the EMT excitation signal source based on pulse width modulation method has been studied.Its performance has been evaluated via circuit simulation.The hardware design scheme has been presented,which can drive EMT transmitter coils with larger current.At the end of thesis,the main works are summarized and some suggestions on system improvement are presented. |
PDF Full Text Request