Research On The Measurement Mechanism Of Dilute Gas-Solid Two-Phase Flow Based On Electrostatic Sensor

Gas-solid two-phase flow is widely applied in the industrial process. On linemeasurement of the critical parameters and subsequent optimized control have greatsignificance to improve operation efficiency, reduce costs and conserve energy. Dueto the features of simple structure and high sensitivity, electrostatic method hasattracted more attention. However, it still has many unsolved problems. This paper isfocused on the measurement mechanism of gas-solid two-phase flow based on theelectrostatic sensor. It has mainly three parts: research on the electrostatic sensorbased correlation velocimetry, research on the relationship between the features fromthe electrostatic fluctuation signal and solids velocity and concentration and researchon the flow dynamics of triple-bed combined circulating fluidized bed. The mainachievement and contributions of the research are as follows:1. Using the finite element model built in COMSOL and the belt electrostaticinduction apparatus and considering the frequency characteristics of electrostaticsensor and the measurement error of the transit time, the principle of selectingsampling frequency is illustrated. After the sampling frequency is selected, takingthe variance of transit time and real application requirements into account, theprinciple of selecting integral time is introduced. The performance of correlationvelocimetry under the selected sampling frequency and integral time is testedusing the belt electrostatic induction apparatus and gas-solid two-phase flow rig.The correlation velocity is similar to the real belt velocity and under differentsolids to gas mass ratios, the correlation velocity has good linear relationship withthe superficial air velocity.2. The influence of sensitivity distribution and velocity distribution on thecorrelation velocimetry is analyzed using the ring-shape electrostatic sensor withdifferent widths. It is concluded that the correlation velocity is influenced by thesensitivity distribution of both the upstream and downstream electrodes. With theincrease of solids concentration, the ratio between the average solids velocity andthe correlation velocity, which is called meter factor K will decrease.3. The electrostatic fluctuation signal is analyzed using multi-scale entropy. Basedon the analysis of multi-scale entropy, it is shown that with the change of solidsconcentration or air velocity, the trends of sample entropy at different scales are different. With the increase of solids concentration or air velocity, sample entropyat small scales will increase. Sample entropy at median scales does not changemuch with the change of solids concentration or air velocity. At large scales, withthe increase of solids concentration or air velocity, sample entropy will decrease.4. The electrostatic signals from2mm and10mm ring-shape electrodes areinvestigated using Hilbert-Huang transform. The frequency characteristics of thetwo type electrostatic signals are analyzed using the margin spectrums fromdifferent intrinsic mode functions (IMFs). The IMFs, which have the principalfrequency components of the original electrostatic signals, are pointed out.Considering the correlation coefficient between the features and the solidsconcentrations and the features’ linear performance under different air flow rates,the energies of IMF3from the2mm and10mm electrodes are considered to be theuseful features to characterize the change of solids concentrations.5. The flow dynamics of triple-bed combined circulating fluidized bed (TBCFB) hasbeen investigated using multi-electrode electrostatic sensor and twin-planeelectrical capacitance tomography (ECT). The multi-electrode electrostatic sensorhas ring-shape and arc-shape electrodes. By a combination of the electrostaticsensor and ECT sensor, the hydrodynamics of the bed has been investigated in awider range of flow regimes. The knowledge of particle velocity profile and solidsdistribution in both the riser and the downer provides guidance to optimize thecoal gasification process of TBCFB in the future.