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Gas and solids mixing characteristics in the bubbling

Choking is commonly defined as a phenomenon where a sudden change in the solids holdup occurs in a gas

Bed dynamic beha®ior in a gas-solid fluidization system is measured in real time using ECT

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This article describes the recent progress in research and development on electrical capacitance tomography (ECT). Specifically, the article highlights several aspects of ECT including the electrical capacitance volume tomography (ECVT), 3D sensor design, 3D neural network multicriterion image reconstruction technique (3D-NN-MOIRT), multimodal imaging based on ECT and ECVT sensors, static-charge effects and the scheme of their elimination in the ECT image reconstruction, and multiphase flow imaging applications. The multimodal capability that enables permittivity and conductivity imaging to be simultaneously conducted is illustrated. The simulation and experimental results are presented to provide quantitative and/or qualitative assessment of the significance of various ECT techniques. The employment of ECVT in conjunction with using electrical capacitance based imaging sensors is shown to represent a favorable tool for industrial multiphase flow imaging.

The bed dynamic behavior in three gas−solid fluidized beds, 0.05, 0.1, and 0.3 m in diameters, is studied using the electrical capacitance tomography (ECT). The ECT employs the neural network multicriteria optimization image reconstruction technique. The time-averaged solids concentrations obtained by the ECT are generally in good agreement with those obtained by the optical fiber probe. The 0.1 m ID fluidized bed exhibits the spiral motion of rising bubbles in the bubbling regime. However, for the 0.3 m ID fluidized bed, more than one spiral motion of bubble swarms is observed in the bubbling regime. The small fluidized bed exhibits the round-nosed slug motion. The ECT studies reveal a radial symmetry of the time-averaged solids concentration distribution for the turbulent regime. Furthermore, the ECT provides the time-averaged and transient properties of the bubble/void phase and the emulsion phase. For a large fluidized bed, the standard deviations of the fluctuations of the cross-sectional averaged solids concentration, bubble/void phase fraction, and solids concentration in the emulsion phase all peak at the transition velocity from the bubbling to the turbulent regimes, U c. For a small fluidized bed, the quantities of these variables peak at the onset to the slugging regime, decrease in the slugging regime, and then level off in the turbulent regime as the gas velocity increases.

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