Measurement of Flow Characteristics in a Bubbling Fluidized Bed Using Electrostatic Sensor Arrays

Fluidized beds are widely applied in a range of industrial processes. In order to maintain the efficient operation of a fluidized bed, the flow parameters in the bed should be monitored continuously. In this paper, electrostatic sensor arrays are used to measure the flow characteristics in a bubbling fluidized bed. In order to investigate the electrostatic charge distribution and the flow dynamics of solid particles in the dense region, time and frequency domain analysis of the electrostatic signals is conducted. In addition, the correlation velocities and weighted average velocity of Geldart A particles in the dense and transit regions are calculated, and the flow dynamics of Geldart A and D particles in the dense and transit regions are compared. Finally, the influence of liquid antistatic agents on the performance of the electrostatic sensor array is investigated. According to the experimental results, it is proved that the flow characteristics in the dense and transit regions of a bubbling fluidized bed can be measured using electrostatic sensor arrays

Experimental study of bubble dynamics and flow transition recognition in a fluidized bed with wet particles

This paper studies the bubble dynamics and flow transition behavior in wet particle systems. Non-coherent algorithm was used to quantitatively calculate the bubble diameters in a three-dimensional fluidized bed system loaded with wet particles, obtaining the bubble dynamics under the action of liquid. The results indicate that the incoherent analysis can detect the formation of even tiny bubbles in the fluidized bed. The kurtosis and skewness of the pressure fluctuation signal was used to obtain the critical transition conditions of the flow pattern from turbulent to laminar. Through the decay index of the incoherent spectrum, the operating conditions of the Levy-Kolmogorov flow pattern to the Kolmogorov flow region were determined. From the comparison of the liquid bridge and the drag forces, the competitive mechanism of different forces acting on the particles that conformed the bed was analyzed, reflecting the change of the apparent minimum fluidization velocity of wet particles

Simultaneous measurement of electrostatic charge and its effect on particle motions by electrostatic sensors array in gas-solid fluidized beds

Repeated particle-particle and particle-wall collisions and frictions lead to the generation and accumulation of electrostatic charges in the gas-solid fluidized beds. Variations of electrostatic signals are a rich source of information on particle motions and charging, which have rarely been explored and interpreted. To gain a more comprehensive understanding of the induced electrostatic signals in the fluidized beds, an array of arc-shaped induced electrostatic sensors were attached to the outer wall of a fluidized bed. Combined with cross-correlation method, induced electrostatic voltage signals and correlation velocity of particles were measured simultaneously. It was found that electrostatic charges accumulation restrained the particle motions while the average correlation velocity of particles increased with the amount of injecting liquid antistatic agent. Based on the analyses of induced electrostatic signals, the particle correlation velocity, and the particles charge-to-mass ratio under different charging levels, a predictive model of the average particles charge-to-mass ratio was established. Compared with the results obtained from Faraday cup, the estimated results showed a relative error no more than 40%. Simultaneous measurement of particle correlation velocity and particles charge-to-mass ratio were complemented by arc-shaped induced electrostatic sensors array combined with cross-correlation method

Monitoring of particle motions in gas-solid fluidized beds by electrostatic sensors

Gas-solid fluidized beds are widely applied in numerous industrial processes. Particle motions significantly affect the performance of fluidized bed reactors and the characterization of particle movements is therefore important for fluidization quality monitoring and scale-up of reactors. Electrostatic charge signals in the fluidized bed contain much dynamic information on particle motions, which are poorly understood and explored. In this work, correlation velocities of Geldart B and D particles were measured, analyzed and compared by induced electrostatic sensors combined with cross-correlation method in the fluidized bed. The results indicated that the average correlation velocity of particle clouds increased and the normalized probability density distributions of correlation velocities broadened when the superficial gas velocity increased in the dense-phase region. Both upward and downward correlation velocities could be acquired in the dynamic bed level region. Under the same excess gas velocity, the average correlation velocity of Geldart D particles was significantly smaller than that of Geldart B particles, which was caused by the smaller bubble sizes caused by the dominant bubble split over coalescence and less volume of gas forming bubbles for Geldart D particles. The experimental results verified the reliability and repeatability of particle correlation velocity measurement by induced electrostatic sensors in the gas-solid fluidized bed, which provides definite potential in monitoring of particle motions

Critical comparison of electrostatic effects on hydrodynamics and heat transfer in a bubbling fluidized bed with a central jet

In many industrial processes, electrostatic charges are inevitable and affect the hydrodynamic behavior and heat transfer ability of chemical equipment. A comprehensive study of the electrostatic effect on bubble behavior, particle fluctuation velocity and heat transfer coefficient in the fluidized bed with a central jet has been evaluated in this paper by Eulerian-Eulerian two-fluid model coupled with electrostatic model and energy model. The simulated voidage profiles at different positions, bubble detachment time and initial bubble diameter are compared with experimental results from the literature without charge. The bubble behaviors including bubble frequency and bubble numbers, combined with particle fluctuation parameters are analyzed in both charged and uncharged system. The electrostatic effect on two kinds of heat transfer coefficients is quantitatively compared, namely bubble to emulsion phase heat transfers based on the gas throughflow velocity and gas-solid local heat transfer coefficient. Simulation results show that electrostatic charges decrease bubble numbers and granular temperature, whereas the averaged heat transfer coefficients are enhanced. Overall, the electrostatic effect on the hydrodynamic and heat transfer characteristics can be revealed.This work was supported by the Project of National Natural Science Foundation of China (No. 91434205), the National Science Fund for Distinguished Young Scholar (No. 21525627), the Science Fund for Creative Research Groups of National Nature Science Foundation of China (No. 61621002)

POSS@TiCl4 nanoparticles:A minimalism styled Ziegler-Natta catalytic system

Heterogeneous catalysis plays a crucial role in industrial olefin polymerization. Mechanistic understanding and optimization of Ziegler-Natta (ZN) catalyst are limited by the considerable complexity resulting from the multiple ingredients and complicated structures. Re-designing ZN catalytic systems with reduced complexity and adequate performance is of great interest. Here, we show that self-assembled polyhedral oligomeric silsesquioxane (POSS)@TiCl4 nanoparticles can effectively immobilize TiCl4 molecules in n-heptane solution, achieving the exceptional utilization of active centres. This uncomplicated system exhibits heterogeneous-like catalytic performance in ethylene polymerization, featured by high activities, fouling-free polymerization and a series of desirable properties of the nascent polymers such as reduced entanglement and spherical morphology. In addition, these catalytic nanoparticles show robust resistance to H2, and enhanced incorporation of comonomer towards ethylene/1-hexene copolymerization. By using DFT calculations the possible structures of the Ti active centres are proposed, of which a flexible double-Ti structure coordinated to Si-O-Si shows the most reduced energy barrier for ethylene insertion