Abstract
The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes. In this paper, electrostatic sensing and high-speed imaging are applied to measure the velocities of polyethylene and sand particles in the binary particle mixtures in fluidization. Experimental studies were conducted on a lab-scale cold circulating fluidized bed. Correlation function between electrostatic signals from upstream and downstream electrodes placed along the riser shows two peaks that represent transit times for the two types of particles. To verify the above results, high-speed imaging was adopted to capture the flow images of particle mixtures. Particle Image Velocimetry and Particle Tracking Velocimetry algorithms were utilized to process the resulted images in order to measure the velocities of polyethylene and sand particles. The reasons for two-peak correlation functions are illustrated based on the frequency spectrums of the mono-solid-phase electrostatic signals and the velocity difference between polyethylene and sand particles. Finally, comparisons on the velocities obtained from electrostatic sensing and high-speed imaging demonstrate the electrostatic sensor can roughly estimate the particle velocity of binary particle mixtures in the near wall region of the circulating fluidized bed.
Highlights
Due to the advantages of homogenous mixing, high heat and mass transfer rate and easy control, fluidized bed is applied in various industrial fields, such as petroleum, chemical and energy processes (Van Der Hoef et al 2006)
It is found that correlation functions of electrostatic signals present two peaks when the particle mixtures with different volume ratios flowing together in the riser
It is supposed that the electrostatic signal contains two components when the PE and sand particles flow simultaneously: one is the signal from PE particles and the other is the signal from sand particles
Summary
Due to the advantages of homogenous mixing, high heat and mass transfer rate and easy control, fluidized bed is applied in various industrial fields, such as petroleum, chemical and energy processes (Van Der Hoef et al 2006). The flow characteristics of binary particle mixtures in the bed should be investigated to deepen the understanding and further optimize the related industrial processes. Particle segregation caused by different particle densities and sizes is the major problem of binary particle mixtures in the fluidized bed. The hydrodynamic behavior and segregation of binary particle mixtures with disparate sizes, as well as the influence of particle composition and operation condition in a gas–solid fluidized bed were examined by both laboratory experiments and computational modeling (Gao et al 2008). The mixing behaviors of binary mixtures comprising spherocylindrical particles and spherical particles in a fluidized bed were evaluated using the computational fluid dynamic–discrete element method (Ren et al 2019). The above researches were mainly focused on the segregation and mixing behaviors of particles in the fluidized bed, whereas, the particle velocity of binary particle mixtures in the fluidized bed has not been fully investigated
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