426167 Monitoring Electrostatics and Hydrodynamics in Gas-Solid Bubbling Fluidized Beds Using Novel Electrostatic Probes

Wednesday, November 11, 2015: 8:30 AM
254B (Salt Palace Convention Center)
Chuan He, Xiaotao Bi and John R. Grace, Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC, Canada

Electrostatic charges in gas-solid fluidized bed reactors, resulting from a balance between charge generation and dissipation, can significantly affect reactor performance. Moreover, accumulation of electrostatic charges can cause hazardous electrical discharges leading to sparks, fires or even explosions. To avoid the adverse effects of electrostatics, effective measurement techniques are needed to monitor the electrostatic charges in fluidized beds. In this study, the ability of recently developed novel electrostatic probes to monitor particle charge density and hydrodynamics in freely bubbling two- and three-dimensional fluidized beds of glass beads and polyethylene particles has been demonstrated. Particle charge density and bubble properties in the beds were altered by abruptly changing the superficial gas velocity or by impulsively adding antistatic agent to the bed. The probes then quantitatively monitored changes in the particle charge density and bubble rise velocity. The current signals from the probes responded quickly and significantly to abrupt changes in the superficial gas velocity. By analyzing time-series signals from the probes, the particle charge density and the bubble rise velocity deduced from the probes were found to be of similar order of magnitudes and changed consistently with those obtained from Faraday cup and video measurements, respectively. The electrostatic probe signal was found to not always be consistent with the charge polarity and charge density on the particles. The probe signals and particle charge densities may have different polarity and relative magnitudes for different operating conditions and particle properties: density, mean size, size distribution, dielectric constant, sphericity, roughness and hydrophobicity. The novel probe has potential for in-situ monitoring of electrostatic charges and hydrodynamic behaviour in gas-solid fluidized beds.

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