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Abstract

Electrostatic charging is a pervasive challenge in gas–solid fluidized beds, arising from continuous contacts among fluidizing particles and between particles and the column wall. In commercial operations such as polyolefin polymerization, pharmaceutical manufacturing, and dust handling, uncontrolled electrostatics can lead to wall sheeting, particle agglomeration, and even safety hazards. Despite decades of research, the interplay between particle properties, gas-phase conditions, and boundary effects remains insufficiently understood, limiting the effectiveness of mitigation strategies. This thesis systematically investigates the mechanisms and controlling factors of electrostatic charging in gas–solid fluidized beds. Fluidization experiments were conducted with high-density polyethylene (HDPE) and glass particles under different fluidizing gases and varying relative humidity levels. The results demonstrate that gas composition regulates the saturation charge via its dielectric breakdown strength, with argon in particular shown to effectively suppress charge accumulation of HDPE particles and the associated wall fouling and agglomeration. Humidity, in turn, critically influences both charge generation and dissipation. Its effectiveness is strongly material-dependent and is especially pronounced for glass beads, which are more hydrophilic and possess relatively lower electrical resistivity. Additional studies highlight the role of wall material and grounding in determining charge polarity and accumulation within the bed. To isolate interparticle charging, a custom-designed acoustic levitation platform was developed to enable controlled collisions between particles of the same or different sizes and materials. These experiments confirmed that for HDPE particles, collisions between dissimilar-sized particles consistently led to size-dependent bipolar charging, while collisions between similar-sized particles produced random polarity outcomes. In contrast, material pairings with large effective work function differences exhibit strongly directional charge transfer, consistent with observations in the fluidized bed system. Pre-charging experiments further revealed that when one particle carried a substantial initial charge, the size-dependent tendency was suppressed, and charge was redistributed to reduce the initial imbalance. A case study on wood dust handling provides additional insights into charge generation and dissipation mechanisms in practical industrial contexts, highlighting materials commonly encountered in wood processing. These findings help explain electrostatic hazards in dust-handling operations and provide guidance for reducing the risks of fires and explosions in industrial environments.