Moisture-Dependent Fluidization Behavior of Zeolite 4A in Fluidized Bed Dryer

Poós, Tibor (2026) Moisture-Dependent Fluidization Behavior of Zeolite 4A in Fluidized Bed Dryer. In: 2026 International Drying Symposium – IDS’26 – Paris, France, 2026.08.25-2026.08.28., Paris, France.

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Abstract

The hydrodynamic behaviour of gas–solid fluidized bed drying systems is governed by particle properties, superficial gas velocity, reactor geometry, and moisture content. Materials classified as Geldart Group D frequently exhibit non-ideal fluidization behaviour, such as spouting, slugging, and pronounced pressure-drop fluctuations, which can adversely affect drying efficiency and operational stability. In this study, the fluidization behaviour of nearly spherical LTA 4A zeolite particles with diameters of 1.6–2.5 mm was investigated at different moisture contents, with a specific focus on fluidized bed drying applications. Fluidization curves were determined by measuring the pressure drop across the particle bed as a function of superficial air velocity. Particle motion and flow regimes were visually documented throughout the experiments. The results clearly demonstrate that increasing moisture content significantly influences both the minimum and maximum fluidization velocities and leads to higher and more unstable pressure drops, indicating increasing deviation from ideal fluidization conditions. To quantify these deviations, the Fluidization Index (FI), defined as the ratio of measured to theoretically predicted pressure drop, was applied. While classical correlations based on the Ergun equation provide satisfactory predictions for more ideal fluidization regimes, considerable discrepancies were observed for the investigated moist, Group D material. To address this limitation, an empirical correlation was developed that expresses the FI as a function of the ratio between the particle Archimedes number and a reference value corresponding to the lower boundary of Geldart Group D. This formulation reflects the increasing distance from the ideal fluidization regime as moisture content and effective interparticle cohesion increase. The proposed correlation showed good agreement with experimental data over the investigated moisture range. The results contribute to a more accurate hydrodynamic description of moist, nearly spherical granular materials and provide practical guidance for the design and optimization of energy-efficient fluidized bed dryers used for zeolite-based drying processes.

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