Separation Experiments in Gas–Solid Fluidized Bed Using Geldart a Dense Medium

Gas–solid fluidized bed separation uses upward gas flow to fluidize a dense medium. By controlling medium properties, gas velocity, and bed height, the apparent bed density can be adjusted so that low-density particles float and high-density particles sink. In practice, separation density may differ from measured bed density. Large feed particles can cause local defluidization near the upper bed, increasing resistance and effective particle weight. Bubble behavior also affects separation: near minimum fluidization, limited bed activity restricts particle motion, whereas higher gas velocities promote bubble growth, coalescence, and wake-induced upward transport of medium particles. Fine low-density particles may also pass through bubbles, disrupting normal separation. These effects are especially important in high-bed Geldart A systems. This study developed a separation-density model for a Geldart A dense-medium gas–solid fluidized bed from the force balance of spherical particles and compared it with a Geldart B model. Forces on spherical simulated feed particles were measured under different operating conditions, and theoretical separation densities were calculated. Separation tests were then performed to evaluate the effects of gas velocity and bed height, compare bed and separation densities, and assess model reliability. The results support density regulation and scale-up of dry beneficiation using Geldart A media.