Modeling and characterization of density distributions for binary dense medium in gas–solid separation fluidized beds

Abstract

This study experimentally investigates and models the fluidization and density distribution characteristics of binary dense medium systems composed of magnetite and coal powders in air dense medium fluidized beds (ADMFBs). Three types of binary systems, namely Geldart B-B, B-A, and B-C, were examined under various superficial gas velocities (N = 1.2–1.8) to analyze axial and radial bed density distributions, density fluctuations, and the effects of fine-particle fractions. For the B-B system, density uniformity is limited due to weak segregation and small particle size differences, and bed density tends to increase with fine-particle fraction. The B-A system exhibits strong axial segregation, and although fine particles reduce density fluctuation intensity, excessive fines can be elutriated, limiting density range adjustment. The B-C system demonstrates an optimal balance: moderate fine-particle fractions (W_f = 6–10%) produce a relatively uniform bed-density distribution with low fluctuation intensity, lowering the density limit while maintaining low fluctuations. A correlation for predicting the average bed density of binary dense medium systems was developed based on particle size ratio and fine-particle fraction, with prediction errors within ±12% for W_f < 15%. The study highlights that particle size, density differences, and gas velocity critically influence bed fluidization, bed-density fluctuation behavior, and the adjustable density range, providing guidance for optimizing binary dense media in ADMFB coal beneficiation.