Dry beneficiation of fine coal using density-segregation in a gas–solid fluidized bed

Abstract

Dry beneficiation of fine coal of +150–500μm in size was conducted using density-segregation in a gas–solid fluidized bed without any separation media. The coal particles in a cylindrical column (inner diameter=100mm and bed height=100mm) were fluidized at a given air velocity u0/umf=1.3–3.0 for thirty minutes where u0 and umf are the superficial air velocity and the minimum fluidization air velocity, respectively. The bulk density of the coal particles in each layer 10mm in height (ten layers in total) was measured after the fluidization to investigate the segregation. It was found that the maximum segregation is produced at u0/umf=2.0; the segregation is less pronounced at smaller and larger air velocities investigated. The origin of the dependence of the segregation on the air velocity is related to the velocity relative to the minimum fluidization velocity, the size of the air bubbles moving up through the fluidized bed, particle movement and vertical mixing. The calorific value and ash content of the ten layers before and after the segregation were estimated by fitting the dependence of calorific value and ash content on the bulk density. If the top 7 layers after segregation are regarded as the product (70% yield), the calorific value is increased from 5063kcal/kg to 6067kcal/kg and the ash content is decreased from 34.0wt% to 22.4wt% at u0/umf=2.0, indicating that fine coal can be upgraded by the dry separation. The combustible recovery and ash reduction resulting from the segregation indicate that the upgrade is mainly caused by rejecting ash into the lower 8th to 10th layers.