Coal Ash Beneficiation and Utilization in Coal Separation Process
In recent years, coal production and consumption increased dramatically, especially in China. So, more and more attentions have been paid to coal preparation and coal ash utilization with the growing concern about the pollution by fly ash. The unburned carbon in fly ash significantly affects its utilization in many fields, especially in concrete production industry. Technologies such as flotation, triboelectrostatic separation and carbon burnout have been developed to remove carbon from coal ash. This paper introduces chemical compositions of a typical coal ash and a dry beneficiation method. For some kinds of fly ash, magnetically stabilized fluidized bed was studied to recover magnetic pearls from fly ash. The magnetic pearls are mainly composed of Fe3O2 and Fe3O4 and are mostly hollow spheres. The size distributions of three kinds of magnetic pearls are from 300 to 25 µm. A magnetic pearls fluidized bed and a magnetically stabilized magnetic pearls fluidized bed for coal dry separation are studied in the paper.
Magnetically stabilized fluidized beds for fine coal separation
Abstract Based on a prior study on air-fluidized dense media for 6–50-mm coal preparation, this paper presents results on magnetically stabilized fluidized bed (MSFB) on fine 1–6-mm coal preparation. Magnetic stabilization improves separation by lowering the lower size limit of separation and by preventing back mixing of the separated solids. This work addresses the fluidization media characteristics, the experimental system and separation results.
Rheology of a magnetically stabilized bed consisting of mixtures of magnetic and non-magnetic particles
Abstract Hydrodynamic fluidization characteristics of an admixture bed consisting of 10 mass % iron (1416 μm) and 90 mass % copper (935 μm) are investigated under the influence of an external uniform magnetic field collinear with the gas velocity vector. The experiments are conducted at ambient conditions for superficial air velocity (Ug) varying in the range 0–4.0 m/s, and for ten values of the magnetic-field intensity (H) in the range 4000-22 000 A/m. The magnetic field is created by a Helmholtz electromagnet and its spatial uniformity is established by detailed direct measurements. Bed-pressure-drop is measured as a function of increasing and decreasing Ug, over a range of H values. These data are employed to determine the minimum fluidization (Umf) and bubbling (Umb) velocities as a function of H; and for the calculation of gross bed voidage (ϵ) as a function of Ug. ϵ is found to increase from approximately 0.4 to 0.8 as Ug is increased but does not exhibit any pronounced dependence on H. Umf is independent of H, but Umb is a weak function of H and increases with increase in H. Of particular interest is the observed bed fluidization behavior and its structural changes as Ug is increased at a given H, and the changes in the nature of bed response as H is increased. At low H (5400 A/m) and Ug values, iron particles form stalagmites at the bed surface but these become unstable as Ug is increased. Increase in H increases stalagmite stability, number and penetration in the bed. Iron particles gravitate toward the central region, channels are formed in the bed, and iron clusters are formed in the outer bed region at larger Ug values. At H = 9000 A/m, stalagmites are replaced with clusters of constant size, and at still greater H values larger stalagmites appear; the majority of iron particles are consumed in this structure with copper particles contributing to major agitation. The stability of the stalagmites increases with H, and at 22 000 A/m stalagmite formation wobbles in the bed and fountain type bubbling occurs from the central bed region.