Coal Cleaning Performance in an Air Fluidized Bed

Abstract

This inuestigation was concerned with the effects of coal properties and process variables, such as fluidized bed depth, superficialgas uelocity, coal to magnetite feed weight ratio, and processing time, on coal cleaning efficiency in a bubblingfluidized bed d y coal purifier. The coal cleaning erperiments were cam'ed out on various size fmctions of Pennsyluania ' s bituminous coal, Rushton coal. Angular magnetite was used as the host material to enhance segregation. The performance of the coal cleaning process was measured with the aid of sulfur and ash remoual efficiencies. Previous experimental results and those obtained in this study showed that coal particle sizes smaller than 30 mesh and larger than 140 mesh can be cleaned with high efficiency in the fluidized bed separator. For coal particle sizes smaller than 140 mesh, bed slugging and channeling occurred due to high interparticle cohesive forces, resulting in a relatiuely poor cleaning performance. The results also indicated that the air fluidized bed should be operated using shallow bed depths and processing times of 30 s or more. Erperiments were also performed to determine the optimum values of superficial air uelocity and the effect of feed weight ratio of coal to magnetite on cleaning performance. It was observed that batch bed should be operated with a supeftcia1 air velocity between about 1.75 and 2.75 times the minimum fluidization velocity. Howeuer, coal cleaning performance in the case of a shallow bed of 3 cm was found to be relatiuely insensitiue to the ratio of coal to magnetite feed weight.

Characterization of the Effective Density for the Separation of Immersed Objects in the Gas–Solid Fluidized Bed Coal Beneficiator

“…The effective density for immersed object separation in the GSFBCB is apparently affected by the physical properties of immersed objects, such as their size, , shape, , and density. − Objects of large size were reported to possibly gain additional weight due to the deposition of defluidized particles on their upper surface, ,,, causing the effective density of large-size objects to be lower than the fluidized bed density. Objects of smaller size, on the other hand, were found to increase their effective density but decrease the separation effectiveness, due to the increasing disturbance by gas bubbles. , For the immersed objects of different shapes, the separation effectiveness decreases with decreasing sphericity, because objects of lower sphericity have a larger specific area (surface area to volume ratio) subject to more viscous effects. , For the immersed objects of different densities, objects with densities close to the fluidized bed density were observed to be easily suspended or move more randomly, whereas objects with densities more different from the bed density were found to float or sink quickly given the higher separation potential. − …”

“…Objects of smaller size, on the other hand, were found to increase their effective density but decrease the separation effectiveness, due to the increasing disturbance by gas bubbles. 37,40 For the immersed objects of different shapes, the separation effectiveness decreases with decreasing sphericity, because objects of lower sphericity have a larger specific area (surface area to volume ratio) subject to more viscous effects. 9, 35 For the immersed objects of different densities, objects with densities close to the fluidized bed density were observed to be easily suspended or move more randomly, whereas objects with densities more different from the bed density were found to float or sink quickly given the higher separation potential.…”

Investigation of Using Table Type Air Separators for Coal Cleaning

“…In this process, fine media particles are transformed from a fixed state to a pseudo-fluid state by fluidizing air through an air distributor plate located at the bottom of vessel. During fluidization as air velocity is increases, the particle bed goes from a fixed bed to a fluidized bed and to a transported bed, respectively [11][12][13][14][15][16]. Zhenfu et al [17] reported that by using the ADMFB a good separation performance was achieved for the 50 Â 6 mm size fraction obtaining clean coal and tailings containing 11.80% and 85.75% ash, respectively, with a Probable Error (Ep) value of 0.03.…”