Coal cleaning performance in an air fluidized bed

This investigation was concerned with the effects of coal properties and process variables, such as fluidized bed depth, superficial gas velocity coal to magnetite feed weight ratio, and processing time, on coal cleaning efficiency in a bubbling fluidized bed dry coal purifier. The coal cleaning experiments were carried out on various size fractions of Pennsylvania'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 removal 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 relatively 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. Experiments were also performed to determine the optimum values of superficial air velocity 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 superficial air velocity between about 1.75 and 2.75 times the minimum fluidization velocity. However coal cleaning performance in the case of a shallow bed of 3 cm was found to be relatively insensitive to the ratio of coal to magnetite feed weight.