Coal cleaning via liquid-fluidized bed classification (LFBC) with selective particle modification

The concept of coal beneficiation by particle segregation in water-fluidized beds (or liquid-fluidized bed classification - LFBC) and its improvement via selective solvent-swelling of organic material-rich coal particles were investigated in this study. Samples of Kentucky #9 and Illinois #6 U.S. coals of varying sizes were used in the investigations, both unswollen and swollen with acetone and saturated phenol-water solution. Both solvents were effective swelling agents for both coals. Leaching of the solvents out of the coal particles into water was also observed to occur. This was found to be more rapid for phenol than for acetone. However, it is concluded that this process is still slow enough to allow sufficient time for segregation and separation of sol vent-swollen coal particles in a water-fluidized bed. Particle segregation by size was observed for all the unswollen coal samples, with particle sizes increasing from top to bottom in the LFBC. Since the organic matter in the coal tends to concentrate in the smaller particles, the larger particles are typically denser. Consequently, LFBC naturally tends to separate coal particles according to mineral matter content, both due to density and size. For samples of the "larger" coal particles, it was found that solvent-swelling did not have a significant effect on improving beneficiation over that obtained for the corresponding unswollen coal particles. This was attributed to "larger" coal particles being more similar in organic/inorganic composition. For the "smaller" coal particle samples, however, a significant improvement in beneficiation was observed due to solvent-swelling. The ratio of bottoms/overflow particle ash content obtained was in the range of 2-4. The size range of these "smaller" particles is quite similar to that typically used in pulverized coal combustion.