Chemical Structure Changes Accompanying Fluidized-Bed Drying of Victorian Brown Coals in Superheated Steam, Nitrogen, and Hot Air

Chemical structure changes during drying of Victorian brown coals, that is, Loy Yang (LY) and Yallourn (YL), in hot air, nitrogen, and superheated steam are quantitatively studied using the FTIR technique. The infrared (IR) spectra of raw and dried coals were curve-fitted to a series of bands in hydroxyl groups (3500-3000 cm(-1)), aliphatic hydrogen (3000-2800 cm(-1)), and carbonyl and aromatic carbon (1850-1500 cm(-1)) adsorption regions. Following air drying, the IR adsorption of aliphatic structures decreased significantly, indicating that oxidation reaction mainly takes place on these structures. Carbonyl and carboxyl groups decreased up to 130 degrees C by 25.9% and 23.9%, respectively, and then significantly increased at higher temperatures due to oxidation. Drying of brown coals in nitrogen resulted in a significant increase in their aromaticity and a lower concentration of oxygen-containing functional groups. The loss of oxygen was confirmed by measuring the O/C ratio of raw and dried samples. The O/C ratio decreased by 30.8% and 40.7% for LY and YL coals, respectively, after drying at 200 degrees C for 10 min. Superheated steam fluidized-bed drying of both LY and YL coals showed the breakage of some weak aliphatic C-H structures. The decrease in adsorption of hydroxyl, carboxyl, and carbonyl groups leads to loss of oxygen in both LY and YL steam-dried coals. Superheated steam drying of brown coals showed only minor changes to the coal organic structure as the aromatic carbon content remained relatively unchanged and aliphatic structures decreased negligibly.