Studies of coals and binder systems for smokeless fuel briquettes

Abstract

Three coals are compared as potential briquetting feedstocks. A variety of chemical, physical and spectroscopic techniques have been used to elucidate their very different performance in a molasses-bound briquetting process. The results demonstrate that the elemental composition of the surface may differ markedly from the bulk chemistry of the coals. While further differences in petrology, mineralogy, and physical properties were evident, the immediate cause of poor briquetting performance was a high mesoporosity resulting in a greater propensity for particle breakage under shear stress. Fractures appear to take place at boundaries with mineral inclusions. 13C NMR spectroscopy was used to optimise the curing regimes (temperature/time) for molasses and modified starch binders. The spectroscopic data could be interpreted in terms of aliphatic, methoxy and aromatic carbon types. Crosslinking, due to the formation of methylene bridges, reached a maximum at ≈ 250°C. It resulted in an increase in the proportion of aliphatic carbon, and a corresponding reduction in methoxy carbon, as low molecular weight oxygenates were lost in condensation reactions. At higher temperatures, charring was accompanied by increasing aromatisation of the ring systems.