Abstract
For high-caking Warkworth and low-caking K-Prima coals, Geiseler plastometry, differential scanning calorimetry (DSC), proton magnetic resonance thermal analysis (PMRTA) and dynamic viscoelasticity were measured at a heating rate of 3°C/min under nitrogen. The amount of solvent-soluble constituent of the coals heat-treated at 3°C/min was also measured by using a solvent extraction with carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent at room temperature, which gives high extraction yields for the heat-treated coals in the softening range. Changes in various chemical and physical parameters from the measurements were compared with one another to investigate the mechanism of softening and fusibility of coals. We suggest that the softening is occurred by a physical relaxation of aggregates in coal macromolecular structure and the amount of the solvent-soluble constituents greatly increases, resulting in enhancing the softening and fusibility. The mobility parameter from PMRTA, the viscoelastic parameter and Geiseler fluidity gave the maximum at similar temperature, showing that fusibility is the result of increased mobility of whole coal. The dynamic viscoelastic measurement was found to be a useful and convenient means for the study on caking behaviors of coals, since it can estimate concurrently both the fluidity and the elasticity of coals.
