Needle penetration and swelling of a cylindrical block of Drummond coal during heating were measured under pressures up to 10MPa in nitrogen and hydrogen gas atmospheres at heating rate of 10K/min and steady temperature of 773K. The measurements were successfully carried out connecting a needle or a piston to a linear-variable differential transformer detector.
The needle penetration into the coal was shown to occur at all conditions presently employed whereas the swelling was suppressed at higher pressures. The maximun swelling ratio decreased with increasing pressure and was greater in H2 than in N2 at the same pressure. The penetration occurred within the same temperature range as the swelling. The temperature at which penetration commencedwas lower in H2 than in N2 and decreased with the pressure. The apparent coal viscosity wasthen estimated analyzing the penetration-temperature and the swelling ratio-temperature curves byan existing relationship between the penetration rate and the viscosity. The results showed that thetemperature dependency of the viscosity is approximately described by Andrade's equation with theconstants depending on gas atmosphere and pressure. The apparent activation energies obtained herewere rather high, i. e., 100-320 kcal/mol.
