Apparent coal viscosity estimated from needle penetration into pellet of pulverized coal particles

Needle penetration and volumetric dilation were measured for cylindrical pellets of six kinds of pulverized coal particles using a needle penetrometer. The measurements were conducted for a range of the heating rate from 1 to 20 K/min, the holding temperature from 698 to 823 K and the nitrogen gas pressure from 0.1 to 3.0 MPa. Both needle penetration and dilation characteristics depended on these operating variables. Especially, an appreciable needle penetration occurred at high heating rate for coals which exhibited little softening property at low heating rate. Unreasonably high activation energies for viscosity were obtained when the needle penetration curves were analyzed on the basis of an equation of motion assuming that the pellet behaves as a Newtonian fluid with a temperature dependency of viscosity given by Andrade's equation.