Abstract
A conventional constant heating rate method (I) is applied and continuous heating method (II) is presented to the measurement of the effective thermal diffusivity of packed coals during carbonization.
The method (II) uses nonlinear maximum likelihood estimation from the measured temperatures and permits the measurement of the thermal diffusivity under an arbitrary heating and initial conditions. Measurement error on temperature dependence of the thermal diffusivity of coals is estimated under 5% and the end effect of measuring cylindrical vessel is negligible with a ratio of the cylinder length to diameter of above 5. Measurements are made for five kinds of coals under the following experimental conditions: temperature range of 3001 100K and heating rate of 0.0170.083K/s. The effective thermal diffusivities of the each coal versus temperature for cases (I) and (II) show a similar tendency without distinction of caking coal and non-caking one: the values are almost constant until 820K and then increase rapidly. The rising of the effective thermal diffusivity shifts from low to high temperature as the fixed carbon content increases.
