Physical properties and oxidation rates of chars from three bituminous coals

Abstract

Intrinsic oxidation rates of coal chars derived from three different bituminous coals were measured at 500 °C and the effects of char formation temperature, conversion, coal particle size and char particle size on the rates were evaluated. Characterization of the various samples including BET surface areas, mercury porosimetry, mercury and helium densities, heating values and in some cases elemental analyses were carried out to better understand the roles and interactions of the various parameters. Optical microscopy observations were also made to verify assumptions wherever possible. The results show that apparent and intrinsic rates as well as the heating values are reduced with increasing char formation temperature. N_2-BET surface areas increase an order of magnitude with conversion and exhibit maxima in the range of temperatures considered (1000 K to 1600 K). Of similar sized chars derived from different sizes of coal particles, those from the smaller coal size fractions had higher apparent reaction rates.