Comparison of coal chars prepared in different devices at similar temperature

Abstract

The characteristics of chars prepared in both a drop tube furnace (DTF) and a flat flame burner (FFB) at 1300 ºC from seven coals of different rank and maceral composition are the subject of this study. Coal samples sized and sieved to 36-75 μm were fed. The flame temperature of the FFB was achieved with a mixture of methane, air and oxygen whereas two different gas compositions were used in the DTF to account for sub-stoichiometric (2.5% O2) and close to stoichiometric (10% O2) oxygen levels. Determination of micropore surface area was carried out by CO2 adsorption isotherms at 0°C and char reactivity to air was measured at 550 °C in a thermogravimetric analyser (TGA). Overall similar combustion trends were obtained in both devices with burnout decreasing as coal rank increases and CO2 surface areas decreasing up to the medium volatile bituminous coal rank and increasing again for the anthracites. The results reveal a reasonable agreement between burnouts of FFB chars and low oxygen DTF chars whereas higher burnouts were obtained for higher oxygen DTF chars. The CO2 surface areas of the chars reasonably scattered without any systematic trend. The intrinsic reactivities of both series of chars from the DTF were similar to the corresponding FFB chars. Increasing coal rank, intrinsic reactivity of chars from the different combustion conditions decreased.