Characterization of low rank alpine coals: Thermogravimetric studies

Triassic Lunzer and Upper Cretaceous Gosau coals from the eastern part of the Northern calcareous Alps and Jurassic Gresten coals from the eastern ultrahelveticum in Austria were characterized through thermogravimetry (TG) curves obtained by slow heating (10 °C min−1) in a nitrogen atmosphere and by proximate analysis. During slow heating of the coal samples in a nitrogen atmosphere, all the samples showed comparatively a small weight loss in the low temperature region (50-150 °C), which is mainly associated with the loss of physically adsorbed water and high volatile organic matter. The weight loss observed with the temperature starting from 300 °C, was attributed to the breaking of chemical bonds. The kinetic parameters for the major weight loss for the coal samples were also evaluated using the Dharwadkar and Kharkhanavala equation and the calculations were performed using software developed in Visual Basic Version 6.0. The percentages of water content, volatiles, fixed carbon and ash content and the weight loss at 200 and 500 °C excluding water were obtained for each coal sample from the proximate analysis. These parameters and the kinetic parameters obtained from TG curves were compared with vitrinite reflectance, one of the classical maturity parameters for coal. Further comparison was attempted using VMwaf (percentage volatile matter from water and ash-free coals) parameter.