The Evaluation of Spontaneous Combustion Characteristics and Properties of Raw and Upgraded Indonesian Low Rank Coals

Abstract

The upgrading process for Indonesian low rank coal by a combined process of vacuum drying and tar coating has been developed to produce the dry upgraded coals that are comparable with a bituminous coal. The coal samples, West Banko raw and upgraded coals, have been subjected to several analyses for evaluating the spontaneous combustion characteristics and properties. The results of proximate and ultimate analyses show that the moisture and volatile matter were found to decrease for improvement of upgrading conditions. The plotting of O/C versus H/C (mol/mol) in a Krevelen Chart shows that the H/C value of the 300-5 upgraded coal (i.e., the coal was upgraded by vacuum drying at 200°C, and tar coating at 300°C with tar dosage 5% of the weight of tar/raw coal) is reduced to the level of a high rank bituminous coal. The liability index (I t ) of the 300-5 upgraded coal (I t =5.72) decreases to a level comparable with an Indonesian high rank bituminous coal (I t =6.01). Finally, Fourier transform infrared spectroscopy (FTIR) analysis for the functional groups shows that the C-H and C[dbnd]O groups content decreased with improvement of the upgrading conditions.