Chemical properties and combustion behavior of constituent relative density fraction of a thermal coal

This work presents the experimental results showing the impact of relative density of coal on its properties and combustion behavior. Coal of different mean relative densities (RDm) in the range of 1.375 to 2.0 was prepared through sink-float method of coal beneficiation from the crushed run of mine (ROM) coal. All the RDm fractions were characterized for proximate analysis (PA), ultimate analysis (UA), and gross calorific value (GCV). Combustion behaviors of different coals were carried out by thermogravimetric analysis in the oxygen atmosphere. Important combustion characteristic temperatures like ignition temperature (T-i), peak temperature (T-p), burnout temperature (T-f), and maximum combustion rate (DTG(max)) were evaluated from differential thermogravimetric (DTG) data. Further different combustion parameters like ignition index (D-i), burnout index (D-f), combustion performance index (S), combustion rate intensity index (H-f), and activation energy (AE) were evaluated to access the effects of RDm on combustion behavior of coal. Experimental results showed that, with increase in RDm, from 1.375 to 2.0, ash increased from 12.2% to 62.1%, GCV decreased from 8,254 to 3,084 kcal/kg, increased from 357 to 421(o)C, T-p increased from 459 to 488(o)C, T-f varied from 543 to 553(o)C, and DTG(max) decreased from 6.735 to 4.831 wt%/minute. With increase in RDm from 1.375 to 2.0, D-i decreased from 5.8 wt%/minute(4), D-f decreased from 9.8 to 4.1 wt%/mintute(4), and S decreased from 11.3 x 10(-8) to 4.0 x 10(-8) wt %(2)/minute(2)C(3) signifies difficulty in combustion process which was further confirmed by an increase in AE from 92.7 to 173.5 kJ/mole. Overall, experimental and theoretical analysis briefs that coal having lower RDm have better combustion properties compared to higher density coals.