Quantifying the heats of coal devolatilization

An experimental apparatus was developed to measure the thermal properties o f coal in order to determine the heats of reactions during devolatilization . Samples were continuously heated from room temperature to 1000 degreesC a t a constant heating rate. Measuring the temperature changes at two selecte d locations within the sample allowed the calculation of the apparent speci fic heat and thermal conductivity by employing an inverse numerical techniq ue to solve the heat conduction equation. Five major reaction regions of co al devolatilization were detected: dehydration, transition, resolidificatio n, secondary reactions and contraction reactions. The most complex region w as the exothermic resolidification reaction, where coking coals exhibited s ignificant differences from the thermal coals due to higher plasticity. Sma ll endothermic reaction related to tar vaporization also appeared in this r egion, becoming stronger at higher heating rates. The exothermic contractio n reactions ranging between 140 and 250 MJ/m(3) appeared above 600 degreesC as a result of the dehydrogenation and,reformation of stronger C-C bonds. The effects of the heating rate within the range of 5 degreesC/min to 100 d egreesC/min were also examined, showing a shift of the reaction peaks to hi gher temperatures at increased heating rates. The thermal conductivity and diffusivity were almost constant until the decomposition point, rapidly inc reasing at higher temperatures.