Experimental and modelling of the thermal regions of activity during pyrolysis of bituminous coals

Computer-aided thermal analysis technique, incorporated with thermogravimetric and Fourier transform infrared (TG-FTIR), and mass spectrometry, were employed in studying the devolatilisation of three thermal bituminous coals under packed bed pyrolysing conditions. The heats of reactions evolved during coal devolatilisation were determined by computational calorimetry and compared with the evolution rate of fourteen volatile species. The devolatilisation was classified into five major regions of thermal activity, according to the analysis, where the first was related to the dehydration of strongly bounded water. The second was the pre-plastic region with an endothermic prepyrolytic reaction, while the third was the exothermic plastic range with primarily evolution of tars and re-solidification reactions. The secondary devolatilisation was found to be endothermic and the major contributors were hydrocarbons, secondary water, CS₂ and H ₂S. The largest reaction was the contraction of carbon planes with evolution of hydrogen. Each reaction region was assumed to follow the first-order Arrhenius kinetic correlation and the activation energy was determined for each of the five regions. The activation energies were then incorporated into a simplified model for predicting the overall heats of reactions.