SLOW PYROLYSIS OF LOW-RANKED TURKISH COAL: A STUDY OF KINETIC MODELLING

摘要

Slow pyrolysis is known as the common step of all thermochemical processes. From this perspective, determination and the interpretation of the thermal and kinetic behaviors of different solid fuels play an important role at the step of design/implementation for real case situations. In this study, low-ranked Turkish coal was employed as solid fuel in order to investigate the pyrolytic behaviors in thermal analyzer. The experiments were conducted from room temperature to 900°C with a heating rate of 5°C/min in N_2 atmosphere. On the other hand, the lignite char was also pyrolyzed under the same conditions for a detailed thermal investigation. After the completion of the thermal experiments, the obtained data were used to determine pyrolysis mechanism and to calculate the kinetic parameters by applying Coats-Redfern model. On the contrary to the most studies in the literature, calculations were not progressed only for the first order assumption but also for the other reaction orders varying from 0 to 2 with the increments of 0.2. The kinetic parameters were recalculated for each pyrolysis stage and reaction order. As a result, it was determined that the highest R~2 values were achieved in the cases of 2 and 1.4 for the first and the second steps, respectively. The calculated apparent activation energies for the best fitted reaction orders were found as 69.53 and 520.24 kJ/mol while the pre-exponential factors were found as 1.41×10~4 and 8.03×10~(27), respectively. As a result of the study, experimental results showed that lignite pyrolysis can be described well as two different reaction stages with different reaction orders instead of employing 1st order assumption for each step.