Thermal characterization and gasification kinetics of thrace-saray region coal

Yıldırım, Betül
In this thesis being up as-received and washed and dried, two different coal samples from Saray-Edirkoy field were experimented in order to determine effects of different variables as coal type, heating rate, gas flow rate, isothermal duration, gasifying medium, and final gasification temperature, on isothermal gasification profiles of the coal samples. In the scope of this study, heating rate was changed in the range of 20-50oC/min as 20, 30, 40 and 50oC/min whereas two different gas flow rate values as 60 ml/min and 100 ml/min were used throughout the experiments. Isothermal period was increased from 60 minutes to 120 minutes to determine increased waiting period effect on process at designated temperature of the reaction. Carbon dioxide (CO2) and dry air were used as gasifying agents whereas nitrogen (N2) gas was selected as the inert gas. To be in the range of 750-950oC, totally five different final temperature values were tested (750, 825, 850, 900 and 950oC) for calculation of activation energies of the coal samples. In the study, important parameters for thermal characterization of the samples as reaction intervals for different stages of the gasification process, weight changes occurred in these reaction intervals, peak temperatures where maximum mass losses of the specified intervals occur, and the ignition temperatures were determined from thermogravimetry/differential thermogravimetry (TG/DTG) curves by TA Universal Analysis software program. As a result, for carbon dioxide gasification experiments, three reaction regions were identified which were matched with moisture loss, volatile matter release and gasification steps. On the other hand, for some of the dry air gasification experiments, four reaction intervals were observed which were correlated with free moisture loss, devolatilization, combustion of light volatile matter and some part of the char, and gasification steps respectively. In kinetic analysis session, first order Arrhenius kinetic model was used as a result of which activation energies (Ea) of the samples were calculated under both carbon dioxide and dry air atmospheres as two different gasification environments. In both environments, washed and dried coal sample was found to be more reactive than as received coal. Moreover, activation energies of both samples were found to be lower under dry air atmosphere than those determined under carbon dioxide gas. Additionally, scanning electron microscope (SEM) and X ray diffraction analysis were conducted in the Middle East Technical University Central Laboratory for determination of the compositional and physical morphologies of the samples at pre- and post- pyrolysis and gasification conditions. With evaluation of SEM results, sequence increment and decrement of porosity was identified with consecutive pyrolysis and gasification reactions especially for carbon dioxide gasification experiments. Moreover, by qualitative SEM and XRD analysis, general information was obtained about mineral matter of the samples.


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Citation Formats
B. Yıldırım, “Thermal characterization and gasification kinetics of thrace-saray region coal,” M.S. - Master of Science, Middle East Technical University, 2015.