Thermogravimetric and evolved gas analyses of high ash Indian and Turkish coal pyrolysis and gasification

High ash coals from India and Turkey are investigated in this study. A coupled thermogravimetric analyzer and mass spectrometer system is used for the thermal decomposition characterization of the coal samples and the identification of the volatiles evolved during the various reaction regions. Coal samples are heated in argon, air, oxygen, steam and blended gas mixtures at the temperature range from 25 to 1250 °C. The experiments are performed to study the pyrolysis, combustion and gasification characteristics of typical Indian and Turkish high ash coals. Thermogravimetry and derivative thermogravimetry studies are applied to measure the conversion level and half-life time of the coals/chars during and after pyrolysis. The maximum mass loss occurs during the devolatilization stage of coals at the temperatures from 350 to 700 °C, where O2, CO2, CO, H2 and a small amount of CH4 are released. Coal particles start to react with steam and produce CO2, CO and H2 when the temperature is increased above 750 °C. The gasification reactions are completed around 950 °C in steam and steam blended ambience. The reactivity of high ash coal chars mainly depends on reagents’ and surrounding gases concentration and also the reaction temperature. The results indicate that the size effect of the char particles is minimal at high gasification temperatures. Char gasification rates determined by TG techniques under isothermal conditions in different reagent flow rates and size effect contribute to enhance the knowledge on high ash coal thermal characterization and gasification and, therefore, to establish the optimum operational conditions for syngas production from high ash coals.