Effect of char generation method on steam, CO2 and blended mixture gasification of high ash Turkish coals

Char particles of high ash Turkish coal of two sizes were produced by pyrolysis in an atmospheric pressure thermo-gravimetric apparatus using 3 heating rates (100 K/min, 500 K/min and 800 K/min). It is observed that the particle size (for particles between 0.8 and 3 mm) did not change the pyrolysis process results. Char gasification rates in CO2, steam and mixture of CO2 + steam are investigated in the same TGA system over the temperature range of 850-950 °C. The pyrolysis heating rate for char formation is observed to have a marked influence on the subsequent gasification reactivity of the char. The results indicate that the char produced from high heating rates show improved gasification rates. Smaller particles exhibit higher char-CO2 and char-steam gasification rates. Increasing the temperature from 850 to 950 °C, leads to a significant reduction of the time required for 50% char conversion both for small and large particles. The maximum reaction rate is shifted to higher conversion degrees when the chars are produced from high heating rates. The gasification rate of char-H2O strongly depends on the H2O partial pressure. Gasification rates in CO2 ambiance are much lower than those in steam. For CO2-steam blended ambiance, no obvious CO2 inhibition effect is observed. But this topic requires more investigation. Kinetic parameters of the char particles are estimated using three different kinetic models. The obtained activation energies for char gasification essentially depend on the particle size and the three kinetic models give very close activation energy values for all the tested conditions.