Investigation into the structural features and gasification reactivity of coal chars formed in CO2 and N2 atmospheres

Coal structure undergoes a series of complex changes during pyrolysis which can affect the gasification reactivity. Lignite was used as raw sample to prepare char samples by pyrolyzing under CO2 and N2 atmospheres in the temperature range 500-800 °C in a fixed-bed reactor. The structural features of chars were characterized by N2 adsorption analyzer and FT-Raman spectroscopy. The reactivity of chars was investigated in a thermogravimetric analyzer under CO2 atmosphere. The results indicated that the yields of char from pyrolysis under CO2 at 500 and 600 °C were higher than that under N2; however, the specific surface area of the chars prepared under CO2 was nearly the same as that prepared under N2. At 700 and 800 °C, the char yields prepared under CO2 were less than that under N2; however, the specific surface areas exhibited reverse trend, which could be attributed to the occurrence of char-CO2 reaction. Notably, the reactivity of chars formed at lower temperatures was higher than that formed at higher temperatures under both CO2 and N2 atmospheres. The reactivity of chars obtained under CO2 atmosphere was lower than that under N2 atmosphere at same pyrolysis temperature, which was mainly due to the higher aromaticity and the low ratio of small to large rings.