Impacts of CO2 on char structure and the gasification reactivity

Abstract

The effects of CO2 as pyrolysis atmosphere on coal char structure and gasification reactivity were investigated. Yining (YN) subbituminous coal and Ximeng (XM) lignite with the particle size of 5–8mm were pyrolyzed to prepare the char samples under CO2 and N2 atmosphere at 800°C in a fixed-bed reactor. The structural features of chars were characterized by nitrogen adsorption and FT-Raman spectroscopy. The reactivity of chars with CO2 was investigated in a thermogravimetric analyzer (TGA). The results indicate that the two coals pyrolysis in CO2 atmosphere demonstrate higher specific surface area, lower char yields, and lower ratio of small to large aromatic rings compared with that in N2 atmosphere. However, the chars obtained from pyrolysis of YN coal in CO2 atmosphere displays better reactivity, whereas XM coal shows reverse trend. In particular, the demineralized char prepared from YN and XM coals pyrolysis in CO2 implements lower reactivity than that of pyrolysis in N2, which can be attributed to the catalytic effect of the inherent inorganic minerals. The gasification reactivity of XM char and demineralized YN and XM chars is affected by char chemical structure rather than specific surface area.