Effects of Alkali and Alkaline Earth Metallic Species and Chemical Structure on Nascent Char–O2 Reactivity

Abstract

Factors influencing the nascent char–O2 reactivity was investigated in this study from the aspects of alkali and alkaline earth metallic species and char chemical structure. Char samples were prepared from the fast pyrolysis of two low-rank coals (Loy Yang brown coal and Collie sub-bituminous coal) in a wire-mesh reactor at temperature ranging from 600 to 1200 °C with holding time up to 5 s. The concentrations of alkali and alkaline earth metallic species in char were determined by inductively coupled plasma-optical emission spectroscopy. The char chemical structure was characterized by Fourier transform-Raman spectroscopy. Our results show that the char–O2 reactivity is greatly related to the Raman sensitive O-containing functional groups at the initial stage of char formation (short residence time at 600 °C during pyrolysis). As char pyrolysis proceeded to higher temperature, the loss of O-containing functional groups and the condensation of aromatic ring systems play a key role in the decreasing magnitude of char–O2 reactivity. The chemical structure of 1200 °C pyrolysis char is relatively stable, thereby posing limited effect on the changes in char–O2 reactivity. For Loy Yang brown coal, the volatilization of alkali and alkaline earth metallic species during pyrolysis at 1200 °C became the dominant reason for the observed decreases in char–O2 reactivity.