Changes in nascent char structure during the gasification of low-rank coals in CO2

Abstract

The purpose of this study is to investigate the structural changes in nascent chars during the gasification of two low-rank coals in CO2 at 1000 °C and 1200 °C. Western Australian Collie sub-bituminous coal and Victorian Loy Yang brown coal were heated up at 1000 K s−1 in He/CO2 in a wire-mesh reactor. FT-Raman spectroscopy was applied to understand the key structural features of nascent chars. For comparison, the Raman data of the chars produced in a drop tube furnace in N2/CO2 at 1200 °C for Loy Yang coal were also included in this study. The results showed that the evolution of char structure was determined by the counteracting effects of thermal annealing and oxygenation during the initial holding at 1000 °C (<1 s). With further holding at 1000 °C or holding at 1200 °C, the rapid formation of O-containing functional groups and the selective consumption of small aromatic rings took place. For each coal, there was no significant change in reaction pathway between gasification at 1000 and 1200 °C. Combining the data from FT-Raman and FT-IR spectroscopy, there appears to be more than one type of O-containing functional groups formed during the gasification in CO2. Some are more sensitive to Raman scattering but some are more sensitive to FTIR absorption.