Effects of char chemical structure and AAEM retention in char during the gasification at 900 °C on the changes in low-temperature char-O2 reactivity for Collie sub-bituminous coal

This study is focused on the effects of char structure and alkali and alkaline earth metallic (AAEM) species on the changes in char-O-2 reactivity for a Western Australian Collie sub-bituminous coal. The char samples used in this study were acquired from the partial gasification of the sub-bituminous coal in a fluidised-bed/fixed-bed reactor in pure CO2, 15% H2O balanced with Ar and a mixture of 15% H2O and CO2 (balancing gas) at 900 degrees C. The structural features of the chars were characterised by FT-Raman spectroscopy. The concentrations of AAEM species in 'the chars were determined by inductively coupled plasma optical emission spectroscopy. The O-containing structures in char that can cause resonance effects to give enhanced Raman intensity tend to improve the retention of AAEM species in char during the gasification at 900 degrees C. However, these O-containing structures do not necessarily ensue a high char O-2 reactivity at low temperature. While AAEM species in char would catalyse the char-O-2 reactions, they are not sufficient to determine the char-O-2 reactivity. The relative ratio of small to large aromatic ring systems in char, as reflected by the Raman spectroscopy, greatly influences the char-O-2 reactivity. The sub-bituminous coal in this study does not behave in the same way as the brown coal in our previous studies in terms of the factors influencing the char-O-2 reactivity. 2017 Elsevier Ltd. All rights reserved.