Changes in char structure during the low-temperature pyrolysis in N2 and subsequent gasification in air of Loy Yang brown coal char

Abstract

This study aims to investigate the changes in char structure during the pyrolysis in N2 and subsequent gasification in air at low temperature in a thermogravimetric analyser. The chars produced from the gasification of Loy Yang brown coal in 15% H2O balanced with CO2 at 850 °C in a fluidised-bed/fixed-bed reactor were used in this work. The evolution of char structure during pyrolysis and in-situ gasification was characterised by FT-Raman spectroscopy. The char-O2 specific reactivity was measured as well. Our results show that, during further pyrolysis, the loss of O-containing structures led to the reduced observed Raman intensity from large aromatic rings and the formation of new cross-linking structures. During the subsequent gasification in air, the newly formed O-containing structures were more readily incorporated into less gasified char (0 min holding at 850 °C), but never reaching the same oxygenation level as those in the chars that had undergone extensive gasification (longer holding at 850 °C). The structural feature of the starting char (obtained at 850 °C) is the main factor determining the reaction pathway for the small/large aromatic ring systems during the low-temperature pyrolysis and in-situ gasification in air.