Physical and chemical structure changes of Huolinhe lignite during thermal treatment and its effect on moisture re-adsorption

Abstract

A lignite from Huolinhe mine in China was dewatered in a fixed-bed reactor at different temperature of 80-160°C under nitrogen and argon respectively. Then different drying levels dewatered samples were undergone the moisture re-adsorption in constant temperature and humidity chamber. The physical and chemical structures of all samples were characterised by nitrogen adsorption instrument and diffuse reflectance in-situ FTIR spectrometer. The dehydration rate of lignite under nitrogen is higher and the moisture re-adsorption capacity of dewatered coal is lower than that of sample received from argon. It is also found that the amount of re-adsorbed moisture reduces dramatically when the dewatered coal is held for another 60 min among nitrogen at room temperature. The physical and chemical structure changes of samples before and after drying are the main factors influencing the moisture re-adsorption capacity of dewatered samples. Both specific surface area and pore volume of lignite decrease during drying under two kinds of atmosphere but more obviously under nitrogen. The changes of contents of hydrophilic oxygen-containing functional groups in lignite, especially COO- and COOH, is directly related to the re-adsorbing moisture capacity of de-watered sample. [Received: December 5, 2013; Accepted: October 28, 2014]