Comparison of some physico–chemical properties of Victorian lignite dewatered under non-evaporative conditions

Abstract

A Victorian lignite, designated Loy Yang low ash, run of mine (LYLA (R)) has been dewatered using mechanical thermal expression (MTE) at 150–200 °C and 6–25 MPa and by hydrothermal dewatering (HTD) at 200–300 °C and the products compared. Total acidity values for all samples as measured by a pyrolysis thermogravimetric Fourier transform infrared (TG–FTIR) method were similar to those measured by barium ion exchange. Stronger (carboxylic) acid values determined by pyrolysis TG–FTIR tended to be lower than ion exchange values, except for the 300 °C HTD sample, for which both methods gave similar values although these were much lower than at all of the other treatment temperatures. Equilibrium moisture contents (EMC) for the MTE products and the 200 °C HTD product were similar to those of the original lignite at relative vapour pressure (RVP) ⩽ 52%, but lower at RVP 92%. EMC values for 300 °C HTD products were all lower than for the original lignite, indicating that processing temperature was the most important factor in determining these properties. CO 2 adsorption surface area was also mainly a function of processing temperature, decreasing with increasing temperature. However, the pore volume as determined by mercury porosimetry was influenced by whether dewatering was effected by MTE or HTD, the mechanical pressure applied in the MTE process resulting in a lower porosity.