Yallourn brown coal – The effect of drying conditions on its VOC emissions

Abstract

Thermal drying of Victorian brown coals is typically accompanied by a characteristic “odour” associated with their emission of Volatile Organic Compounds (VOCs). Evaluating the health implications of VOC emissions from coal mine fires and large scale coal mining or drying operations requires the yield and composition of these chemicals to be investigated. This paper focuses on the hydrophobic compounds released during the mild (40°C–105°C) thermal treatment of Yallourn coal utilising various purge and trap systems coupled with Gas Chromatography Mass Spectrometry (GC/MS). These VOCs comprise a complex mixture dominated by ppm yields of isoprenoids with trace (ppb) amounts of BTEX and aldehydes and ketones. No evidence was found to suggest these isoprenoids would cause health and safety concerns at the ultra-low levels predicted in ambient air samples. Emissions under inert and oxidising atmospheres both showed increasing VOC yields in response to higher temperatures and the amount of water removed. The presence of inherent “free” or bulk water was found to markedly enhance VOC release. The use of oxidative purge gas during brown coal drying was only effective in producing higher yields of oxidative products such as aldehydes once bulk water was removed. The predominant VOCs released during drying were found to be resin derived hemi and monoterpenes which would account for the typical odour associated with drying brown coals.