Hydrothermal carbonisation of Australian saltbush

Abstract

Hydrothermal carbonization (HTC) is a thermochemical process, wherein biomass is subjected to high-pressure, high-temperature subcritical water to improve the combustion characteristics of biomass as a solid fuel. Australian saltbush was subjected to HTC at three temperatures (200, 230, and 260 °C) and four holding times (0, 15, 30, and 60 min) using a custom-built batch reactor. The resultant hydrochars demonstrated improved higher heating values (HHVs), with temperature more influential than time. At the most severe condition of 60 min and 260 °C, the hydrochar possessed numerous key similarities to fossil coal, such as a HHV of 27.5 MJ/kg, similar ratios of carbon/oxygen and hydrogen/oxygen, and equivalent levels of volatile matter, fixed carbon, and ash. The HTC process also proved effective in reducing the high levels of inorganic elements naturally present within saltbush, with 60 min at 260 °C again shown to be the most effective condition, removing almost 95% of sodium, chloride, and potassium.