Upgrading of palm empty fruit bunch for solid biofuel production through hydrothermal carbonization

Abstract

In this study, palm empty fruit bunch (EFB) was upgraded into solid fuel called biochar through hydrothermal carbonization process (HTC). The experiments were performed at different temperatures of 160, 180, 200 and 240 °C for 30 min. The properties of biochar products in terms of proximate and ultimate analysis, heating value and thermal decomposition were characterized. The results indicated that hydrothermal carbonization decreased the biochar yield from 79.2% at 160 °C to 39.5% at 240 °C. As the reaction temperature increased, the fixed carbon and heating value increased due to the decreasing of volatile matter and oxygen content involving dehydration and decarboxylation reactions. The heating value increased from 19.8 MJ/kg (raw EFB) to 23.0 MJ/kg at 240 °C. The H/C and O/C atomic ratios of biochar after treated with HTC decreased from 1.52 and 0.62 (at 160 °C) to 1.09 and 0.38 (at 240 °C) as similar to low rank coal. In addition, the potassium in the feedstock was extracted and removed to the aqueous phase during HTC. The maximum potassium removal efficiency reached up to 91.8% at reaction temperature of 240 °C. The removal of potassium led to lower deposition tendency of slagging and fouling indices. The results reveal that the HTC has the potential for upgrading EFB into energy-dense and durable solid fuel for use in energy generation.