Hydrothermal carbonization of oil palm trunk: Hydrochar properties and combustion behaviors

Abstract

Oil palm trunk (OPT) is a solid residue discharged from palm-oil upstream industry, with high potential as a feedstock for solid fuel production. However, its high moisture content and low energy density causes the limitation of utilization. In this research, hydrothermal carbonization (HTC) was applied to upgrade OPT. Effect of different reaction temperature and residence time on thermal characteristics and combustion behaviors of hydrochar obtained from HTC were investigated. OPT gradually converted into hydrochar with higher carbon content and heating values. The proximate and ultimate analyses indicated that fuel properties of hydrochars enhanced by increasing HTC temperature and residence time. The high heating values (HHV) increased by 7.18% at 180 °C, 30 min and reached up to 48% at 240 °C, 60 min. Meanwhile, combustion behaviors of hydrochars based on thermogravimetric analysis (TGA) were examined. The results showed that hydrochars had a higher ignition temperature than that of the raw OPT, leading to a more stable combustion. Furthermore, slagging and fouling problems were greatly minimized owing to the removal of a significant portion of alkaline remained in OPT, especially potassium (66% removal) and calcium (48% removal). The results revealed that OPT is of great potential as a solid fuel employing HTC process.