Fuel properties characterization of hydrochars derived from agricultural digestate

Agricultural digestate is a by–product of biogas plant processes. Its composition is variable and depends on the type of raw feedstock used. Due to its high moisture content the digestate is suitable for hydrothermal carbonization (HTC). The HTC process is performed in a reactor where the feedstock is heated to a high temperature in an aqueous environment. As a result of the reaction, a solid product, process water and a gaseous product are generated. The gaseous product is obtained in trace amounts unlike the process water where the amount is significant. The rich in carbon solid product of the HTC process is hydrochar. Hydrochars can be used as an alternative to non–renewable fossil fuels. The aim of this paper was to investigate and characterize hydrochars derived from agricultural digestate at 190 °C, 200 °C and 210 °C and residence times of: 0.5, 1, 1.5, and 2 h. In addition, the fuel properties and combustion performance supported by an activation energy determination were evaluated. In brief, it was found that a higher temperature and longer residence time produced a more carbonaceous biofuel.