Hydrothermal carbonization of olive oil industry waste into solid fuel: Fuel characteristics and combustion performance

A low-cost treatment of wet wastes generated by olive oil industry still remains a challenge for the industrial scale applications. In the concept of waste-to-energy, the hydrothermal carbonization (HTC) is suggested as a low-cost valorization way for the wet wastes. In this study, the HTC process was used to obtain clean solid fuel from the wet waste of the two-phase olive mill system. Variation of the fuel properties and combustion per-formance of obtained solid fuel, hydrochar, with process conditions (temperature and duration) was investigated by carrying out proximate analysis, elemental analysis and thermal analysis. The lignite-like hydrochars having calorific value of 28.4-33.9 MJ/kg were obtained at the temperatures higher than 200 degrees C. The combustibility index (S) revealed that all obtained hydrochars were suitable solid fuels having reasonable combustion perfor-mance and short combustion time. Alkali index values of hydrochars predicted that their combustion in a boiler would be safe. The calculated net energy generation of process was found as 10.2-14.1 MJ/kg dry biomass.