Energy analysis of olive pomace valorization via hydrothermal carbonization

Abstract

This research investigates the hydrothermal carbonization (HTC) of olive pomace (OP) while studying the energetic valorization of the hydrochar and by-products produced. Experiments were carried out in accordance with a Doehlert experimental design to optimize two experimental variables: operating temperature (180°C-250 °C) and holding time (0–60 min). Three different process scenarios were examined. They were designed based on new value-added applications for HTC products namely, energy production, agricultural and environmental applications. The first scenario A focuses on the valorization of the HTC liquid phase product. Scenario B introduces residual oil recovery using evaporation and finally in scenario C, the HTC liquid product is treated by wet peroxide oxidation (WO) in view of its discharge in the natural environment. These scenarios were investigated under three process regimes: adiabatic reactor (idealized process), steady state and start-up conditions (the most realistic case). The energy analysis relied on an experimental measurement approach and thermodynamic calculations. Negative and positive values in the energy balance were found for both scenarios A and B, however only positive values were found in scenario C throughout all the process regimes. Ultimately, along with the conceptual scenarios proposed, the influence of the main process parameters (i.e., temperature, holding time) on the performance of each specific application is discussed, which can be exploited to further improve the HTC technology.