Thermo-fluid dynamic and kinetic modeling of hydrothermal carbonization of olive pomace in a batch reactor

Hydrothermal carbonization (HTC) represents one of the emerging and most promising technologies for upgrading biomass. Among the residual biomass waste, olive pomace and olive mill wastewater may be seen as valuable energy sources, especially for the Mediterranean countries, given the key role of the olive oil industry in those regions. This paper deals with the thermo-fluid dynamic performance of the HTC process of olive pomace. Computational Fluid Dynamics (CFD) modeling is employed in this study to numerically simulate such a process in batch reactor with the aim of understanding the complex fluid dynamics, heat transfer and reaction kinetics phenomena occurring under hydrothermal conditions. A parametric analysis is performed to evaluate the temperature fields inside the reactor and the output mass yields as a function of the power input required by the process. Velocity flow fields and the spatial distribution of the mixture during the process are also investigated to understand the change in feed conversion at different regions within the tubular reactor under different reaction times. The numerical results are validated and compared with experimental measurements conducted previously on a similar batch reactor. The model predictions are found to be in line with the experimental findings, thus laying the foundations for further modeling improvements towards the design optimization and scale-up of HTC reactors.