Thermal modelling of hydrothermal carbonization pilot-scale reactor for bio-waste processing

The paper illustrates the thermal analysis of a pilot-scale reactor for converting putrescent and high moisture content biowaste into a stabilized product, called hydrochar; the process is intended as a final treatment for recovery of material or as a pre-treatment before the final disposal, that can be incineration or landfill. The hydrothermal carbonization (HTC) is a thermochemical process in which biomass is converted into hydrochar by different steps with mild reaction conditions at low temperatures, 180–250 °C, absence of oxygen and Sub-Critical Water conditions, under autogenous pressure for several hours. The modelled pilot-scale reactor has a volume of 0.1 m3 and is designed with a maximum operating temperature of 300°C. The main results arising from the process design step are the evaluation of the amount of heat to be provided by an external source, the related reaction time necessary to reach the set point temperature and the energy efficiency of the process. The paper describes the thermal process comparing the numerical data obtained both with simple lumped thermal network models and a 2-D model in the transient regime with the actual data obtained during the commissioning phase of the reactor. The comparison between the experimental results and the design input dataset is also used to improve the control temperature system inside the reactor and assess the energy efficiency of the heating process.