Numerical heat transfer modelling in a hydrothermal carbonization reactor

The purpose of the paper is to illustrate the basis of the thermal design of a pilot-scale reactor built to convert putrescent and high water content biowaste into a stabilized product. The hydrothermal carbonization (HTC) is a thermochemical process in which biomass is converted into hydrochar by several different steps with mild reaction conditions at low temperatures (180–250 °C), absence of oxygen and Sub-Critical Water conditions 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 result from the process design step is the evaluation of the amount of heat to be provided by an external source, the method to provide it as well as the related reaction time necessary to reach the given yield. The paper describes the thermal design process comparing the design data obtained both with simple thermal network models and a 2-D model during 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.