Characterization of hydrochar and process water from the hydrothermal carbonization of Refuse Derived Fuel

In this study, hydrothermal carbonization (HTC) was used as a thermochemical conversion process to upgrade Refuse Derived Fuel (RDF). The effect of process temperature (250 degrees C, 275 degrees C and 300 degrees C), residence time (30 min and 120 min), and RDF-to-water ratio (1:15 and 1:5) on the main characteristics of the produced hydrochars and process waters was assessed. The HTC process yielded hydrochars with enhanced fuel properties when compared to the original feedstock, namely higher carbon content and heating value. The hydrochars also presented reduced oxygen and ash contents. The hydrochar produced at 300 degrees C for 120 min presented the lowest ash content (3.3 wt%, db) whereas the highest heating value was found for the hydrochar obtained at 275 degrees C for 120 min (28.1 MJ/kg, db). The HTC process was also responsible for a significant reduction in chlorine concentration, showing dechlorination efficiencies between 69.2 and 77.9%. However, the HTC process generated acidic process waters with high COD values (maximum 27.2 gO(2)/L), which need to be further managed or valorized. Energy calculations were also performed, revealing that lower water amounts, lower temperatures, and longer residence times, represent optimal conditions for higher hydrochar yields and consequently good process efficiencies. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Hydrothermal carbonization (HTC) was used to upgrade Refuse Derived Fuel (RDF), resulting in hydrochars with enhanced fuel properties. The process parameters had significant effects on the characteristics of the produced hydrochars. HTC process led to dechlorination and generation of acidic process waters, which require further management.