Hydrothermal carbonization of agricultural residues: A case study of the farm residues -based biogas plants

Hydrothermal carbonization (HTC) of biomass is a promising method to produce carbonaceous materials. The work presented in this article addresses the application of hydrothermal carbonization (HTC) to produce a solid fuel named HTC-Biochar, whose characteristics are comparable to lignite coal. Biogas sludge (SD), maize silage (MS), and barley silage (BS) as a substrates were hydrothermally carbonized in a 1.5 L batch reactor at 200 °C for 6 h. The effect of mixing ratios of different substrates on HTC was investigated. Chemical compositions and combustion characteristics of hydro-chars obtained from mono- and co-carbonization were evaluated. Result showed that HTC increased carbon contents and higher heating values (HHV) by 1.4–14.4% and 13–36%, respectively. The evolution of the H/C and O/C atomic ratios indicated that dehydration and decarboxylation occurred during hydrothermal carbonization for all samples. Furthermore, a significant synergistic enhancement was observed for HHV and carbon content. A mixing ratio of 1:1 for BS and SD showed the best performance for co-HTC. In summary, hydrothermal co-carbonization is a promising strategy to tailor high-performance hydro-char for energy applications.