Hydrothermal carbonization of the waste straw: A study of the biomass transient heating behavior and solid products combustion kinetics

Abstract In this study, HTC impact on the waste straw fuel properties and waste straw hydrochars combustion kinetics have been presented. HTC experiments were carried out at Parr 4650 250 ml batch reactor, at temperatures of 225, 250, and 275 °C. Each temperature was investigated at 4 residence times: 10, 20, 30, and 40 min. Denoted hydrochars yields were more influenced by temperature than residence time, with different decomposition patterns observed at 275 °C compared to 225 and 250 °C, with final solid yields of 42.0%, 66.9%, and 65.3% at 40 min residence times respectively. The study of the transient HTC period resulted in the determination of the exothermal WS activity with the heat release of the 254.9 ± 48.8 kJ/kg of biomass. LHV values of the obtained hydrochars were 18.7–20.2 MJ/kg, 19.9–22.2 MJ/kg, and 23.1–26.2 MJ/kg for HTC temperatures of 225, 250, and 275 °C respectively. TGA analysis of the hydrochar combustion highlighted significant changes in the kinetic interpretation of the combustion profiles throughout investigated temperature ranges. The influence of residence time was only significant in the case of the 275 °C HTC samples, where a major shift of the combustion reactivity towards higher-temperature char oxidation was denoted. Hydrochars combustion kinetics were modeled with the implementation of Fraser-Suzuki deconvolution, and model-fitting of nth-order Arrhenius equation, with R2 values within 0.98–0.99.