Combustion characteristics, kinetic and thermodynamic analyses of hydrochars derived from hydrothermal carbonization of cattle manure

Abstract

The physicochemical properties and combustion behavior of the hydrochar derived from hydrothermal carbonization (HTC) of cattle manure were thermogravimetrically investigated. The kinetic and thermodynamic analyses based on Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods were also carried out. The results showed that HTC of cattle manure increased the carbon content (12.79–18.87%), fixed carbon content (22.90–57.76%) and higher heating value (14.73–21.02%) of the hydrochar. The thermogravimetric analysis indicated that cattle manure and the derived hydrochars had three decomposition stages during combustion process, and the hydrochars had higher ignition temperature, lower burnout temperature and lower comprehensive combustion index than that of cattle manure. The kinetic and thermodynamic analyses demonstrated that the hydrochar prepared at 200 °C with the lowest average activation energy value (137.40 and 134.06 kJ/mol by FWO and KAS, respectively) showed the highest combustion reactivity. These findings suggested that HTC offered an effective and alternative approach for the disposal of cattle manure to produce the energy-dense hydrochar with improved fuel properties and combustion performance.