Upgrading of cow manure by hydrothermal carbonization: Evaluation of fuel properties, combustion behaviors and kinetics

The rational thermochemical conversion of livestock manure holds significant implications for the recovery and utilization of wastes. In this study, cow manure (CM) was treated by hydrothermal carbonization (HTC) to evaluate the fuel properties, combustion behavior and kinetics of hydrochars. The results showed that HTC increased the carbon content of CM from 37.02% to 43.68% and the H/C and O/C ratios comparable to lignite. The oxygen-containing functional groups of hydrochars decreased and displayed typical deposition micromorphology of secondary char. For aqueous phase, furans and phenols were enriched at 200 degrees C and 260 degrees C respectively, which were the main precursor or/and components of secondary char. The thermogravimetric analysis displayed hydrochars combustion were more stable and lasting. The secondary char reduced ignition temperature, but limited impact on volatilization during combustion. Compared with CM, hydrochars showed lower activation energy in initial combustion, and higher at high conversions (except for CM260). The relative lower activation energy of CM260 was mainly attribute to the loose ash structure. Besides, HTC could alleviate slagging/fouling of CM combustion and high temperature strengthened the effect. These results indicate that HTC is a promising approach to treat CM for solid fuels, and 240 degrees C is suggested to upgrading the characteristics.