Predictions of energy recovery from hydrochar generated from the hydrothermal carbonization of organic wastes

Hydrothermal carbonization (HTC) is a wet, low temperature thermal conversion process that continues to gain significant attention for the sustainable generation of value-added solid, liquid, and gas products from organic waste streams. Although it is well documented that both waste properties (e.g., elemental composition) and carbonization process conditions influence hydrochar properties, their specific influence on the total energy that can be recovered using HTC remains unclear. Non-linear random forest models were developed based on data collected from HTC-related literature to describe hydrochar yield and energy content, both of which are required to determine the total energy recovered in the hydrochar. Results indicate that total recoverable energy from organic wastes using HTC is correlated with feedstock carbon content; overall, the total energy content for feedstocks with carbon contents ranging from approximately 40 - 48% are similar. In addition, the total energy that can be recovered from the feedstock remains fairly constant when the initial solids concentrations are greater than 20%. Reaction time appears to have little influence on total recoverable energy from each feedstock at reaction times greater than approximately 150 min, while increases in reaction temperature result in a slight decline in total recoverable energy because of decreases in hydrochar yields at higher temperatures.