Properties of animal-manure-based hydrochars and predictions using published models

Abstract

In order to fully utilize hydrothermal carbonization (HTC) to produce value-added hydrochars from animal manures, it is important to understand how process conditions (e.g., temperature, reaction time, solids concentration) influence product characteristics. The effect of process conditions on the extent of carbonization, solid yield, energy density, and combustion characteristics of the hydrochars, as well as the fate of carbon and nitrogen in the three phase process was investigated for swine solids and poultry litter. While hydrothermal treatment increased the percentage of fixed carbon in the solids compared to the original feedstock, increasing the reaction time 5-fold did not increase the percentage of fixed carbon in the hydrochars. Increasing the temperature had an inverse effect on solid yield and, to a lesser extent, energy content. Three different published statistical models in the literature were evaluated for their ability to predict hydrochar properties, based on feedstock properties and process parameters. All three models reasonably predicted the yields and carbon contents; however, prediction of energy contents of animal manure hydrochars was not satisfactory. It is important to develop better predictive models for energy contents of hydrochar for energy application. Furthermore, the current models should be expanded to be able to predict other important properties for developing a sustainable manure-management such as concentration of nutrients and other elements in the hydrochar and process water.