Pelletization of nitrogen-containing biowaste hydrochar for solid biofuel preparation

In this study, typical N-containing biowaste including food waste (F), sludge (S), and chlorella (C) was modeled using pine (P) as a carbohydrate component and protein/glycine as a nitrogen-containing component, and hydrothermal carbonization and pelletization were performed to investigate the fuel properties of hydrochar pellet including proximate analysis, elemental composition, tensile strength, and combustion characteristics. Results suggested that the introduction of N can obviously enhance the compressive strength of hydrochar pellet, of which chlorella model derived hydrochar pellet possessed higher tensile strength (1–3.75 MPa) compared to others. Protein/P model hydrochar had a higher water resistance index, but glycine/P model hydrochar had higher hydrophily than that of protein/P model. Most importantly, H/C in all protein/P model hydrochar was lower than that of glycine/P, and bio-oil derived “liquid bridge” may account for the high tensile strength. Moreover, combustion analysis showed that glycine in model enhanced volatile matter combustion of hydrochar with a low ignition temperature. This work suggested that N in biowaste had significant effect on the fuel properties of hydrochar pellet, and proper strategy of N-containing biowaste for HTC can be expected for the value-added utilization as solid biofuel.