Hydrothermal Carbonization of Agricultural Biomass: Characterization of Hydrochar for Energy Production

This paper shows the results of hydrothermal carbonization of biomass from seven different crops used as biofuel: wheat straw, soybean straw, corn cob, corn stalk, sunflower stalk, walnut shell, and hazelnut shell. The hydrothermal carbonization process was investigated at 200 and 250 degrees C reaction temperatures, a pressure of 8.0 MPa, and 120 minutes of process duration. The obtained dry hydrochar was characterized. The hydrothermal carbonization process increased carbon and decreased oxygen and, to a lesser extent, hydrogen. Higher heating value of hydrochar increased compared to the feedstock. The hydrothermal carbonization process influenced the increase in the share of ash and bulk density. At lower process temperature, a higher mass yield of hydrochar was obtained. The color of the hydrochar correlated with carbon content; lower process temperatures gave brown lignocellulosic color, and higher temperatures resulted in charcoal black. Depending on the raw material, hydrochar was improved in terms of its basic composition and heating value, and it showed to have the potential to be used in coal dust combustion plants.