Effect of hydrothermal carbonization reaction parameters on the properties of hydrochar and pellets

Abstract

Hydrothermal carbonization (HTC) is a promising upgrading process to convert various low energy‐density lignocellulosic biomass materials to homogeneous, energy‐dense HTC biochar, known as hydrochar. A novel two‐chamber reactor was designed and built to investigate the effects of HTC reaction parameters on the resulting hydrochar produced from woody biomass. Reaction parameters investigated included temperature (200–230°C), feedstock particle size (0.60–2.38 mm), and reaction time (1–5 min). Mass yield and higher heating value (HHV) of the hydrochar products were determined as two important measures. Reaction temperature was found to have a much stronger influence on mass yield and HHV than particle size or reaction time. Hydrochar can be formed readily into robust, dense pellets, without requiring any additional binding agent. Pellet density ranged from 1260 to 1320 kg m−3, while volumetric energy density ranged from 27.3 to 29.5 GJ m−3. Several analyses were performed on hydrochar pellets, including ultimate analysis, proximate analysis, and water immersion tests. Results are presented and discussed to illustrate the chemical composition, energy density, and water resistance of hydrochar pellets. This study confirmed that the HTC process can transform lignocellulosic biomass into a solid fuel with favorable properties, and provides insightful guidance regarding optimum reaction parameters for producing hydrochar and pellets in a continuous, industrial process. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 676–680, 2014