Combined Hydrothermal Carbonization and Pelletization for High-Quality Biofuel Production

Abstract

Hydrothermal carbonization (HTC) pretreatment is proven to be a good method to produce high-quality biofuel. In this work, a lignocellulosic biomass of corn stalk was selected as main subject to investigate the relationship between HTC operating conditions and fuel properties as well as pelletizing characteristics. Biomass was firstly carbonized at 180-240 °C for 60-240 min using a miniature high-pressure reactor and the fuel properties were analyzed. Then, the obtained solid product, called hydrochar, was densified and the pelletizing properties were investigated in the pelletization system. The results indicated that rising the HTC temperature and prolonging the residence time could significantly improve the heating value of hydrochar by 15%-65%, and the residence time had less effect on lower heating value than HTC temperature. Four important pelletizing properties were improved via HTC process, while the energy consumption during the pelletization process increased, resulting in a poor economy. The HTC operating conditions were analyzed and optimized via response surface methodology (RSM). It could be concluded that the fuel and pelletizing characteristics were more sensitive to the HTC temperature than residence time. HTC operating conditions of 210-220 °C for 190-200 min was recommended to produce hydrochar pellet with high qualities.

Keywords: biomass, hydrothermal carbonization, Pelletization, Pelletizing property, Response surface methodology