The effects of hydrothermal carbonization operating parameters on high-value hydrochar derived from beet pulp

Abstract

Beet pulp is an extremely very wet organic waste derived from sugar production. It can be utilized for energy purposes, e.g. biogas production or as very valuable fodder for animals, mainly horses. The high moisture content (80%) in beet pulp makes it an adequate feedstock for the hydrothermal carbonization process. Therefore, this study is focussed on the hydrothermal carbonization of beet pulp. The following parameters were studied: temperatures of 180, 200, and 220 °C through 1, 2, 3, and 4 h of residence time. The optimal conditions of the process were determined (220 °C and 1 h), based on the physical and chemical properties of solid product hydrochar. The ultimate and proximate analyses, high heating value, energy and mass yields, and energy densification ratio were investigated. The obtained hydrochars were of a coal-like solid biofuel, with high heating values much higher than raw feedstock (c.a. 150% higher). The combustion performance and kinetics of hydrochar based on TGA were determined, indicating better combustion. Moreover, the fibre analysis of hydrochar, supported by infrared spectra and scanning microscope analysis confirmed the changes in its structure. Concluding, organic waste, beet pulp, is of great potential as an energy source using the hydrothermal pretreatment process.