Hydrothermal carbonization of biomass: experimental study, energy balance, process simulation, design, and techno-economic analysis

In this study, the energy balance and techno-economic analysis of hydrothermal carbonization (HTC) of avocado stone (AS) were carried out to determine the use of hydrochar as a solid fuel. The experimental data obtained for HTC of AS were used to adjust a simulation model at an industrial scale using Aspen Plus®. The process was simulated, including all required equipment and stages to transform this biomass into dry hydrochar. The simulation result showed that the HTC process is energetically efficient for biomass water ratios above 10 wt.% at different operating temperatures (190–250 °C). The hydrochar obtained at 250 °C has a higher heating value (HHV) of up to 25.81 MJ/kg, and the energy yield of the process can reach 63.45%, while thermal efficiency reached up to 3.56 kWh of hydrochar per kWh of energy used in the process. In addition, the techno-economic analysis of the process showed that the process is economically feasible using hydrochar as pellet which has a competitive price compared to pelletized bulk pine wood, with hydrochar cost 9.64 $/GJHHV. Moreover, under the conditions studied, the initial capital recovery period was 3.7 years. This study could encourage the development of HTC plants and, therefore, the market for hydrochar pellets.