Combustion global kinetic analysis of a hydrochar obtained from grape pomace

Abstract

This research explores the hydrochar production from grape pomace via hydrothermal carbonization and the determination of the kinetic parameters of its combustion process. The hydrochar was obtained by hydrothermal carbonization at 220 °C for 240 min with self-generated pressure. The process indicated a mass yield of 65.21 %, and the hydrochar exhibited an HHV of 26.60 MJ/kg, showing its potential as an efficient biofuel. Thermokinetic analysis of hydrochar combustion was conducted using multiple complementary methods: isoconversional analysis, mathematical deconvolution, combined kinetic analysis of each step, and optimization of parameters through nonlinear regression. The findings indicate that the overall process starts at ~152 °C and involves three apparent overlapping steps. The apparent activation energies were 165, 122.9, and 185.6 kJ/mol, while the apparent $ln\left(A/s^{-1}\right)$ were 29.1, 15.4, and 26.81, respectively. The apparent kinetic models suggest a gamma distribution of frequency factors for volatile loss in step 1, a diffusion-controlled in step 2, and a final step for the combustion of fixed carbon through a type-geometry contraction in step 3. Finally, the obtained kinetic model allowed successful predictions of thermal programs outside the analysis range under non-isothermal and isothermal conditions.