Pyrolysis of large biomass particles: Model validation and application to coffee husks valorization

Coffee husk is a valuable source of energy in Ethiopia. Pyrolysis of thermally thick biomass particles plays a crucial role across several industrial applications. Despite its significance, the enthalpy changes associated with volatile species release and residual biochar formation during the process are often overlooked. Predictive models for the pyrolysis of large particles and designing a new generation of pyrolyzers are crucial, particularly for industrial-scale applications. Thus, this work introduces a comprehensive one-dimensional (1D) model, BioSMOKE1D, to capture the intricacies of pyrolysis in thick biomass particles and aid in designing optimized pyrolyzers. The model integrates a solid-phase kinetic mechanism, transport limitations, and secondary gasphase tar-cracking reactions. The BioSMOKE1D has been thoroughly validated and exhibits impressive predictive accuracy by replicating various experiments on large biomass particles. The model successfully reproduces temperature measurements, mass loss profiles, and speciation data at lower temperature measurements. However, incorporating gas-phase mechanisms and secondary tar-cracking reactions has achieved better accuracy at higher temperatures (above 650 degrees C). Unfortunately, to the authors' knowledge, no experimental data is available for the pyrolysis of large coffee husk particles. Therefore, several parametric analyses are performed to determine the effect of model parameters on the pyrolysis yields for pelletized coffee husks. The findings indicate that biomass particle size, temperature, and initial moisture content significantly affect conversion time, energy consumption, pyrolysis product yields, and species distributions. Larger biomass particle sizes correspond to slower conversion rates and increased energy consumption. This modeling tool holds promises for optimizing the utilization of coffee husks as a renewable energy source, mitigating agricultural waste, and boosting economic growth. Furthermore, the insights from this study provide valuable inputs for optimizing pyrolysis processes in industrial-scale applications of these resources.