Study on the modeling and simulation of the pre-treatment process of coffee husks for renewable energy production in the Brazilian agro-industrial sector

Abstract

Brazil, the world's largest coffee producer and exporter, generates substantial quantities of coffee husks, the main residues from wet processing. Recent research has demonstrated their energy potential. However, the high moisture content, low density and irregular particle size require a pre-treatment for efficient thermochemical conversion. This study analyzes the economic viability of a pre-treatment and combustion plant of coffee husk briquettes for electricity generation. The pre-treatment design, cost estimates, and sensitivity analysis were conducted, focusing on the influence of drying operational variables. Energy studies showed that the Southeast region produced 85.5 % of Brazil's coffee husks in 2024, potentially generating 178 GWh yr⁻¹. Nonetheless, most scenarios were economically unviable, presenting a negative Net Present Value (NPV) equal to −$7.92 million, mainly due to the high investment in combustion technology (63.7 % of the total), and high drying costs (56.8 % of operating costs). The lowest Levelized Cost of Electricity (LCOE) was $198 MWh⁻¹, achieved at the highest drying air temperature in the optimistic scenario, though still above the base tariff ($67.3 MWh⁻¹). The air temperature, followed by the bed height, were the drying variables with the greatest influence on the bioenergy plant's economy, while the air velocity proved to be inelastic. This paper highlights the importance of key design parameters in reducing total costs.