Enhancing Energy Efficiency and Waste Valorization Through Optimization of Co-firing Pellet Fuel from Coal and Coconutshells

Abstract

This study presents the optimization of co-firing pellet fuel produced from Nigerian bituminous coal and coconut shell waste using wastepaper as a sustainable binder. Response Surface Methodology (RSM) coupled with Central Composite Design (CCD) was employed to investigate the interactive effects of coal proportion (30–90%), coconut shell concentration (10–70%), and wastepaper binder level (5–15%) on the calorific value of the resulting pellets. A quadratic model with high statistical significance (F-value = 45.91, p < 0.0001) and excellent predictive capability (R² = 0.9425, Adjusted R² = 0.9220, Predicted R² = 0.8935) was developed. Results revealed that wastepaper binder content exerted the strongest influence, with an optimal dosage of approximately 10% yielding the highest calorific values (up to 44.73 MJ/kg). Coal proportion showed a positive linear effect, while excessive binder addition led to a notable decline in energy density due to dilution. The optimized formulation effectively balances energy performance, mechanical integrity, and waste valorization. This research demonstrates the potential of coal-coconut shell pellets as a cleaner, high-energy-density fuel for co-firing applications, contributing to sustainable energy production and circular economy principles in biomass-rich developing regions.