Effect of Optimization Ratios on Proximate and Ultimate Compositions and Heating Values of Palm Kernel Shell and Groundnut Shell Co-Fired Pellets Bound with Wastepaper

Abstract

Optimizing blending ratios in biomass pellet production is pivotal for enhancing combustion efficiency and minimizing emissions in sustainable bioenergy applications. The objective of this paper was to assess the effect of optimization ratios (100:0 to 10:90) on proximate and ultimate compositions and energy values of palm kernel shell (PKS) and groundnut shell (GS) co-fired pellets bound with wastepaper, systematically formulated and characterized using standard laboratory procedures. Results revealed a progressive decline in higher heating value from 21,567 kJ/kg (100% PKS) to 18,635 kJ/kg (10% PKS:90% GS) with increasing GS content. Proximate analysis showed increases in volatile matter (68.70% to 89.79%) and ash content, while ultimate analysis indicated decreases in carbon and increases in oxygen, nitrogen, and sulphur. Stoichiometric combustion modeling demonstrated improved carbon oxidation with higher GS ratios, evidenced by increasing CO₂ concentrations (wet basis: 17.21% to 19.07%; dry basis: 19.83% to 22.47%). SO₂ emissions remained very low (<0.085%) across all blends, despite a modest increase. The 50:50 to 70:30 (PKS: GS) ratios offered the optimal balance between energy density, combustion performance, and emission characteristics. This work highlights the potential of PKS-GS co-pelletization as a viable strategy for valorizing agricultural residues, supporting cleaner energy production, and advancing circular economy practices in biomass-dependent regions.