Production and Performance Evaluation of Biomass Pellets from Mixed Agricultural Residues with Waste Oil Additive

Abstract

The growing demand for sustainable energy and the environmental impacts associated with open-field burning of agricultural residues have accelerated interest in biomass densification technologies. This study investigates the production and performance enhancement of biomass pellets manufactured from a blend of rice husk, wheat straw, and sugarcane bagasse with controlled incorporation of waste engine oil (WEO) as an energy-enriching additive. Pellets were produced using a flat-die pellet mill while maintaining constant processing parameters to isolate the influence of additive concentration. Four formulations containing 0%, 1%, 3%, and 5% WEO were evaluated for bulk density, mechanical durability, moisture, ash content, and higher heating value. Results revealed that moderate oil addition improved particle rearrangement and compaction, increasing bulk density from 612 to 668 kg/m³ at 3% WEO. The calorific value showed a continuous rise from 16.8 to 20.2 MJ/kg, representing nearly a 20% enhancement compared with the reference blend. Durability slightly decreased at higher additive levels due to lubrication-induced reduction in inter-particle friction, yet remained within acceptable commercial limits. Ash content declined marginally with increasing oil proportion, supporting cleaner combustion behavior. Considering the trade-off between energy gain and mechanical strength, the formulation with approximately 3% WEO was identified as the optimum mixture. The study demonstrates a practical pathway for simultaneous valorization of agricultural waste and used lubricating oil, contributing to circular economy practices and decentralized renewable energy solutions.