Optimization of parameters associated with pellets made from biomass residue from anaerobic digestion using Box-Behnken design

Fuel pellets were produced with biomass residue from anaerobic digestion. Single-factor experiment and Box-Behnken design were employed to investigate the effects of pellets-associated variables on the mechanical properties of pellets, and the optimal condition was determined. The results revealed that the pellets-associated variables, including particle size, moisture content, die temperature, and molding pressure had significant influences on the mechanical properties of pellets, such as compressive resistance (CR), durability (DU), and density (DE). The regression models were obtained with the R2 values of 0.9802, 0.9628, and 0.9610 for CR, DU, and DE, respectively, suggesting that the differences between the actual and predicted values could be explained by the regression models. The optimal values of pellets-associated variables were determined (particle size of 0.4 mm, moisture content of 8.4%, die temperature of 115 °C, and molding pressure of 150 MPa); the corresponding responses were 1470 N, 99.6%, and 1180 kg/m3 for CR, DU, and DE, respectively. The results of verification showed a good agreement between the predicted data and experimental outputs. In summary, a novel approach was presented for the preparation of pellet fuels made from biomass residue from anaerobic digestion, and a reliable reference was therefore provided for the comprehensive utilization of biomass materials.