Optimizing the Production Parameters for Pellets Made from Pistachio Tree Pruning Using Multi-response Optimization

Biomass is considered as a renewable source of energy that can be used as a partial replacement for fossil fuels. Biomass pellets are produced by pressing the ground plant residues and they are directly burned to generate heat. Production variables can highly affect the final heat quality of the pellets. In this study, pellets were made from the pruning residues of pistachio trees and the effects of production variables including: moisture content in three levels of 8, 12 and 16%, wb; particle size in three levels of fine, medium and coarse; and temperature in three levels of 100, 75, 50 °C on the quality characteristic of the pellets were investigated. The quality characteristics included: strength factor, durability, density and friction of the pellets. The production variables were also simultaneously optimized using a multi-response approach by RSM and desirability function. The experimental results, based on full factorial experimental approach, indicated that the considered production factors had significant effect on all of the quality characteristics (α = 0.05). The quality characteristics were expressed as functions of production variables using a quadratic model for each characteristic. The models showed high degrees of fit for each case (R2 > 0.97). The resulted optimized values were: 100 °C for temperature, 11.7% for moisture content and 1.65 mm for particle size.