Mechanical Characteristics and Energy Consumption of Solid and Hollow Biomass Pellet Production Using a Statistical Analysis of Operating Parameters

Biomass pelletization technology overcame the poor utilization and handling properties of loose materials. The quality of pellets is sensitive to the pelletization conditions. In this work the impact of the operating parameters as pressure, temperature, and moisture content on the mechanical characteristics as the compression strength ([Formula: see text]) and durability ([Formula: see text]) and energy consumption for both production ([Formula: see text]) and ejection ([Formula: see text]) of rice straw (RS) pellets was studied. Furthermore, the synergic effect of these parameters on the pellet characteristics was evaluated at the optimum conditions. The operating parameters were optimized using a multi-objective optimization approach of Response Surface Method (RSM) based on the predicted significant models that describe the physical characteristics of the pellets. The optimization results showed that high quality pellets could be produced at a pressure of 68.4 MPa, temperature of 110.0 °C, and moisture of 8.2% for solid pellets and 63.6 MPa, 110.0 °C, and 8.7% for hollow pellets. Significant individual and interaction effects of all independent parameters on the pellets characteristics were investigated using statistical analysis results, main plot curves and 2D interaction contour plots. New significant empirical dimensionless relationships that correlate the characteristics of pellets were proposed. These relationships can be generalized for any type of pellets that produced under various operating conditions. Hollow pellets are recommended to be used in the industrial sector due to their enhanced heat transfer which resulted from the high surface to volume ratio besides their ease production at normal operating condition similar to that required for solid pellets.