Investigation of bulk density and friction coefficient of olive residues and sawdust prior to pelletizing

Abstract

This paper focuses on the influence of numerous parameters involved in the pelletizing process on bulk density and friction coefficient of olive residues and sawdust. The bulk density is measured for different grain size and mixture composition. The bulk density of sawdust decreases is inversely proportional to the grain size, whereas for olive residues, there isn’t a clear correlation. Regarding the friction test, numerous experiments are conducted under different test conditions: pressure, grain size, velocity, moisture content, temperature, and mixture composition. The friction coefficient decreases linearly with increasing test velocity for both raw materials. An increase in temperature from 25 to 250 °C causes an exponential decrease for the sawdust friction coefficient, whereas for olive residues, it remains constant between 25 and 150 °C and then decreases linearly from 150 to 250 °C. Increasing the moisture content also results in an exponential increase of the friction coefficient for both raw materials. All empirical correlations are embedded in a MATLAB code that predicts the presumed friction coefficient of any mixture of sawdust and olive residues under different conditions. Finally, a better understanding of bulk density and friction coefficient aids in improving pellet production in terms of reduced power consumption and enhanced pellet quality.