The pneumatic conveying of plastic pellets is a process widely used in the chemical industry. Different products can be transported using the same conveying system thanks to the great flexibility that this technology offers. However, there are also challenges due to the significant variation on pressure drop produced by different products. This has a direct impact on the conveying capacity due to the limited pressure that the air mover can provide. The present work explores the effect of material elasticity and surface friction on pressure drop by performing experiments using blends of hard and soft pellets with different blending ratios in a dilute conveying system. The two component pellets have similar particle size, shape and material density but different modulus of elasticity and surface friction. Using experimental data from the conveying trials, friction factors were calculated by the most commonly used theoretical correlations as well as experimentally. The results showed a significant lack of fit for the friction factors calculated when conveying blends with a high ratio of soft pellets.
Furthermore, to isolate the material surface friction effect from elasticity, a series of experiments were performed adding water to the surface of the soft pellets. This effectively reduced their particle-wall friction without changing their elasticity. The effect of this change demonstrates that the particle-wall friction has a strong influence on particle dynamics during pneumatic conveying, and it should be included when predicting the friction factor.