Permeability of wood pellets in the presence of fines

Broken pellets and fines are produced when pellets are handled. The resistance to air flow was measured for clean pellets and for pellets mixed with 1–20% broken pellets (fines). A pellet diameter was 6 mm. The lengths ranged from 6 to 12 mm. Clean pellets were defined as particles that remained on a 4 mm screen. A typical sieve analysis showed 30% of the mass of particles that passed through the 4 mm screen was smaller than 1 mm. The airflow rates used in the experiment ranged from 0.004 to 0.357 ms−1. The corresponding pressure drop ranged from 1.9 to 271 Pa m−1 for clean pellets, from 4.8 to 1100 Pa m−1 for 10% fines content, and from 7.9 to 1800 Pa m−1 for 20% fines content. Coefficients of Hukill and Ives’ equation were estimated for clean pellets and a multiplier was defined to calculate pressure drop for pellets mixed with fines.