Effect of chaff on bulk flow properties of wheat

• Flowability of bulk wheat reduces with increase in moisture content and percent chaff.
• Energy required to initiate flow of wheat with chaff is higher than for clean wheat.
• Compressibility of wheat increases with chaff percentage.
• During handling, there exists minimum segregation potential of chaff from clean wheat.

Consistent and reliable flow of bulk wheat from hoppers and silos is vital in handling, processing, and storing wheat. The presence of impurities in bulk wheat might influence the discharge of wheat from hoppers and storage vessels. Chaff is one common impurity, amounting to about 2–7% (weight basis) in bulk wheat. This study focused on measuring the bulk and flow properties of bulk wheat in the presence of chaff at different moisture content levels. Bulk density, tapped density, and true density varied from 805.50 to 718.36 kg/m3, 831.52 to 746.31 kg/m3, and 1404.63 to 1367.13 kg/m3, respectively, with varying chaff proportions and moisture contents. The stability of bulk wheat samples remained the same, indicating that sample properties did not change during repeated handling. Compressibility ranged from 4.84 to 7.99%. The unconfined yield strength (UYS) of chaff was approximately 3 times higher than clean wheat samples. High UYS values indicate that arching could occur during bin discharge of bulk wheat containing impurities.