Design and use of an adjustable clearance flailing knife biomass shredder to mechanically increase particle surface area

Shawn G Ehlers, Purdue University


A flailing knife shredder was designed and tested as an alternative to a hammermill for processing biomass. The machine was comprised of two cylinders with four rungs, each with five free-swinging blades. Each of the two cylinders had adjustable clearance hoods and variable speed drives. Energy usage, output characteristics and device capacities were compared with corn stover processed at moisture contents (MC) of 10%, 35% and 50% wet basis (WB). The hammermill produced a more uniform particle size distribution in comparison to the shredder. Accessibility, indicated by conductivity index, to plant constituents, revealed that the method of treatment was not-significant (p<0.05) when stover was processed at 50% MC. However, the flailing knife shredder processed 50% MC material at a rate 9.2 times greater than the hammermill. When processing biomass at 50% MC the specific energy consumption was 3.75 kWh/Mg with the flailing knife shredder and 5.8 times higher at 16 kWh/Mg for the hammermill. When processing material at 10% and 35% MC WB, the flailing knife shredder achieved material accessibility of 65% and 71% respectively to the level of the hammermill with similar material. While lower moisture material had decreased levels of material accessibility in the shredder in comparison to the hammermill, the specific energy to process the same amount of material was 23% and 171% more with the hammermill at moisture contents of 10% and 35% WB respectively.




Buckmaster, Purdue University.

Subject Area

Agriculture|Agricultural engineering

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