Direct measures of mechanical energy for knife mill size reduction

Journal Article · Sat Aug 01 04:00:00 EDT 2009 · Bioresource technology

DOI:https://doi.org/10.1016/j.biortech.2009.07.069· OSTI ID:984789

Bitra, V S.P. ^[1]; Womac, A R ^[1]; Igathinathane, C ^[2]; Miu, P I ^[1]; Yang, Y T ^[1]; Smith, D R ^[1]; Chevanan, Nehru ^[1]; Sokhansanj, Shahabaddine ^[3]

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1. University of Tennessee
2. Mississippi State University (MSU)
3. ORNL

Lengthy straw/stalk of biomass may not be directly fed into grinders such as hammer mills and disc refiners. Hence, biomass needs to be preprocessed using coarse grinders like a knife mill to allow for efficient feeding in refiner mills without bridging and choking. Size reduction mechanical energy was directly measured for switchgrass (Panicum virgatum L.), wheat straw (Triticum aestivum L.), and corn stover (Zea mays L.) in an instrumented knife mill. Direct power inputs were determined for different knife mill screen openings from 12.7 to 50.8 mm, rotor speeds between 250 and 500 rpm, and mass feed rates from 1 to 11 kg/min. Overall accuracy of power measurement was calculated to be 0.003 kW. Total specific energy (kWh/Mg) was defined as size reduction energy to operate mill with biomass. Effective specific energy was defined as the energy that can be assumed to reach the biomass. The difference is parasitic or no-load energy of mill. Total specific energy for switchgrass, wheat straw, and corn stover chopping increased with knife mill speed, whereas, effective specific energy decreased marginally for switchgrass and increased for wheat straw and corn stover. Total and effective specific energy decreased with an increase in screen size for all the crops studied. Total specific energy decreased with increase in mass feed rate, but effective specific energy increased for switchgrass and wheat straw, and decreased for corn stover at increased feed rate. For knife mill screen size of 25.4 mm and optimum speed of 250 rpm, optimum feed rates were 7.6, 5.8, and 4.5 kg/min for switchgrass, wheat straw, and corn stover, respectively, and the corresponding total specific energies were 7.57, 10.53, and 8.87 kWh/Mg and effective specific energies were 1.27, 1.50, and 0.24 kWh/Mg for switchgrass, wheat straw, and corn stover, respectively. Energy utilization ratios were calculated as 16.8%, 14.3%, and 2.8% for switchgrass, wheat straw, and corn stover, respectively. These data will be useful for preparing the feed material for subsequent fine grinding operations and designing new mills.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: EE USDOE - Office of Energy Efficiency and Renewable Energy (EE)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 984789
• Journal Information: Bioresource technology, Journal Name: Bioresource technology Journal Issue: (2009) Vol. 100; ISSN 0960-8524
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
ACCURACY
AGRICULTURAL WASTES
BIOMASS
CROPS
FEEDING
GRINDING
MAIZE
Mechanical energy
POWER INPUT
ROTORS
SCREENS
STRAW
VELOCITY
WHEAT
knife mill
power
stover
straw
switchgrass