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Size Reduction of Wet and Dry Biomass by Linear Knife Grid Device

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2007 ASAE Annual Meeting  076045.(doi:10.13031/2013.22951)
Authors:   Igathinathane Cannayen, Alvin R Womac, Shahab Sokhansanj, Sundar Narayan
Keywords:   Biomass, Cutting, Energy, Knife, Press cutting, Size reduction, Stress

Linear action of forcing biomass materials through a grid of interlocking knives is an alternative method of size reduction, contrast to rotary action involved in existing size reduction machines. A laboratory-scale linear action knife grid device prototype developed earlier was used to determine the size reduction characteristics of selected biomass, namely, corn stalks and switchgrass at several material and operating conditions. This study was aimed at determining and comparing the ultimate cutting stresses and cutting energy variation between corn stalks and switchgrass, moisture conditions (high- and low-moisture), knife grid spacing (25.4, 50.8, and 101.6 mm), and packed bed depth (50.8, 101.6, and 152.4 mm). The device is composed of ram – attached to crosshead of universal testing machine (UTM), feed block – holds feed, knife grid –arranged at variable grid spacing, knife holder block – holds knife grid, and product block – collects product, and the whole assembly is tested in UTM fitted with 222.41 kN (5000 lb) load cell. New surface area generated during size reduction was evaluated based on circle packing theory. Ultimate cutting stresses were evaluated as the ratio of peak load to the cutting plane area (MPa) represented by the knife grid. Cutting energies were evaluated from the area under load-displacement curves and expressed in moisture free basis mass-based energy (MJ/dry Mg) and new surface area-based energy (kJ/m2). Overall results indicated that ultimate cutting stress and cutting energy of corn stalks were significantly (P<0.05) greater (2.2 times) than that of switchgrass. High-moisture material required significantly greater stress and energy (1.3 times) than low-moisture material. Grid spacing produced significant difference in cutting energy but not with ultimate cutting stress. Energy values required in size reduction using linear knife grid device was much smaller than that reported for similar biomass using other methods of size reduction. Therefore, a pre-processing machine, based on linear knife grid principle, with 50 to 100 mm and greater grid spacing would be an efficient first stage size reduction for biomass materials.

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