Data-based equation to predict power and energy input for grinding wheat straw, corn stover, switchgrass, miscanthus, and canola straw

This study investigated size reduction of five herbaceous species: wheat straw, corn stover, switchgrass, miscanthus, and canola straw. The biomass samples were air-dried to moisture content of 10%. The instantaneous power input to grind the material was recorded. Grinding wheat straw, corn stover, and canola straw using a 3.2 mm screen inside the hammer mill consumed 32 to 35 kWh/t whereas grinding switchgrass and miscanthus on the same screen used 22 kWh/t of energy. All five biomass samples required almost the same amount of energy input (13 to 20 kWh/t) when a 6.4 mm screen was installed in the hammer mill. Some species like corn stover produced strings of fiber causing blockage of the inlet to the grinder. A linear relation was developed between geometric mean diameter (dgw) of the ground particles and the screen size (SS). The screen size inside the hammer mill was used as the representative size of the particles. The Rittinger equation was fitted to the size data to estimate the equation constant kR from energy input vs. screen size. The kR value ranged from 96 to 267 J mm/g depending on the species.