Size distribution analysis of wheat, maize and soybeans and energy efficiency using different methods for coarse grinding

This research investigated three grinding technologies to reduce the size of maize, wheat and full fat soybeans to a course particle. To correct for the different mechanisms of particle size reduction between the different mills, the relationship between specific mechanical energy (SME) and its resulting mean particle size was expressed per ton of ground product. Analysis of co-variance was used to estimate differences between the treatment means after correction for energy consumption. Experimental results, obtained under pilot scale grinding tests, showed that type and conditions used for the three mill types affected size reduction ratios for maize, soybeans and wheat. The RR of particles was smallest for the roller mill and multicracker device and largest for the hammer mill for all feed materials studied and varied between 1.60 (roller mill, wheat) and 5.95 (hammer mill, maize). The mean particle size was smallest when grinding using a hammer mill with a 5 mm screen. The efficiency of energy use was calculated as effective SME (kJ/kg). Total energy use was shown to be the highest for the hammer mill. Soybeans required the largest amount of energy for grinding, with maize the smallest. The constant for Kick's law (Ck values, kJ/kg) per grinding device was calculated to relate particle sizes and energy demand: both roller mill and multicracker device showed lower Ck values, indicating a better grinding efficiency of these devices. For coarse grinding, the roller mill was shown to be the most energy efficient device followed by the multicracker device and the hammer mill was the least efficient. For feed manufacturers it is important to use/combine these devices to ensure an efficient milling operation and to match the grinding device with its specific grinding objective (fine, coarse or with a specific particle size distribution). Tasks are different per animal species and were discussed.