Effect of screen size on particle size distribution and performance of a small-scale design for a combined chopping and milling machine

Mitigating environmental concerns of climate change and global warming requires renewable and sustainable alternatives to reduce over-reliance on fossil fuels. Cleaner production practices have adopted the use of renewable alternatives to energy and material development with biomass playing a key role. With increasing potential of biomass technologies for rural and domestic applications, the development of cost-effective and efficient machines for particle size reduction is necessary. Previous studies investigated the performance of choppers and hammer mills as separate units. In this study, a small-scale combined chopping and milling machine was designed and evaluated using corncobs and corn stalks. The particle size distribution and crushing efficiencies of the machine using different screen sizes were determined. The machine was operated using a prime mover rated at 4.4 kW. The moisture contents of corncobs and corn stalks processed were 7.76 and 7.65%. The crushing efficiencies of the machine ranged from 62.0 to 80.4% for corn stover and 70.8–84.8% for corncobs and depended on the screen size. The mean geometric particle size was approximately similar for both milled corncobs and corn stalks produced using the same screen size. The combined chopping and milling machine can process biomass of various forms and can be integrated with other small-scale biomass technologies. Future work should consider the optimization of various parameters which would affect the operation of the machine.