Discrete element method simulation of the hulling process of Jatropha curcas L. fruits

Abstract

Hulling of Jatropha curcas fruits is an important step to isolate seeds from hulls. Physical characteristics of fruit such as length, width, thickness, geometric mean diameter, solid density, rupture force, deformation at rupture point, Poisson's ratio and shear modulus as well as interaction properties such as coefficient of restitution, static and rolling friction were measured. A prototype of a motor-driven huller was developed based on discrete element method (DEM) simulation by applying the Hertz–Mindlin contact model. Optimum upper and lower concave clearance were studied in terms of compressive force occurring in the system. Rotor torque and specific energy input ranged from 60 to 110 Nm and 0.013 to 0.021 kWh kg−1, respectively. The maximum throughput of fruits was 1152 kg h−1. The highest hulling efficiency of 98.8% was achieved at a throughput of 477 kg h−1. Grading of J. curcas fruits to achieve size homogeneity and the removal of stones and sand are suggested as further improvements in the hulling process.