(302h) Simulating the Wheat Flour Particle Separation Process during Sieving

Size based separation of flour is an important processing operation during wheat milling. The flour particles are highly cohesive that leads to discontinuous flow and agglomeration during the size separation process. Differences in particle and bulk behavior exist between the wheat flour from different classes and varieties. In general, wheat is classified as either hard wheat or soft wheat with inherent differences in chemical composition. Noticeable loss in throughput has been observed during size based separation of soft wheat flour compared to that of hard wheat flour due to differences in inter-particle cohesion. Similar to other particulate materials, the cohesion of wheat flour is highly dependent on the moisture content, particle size and on compaction. In this research, our objectives are to develop a prediction model for wheat flour flow behavior and to simulate the flour particle separation process using discrete element method (DEM). A granular bond number (GBN) model, based on Rumpf equation, was developed to predict the particle flow during the size based separation process. The GBN model, predicted the flow pattern of wheat flour with 0.05-0.2 standard error of prediction (SEP). The cohesion values predicted using GBN model was used as particle input parameters during DEM simulations. The DEM model was verified by the SEP values between the numerical and experimental results in terms of the percentage particles passing through the sieve screens. The effect of variables such as particle size, moisture content, and particle cohesion were studied with respect to overall separation efficiency and rate of separation for different sized particles. Based on the SEP values (0.02-0.07), it is demonstrated that the size based separation of wheat flour could be simulated using DEM method. The DEM model can satisfactorily estimate the sieving performance in terms of separation efficiency and the sieve blinding phenomenon specifically when there is significant interaction between particle-particle and particle-screen material.