Pneumocentrifugal Classification of Dispersed Particles during Grain Milling

Abstract

Russia enjoys a stable demand for flour products, including those obtained by the dry method of starch and gluten production. This study featured pneumocentrifugal parameters of fine particles in a spiral separator that classified milled grain into fractions, separated the solid phase from air, and identified the high-protein flour fraction in the flow. Pneumatically classified flour was subjected to mathematical modeling and experimental research. The analysis of movement and deposition of particles in the working area covered particle mass, density, air-flow rate, and geometry, as well as their effect on the trajectory of particle movement and deposition. The experiment also involved the effect of air-flow rate and air-mix concentration on the classification efficiency. Particles from various grinding and break systems demonstrated classification modes that differed in soaring rate, size, and density. At an air-flow rate of 6–8 m/s, turn 1 of the spiral separator had the ratio of the internal coil radius to the inner pipe diameter as r1/dpipe = 7.9; it was r1/dpipe = 7 on turn 2 and fell down to r1/dpipe = 6.25 on turn 3; for all subsequent turns, the ratio was r1/dpipe < 5. Under these conditions, the fraction reached 160 µm and included small high-protein flour fractions with a particle size of 17–20 µm. The percentage of product accumulated on turns 1, 2, and 3 was 80, 12, and 8%, respectively. The maximal product separation efficiency of the third drain system was as high as 98% at an input rate of 6 m/s. The maximal separation efficiency for premium flour reached 99.2% at an input rate of 4.2 m/s. The separator proved efficient in classifying wheat grain flour into fractions as it was able to separate high-protein fraction and dispersed particles from the air flow. The separator could be used both as an independent device and as part of a complex technological scheme at the stage of pneumatic separators and unloaders.