CHARACTERIZATION AND MODELING OF A HIGH-PRESSURE WATER-FOGGING SYSTEM FOR GRAIN DUST CONTROL

Abstract

Grain dust, a health and safety risk, is generated whenever grain is loaded into or unloaded from hoppers andequipment. This research investigated airflow models and evaluated the particle dynamics from a high-pressure water-foggingsystem for potential dust control at a grain-receiving hopper. Experiments were performed in a test chamber, representinga narrow section of a grain-receiving hopper. A 0.2 mm (0.008 in.) spray nozzle was used to produce a plume of fog directedacross a free-falling grain column. More than 90% of the fog droplets ranged from 10 to 40 .m in diameter. Average dropletvelocities in the plume cross-section were over 10 m s-1 at 7.6 cm from the nozzle. The air-velocity pressures at 7.6 cm wereparabolic in the radial direction, with maximum pressures over 275 Pa (1.1 in. H2O). Airflow distributions, grain dusttransport, and spray droplet trajectories within the test chamber were modeled in three dimensions using FLUENT, whichis a computational fluid dynamics (CFD) software program. Induced airflow from the spray fog caused recirculation of theair and dust particles in the lower part of the chamber. This recirculation pattern transported the dust from the grain pile backinto the spray plume, where it mixed with the spray fog. The spray produced deposits on the surface of the grain pile rangingfrom 0.1 to 0.4 mg cm-2 s-1. However, when the grain pile filled the chamber and was positioned directly in the spray plume,the grain surface deposits were 1.2 mg cm-2 s-1 at the grain peak. The spray produced deposits on the sidewall of the chamber.Sidewall spray deposits were 11 mg cm-2 min-1 in the middle of the test chamber and 1.5 mg cm-2 min-1 near the outlet. Thesidewall dust deposits during spray treatment ranged from 1.2 to 0.5 mg cm-2 min-1 and correlated with the spray depositswith an R2 of 0.95.