Professional Articles

Silo Technology

Large Screw-Floor Discharge in a Squat Steel Silo in Brazil - Flow and Pressure Analysis

Squat silos have well known funnel flow behavior in central discharge and the multiple screw-floor discharge system has the advantage to extract the grain with near constant humidity. The discharge system consists of parallel screws below bottom level, which make possible a large discharge under gravity forces. The resulting flow allows the grains to flow almost in the same level, sliding, by one side, near the wall, and resting, in the other side of the opposite wall and also near the bottom. Therefore, the flow obtained is one that tends to a mass flow, non-axissymmetric, that permits a large surface of grains to be discharged evenly. This situation occurred in Brazil with a large squat steel silo of 27.28 m diameter and 20.25 m cylinder height. As a conclusion, it is shown that the stored products can be dried up to 3% and that the pressures distribution on silo during the discharge based on wall deformations problems is higher than those predicted by funnel flow.

Introduction

In Brazil , large squat steel silos are very common for the storage of granular products. The discharge of these silos is performed with multiple large screws installed in the silo bottom. The type of flow is usually the funnel flow. A standard squat steel silo with flat bottom with 27.28 m diameter and 20.25 m cylinder height is constructed with central discharge and it propitiates a funnel flow inside silo. With the aim to have a discharge with all the grains descending in the same level, four screws were installed in the silo…