Pedro J. Aguado

Determination of parameters used to prevent ignition of stored materials and to protect against explosions in food industries.

There are always risks associated with silos when the stored material has been characterized as prone to self-ignition or explosion. Further research focused on the characterization of agricultural materials stored in silos is needed due to the lack of data found in the literature. The aim of this study was to determine the ignitability and explosive parameters of several agricultural products commonly stored in silos in order to assess the risk of ignition and dust explosion. Minimum Ignition Temperature, with dust forming a cloud and deposited in a layer, Lower Explosive Limit, Minimum Ignition Energy, Maximum Explosion Pressure and Maximum Explosion Pressure Rise were determined for seven agricultural materials: icing sugar, maize, wheat and barley grain dust, alfalfa, bread-making wheat and soybean dust. Following characterization, these were found to be prone to producing self-ignition when stored in silos under certain conditions.

Simulation of silo filling and discharge using ANSYS and comparison with experimental data

Experimental tests have been conducted in bin-hopper silos.Results of Finite Element Models (FEMs) are close to the experimental values.The FEM predicts higher peak pressures than the experimental values.The FEM predicts that the peak pressure is located closer to the transition. Silos are structures widely used in the industrial and agricultural sectors. Despite the advances in research during the last century, many uncertainties still remain. Some of the still unresolved questions in silos are the knowledge about the laws which control the behavior of materials stored in silos or the phenomena produced during the discharge process, when the highest thrust forces exerted by the stored materials on the walls appear.Numerical methods have been extensively employed for the understanding of these complex structures. Among them, the Finite Element Method is a suitable technique to determine the stresses and displacements appeared on the walls or the bulk solid both for filling and discharge of the silo. However, numerical models must be validated by experimental assays. Due to the high investment required, there are very few experimental installations in the world with full-scale silos for determining the actions produced by the stored materials. Therefore, very few assays can be found in the literature.In this article, it has been accomplished a comparison of the results obtained in several assays conducted using an experimental cylindrical silo with those calculated using a Finite Element Model (FEM) developed by using ANSYS software package. A mid-scale test silo was used to carry out the assays, which is equipped to measure the normal wall pressures and the friction forces. The numerical pressures predicted by the FEM are quite close of those experimentally obtained, both for filling and discharge. In addition, the mean vertical pressure obtained at transition is the same for both sets of results during the filling process. Some differences appear during the initial instants of the discharge, when the numerical model predicts higher mean vertical pressures at transition than those experimentally measured. The FEM predicts higher peak pressures than the experimental ones measured, and at a location closer to the transition than the real position of the sensor placed in the hopper to detect this peak.

Experimental tests to validate numerical models in silos design

The main objective of the research project described in this paper is to provide information about the behaviour of silos in order to improve their safety and their economic design. Hence, an installation of full-scale silos has been designed and performed for this purpose. Different experimental tests have been proposed to be carried out in these silos. Therefore, the experimental results will be compared to those obtained with numerical models developed in a commercial Finite Element (FE) software. The construction of a FE model requires the determination of mechanical properties for the stored material to obtain accurate results. In consequence triaxial, direct-shear or oedometer tests have been carried out in some common agricultural materials to determine their main mechanical parameters. In addition, ignitiability and explosibility properties of different agricultural materials have been also determined due to the existing lack of data. It may contribute to the understanding of dust explosions and propagation of flames in silos. The aforementioned installation consists of three smooth steel silos where normal and frictional wall pressures were measured during the filling, storage and emptying of the silo. The experimental silos have a cylindrical bin and a conical hopper. The cylindrical bin has an aspect ratio of 2.50 (height 5.00 m; diameter 2.00 m). The hopper is 1.54 m height and the outlet has a diameter of 0.32 m. The outlet eccentricity is the only difference between the three silos, whose values are 0%, 50% and 100%.