Alvaro Ramirez

Experimental determination of self-heating and self-ignition risks associated with the dusts of agricultural materials commonly stored in silos.

Agricultural products stored in silos, and their dusts, can undergo oxidation and self-heating, increasing the risk of self-ignition and therefore of fires and explosions. The aim of the present work was to determine the thermal susceptibility (as reflected by the Maciejasz index, the temperature of the emission of flammable volatile substances and the combined information provided by the apparent activation energy and the oxidation temperature) of icing sugar, bread-making flour, maize, wheat, barley, alfalfa, and soybean dusts, using experimental methods for the characterisation of different types of coal (no standardised procedure exists for characterising the thermal susceptibility of either coal or agricultural products). In addition, the thermal stability of wheat, i.e., the risk of self-ignition determined as a function of sample volume, ignition temperature and storage time, was determined using the methods outlined in standard EN 15188:2007. The advantages and drawbacks of the different methods used are discussed.

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.

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%.

Determination of Mechanical Properties of Agricultural Powder Materials and Sugar to be Used in Silos Design

Powder agricultural materials are usually stored inside silos. However, there is a lack of data in the literature about mechanical properties of these materials. Numerical methods are commonly used for the analysis of the behavior of the agricultural materials stored in silos. Nevertheless, the accuracy and efficiency of the results obtained when using these methods depend on the values of the material properties. A methodology previously used for granular agricultural materials is proposed in this research for powder materials. Thus, mechanical properties for some of these materials can be determined. Triaxial, direct shear and oedometer tests among others were carried out for determining different parameters such as Poisson’s ratio, dilatancy angle and elasticity modulus. The materials tested were sugar and five types of flour, confectioners’ sugar, barley, corn, soya and wheat.

Discrete Element Modeling of a 3D Scale Silo With Hopper

The discrete element method (DEM) is a numerical technique widely used to study the behavior of granular materials. It has proven to be reliable and effective in simulating many flow scenarios as well as the interaction between granular materials and the physical elements of the machinery or the physical system where they are contained.

Computational Methods for the Design of Formworks Used in Rural Works

Formworks play an important role in the support of lateral pressures exerted by fresh concrete on rural infrastructure works such as bunker silos, earth retaining walls or bridges in low volume roads. Traditionally, these elements have been designed assuming a non-viscous fluid behavior for the fresh concrete. Nevertheless, this procedure tends to overestimate the lateral pressures because the internal friction of the material and the existing friction between the material and the formwork wall are not considered. So, significant overpressures can be detected for high formworks.