The practical aim of the project is to build and test in industrial conditions an installation for milling mineral materials which uses a unique construction of electromagnetic mill. The project involves creating a control system for the installation to ensure high technological efficiency and low energy consumption in as diverse industrial applications as possible. Comminution of raw materials is commonly used in many industries, from processing of mineral materials to chemical, construction, food and pharmaceutical industries. Thus, the expectations as to the particle size and properties are very diverse. For example, during enrichment of ore output, which is one of the stages of copper production, material of granularity 1000-1500 mm needs to be ground to particles less than 0.1 mm before it can be further processed. This operation is particularly energy intensive, time consuming and expensive, because it applies to all of the mining output and as such, it regards processing of enormous amounts of raw material. Indices of energy consumption per unit of processed material for milling of medium-sized particles (about 1 mm) fall within the range 2-10 kWh/Mg. With the decrease of the target particle size, the demand for energy increases rapidly. Analogous problems occur in the process of dry milling with drying and classification of fine-grained materials in the industry of construction chemicals and cement-and-lime powders or when producing sorbents for flue gas desulphurisation in power industry. Construction chemicals production plants, which manufacture a wide variety of finished products (mortars, plasters, finishing coats, cements, paints, pigments, emulsions, glues etc.), as well as power industry, search for milling installations which give fine-grained lime products with the best possible quality parameters, such as sharpness of separation curve, high porosity, maximum content of regularly shaped particles, the best possible indicators of reactivity and absolute sorption. Conventional milling of raw materials occurs by means of attrition of the particles by grinding media in tumbling mills (ball or rod mills), where the motion of grinding media is caused by rotation of the mill's drum - a cylindrical working chamber filled with grinding media and milled material. Disadvantages of such mills are high energy consumption and fast wear-out of replaceable parts (for example, the lining) and of the grinding media themselves. Low process efficiency results from the fact that the energy that causes the motion of grinding media only to a small extent translates to grain comminution. Moreover, in conventional mills it is not possible to shape the particles and the product is often of low technological value. Besides, grinding media content in the working chamber cannot be regulated - especially, it cannot be decreased. The most recent designs eliminate these drawbacks only to a small extent.
Hence, the main practical goal of the project arises from the need to design a modern, competitive installation for fine milling with recirculation of particles that do not meet the quality requirements, an installation which may possibly be applied to different kinds of raw materials and may be configured using an appropriate measurement and control system with a dedicated HMI/SCADA application.
Since 2009, ELTRAF company has been manufacturing magnetic field inductors of their own construction, that operate as flow-through electromagnetic mills for dry materials or for suspensions of dry materials in liquids. In contrast to typical mills (ball, rod or cylpebs), the casing of the mill remains motionless and the milling (or mixing) occurs in the working chamber. Inside the chamber, small ferromagnetic elements (which are the grinding media) are moving. Their motion is caused by rotating electromagnetic field. At present, the mill is not equipped with any automatic control nor measurement system; nevertheless, it aroused great interest in several enterprises in which it has been installed. The users appreciated the potential of the device, however, they drew attention to the necessity to develop a system which would ensure a preset technological efficiency. The productivity and efficiency of the process carried out in such a mill depends on the chosen physical parameters of the device and on the operational parameters of the process, such as feed material flow rate (which determines the residence time of the particles in the chamber), input granularity, rotational speed and intensity of the rotating electromagnetic field, temperature, moisture and other parameters of the processed material (for example, lithological composition). Therefore, to fully exploit the extraordinary capabilities of the electromagnetic mill, it is necessary to carry out research in order to implement a proper measurement and control system.
In the course of the work performed, an installation for material feeding and reception was developed for the electromagnetic mill, as well as the control system structure was designed. A control cabinet with measurement and control devices was built. Such a research stand is currently used for experiments with diverse propositions of measurement and control algorithms.