Browsing by Author "Mitov I."

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    ASSESSMENT OF THE IMPACT OF SOME METEOROLOGICAL FACTORS ON THE ENERGY AND ENVIRONMENTAL EFFICIENCY OF TUBE ROTARY KILNS
    (2023-01-01) Stanev R.; Mitov I.; Shtaplev I.; Harizanov V.
    It is emphasized that rotary kilns are units for high-temperature heat treatment of a wide range of materials in a continuous technological process. This type of equipment is used intensively in many industrial branches such as chemical, metallurgical, silicate, pharmaceutical and others. In metallurgy, these installations find application at heat treatment of bulk materials, for example at reduction of oxide ores, at calcination of limestone, drying of copper sulfide charge, cleaning of metal shavings from machine oil and others. An overview of the ways of heat transfer to the material processed in a given rotary kiln, as well as of the basic mathematical models for describing the complex transport phenomena in the considered units is made. An accent is put on the fact that due to their large size, rotary kilns are often installed on open areas within the industrial sites to whose equipment they are included. The variable weather conditions can have a significant impact on the energy flow that leaves the cage of such a unit. It dissipates uselessly in the environment, which is accepted as a reason to be widely characterized as “heat loss”. This concept contains some conditionality, because according to the law of conservation of energy, it can not be created and disappear, but is transformed from one species to another. Nevertheless, the convenience of expression it offers has led to its use in the present statement. The proposed work is focused on the analysis of results obtained from calculating the heat loss from a rotary kiln to the surrounding outside air at typical for the latitude and climatic features of Bulgaria average annual temperature and a presence of relatively weak constant wind. As a result of the performed calculations, conclusions have been made about the ratios between the individual heat fluxes from the outer surface of the unit to the environment, as well as practically oriented recommendations for improving the energy and environmental efficiency of the discussed equipment
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    Geometrical characteristics of the solid bed in a rotary kiln
    (2014-02-25) Stanev R.; Mitov I.; Specht E.; Herz F.
    Rotary kilns are aggregates for high temperature thermal treatment of a wide range of materials in a continuous technological process. This type of furnaces is used intensively in many industrial branches such as chemical, metallurgi-metallurgical, silicate, pharmaceutical, etc. In the metallurgy these units find application for heat treatment of bulk materials (e.g. oxide ores reduction, limestone calcination, sulphide copper stock drying, cleaning of metal swarfs from machine oil, etc). The present study enlarges the opportunities for a fast and reliable thickness determination of the separate zones of the solid disperse bed at rolling motion as the most widespread regime of its transverse transport. Data published in a previous work of the authors are used. They are obtained by a mathematical model established on the basis of regularities in the particles movement in a cylindrical rotary kiln, allowing determination of the total thickness of the layer of processed material and the active part of it, occupying the area immediately below the free surface of the bed. Approximation equations for prediction of the maximal values of the enumerated indicators depending on the inner diameter of the rotary kiln, its rotation speed, the filling degree of the drum with material, the dynamic angle of its repose and the particles diameter are proposed.
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    HEAT TREATMENT INFLUENCE ON THE ABRASIVE WEAR RESISTANCE OF HYPOEUTECTIC CROMIUM CAST IRON
    (2022-01-01) Yordanov B.; Krastev D.; Mitov I.
    In the present work the variation of hardness and wear resistance of a machine specially designed to simulate the service conditions of abrasive wear were investigated depending on the type of the heat treatment of a hypoeutectic chromium white cast iron with composition C - 2.19 %, Mn - 0.46 %, Si - 0.51 %, Cr - 11.6 %, P - 0.031 %, S - 0.046 %, Ni - 0.23%, Mo - 0.077 %, V - 0.052 % and Al - 0.006 %. Maximum hardness of HRC 67 after quenching at 980ºC in oil and tempering at 200ºC is obtained which is a heat treatment suitable for workpieces operating under frictional and grinding conditions without high impact and dynamic loads. The wear rate after quenching at 980ºC in oil and subsequent low temperature tempering at 200ºC is V = 2.42.10-5 g m-1 and the abrasive wear resistance E = 41284. In cast condition the values of these indices are V = 1.33.10-5 g m-1 and E = 75157, respectively, and reduced to V = 0.30.10-4 g m-1 and E = 3331 after annealing at 870ºC and 180 min holding.
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    Mössbauer study of iron-based perovskite-type materials as potential catalysts for ethyl acetate oxidation
    (2010-01-01) Paneva D.; Dimitrov M.; Velinov N.; Kolev H.; Kozhukharov V.; Tsoncheva T.; Mitov I.
    La-Sr-Fe perovskite-type oxides were prepared by the nitrate-citrate method. The basic object of this study is layered Ruddlesden-Popper phase LaSr3Fe3O10. The phase composition and structural properties of the obtained materials are investigated by Mössbauer spectroscopy, X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and temperature programmed reduction (TPR). The preliminary catalytic tests show a high potential of these materials for volatile organic compounds (VOCs) elimination as they possess high conversion ability and selectivity to total oxidation of ethyl acetate. Catalytic performance of LaSr3Fe3O10 is depended on the stability of structure and Fe4+-oxidation state. © 2010 IOP Publishing Ltd.
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    Technological research on converting iron ore tailings into a marketable product
    (2021-05-01) Mitov I.; Stoilova A.; Yordanov B.; Krastev D.
    We present three technological scenarios for the recovery of valuable components from gangue, stored in the tailings dam at Kremikovtzi metallurgical plant in Bulgaria, into marketable iron-containing pellets. In the first approach the iron concentrate was recovered through a two-stage flotation process, desliming, and magnetic separation. In the second proposed process, the iron concentrate was subjected to four sequential stages of magnetic separation coupled with selective magnetic flocculation. The third route entails the not very common practice of magnetizing roasting, followed by selective magnetic flocculation, desliming, and magnetic separation. The iron concentrate was pelletized in a laboratory-scale pelletizer. Each technology has been assessed with regard to the mass yield of iron concentrate, the iron recovery. and the iron, lead, and zinc content in order to identify the most effective route.