Browsing by Author "Paunova R."
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Item Activity investigation of FeO, SiO2 and V2O5 in V2O5- FeO - SiO2ternary systems(2017-01-01) Grigorova D.; Paunova R.The activity of FeO, SiO2, and V2O5 in V2O5 - FeO - SiO2 ternary systems has been investigated. Pure oxides were used as reference mixtures, included in the system in ratios, analogous to those of mixtures, containing waste vanadium catalyst. Two mixtures were prepared: 1st mixture - V2O5 - FeO - SiO2 (pure oxides), 2nd mixture - waste vanadium catalyst - FeO - SiO2. The oxygen potential in the systems was determined by the EMF method. The solid electrolyte was ZrO2 (Y2O3), and the reference electrode - a mixture Mo/MoO2 in 1: 1 ratio, was used as a galvanic cell. The investigations were carried out in an isothermal and a non-isothermal condition. The Gibbs free energy and the activity coefficient were calculated from the experimentally obtained oxygen potential. Equations for ΔGT = f (T) were derived for different temperature ranges. New phases were observed in the mixture containing vanadium catalyst.Item Balance modeling of the process for SiCaV alloy producing from waste vanadium catalyst(2014-02-25) Petrov P.; Marinov M.; Todorov P.; Alexandrova R.; Paunova R.The modern steel industry is characterized by continual improving the quality of the produced steel with constantly increasing range and quantity of deoxidation and alloying alloys. Among them falls SiCa with vanadium. Consider the absence in the Republic of Bulgaria of raw materials containing vanadium for example, the needs of metallurgy are provided mainly by imports of ferro-alloys. At the same time our country has an active chemical and metallurgical industries where significant polluting quantities of vanadium catalyst drop from production of sulfuric acid, which contains Si and V. Both material and heat balance models are developed for carbothermal producing of SiCa with a high content of vanadium. Vanadium waste, metallurgical lime and metallurgical coke are the raw material. The elements in the alloy after the carbothermal reduction are: V - 9.09 %, Fe - 9.06 %, Si - 66.45 %, Ca - 12.26 %, P - 0.02 %, S - 0.04 %, C - 0.21 %, Al - 2.83 % u Mn - 0.03 %. The main contributor into the alloy of V, Si and Fe is the waste vanadium catalyst. The relative consumption of electricity according to the heat balance model is 11505 kWh/ton alloy.Item Electric-arc-carbothermic processing of agglomerated waste dispersal materials from ferrous metallurgy(2014-01-01) Grigorova D.; Marinov M.; Paunova R.The present paper reports results referring to the production of pig iron under laboratory conditions using a low shaft electric furnace. Wastes from ferrous metallurgy subjected to a preliminary agglomeration are used as iron containing raw materials in the sintering charge. Material and heat balance calculations are carried out. It is found that sinters of high waste powders and sludge content can be used to give pig iron of low content of sulphur, phosphorus and non ferrous metals. The chemical composition, the yield and the specific energy consumption are found close to the existing standards.Item Kinetics of reduction of waste fayalite by calcium carbide(2019-01-01) Grigorova D.; Paunova R.Investigations of the slag, obtained from the non-ferrous metals, are of great importance to expand the raw material base for complex utilization, to increase the extraction of useful elements and to protect the environment. The kinetic of reduction of the waste fayalite by calcium carbide was investigated for two ratios of 1:1 and 1:10. Thermogravimetric analysis was carried out. Activation energy was determined, the maximum for the ratio 1:1 was 18.81 kJ/mol, and for ratio 1:10, Ea = 21.31 kJ/mol. The rate constant is also determined and the equations for the two defined temperature ranges were respectively derived. The maximum rate of reactions for the two mixtures is obtained, for the first mixture υ = 1,7176.10-3 mg/min at a temperature 1221 K, and for the second mixture the maximum rate is υ = 1.2339.10-3 mg/min at 1230 K.Item Production efficiency of a ferro-molibdenum alloy(2014-02-25) Marinov M.; Mushev G.; Petrov P.; Paunova R.; Aleksandrova R.Ferro-molybdenum alloys are widely used in the production of heat-resistant stainless steel, acid-proof, tool steels. They give an uniform grain size, increase the tenderness, etc. Imported in the iron, molybdenum increases the hardness, the elasticity and the durability. FeMo is not produced in Bulgaria. The need of this ferro-alloy is covered by imports, which significantly increases the cost of the production. In this aspect, it is of an great interest the evaluation of the profitability of the organization at such proceedings in the country, based on the imported concentrate of MoO3, defining the necessary quantities of raw materials, technological operations, material flows and machines for a set annual production of FeMo60. The relative fuel charge materials is calculated based on the composed material and heat balance models of metal heat outside furnace production of ferro-molybdenum with an use of both aluminum and ferrosilicon as a gear. The technical and economic feasibility of profitable production is examined. The necessary raw materials for an annual production, both the daily and the hourly average and the one for the combustion furnace hearth are determined. A block diagram of a small factory, a sample processing of raw materials and necessary equipment are proposed.Item Study on the behaviour of flotation fayalite waste from copper production at nonisothermal heating(2014-02-25) Alexandrova R.; Paunova R.; Marinov M.; Petrov P.The behaviour of flotation fayalite waste from copper slag at non-isothermal heating has been studied. Only a small part from this product (about 2 %) is used in the cement production. The other part, containing rather high percentage of iron is not used and it is deposited thus polluting the environment. DTA method was used to study the behavior of this waste at the non-isothermal heating up to 1273K and 1673K. Phase transformations have been defined by chemical and X-ray analyses. The phases of hematite, magnetite and cristalobalite were determined in the end product after flotation. Thermograms, obtained by DTA show that the oxidation processes run into two stages at the non-isothermal heating - the first stage up to T = 894K and the second one up to T = 1155K. Experimentally, the melting temperature of the flotation fayalite waste (Tmelt ≈ 1457K) was found. The melting of the sample in the crucible was observed at this temperature.Item THERMODYNAMIC AND KINETIC INVESTIGATION OF IRON SILICATE REDUCTION WITH DIFFERENT REDUCING AGENTS(2022-01-01) Grigorova D.; Paunova R.The thermodynamics and kinetics of the reduction of iron silicate (fayalite), generated as a result of flotation processes in the production of copper concentrates, were studied. Three reducing agents were used - coke, charcoal, and graphite, in ratios to the stoichiometrically calculated amounts of reducer: 1: 1.5; 1: 2; 1: 2.5. The free Gibbs energy in the temperature range from 973 K to 1040 K was determined experimentally and the corresponding equations for 4G = f(T) were derived. The kinetic parameters were determined using thermogravimetric and differential methods at temperatures up to 1273 K. The results showed that the reduction process using coke went through three stages, and using charcoal - two stages. The reactions that took place were of the first order. Carbonated reduction of iron silicate occurred in the kinetic region. The highest values of the apparent activation energy were obtained as 67.83 kJ mol-1 when using coke (1257 K), and when using graphite - 60.29 kJ mol-1 at 1318 K. The lowest values of the activating energy 36 kJ mol-1 were observed with a charcoal reducer in the temperature range 966-1573 K.Item Thermodynamic investigation of briquette obtained from waste fayalite with calcium carbide(2017-01-01) Grigorova D.; Stoyanov D.; Paunova R.The iron content in fayalite, wasted from the copper production, is high and can be used as a raw material in the ferrous extractive metallurgy. This material has a fine dispersal structure, and it is necessary to be agglomerated for next refining processes. An experimental investigation for briquetting was carried out. X-Ray analysis of the initial sample showed fayalite and magnetite as main phases. Thermodynamics of the reduction of the fayalite using calcium carbide as a reductor was studied. Calcium carbide was used also as a regulator of the basicity of the charge. The experiments were carried out at ratios for fayalite - calcium carbide 1:1 and 1:10, relative to the stoichiometrically calculated quantity of calcium carbide, in the temperature range from 773 K to 1173 K. The oxygen potential, respectively Gibbs energy, has been calculated using EMF method with galvanic cell with solid electrolyte ZrO2 (Y2O3) and reference electrode Ni/NiO. Equations for DGT = f (T) for different temperature ranges were derived from the data experimentally obtained. The obtained briquettes were heat treated at temperatures 1125 K and 1423 K. The toughness, physical and mineral structure of the heated briquettes, were investigated. It was established that the melting temperature of the investigated mixtures decreased by increasing the amount of calcium carbide.Item THERMODYNAMIC STUDY OF SOLID-PHASE REDUCTION OF POLYGRADIENT IRON-CONTAINING MATERIAL(2022-01-01) Grigorova D.; Paunova R.The studied iron ore material is a polygradient with increased content of manganese, barium, and lead. The thermodynamics of the reduction of this pelletized material, using the Electromotive force (EMF) method, has been investigated. Coke breeze and brown coal/lignite were used as reducing agents. The solid reducer was added in two ways - into the charge for the production of raw pellets and in the layer of the pellets and reducer, i.e. outside the pellets. The effects of pellets reduction and the ongoing temperature-dependent reduction processes were performed experimentally. Based on the experimental data, the equations Δ = f(T) of the studied pellets were derived. The stages of pallets heating, when the main solid-phase interactions and the possible reduction processes take place, were described. It was found out that, in the temperature range 933 K - 1213 K, the reduction of hematite to magnetite takes place as a priority. The barium and lead oxide are completely reduced. The macrostructure and phase changes were observed metallographically. The results showed that when adding the reducer into the composition of the pellets, up to 90 % degree of metallization was reached.