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The permanent control and continuous improvement of the ferrosilicon smelting process in the submerged-arc furnace is the primary task of the technological services and process management. This has a significant impact on the economic performance and competitiveness of the plant. This requires a precise definition and specification of all input and output components that affect the process technical and economic indicators. This procedure should be based on the identification of appropriately grouped components under the popular 6M principle (Man, Machine, Material, Method, Measurement, Management) presented in the form of Ishikawa cause and effect diagram. It is also useful to improve the process by the method of "small steps" in which employees of all levels participate (Kaizen method). The basic tool for improvement is statistical process control (SPC). The task of the SPC is to monitor parameters that are important for the physicochemical process and production results. Periodic material and energy balances of the process at discreet time intervals are also very useful. This allows us to monitor and provide information about the course of important parameters of the technological process and to respond quickly to irregularities.

Based on the minimum Gibbs Free Enthalpy algorithm (FEM), model of the ferrosilicon smelting process has been presented. It is a system of two closed isothermal reactors: an upper one with a lower temperature T1, and a lower one with a higher temperature T2. Between the reactors and the environment as well as between the reactors inside the system, a periodical exchange of mass occurs at the moments when the equilibrium state is reached. The condensed products of chemical reactions move from the top to the bottom, and the gas phase components move in the opposite direction. It can be assumed that in the model, the Reactor 1 corresponds to the charge zone of submerged arc furnace where heat is released as a result of resistive heating, and the Reactor 2 corresponds to the zones of the furnace where heat is produced by electric arc. Using the model, a series of calculations was performed for the Fe-Si-O-C system and was determined the influence of temperatures T1, T2 on the process. The calculation results show a good agreement model with the real ferrosilicon process. It allows for the determination of the effects of temperature conditions in charge zones and arc zones of the ferrosilicon furnace on the carbothermic silica reduction process. This allows for an explanation of many characteristic states in the ferrosilicon smelting process.

The electric arc is one of the most unstable parts of the electrical circuit of submerged-arc furnaces in the ferrosilicon smelting process. In the carbothermal silica reduction electric arc has an important role as a high temperature heat source, and its presence is essential for the proper ferrosilicon process flow. Presence of the of electric arc and temperature conditions of the ferrosilicon process have a direct relationship with position of the electrodes tip and electrodes slipping. In the ferroalloy industry position of electrodes tip as similar as metallurgical parameters of the process are not directly measured. Most often these assessments are still based to a large extent on intuition and experience operating staff of the furnaces, and have qualitative and subjective character. In order to check the existing algorithm of electrodes slipping was carried out statistical studies of the FeSi75 ferrosilicon smelting process. The study was conducted at discrete intervals ∆t = 8h using data recorded by the furnace computer measuring system and methods of statistical data processing. It was found that the size of the electrodes slipping, and Cfix ratio in the feed are correlated and are among the most important parameters which have an impact on the technical and economic indicators of the process.

Selection of reducing agents for the ferrosilicon smelting process requires consideration of several difficult to reconcile criteria. The carbon reducers are not only a source of carbon as a substrate of the silica reduction reaction, but also play an important role by acting as a gas filter at the upper zones in working space of the ferrosilicon furnace. Reactivity of carbon reducers to SiO and degree of conversion on the SiC carbide are directly affecting the silicon recovery as well as the efficiency of the ferrosilicon process. The simultaneous fulfillment all requirements are difficult to satisfy by using only one type the reducer in the charge for the ferrosilicon process. This requires the use of a mixture reducers, and the adoption of a compromise that all requirements are met in the best possible extent. To choose the composition of carbon reducers mixture has been used simple physico-chemical model of the ferrosilicon process with two reaction zones between which there is a mass transfer. It has been shown that in the charge for the ferrosilicon furnace about 30% mass of Cfix carbon resulting from the reaction stoichiometry of silica reduction process should be in the form of the reducer with increased to SiO reactivity.

The most objective methods of determining the usefulness of quartzite for the ferrosilicon smelting process are industrial research methods, but such studies are long-lasting and costly. In order to test the usefulness of thermo-gravimetric method to evaluate technological properties of quartzites in a laboratory, thermo-gravimetric studies of quartzites samples from various deposits were carried out. These quartzites are used or were used as a raw material in industrial ferrosilicon process. The study consisted of measuring the weight loss of powder samples in the form of mixture of quartz with graphite of molar ratio SiO2 + 3C during heating under an argon atmosphere in the temperature range up to 1500°C. The evaluation of technological properties of quartzites was done by comparing the curves of relative weight loss with industrial technological data of the ferrosilicon smelting process. It was established that the results of thermo-gravimetric studies show satisfying agreement with observations of industrial process, whereas quartzites of improved technological properties revealed a lower weight loss in thermo-gravimetric studies. Studies of this type can be useful as one of the methods of objective assessment of usefulness of quartzites for the ferrosilicon smelting process.

Based on the electrical parameters of a 20 MVA ferrosilicon furnace, a methodology of identification of characteristic ferrosilicon smelting states described as carbon excess and carbon deficiency in the reaction zones ('over-coked', 'under-coked') has been presented. Relations between the electrical parameters and assessments made by furnace operators regarding characteristic furnace states related to amounts of carbon in the reaction zones have been demonstrated. The results show that the reactive power measurements as well as the k, c3 (Andreae’s, Westly’s) parameters, provide the same information on the furnace state and have a close relation with resistivity of the current-conducting zones. Similar information on the level of carbon balance in the reaction zones is obtained from the harmonic analysis of phase voltages and currents or measurements of higher harmonic components using high-pass filters.

The classical models to optimize the batch of electric arc furnace require precise and predetermined numerical values. In order to determine the scrap steel properties (eg. chemical composition), we are not able to define these values precisely and accurately. This situation is due to the heterogeneity and specificity of this material, which is related to its origin and way of obtaining. Therefore the usefulness of classical models to optimize the batch of electric arc furnace is limited. The fuzzy numbers with trapezoidal membership function were applied as a model in order to describe the technological process of steelmaking, which is neither accurate nor of ambiguous nature of the parameters. The advantage of trapezoidal numbers is a simple algorithm of arithmetic operations as well as easy and intuitive interpretation. The structure of optimization model with fuzzy parameters is similar to the classical linear optimization model of the mixtures composition. The optimization model, that is formulated on the fuzzy ranges arithmetic principles, allows to ensure that the quality parameters of the batch mix for the electric arc furnace are as precise as the ones described by electro-steel works, even though the quality parameters of scrap steel as well as some of the parameters of steel melting technological process are described ambiguously.

Based on the Minimum Gibbs Free Enthalpy algorithm (FEM) and a model of reaction zones located around electrode tips in the submerged arc furnace, an analysis of the raw material chemical composition influence on the ferrosilicon smelting process was carried out. A model of the ferrosilicon process in the submerged arc furnace is a system of two closed isothermal reactors: an upper one with a lower temperature T1, and a lower one with a higher temperature T2. Between the reactors and the environment as well as between the reactors inside the system, a periodical exchange of mass occurs at the moments when the equilibrium state is reached. Based on the model, sets of calculations were performed: for a Fe-Si-O-C system and, subsequently, for a more complex Fe-Si-O-C-Al-Ca-Mg-Ti system. For both systems, the energy and mass balance values were calculated and the effects of raw material contaminants on the efficiency of the ferrosilicon melting process were determined.

Based on archival temperature measurement data regarding a blast furnace (capacity of 3200 m3) hearth and bottom refractory lining, empirical isotherms T = 300°C, for various periods of the first five years of the furnace campaign were determined. This resulted in an attempt to assess the hearth and bottom refractory lining in the third month and subsequently, in the next years of the blast furnace operation. The empirical isotherms, determined after the first three months, were compared to the isotherms determined using the method of mathematical modelling. These empirical isotherms were compared to each other, respectively in one-year intervals. The most distinctive changes of the hearth and bottom refractory lining were observed during the first three months of the furnace campaign. In the further period of five years, the changes were insignificant. During the early stage of furnace operation, observed deterioration of the refractory lining was associated with partial damage of the bottom ceramic layer and elephants foot-shaped defects of the refractory lining in the lower, thickened parts of the hearth walls. Early, elephants foot-shaped wear of the refractory lining is related to the mechanism of its wash-out by liquid products of the process during tapping, which results from certain maladjustment of the hearth and bottom inner geometry in modern furnaces to the hydrodynamic conditions of metal and slag flow.