New Segregation Method of Sic During Carbo-Thermal Silica Reduction

The focus on SOG-Si for solar cell production have been increased in the recent years. A low cost Si requires a production with less electric energy used, less impurities and fast process. Reducing C presence in Si ingots generally is necessary. In the present work, we attempted to develop a new method to segregate SiC from the bulk Si by means a new shape of ingots that we designed. We have used a conventional induction furnace for this process. A comparison study between 2 shapes of graphite ingots was performed. We have succeeded in segregation of SiC from Si during the carbo-thermal reduction process of silica. the results revealed that The first ingot contained 34.3% of SiC while the second ingot had 100% of Si from about 13mm distance from the ingot bottom.

Comparison the Physico-Chemical Model of Ferrosilicon Smelting Process with Results Observations of the Process under the Industrial Conditions

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.

Selection of Carbon Reducers for the Ferrosilicon Smelting 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.

Importance of Electrodes Slipping Algorithm for 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.

Usefulness of Quartzites for the Production of Ferrosilicon

The selection of quartzites most suitable for the production of ferrosilicon is realized by way of time-consuming industrial trials or laboratorial studies of, among others, the ability of the silica contained in quartzite to form silicon carbide with a selected reducer. Under industrial conditions, the basic criterion for the evaluation of the suitability of a raw material for the production of ferrosilicon are the technical and economic indicators of the process. Under laboratorial conditions, simple and reliable research methods are searched for, which would allow to determine the usefulness of quartzite in the process of carbon silica reduction. The article discusses comparative thermogravimetric studies as well as alternative investigations of the specific heat of three selected quartzites which fulfill the chemical composition criterion, used in the mixed charge as raw materials for ferrosilicon FeSi75 smelting.

Analysis of the Possibilities Using of the Post-Reaction Gases Enthalpy from the Ferrosilicon Smelting Process

The paper presents an analysis of the possibilities of using the enthalpy of post-reaction gases from the ferrosilicon smelting process to produce electricity. Ferrosilicon smelting in the submerged arc furnace is one of the most energy-consuming electro thermal processes. Post-reaction gases, generated during the silica reduction process with carbon, contain significant amounts of energy. In the past the issue of energy recovery from the ferrosilicon process has been repeatedly taken, but for the Polish ferroalloy industry it is still valid. In order to determine the amount of energy possible for recovery calculations based on mass and energy balances has been carried out and determined the stream enthalpy of post processing gas. For preparing the balance sheets has been used operational data from the 20 MVA furnace and the overall reaction of the silica reduction process. It was assumed that the reduction process occurs at a temperature of 1650°C, and the temperature of leaving post-reaction gas, whose main ingredients are oxides CO and SiO, is 750°C.