Processes in the Charge and Hearth Zones of Furnace Working Spaces and Problems in Controlling the Batch Dosing Mode dur
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PROCESSES IN THE CHARGE AND HEARTH ZONES OF FURNACE WORKING SPACES AND PROBLEMS IN CONTROLLING THE BATCH DOSING MODE DURING THE SMELTING OF INDUSTRIAL SILICON AND HIGH-SILICON FERROALLOYS A. V. Sivtsov,1 K. S. Yolkin,2 I. M. Kashlev,3 and A. I. Karlina4
UDC 669.16
This study describes the conversion processes of charge materials and the chemical processes in the charge and hearth zones of furnaces that smelt industrial silicon and high-silicon ferroalloys. The primary factor that determines the efficiency of the charge mode and the technological process is the coefficient of excess carbon in the furnace bath. The fluctuations in the effective capacity of the furnace; its distribution over the zones of the arc, charge, and melt; and the active resistances of these zones are caused by the regular deviations of this coefficient from unity. Such deviations are induced by uncontrolled changes in the humidity of the reducing agents. Carbon deficiency and excess modes affect the state of charge and melt zones and the distribution of electric energy on the arc discharge power. Transient processes that occur when the composition of the charge on the dosing unit is changed, as well as the direct supply of the reducing agent to the furnace mouth and reflecting changes in the charge zone conductivity, are studied. Results reveal that transient processes are accompanied by high material and energy losses and their duration, depending on the volume of the bath and the effective capacity of the furnace, can exceed 4 h. On the basis of the analysis of the changes in charge conductivity and arc power, the negative consequences of the layer-by-layer charge loading method adopted for smelting industrial silicon are presented; these consequences are based on the alternation of charge supply, with an excess and shortage of the reducing agent. In the absence of reliable methods for the continuous monitoring of the moisture content of reducing agents in the charge stream, the coefficient of carbon excess must be evaluated by changing the resistance of the melt zone, which reflects changes in the size of the carbide layer that is formed due to the imbalance of silicon carbide and silicon monoxide. Such evaluation can determine the degree of imbalance of the reducing agent in the mixture and apply the currently required control effect on the composition of the charging material in a timely manner. Keywords: silicon, silicon reduction, ore-thermal furnace, industrial silicon, process control in the charge, furnace bath, electric mode of the furnace, control of the furnace mode.
In any electrothermal technology of carbothermal metal reduction, the properties of charge materials, particularly the electrical conductivity of carbonaceous reducing agents (such as coke, semicoke, charcoal, and mineral coal) are emphasized. An important factor is ash content. The requirements for this parameter are much stricter in the production of industrial silicon compared with that in the production of ferroalloys. The stability of the properties of the char
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