Specialized metallurgical processes – compositions for use therei – Compositions – Solid treating composition for liquid metal or charge
Patent
1996-03-13
1998-12-22
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Compositions
Solid treating composition for liquid metal or charge
75 105, C22C 3304, C22C 3500
Patent
active
058512640
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for production of ferrosilicon, according to the introductory of claim 1, and agglomerates for use in said method.
TECHNICAL BACKGROUND
In the production of ferrosilicon in an electric reducing furnace, quartz, a carbonaceous reducing agent, which can comprise coke and coal, is charged, and usually char coal or wood chips. The iron components are usually charged as iron oxide pellets, and in some particular cases as particularly selected scrap iron.
The reduction of the silicon component, quartz (SiO.sub.2), occurs in two steps. The first oxygen molecule is removed by reacting the quartz with a carbonaceous component to form CO and SiO,--a gas which is stable at elevated temperatures. A substantial part of the energy supplied to the reduction furnace is consumed to effect the removal of this oxygen molecule and form the SiO gas:
In this technical field it is an acknowledged opinion that in order to obtain an energy effectice production of ferrosilicon, the gas must be conserved or kept inside the furnace. This is typically performed by two reactions; in the upper part of the furnace SiO reacts with C from the reduction materials for the formation of silicone carbide. If reducing agents having high reactivity with respect to gaseous SiO is used, the reaction occurs until all free carbon has been comsumed to form carbide: phases which results in a worsened operation of the furnace: formation of silicone or ferrosilicon and CO gas, or ferrosilicon if iron is present:
Farther down in the furnace, SiC in reactant mass flowing downwards contacts a gas having a higher content of SiO an less CO. Thus, the chemical equilibrium allows for conversion of more SiO gas to Si or FeSi from the reaction with SiC and iron flowing downwards.
The chemical equilibrium conditions promise reaction of only a limited amount of the gaseous SiO to form Si or FeSi. These reactions occur, according to persons skilled in the art, in the lowest and hottest part of the melting furnace.
Some SiO gas will usually pass the carbon ureacted, and in part there will be to little free carbon to support the reaction with the gaseous SiO flowing upwards towards the top of the furnace. Some of this gas can however condense and liberate heat to the charge in the upper parts of the furnace and effect heating of the same. The amount of condensing SiO gas-at the upper parts of the furnace will decrease with increasing temperature in the furnace top. A simlified progress of such condensation is as follows:
The portion of the gas which remains un-condensed will however flow out of the furnace to the environments and oxidize to form silicone dioxide, and will in this way result in loss of mass and energy from the process. The yield with respect to elementary silicon from such a process is, when the process is run at equilibrium, limited to about 11 percent. If the furnace is charged with SiO.sub.2 in excess to consume SiC, the yield of elementary silicone can be increased to 19.2 percent. This yield at equilibrium can be further increased, to about 32 percent, by allowing the carbon component in the charge to react with the gaseous SiO leaving the furnace to form SiC and CO.
In practice, such processes are however not run at equilibrium in the silicone producing part of the furnace, whereby the yield with respect to elemental silicone is increased to 85-94 percent. The remaining of the silicone component charged to the process is lost as SiO gas or evaporated silicone.
We are familiar with experiments with iron containing coke for the production of ferrosilicone at the end of the 1960's. This project was not continued since the experiments failed to exhibit the properties as performed by the material used in the present invention.
OBJECT
The main object of the present invention is to provide a method and a means to increase the Si yield further by the production of ferrosilicon, and thus decreasing the energy and material consumption in such production.
THE INVENTION
We have surprisingly discovered that if
REFERENCES:
patent: 3759695 (1973-09-01), Downing
Andrews Melvyn
Sinvent AS
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