Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1994-08-29
1995-11-14
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 1047, C21C 102
Patent
active
054662753
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This application corresponds to German Patent No. P 42 06 091.5 filed Feb. 27, 1992 and claims priority to that date under the Patent Cooperation Treaty and Paris Convention.
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for desulphurizing iron with minimal slag formation. Molten pig iron coming out of the blast furnace usually contains about 0.03% to 0.08% sulphur. Depending on the purpose of the final product, the sulphur content of the molten pig iron or "hot metal" is usually reduced to a range of from 0.01% to 0.005% by various desulphurization methods before further processing in the steelworks.
Prior art methods of desulphurizing pig iron include the use of carbide-containing desulphurizing agents or, to an increasing extent, mixtures containing metallic magnesium. Soda desulphurization is also common. Iron desulphurization according to these methods forms large amounts of sulphur-containing slags also containing about 50% iron. A large blast furnace producing 10,000 tons of pig iron per day produces about 300 tons of this waste, iron-containing desulphurization slag. Recovery of the iron from this slag is labor-consuming and expensive.
Disposal of large amounts of this waste slag is also a serious problem. Because the slags contain sulphur-compounds, they emit toxic and ill-smelling hydrogen sulfide gas when exposed to water. Moreover, these waste slags can also contain unreacted carbide, which releases toxic and explosive acetylene gas when exposed to water. A primary solution has been use of very expensive, wet-chemical techniques for processing these slags, such as that disclosed in German Patent DE 3837249 A1.
A further problem with prior art desulphurization techniques is that, in addition to producing large amounts of slag, these processes utilize an immersion lance to inject the desulphurization mixtures in the torpedo or the charging ladle. Injection of the desulphurization mixture causes a considerable temperature drop in the hot metal, which if not carefully controlled, may cause large amounts of pig iron to solidify causing considerable financial loss.
Accordingly, a principal object of the present invention is to provide an iron desulphurizing method and apparatus that produces little or no sulphur-containing slag to be processed or disposed, and which does not require precise control to avoid causing the molten iron to solidify.
Another significant object of the present invention is to provide an iron desulphurizing method that docs not require expensive desulphurizing agents such as carbide or magnesium.
SUMMARY OF THE INVENTION
According to the present invention, desulphurization is accomplished by melting and heating, to a temperature of about 1400.degree. to 1800.degree. C., a slag having the following chemical composition: CaO plus MgO divided by the percentage by weight of SiO.sub.2 plus one-half the total percentage by weight of Al.sub.2 O.sub.3 is at least two--i.e. ##EQU1## and where the ratio of the percentage by weight of Na.sub.2 O plus K.sub.2 O to SiO.sub.2 is no more than one--i.e. ##EQU2## plus other trace impurities. The sulphur-containing hot metal is desulphurized by mixing it with this bath of molten slag and allowing the purified molten iron to be drawn from underneath. The process may be accomplished using a low shaft furnace according to the present invention comprising a furnace body lined with carbon bricks or carbonaceous, basic or high-alumina refractory bricks and having a discharge pipe extending down to the bottom of the furnace chamber for discharging the purified molten iron.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, aspects, features and attendant advantages of the present invention will become apparent from a consideration of the ensuing detailed description of presently preferred embodiments and methods thereof, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is an cross section of a low shaft furnace according to the prese
REFERENCES:
patent: 3802865 (1974-04-01), Ohkubo
patent: 4534791 (1985-08-01), More
Metals, vol. 2 #20, Jan. 1968, p. 51.
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