Manufacture of ferroalloys using a molten bath reactor

Details Manufacture of ferroalloys using a molten bath reactor Manufacture of ferroalloys using a molten bath reactor

1991-09-26

1994-04-12

Andrews, Melvyn J.

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

75502, 75623, C22C 3500, C22C 3818

Patent

active

053021843

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to the manufacture of certain ferroalloys by the addition of alloying metal-containing ores plus fluxing agents and solid carbonaceous reductants to a molten bath reactor. This invention also provides for the upgrading of the alloying metal to iron ratio of ferroalloys by oxidation and reduction refining operations.
In this specification, the term `ferroalloy` refers to ferrochromium, ferromanganese, ferronickel and ferrovanadium. The term `alloying metal` has a corresponding meaning, that is, chromium, manganese, nickel and vanadium, as have the terms `alloying metal-containing ores` and `alloying metal-containing material`. The latter, wider term includes alloying metal-containing ores or concentrates, or preheated alloying metal-containing ores or concentrates or preheated and prereduced alloying metal-containing ores or concentrates. The preferred alloying metal is chromium and the particular description refers to chromium to exemplify the invention.


BACKGROUND OF THE INVENTION

The conventional industrial method of manufacturing ferrochrome or charge chrome is in the submerged arc electric furnace. Chrome ore, reducing agent and flux are fed continuously into the smelting furnace. Fine feed material makes furnace operation difficult and can lead to large chromium losses. Hence fine feed materials are either avoided or agglomerated before charging. Optionally agglomerates of ore and reducing agent can be preheated and/or prereduced before being fed to the electric furnace. Fine feed materials can be used if they are firstly agglomerated; for example by pelletizing or by high temperature fusing.
In the electric smelting furnace, energy is supplied through carbon electrodes immersed in the charge. Gases, resulting from the reaction of ore and carbon deep in the furnace, flow upward and are released at the top of the furnace charge.
Often the furnace tops are closed with a water-cooled cover which has openings for electrodes and charge delivery. The cover permits the collection of the gases generated. Much of this gas consists of carbon monoxide, which can then be used as a fuel. In some installations the furnace top is left uncovered and the gases are burned at the surface.
Accurate weighing and proportioning of the feed materials is essential for the successful operation of the furnace. The feed above the reaction zone should be porous so as to permit the flow of product gases. Furthermore, the feed should be proportioned and fed in such a manner to allow the feed to descend freely into the furnace without bridging. Feed mixes of too large a particle size or particle size range are generally not used since they can be difficult to procure and cause furnace charging and bridging problems. They may also cause greater electrical resistance. However, too small a particle size in the feed mix can lead to losses by gas entrainment, low bed porosity and mix bridging.
The liquid slag and alloy products are drained from the furnace through a taphole either continuously or intermittently. The slag may separate from the alloy by decantation, skimming or bottom tapping of the receiving ladle. The ferrochrome product is then cast in chills.
Whilst this method of ferrochrome production is most widespread, it does present several disadvantages. Firstly, most or all of the energy requirements of the smelting process are supplied by electricity, which is an expensive form of energy. Secondly, the reductant requirements are met by using coke. Coke is a costly reductant, and is becoming more difficult to obtain as world supplies of coking coals are depleted and increasingly stringent environmental restrictions are placed on the operation of coke oven batteries. Thirdly, the feed particle size limitations preclude the direct use of cheaper fine-sized ore feed.
An alternative technology for the production of ferroalloys (including ferrochrome) which is now emerging is plasma carbothermic smelting reduction. This method has a number of advantages over the submerged arc furnace

REFERENCES:
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patent: 4259296 (1981-03-01), Hennion et al.
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patent: 4961784 (1990-10-01), Tanabe et al.
patent: 5050849 (1991-09-01), Hardie et al.
Moodie et al, "Numerical Modelling for the Analysis of Direct Smelting Processes", 1988, Process Technology Conference Proceedings, pp. 55-64.
Patent abstract of Japanese Published Patent Application, Pub. No. 58 104153, Pub. Date: Jun. 21, 1983.

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