The present invention relates generally to steel production and, more particularly, to a method for the recovery of iron units from flue dust generated in a steel making process.
In the production of steel in an electric arc furnace or any other type of steel making furnace, a considerable amount of iron-bearing dust or fume is generated. A generally accepted method of capturing the fume or dust to meet environmental obligations is through a dry collection system, whereby the very fine dust is separated from the effluent air in a pollution control apparatus, such as a baghouse filtration system. The disposal of the collected dust presents an ever increasing problem and it has become mandatory to find suitable environmentally accepted methods of dust disposal. However, the collected dust must be put in a form that will show no signs of degradation over a period of time, to prevent any adverse reaction with the environment and to avoid contamination of the surrounding air, water or soil.
There currently exist a wide variety of proposed solutions to the disposal problem, but none of these proposals have proven to be acceptable to the steel making industry. One approach proposed re-utilization of the iron or Fe units contained in the collected dust and suggested placing the collected dust into a stable form which can be recycled back into the furnace for recovery of the Fe units. This approach specifically involved the preparation of stable, green pellets from the collected dust, the handling of the pellets and the charging of the pellets into the furnacing operation.
Processes and methods for making such green ball pellets from the dust or fume generated in the steel making process are generally well known in the art and one such method is described in U.S. Pat. No.4,003,736, issued Jan. 18, 1977, to Kreiger et al. and entitled "Method for Preparing Dry-Collected Fume for Use in Metallurgical Furnaces", which is incorporated herein by reference. In addition, numerous articles have been published on the subject of making such green ball pellets. Although the prior patents and publications detail the methods and processes for the preparation of the green ball pellets, the known prior art is devoid of any specific teaching concerning how to successfully recycle or reuse the green ball pellets into a furnace for the recovery of the iron units contained therein.
Various prior art methods have suggested charging the green ball pellets into a basic oxygen furnace or an open hearth furnace. Primarily, these methods involve merely dumping the pellets into the furnace. Although dumping the green ball pellets directly into an open hearth or basic oxygen furnace is an inexpensive and convenient way to dispose of the green ball pellets, it has been found that the recovery of the Fe units by this method has not accomplished the desired result and this method of recycling merely increased the amount of fume or dust generated in the steel making process. In addition, the "dumping" methods employed in connection with the basic oxygen furnace and open hearth furnace are not susceptible to successful utilization in connection with an electric arc furnace.
The present invention overcomes the deficiencies of the prior art methods for recycling the flue dust generated in a steel making process and for recovering the iron units contained in the dust by providing an improved method for the handling and placement of the green ball pellets in the furnace charge of an electric arc furnace. By employing the method of the present invention the problem of disposing of the collected flue dust is solved and, in addition, valuable steel making material is recovered from the collected dust and added to the furnace melt, thereby adding of the economy of the steel making process.
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USPTO Backgrounds