Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2000-11-29
2003-02-04
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S751000, C264S030000, C266S044000
Reexamination Certificate
active
06514312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of slag conditioners in steelmaking operations. The invention further relates to the use of slag conditioners to protect the basic oxygen furnace vessel linings used in a steelmaking operation and thus increase the life span of the BOF vessel lining. In particular, the present invention is directed to the use of recycled materials as slag conditioners to reduce the amount of raw materials needed and the amount and costs of waste disposal.
BACKGROUND OF THE INVENTION
Historically, steel production utilizes blast furnace iron and a scrap charge in a Basic Oxygen Furnace (“BOF”) or scrap melting in an electric arc furnace to produce steel for rolling or other processing into manufacturing stock. The BOF vessel is lined with a refractory coating that protects the steel wall of the furnace shaped vessel from the molten steel during the refining process. The refractory brick lining eventually wears away due to the constant bombardment from scrap charging and the corrosive nature of the molten steel-slag combination. Once the coating has eroded, it is necessary to reline the BOF vessel, which requires a shutting down of the steelmaking process at a significant cost of time and money. Thus, any increase in the life span of the refractory lining can greatly increase the efficiency and profitability of the steelmaking operation over the course of time.
One way to maintain the refractory walls of the furnace is through a process known as slag splashing in which a lance is used to blow an inert gas toward the slag layer. This causes the slag to be splashed upwardly onto the refractory walls and to coat portions of the refractory walls that have been worn. The slag cools on the refractory walls, effectively repairing worn portions of the walls. However, the slag splashing process can create other problems such as increasing build-up at the cone of the furnace of a mixture of molten metal and oxides, commonly known as skull. The formation of skull at the cone of the BOF is undesirable because it restricts the ability to lower lances and charge scrap into the cone of the furnace.
In the steelmaking process, fluxing agents or slag conditioners are often employed not only to provide consistency and/or viscosity to coat the BOF vessel during the slag splashing step but also to condition the molten slag layer to aid in the removal of impurities. Slag conditioners can also be used to promote the extraction of impurities from the molten metal bath and to further provide reactive substances for combining with impurities such as sulfur and phosphorus that migrate to and can be effectively extracted with the resultant slag layer.
The basic flux employed in iron and steel-making operations is lime or limestone, and particularly, “burnt lime” (CaO), which is effective to provide consistency/viscosity to coat the BOF vessel during the slag splashing step and to condition the molten slag upon dissolution therein. Sometimes lesser amounts of supplemental slag conditioners and fluxing agents such as fluorspar (CaF
2
) are utilized for increasing the fluidity of the slag and to further enhance the rate of dissolution of the lime and its chemical reactivity with the impurities present. However, the various prior art slag conditioning agents used to date have problems including reduced effectiveness and/or their relatively high cost and/or the difficulty associated in their handling and control of the chemistry of the molten bath.
An additional problem is that during the steelmaking process, large quantities of various waste materials containing iron bearing dusts and sludges are generated from pollution control devices such as bag houses, precipitators, cyclones, scrubbers, dust collectors, and the like. These waste materials are typically disposed of in a landfill due to the residual metal content that precludes their use in steelmaking operations. Currently, environmental regulations require the cleaning of these waste materials before disposal to remove these residual metals, such as zinc, lead and the like. These residuals metals can often be found in their oxide forms. However, de-zincing and other residual metal removal operations require a high capital expenditure for the necessary and complex equipment required to comply with these environmental regulations. For example, hydrocycloning can be used for de-zincing. However it is costly, and results in a zinc bleed that requires stabilization and landfill disposal. As described in U.S. Pat. No. 5,871,561, the zinc can be evaporated from a dust by heating under substantial vacuum in a furnace for 6 to 10 hours. Again, the capital equipment costs, time required, and the possibility of environments mishaps are high.
SUMMARY OF THE INVENTION
In accordance with the present invention, it has been found that residual metal containing waste material such as blast furnace filter cake (BFFC) can be used with considerable advantage in various facets of iron making and steelmaking processes.
In particular, the blast furnace filter cake and other residual metal containing waste materials can be utilized in a slag conditioner in the basic oxygen furnace of a steelmaking operation not only to reduce the amount of waste generated, but also, unexpectedly, to increase the life of the BOF vessel lining. This increased life allows a greater number of heats per lining cycle of the BOF vessel, thus reducing downtime, and increasing the efficiency of the steelmaking operation. This also results in recycling of residual metal containing waste materials in the steelmaking process, thus rendering the steelmaking process more environmentally friendly and decreasing the costs associated with cleaning and disposal of the waste material.
The BFFC is dewatered by admixing it with hot BOF slag for a period of time to allow the hot slag to cause water vaporization and reduce the moisture content of the BFFC/slag admixture to about 4% by weight. The resultant dewatered BFFC/slag admixture is utilized as a slag conditioner without the need for any binders or agglomerating agents or without the need to form briquettes or particles.
These and other objects and advantages of the present invention will be readily apparent in view of the following description and drawings.
REFERENCES:
patent: 5435832 (1995-07-01), Kepplinger et al.
patent: 5435835 (1995-07-01), Lynn et al.
patent: 5439505 (1995-08-01), Krofchak
patent: 5554207 (1996-09-01), Bogdan et al.
patent: 5573576 (1996-11-01), Krofchak
patent: 5772931 (1998-06-01), Farrand
patent: 5776226 (1998-07-01), Edlinger
patent: 5785737 (1998-07-01), Lynn et al.
patent: 5855645 (1999-01-01), Myerson et al.
patent: 5871561 (1999-02-01), Okada et al.
patent: 5992335 (1999-11-01), Nakamura et al.
patent: 6085672 (2000-07-01), Nakamura et al.
Fekete Richard V.
Lynn John D.
Smith Colvin W.
Andrews Melvyn
Bethlehem Steel Corporation
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