Metallurgical apparatus – Process
Patent
1992-03-20
1993-10-12
Kastler, Scott
Metallurgical apparatus
Process
266225, F27D 316
Patent
active
052518795
DESCRIPTION:
BRIEF SUMMARY
This invention provides an improved top submerged lancing system and an improved method for top submerged injection of fluid in a pyrometallurgical operation.
Top submerged lancing provides a method of injecting gas into a pyrometallurgical bath wherein the gas is injected through a lance having an interior duct for flow of gas therethrough and a discharge end at which the gas is discharged. Such method is disclosed in U.S. Pat. No. 4,251,271 issued 17 Feb. 1981 to Floyd. The method disclosed by Floyd is characterized by the steps of presenting the discharge end of the lance to a molten bath of slag, forcing gas through the lance to cool and splash-coat the discharge end of the lance with molten slag, and inserting the thus coated discharge end of the lance into the pyrometallurgical bath. Also disclosed is a lance for submerged injection of gas into a liquid pyrometallurgical bath comprising a duct for flow of gas longitudinally through the lance characterized in that the outer wall of the duct is defined by an elongate tube constituting an outer wall of the lance, with a gas flow swirler means being provided within the tube to impart swirl to gas passed through the duct.
The lance disclosed in U.S. Pat. No. 4,251,271 (hereinafter referred to as the Sirosmelt lance) has allowed the development of a wide range of metallurgical processes using a slag bath as a heat and mass transfer medium for submerged combustion and metallurgical process reactions. Examples include smelting, fuming and slag treatment processes to recover tin, lead, zinc, nickel, copper, precious metals and other valuable metals from ores, concentrates, slags, fumes and waste materials.
In practice the operation of the Sirosmelt lance gives many advantages over other metallurgical processes and, as a result, systems using the Sirosmelt lance have become accepted as efficient and cost effective. However the operation of the Sirosmelt lance has certain limitations which cause its use to be problematical for operators. The tip of the lance is subject to wear, and lance removal is required on occasions to replace the tip of the lance. The use of high-temperature steels or other special materials for the tip can be beneficial in prolonging its life, but tip repairs are an essental part of the maintenance of systems using the Sirosmelt lance. The base cause of this tip erosion is the fact that the gases passing through the lance become too hot to prevent reaction between the material of the lance and the bath content or the injected gas. Under some conditions, tip wear can be so severe as to necessitate use of several lances in succession in each shift of operation.
For steel lance tips it is found that the gases must be maintained at temperatures below about 400.degree. C. for many operations to avoid the wear. There are certain circumstances where it is not possible to maintain temperatures below 400.degree. C. in the gases because the quantity of heat transferred through the outer wall of the lance is too great for the quantity of gas flowing through the lance. The quantity of heat flowing through the lance wall is proportional to the heat transfer rate through the slag coating and lance wall, and also proportional to the outer surface area of the lance. The quantity of gas passing through the lance is determined by the process requirements. Thus the design of a lance for a particular application is constrained by the gas flow rate for a given operating regime and the total outer surface area to prevent lance tip wear.
The lance operating regimes which cause lance tip wear problems are as follows:
1. Use of a lance in a furnace where a large height above the bath is needed and limited gas flowrate is needed. An example of this is the use of a lance in an Outokumpu flash furnace for removing furnace accretions. The gas flowrate useable may be limited by the degree of splashing which can be accepted without causing undue wear of roof refractories, which are not designed for splashing contact with slag. Thus there is not enough gas injected to c
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Abstract Accession No. 84-167341/27 re JP-A-59-089710 (Kawasaki Steel KK) Nov. 11, 1982 "Simultaneous Increase of Scrap Rate and Metal Yield in the BOF in Combination with Bath Stirring" by Kreijger.
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