Abstract:
A method of removing slag and/or steel build-up from lances in steel making furnaces includes blasting dry ice (solid CO 2 ) pellets on to a hot lance as it is being drawn out of a furnace. A refractory or ceramic coating may be applied to the lance while it is being inserted into the furnace.

Description:
RELATED APPLICATION 
     This invention claims priority from U.S. provisional patent application No. 60/041,196 filed Mar. 25, 1997. 
    
    
     FIELD OF INVENTION 
     This invention relates to the removal of slag and/or steel build-up from lances in steel making furnaces, such as basic oxygen furnaces, in which a lance is used to supply oxygen to the furnace. 
     BACKGROUND OF INVENTION 
     Although various attempts have been made in the past to provide a method of removing slag and/or steel build-up from such lances, none of the prior attempts have been particularly successful, particularly since the 1980&#39;s when introduction of a new technique in which slag is splashed onto the walls of the furnace made the problem worse. U.S. Pat. No. 5,152,952 (Brenczek et al) issued Oct. 6, 1992 is an example of the prior art. 
     It is therefore an object of the invention to provide an improved method for removing slag and/or steel build-up from such lances. 
     STATEMENT OF INVENTION 
     According to the present invention, dry ice (solid CO 2 ) pellets are blasted onto a hot lance as it is being drawn out of a furnace. Also, a refractory or ceramic coating may be applied to the lance while it is being inserted into the furnace to minimize the build-up. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic plan view of an arrangement for blasting CO 2  pellets onto a lance in accordance with one embodiment, 
     FIG. 2 is a side view of the arrangement of FIG. 1, 
     FIG. 3 is a diagrammatic plan view of an arrangement for spraying a refractory or ceramic coating onto the lance in accordance with another embodiment, and 
     FIG. 4 is a side view of the arrangement of FIG. 3. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIGS. 1 and 2 of the drawings, a water-cooled lance 10 is sprayed with dry ice (solid CO 2 ) pellets from nozzles 12 as the lance 10 is being withdrawn from a basic oxygen furnace. There are six nozzles 12 equi-angularly spaced around the lance 10 and oriented such that the dry ice pellets impinge on the lance 10 at an angle in the range of from about 30° on one side of a plane perpendicular to the longitudinal axis of the nozzle 10 to about 30° on the opposite side of the plane, although preferably in the range of from about 15° on one side of the plane to about 15° on the opposite side of the plane (as indicated in FIG. 2). 
     The dry ice pellets are sprayed from the nozzles 12 in a high velocity air stream, preferably supersonic, at a pressure in the range of from about 50 to about 300 psi, preferably in the range of from about 90 to about 250 psi. The nozzles 12 should preferably be at a distance from the lance 10 in the range of from about 1 to about 6 inches, more preferably in the range of from 1 to about 4 inches. In practice, the number of nozzles 12 will depend on the diameter of the lance. The lance 10 should be blasted while it is at an elevated temperature, preferably above about 250° F. 
     Referring now to FIGS. 3 and 4, the lance 10 is sprayed with a refractory or ceramic coating as it is being lowered into the furnace to minimize subsequent buildup, the coating being sprayed onto the lance 10 from nozzles 16 carried by a coating supply ring 18 extending around the lance 10. It will be noted that the nozzle 16 and supply ring 18 are also shown in FIG. 2. The refractory or ceramic coating should be of the kind which will withstand temperatures of the order of 3000° F., and the coating system should be regularly cleaned, i.e. the nozzles 10, supply ring 18 and associated piping (not shown) should be routinely purged by passing a cleaning solution such as water or a suitable solvent therethrough. As shown, the nozzles 16 are positioned in an annular configuration, the number of nozzles being dependent on the diameter of the lance. 
     In use, the lance 10 is blasted with CO 2  pellets as it is being raised from the furnace, and is coated with a refractory or ceramic coating as it is being lowered into the furnace. The CO 2  pellet blasting and the application of the coating may be effected as often as necessary, and may be effected each time the lance 10 is raised and lowered from and into the furnace. The lance 10 should of course be coated prior to the first use. Suitable coatings are DAG 193 or DAG 395, manufactured by Acheson Colloids Company of Port Huron, Mich., U.S.A., which are normally used as permanent mold coatings and act as a releast agent. 
     Since the lance 10 will still be glowing red as it is being withdrawn from the furnace, the chilling action of the dry ice along with the rapid increase in gas volume generated causes the slag and/or steel build-up on the lance 10 to crack and fall back into the furnace. 
     Other embodiments of the invention will be readily apparent to a person skilled in the art. For example, the invention may be used with an electric arc furnace. Also, the lance may move vertically, horizontally or at any other required angle into and out of the furnace concerned. Further, there are other ways of blasting the CO 2  pellets onto the lance, for example by means of a centrifugal pellet blaster. The scope of the invention is defined in the appended claims.