Steel conversion method

#This invention relates to a pneumatic method of converting ferrous metal to steel.

#Pneumatic methods of producing steel from scrap and hot metal generally include blowing oxygen, air or mixture of oxygen and an inert gas, such as argon, into a metallic furnace charge for oxidizing such unwanted constituents as carbon, phosphorous and silicon. The oxygen or air can be delivered by tuyeres, the inner ends of which may be submerged or above the bath level. When submerged tuyeres are employed, they may be protected by a sheath of hydrocarbon shielding fluid injected in surrounding relation to the oxygen stream. It has also been suggested that oxygen may be introduced by tuyeres above the bath for the oxidizing of combustible off-gases whereby heat is added to the furnace charge. Such top tuyeres are shown, for example, in U.S. Pat. No. 3,839,017.

#While conventional top-blown systems are satisfactory for the production of ordinary low-carbon steels, they are not wholly satisfactory. For example, bath mixing in the top-blown process is relatively poor in comparison to bottom blown systems. As a result, the iron content of the slag tends to be relatively high, that is, in the range of 15 to 30%. Such slags tend to foam resulting in considerable furnace slop and loss of iron from the system. As a result of these and other disadvantages, there have been attempts to convert top-blown systems into submerged tuyere furnaces.

#The single FIGURE of the drawing schematically illustrates a metallurgical vessel in which the method of the invention may be practiced.

#The method of the invention may be carried out in the vessel 10 shown in the drawing, although those skilled in the art will appreciate that it is exemplary. The vessel 10 is generally pear-shaped in vertical section and includes a metallic shell 11 and a refractory lining 12. A plurality of tuyeres 13 extend through the lower end of the vessel and each includes an inner pipe 13a and a concentric outer pipe 13b spaced from the inner pipe to permit the injection of oxygen and a surrounding sheath of hydrocarbon shielding fluid as will be discussed more fully below. Converter vessels of the type illustrated are generally supported in a conventional manner by means of a plurality of peripherally spaced-apart brackets 14 which engage and are releaseably secured to a hollow trunnion ring 16 surrounding the vessel 10. Trunnion pins 18 extend from each of the opposite sides of ring 16 and are suitably supported in a well-known manner on conventional bearing structures (not shown) and one is coupled to a suitable drive mechanism (not shown) for tilting the vessel to each of a plurality of positions as may be required during a process cycle.

#The trunnion pins 18 may each have a hollow bore 22 for respectively receiving a gas delivery pipe 22 and a hydrocarbon shielding fluid delivery pipe 24. Additional pipes (not shown) may also be provided for delivering cooling water to the hollow trunnion ring 16 and other areas of the vessel, and in particular those portions adjacent its upper end. Pipe 22 is connected at its lower end to a first manifold 26 which in turn is connected to each of the central tuyere pipes 13a. Similarly, pipe 24 is connected at its lower end to manifold pipe 28 which in turn is connected by short feeder pipes 29 to the gap between tuyere pipes 13a and 13b. For a more detailed description of the manner of passing pipes 22 and 24 through trunnion pins 16 and 18 and of connecting the same tuyeres 13, reference is made to U.S. Pat. No. 3,810,297.

#The vessel 10 has an opening 30 at its upper end for receiving an oxygen lance 32. Disposed at the lower end of lance 32 is a nozzle 34 or a plurality of nozzles for projecting oxygen downwardly toward the furnace charge 36 and the slag layer 38 on its upper surface. In addition, sidewardly directed orifices 40 may be provided in lance 32 for projecting oxygen into the space 42 above the surface of slag layer 38. Lance 32 may otherwise be conventional and may be suitably cooled in any well known manner.