FIELD OF THE INVENTION

The invention concerns the field of metallurgy, more specifically, equipment for the post combustion of the atmosphere gases in smelting installations.

BACKGROUND OF THE INVENTION

The term "post combustion" is also known in the art as "after-burning".

Therefore, these terms will be used interchangeably in this application.

A known method for post combustion of combustible components in the atmosphere in steel smelting vessels includes, feeding a jet of oxygen through an oxygen lance into the working space of the steel smelting unit (vessel) above the level of the metal in the vessel. In this method, the oxygen is fed through an apparatus having several rows of outlets in the form of jets which are aimed in a direction which is inclined with respect to the horizontal plane. The outlets are positioned at different levels in the vessel or furnace.

The apparatus includes an oxygen lance in the form of concentric pipes for the introduction of oxygen into the vessel, and for providing cooling water for the apparatus. At the discharge end of the lance apparatus and extending along its length, blowholes are positioned for the oxygen, in the form of jets, to exit the lance. Such a device is shown by E.D. Merker in his publication "Gas Dynamic Protection ofthe Blasting Zone in Steel Smelting Installations," Moscow, Metallurgiya, 1994, at page 20, Figure 5.

A disadvantage of using the known device is the low efficiency seen in both the process of post combustion (after-burning) of the gases evolving in the steel smelting unit and in the creation of a gas dynamic curtain.

Due to the fact that the jets are discrete entities, the necessary intermixing of the furnace atmosphere with the oxygen jets does not take place.

Moreover, when the known method and device are used, the heat evolving during the after-buming of the combustible components is not returned to the molten metal. The discrete feeding of oxygen in separate jets does not create a continuous gas dynamic curtain over the metal bath. Under these conditions the efficiency of after-buming of the combustible components will not exceed 50-60%.

US Patents 5,050,848 and 5,051,127 disclose an apparatus and method for post combustion over a molten bath using a swirling gas flow by means of one or more tuyeres directed at the surface of the metal.

US Patent 5,166,950 discloses a process for post combustion (after- burning) in a metallurgical furnace.

European Patent Publication 0 544 044 A1 discloses another post combustion process.

SUMMARY OF THE INVENTION

A lance assembly for introducing an oxidizing gas, e.g. pure oxygen has a first or oxygen delivery end and a second or oxygen supply end. The oxygen delivery end contains at least one outlet for delivering oxygen into a metallurgical vessel. Spaced apart (toward the supply end) from the delivery end of the lance are at least two apertures for delivery of oxygen in a direction generally peφendicular to the longitudinal axis of the lance. Disposed around the lance and positioned to

communicate with the two apertures in the side of the lance is a radiant injector with a funnel- (conically-) shaped diffuser and a capped cylindrical section surrounding the apex opening in the funnel-shaped diffuser. The capped cylindrical portion contacts the lance so that oxygen exiting the side apertures strikes deflection plates (e.g., baffles and vanes) disposed in the capped cylindrical portion of the radiant injector.

When installed on the lance the funnel-shaped diffuser of the radiant injector is positioned so that the mouth (opposite the apex) faces the first end of the lance. The lance with the radiant injector can be installed in a metallurgical vessel, e.g., electric arc furnace, basic oxygen furnace, reverberatory furnace, rotary furnace or the like, used to smelt and/or refine metals by placing the assembly in a roof, wall or other opening in the furnace so that oxygen can be directed toward the metal in the furnace. Oxidizing gas (e.g., oxygen) introduced into the lance is directed at the metal in the vessel (furnace) and at the deflection plates in the diffuser. Oxidizing gas directed at the deflection plates is caused to swirl and expand along the inner surface of the funnel-shaped diffuser. The swirling oxidizing gas reacts with the combustible components in the furnace gases to effect after-burning or post- combustion. As after-burning proceeds, the diffuser becomes hot and is a source of radiant heat to be directed at the metal in the vessel.

The lance and/or radiant injector can be constructed of metal and provided with water cooling, however, the portion of the diffuser facing the metal must be coated with a high temperature refractory material. Altematively, the diffuser can be fabricated from a refractory material by well known techniques such as casting.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a longitudinal section through a device according to the invention.

Figure 2 is a view taken along lines 2-2 of Figure 1.

Figure 3 is a longitudinal section through a device representing an altemate embodiment of the present invention.

Figure 4 is a view taken along lines 4-4 of Figure 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, the lance assembly according to the invention, which is shown generally as 10, includes lance 12 and radiant injector 14.

Lance 12 has first or oxygen delivery end 16 and second or oxygen supply end 18, which is not shown, since technology for delivery of oxygen to a lance is well known. Lance 12 includes at least one and preferably a plurality of oxygen delivery ports 20 and 22 at oxygen delivery end 16 for directing a supply of oxygen toward the metal contained in a metallurgical furnace. Oxygen is delivered to ports 20 and 22 via oxygen passage 26 formed by manufacturing lance 12 from a series of concentric tubes or pipes as is well known in the art. Disposed upwardly toward the oxygen supply end 18 of lance 12 are a plurality of apertures 28, 29, 30 and 31 which communicate with oxygen supply passage 26 and are adapted to introduce oxygen peφendicular to the longitudinal axis of lance 12. Lance 12 includes central passage 32 and concentric passage 34 for introducing and removing cooling water in lance 12.

Radiant injector 14 comprises funnel-shaped diffuser 35 and capped cylindrical portion 38 disposed around lance 12 at a location so that the capped cylindrical portion 38 of radiant injector 12 surrounds oxygen apertures 28, 29, 30, and 31. Disposed inside of capped cylindrical portion 38 are deflection plates (e.g., baffles or vanes) 40, 42, 44 and 46, these plates being juxtaposed to oxygen apertures 28, 29, 30 and 31, respectively. The puφose of deflection plates 40, 42,

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44 and 46 is to contact and direct the oxygen inside of capped cylindrical portion 38 so that a swirl of oxygen is created within capped cylindrical portion 38 which expands downwardly and outwardly along interior wall 37 of funnel-shaped diffuser 35. As shown in Figure 1, deflection plates 40, 42, 44 and 46 can be positioned inside capped cylindrical portion 38 by support brackets 41 (for vane 40) and 45 (for vane 44).

Radiant injector 14 of Figures 1 and 2 is preferably made from refractory material such as corundum, mullite-corundum or periclase chromite.

In operation, the apparatus 10 is installed in the roof, wall or other suitable opening in a metallurgical furnace, so that the oxygen exiting ports 20 and 22 are directed toward that portion of the vessel, e.g., the hearth, where the metal is contained. Oxygen is introduced into lance 12 and exits through both ports 20 and 22 and apertures 28, 29, 30 and 31. Oxygen exiting apertures 28, 29, 30 and 31 swirls inside capped cylindrical portion 38 of radiant injector 14 and then expands downwardly and outwardly along inner wall 37 of funnel-shaped diffuser 35 of radiant injector 14. Oxygen mixes and reacts with the furnace gases at inner surface 37 of diffuser 35 whereby such inner surface is further heated and becomes a radiant heat source for the furnace.

Referring to Figure 3, apparatus 50 includes lance 52 which is identical to lance 12 of Figures 1 and 2. Radiant injector 54 of Figures 3 and 4 is identical in shape to radiant injector 14 in Figure 1 except that it is fabricated as a hollow section with intemal baffle 56 which is used in conjunction with annular passages 58 and 60 to introduce and remove cooling water to and from radiant injector 54. Inner surface 62 of funnel-shaped diffuser 64 of radiant injector 54 is coated with a refractory material so that, when used, it will function in a manner substantially identical to the

apparatus of Figures 1 and 2. All of the other features of the apparatus of Figures 1 and 2 are incoφorated into the apparatus of Figures 3 and 4 as indicated by the use of identical reference numerals for such other features.

As in the device of Figures 1 and 2, deflection plates 40, 42, 44 and 46 are affixed by support brackets which are made from a refractory material such as corundum, mullite-corundum or periclase chromite. In the general case, it is possible to fabricate the vanes from a refractory alloy or metal. These deflection plates are positioned adjacent to each of oxygen apertures 28, 29, 30 and 31 and are positioned so as to direct oxygen tangentially to the capped cylindrical portion of radiant injector 54. In one embodiment, the number of oxygen apertures and, accordingly, the number of deflection plates is four, which are uniformly spaced around the circumference of lance 52. The oxygen flowrate in the lance is between two (2) and six (6) normal cubic meters per tonne of metal per minute.

Diffuser 64 can also be made from refractory material such as corundum, mullite-corundum or periclase chromite. The angle between the walls of diffuser 64 is between 140-179°.

An increase in the efficiency of the post combustion (after-buming) process of the combustible components of the atmosphere in metallurgical vessels can be accomplished as a result of the creation of a continuous gas dynamic curtain of oxygen in the form of a "fan-like" jet above the metal. At this time, intensive catalytic combustion of carbon monoxide and hydrogen occurs on ceramic surface 37, 62 of diffuser 35, 64. In addition, there is intensive radiation onto the metal from the surface of the diffuser. Under these conditions, the discrete spectrum of the gas radiation from carbon dioxide and water molecules is transformed into a continuous spectrum of radiation from the surface of the diffuser. The swirling tangentially

guided jets of oxygen create the necessary vacuum in the axial region of the diffuser, thus assuring intensive inflow of the combustible components of the fumace gases toward the stream of oxygen on the inner surface of the diffuser.

The presence of the closed end of the capped cylindrical portion at the apex of the diffuser prevents the entrainment of burnt gases from the space above the radiant injector.

A device according to the present invention could be operated as follows.

During the production of a typical carbon structural steel having a carbon content between 0.14 and 0.22 percent by weight (Russian steel specification

St3), in a converter with a capacity of 160 tons, lance assembly 10 is positioned in the mouth of the converter above the surface of the metal for post combustion (after- buming) of the combustible components of the converter atmosphere.

In such a use, the outer diameter of lance 12 will be 400 mm, that of the outer diameter of diffuser 14 is 1000 mm, the inner diameter of capped cylindrical portion 38 is 500 mm.

Deflection plates 40, 42, 44 and 46 provide tangential direction to the oxygen jets emerging from apertures 28, 29, 30 and 31, respectively. In this case, upon exiting from capped cylindrical portion 38 of radiant injector 14, the oxygen jets, as a result of gas dynamic laws (centrifugal forces and the Coanda effect), spread out in a continuous Iayer over the inner surface 37 of diffuser 35 thereby creating a continuous gas curtain above the metal in the converter. Under these conditions, in the region under radiant injector 14, a vacuum is created which leads to entrainment of converter gases containing combustible components into the flow of oxygen. Upon the movement of the mixture of oxygen and combustible components along the

inner surface of the diffuser, combustion takes place. Under these conditions, the body of diffuser 35 radiates heat in the direction of the metal, thereby increasing its temperature. The gas layer of the burning mixture also reflects the spatter of liquid metal or slag in the direction away from the surface of the diffuser.

When there are insufficient quantities of combustible gases in the fumace atmosphere an outside fuel, e.g., natural gas can be mixed with the oxygen in the radiant injector so that the radiant injector is maintained as the radiant heat source. The fuel can be introduced in any known manner, such as by a pipe disposed inside passage 32 of lance 12 or 52 or via a separate pipe terminating inside the capped cylindrical portion of radiant injector 14 or 54.

When the diffuser is made of metal and water cooled, the diffuser and the capped cylinder portion are made with two walls with a gap in between. The walls are made from steel having a carbon content between 0.08 and 0.14 percent by weight (Russian specification St10) or stainless steel. The inner surface of the diffuser and capped cylinder are covered with refractory material such as corundum, mullite-corundum or periclase chromite. In addition, the refractory Iayer can be formed by plasma or gas-flame sputter coating.

In the foregoing discussions of the device and process of the present invention, the term oxygen is used. Nevertheless, any suitable oxidizing gas could also be used.

The use of the apparatus permits an increase in the efficiency of the after-buming of the combustible components of the atmosphere in steel smelting installations by twenty to thirty percent (20-30%).

The industrial benefit resulting from the application of the invention is increased efficiency of the process of after-burning of the combustible components of

the atmosphere in the steel smelting installation and also higher efficiency of the transfer of the evolving heat to the metal.