US3427151A - Process and apparatus for introducing a gaseous treating stream into a molten metal bath - Google Patents

Description

3,427,151 ous Feb. 11, 1969 KOUDELKA ETAL APPARATUS FOR INTRODUC STREAM INTO A MOL'IEN ING A GASE METAL BATH PROCESS AND TREATING Sheet Original Filed Jan. 6, 1964 RS UDELKA ARNOLD LLEY Lw RPM:

0 T HOSE V WEUT T ENW B O R ATTORNEY Feb. 11, 1969 PROCESS AND AP TREATING STRE KOUDELKA ET AL PARATUS FOR INTRODUCING A GASEO AM INTO A MOLTEN METAL BATH United States Patent 3,427,151 PROCESS AND APPARATUS FOR INTRODUC- ING A GASEOUS TREATING STREAM INTO A MOLTEN METAL BATH Robert E. Koudelka, Long Branch, Cornelius S. Arnold, Cranford, and Dewitt T. Kelley, Nixon, N.J., assignors to Union Carbide Corporation, a corporation of New York Continuation of application Ser. No. 340,844, Jan. 6, 1964. This application June 19, 1967, Ser. No. 649,073 US. CI. 75-59 11 Claims Int. Cl. C21c /32, 5/46 ABSTRACT OF THE DISCLOSURE Process consists of providing a stream of hot combustion gases to surround a high velocity treating stream, such as oxygen, being discharged from a roof jet into a molten metal bath. The burning gases form a continuous shroud which acts to confine the treating stream and prevent such stream from naturally diverging after it is discharged from a metallurgical lance nozzle. This permits penetration of the treating stream through a slag layer without appreciable splashing, and allows the lance to be operated from heights substantially above the molten metal bath surface.

This is a continuation of application Ser. No. 340,844, filed Jan. 6, 1964, now abandoned.

This invention relates to a method and apparatus for introducing a gaseous treating stream into a molten metal bath and more particularly relates to the use of such a method and apparatus to cause the treating stream to react with the molten metal without inducing appreciable splashing thereof. A particularly valuable phase of the invention is related to the manufacture of steel wherein an oxygen stream may be introduced into a slag covered molten metal bath from nozzle discharge heights above the bath which were heretofore commercially unfeasible.

Although the invention will be described in connection with the refining of a molten steel bath by the introduction of gaseous oxygen thereto, it is not intended to limit the invention to this application as it will become apparent that the general method taught as well as the apparatus shown in the drawings can be used over a broad spectrum of applications.

In the refining of metallurgical baths such as in the production of steel it is usual to employ metallurgical lances supported such that the discharge openings thereof are only a few inches above the bath surface, when introducing large quantities of gaseous oxygen into the bath to refine the metal. In the manufacture of steel by the open hearth process it is common practice to actually operate the oxygen lance with its nozzle face in the slag covering the molten steel.

Present-day metallurgical lances generally consist of a number of concentrically disposed pipes, forming a series of longitudinal passageways, joined and supported by a manifold at the upper end and terminating at the lower end in a discharge face having one or more orifices therein. Treating gases and cooling water are separately introduced into the manifold whereupon they flow through separate longitudinal passageways toward the lower discharge end. This lower end is generally made of high conductivity copper and is constructed so that the treating gases are discharged through one or more orifices into the metallurgical bath while the cooling water circulates through the lower end and returns to an exit pass-age within the manifold wherefrom it is drained.

When treating a metallurgical bath with a gaseous treating stream such as oxygen, argon, powdered lime in a gas carrier, fluorine, etc., it is usually desirable to obtain a high degree of penetration into the bath without causing an excess amount of molten metal splash. Substantial metal splashing is unwanted because of the detrimental atfect it has upon the refractory lined walls of a furnace. To obtain deep penetration into the bath without serious splashing being produced it has become a general practice to operate metallurgical lances with their discharge end close to, or in the slag covering the molten metal surface.

When metallurgical lances are operated with their discharge end close to the metal surface, molten spray particles transferred to the lance from the bath in addition to the intense heat existing in this area to which the lance is exposed, cause such wear to the lance that its service life is extremely short. Under normal conditions its life is determined by the time it takes for the nozzle orifice edges to progressively wear away until the water passages become exposed. When the wear begins, it usually proceeds at an increasing rate. It would generally be impractical and uneconomical to repolish, plate, or coat the lower end of each lance after it has become rough and crazed, in an attempt to retard further wear.

A seemingly desirable method of increasing the useful life of a metallurgical lance would consist of operating the lance with its discharge end located at a substantial distance above the metal surface so as to be above the zone of most intense heat and metal spray. However, when conventional lances are operated in accordance with present practices, unwanted metal splashing and decreased penetration into the bath occur whenever the lance is operated with its discharge end located more than a few inches above the metal bath surface. Many of the particles of molten metal and slag splash would adhere to the lance outer surface where a metallic buildup would gradually form in the vicinity of the lance discharge end. Moreover, the hot metal particles caused by the splashing would strike the refractory walls of the furnace and thereby cause such damage to the refractory that it would rapidly deteriorate. At the present time there is no generally accepted practical method for mini mizing the damaging splash effects to either the lance or to the furnace walls whenever the lance is operated with its discharge end located more than a few inches above the bath.

As mentioned hereinabove, whenever metallurgical lances are operated to discharge a gaseous stream from a height in excess of a few inches above the molten metal surface, excessive splashing and decreased penetration of the stream into the bath occur. In most processes in which gaseous treating streams are introduced into molten metal baths, penetration into the bat-h is very desirable, since it is believed that a minimum quantity of gas is necessary when there is penetration.

iPenetration is of particular importance in most steelmaking processes. In the open hearth production of steel, for example, it has been found that poor penetration when introducing oxygen to refine the metal is a (factor which will accelerate roof wear. A primary cause of roof wear is radiation from the slag floating upon the molten metal. A large percentage of oxygen which does not penetrate deeply into the metal becomes dissolved in the slag. Since the slag usually contains substantial amounts of dissolved iron, the oxygen remaining in the slag reacts with the iron to form iron oxides. This reaction is exothermic and thus increases the temperature of the slag such that more heat is radiated therefrom to the refractory roof.

In certain metallurgical processes, splashing is not as critical a problem as in others. In the basic oxygen process, sometimes also termed an L-D process for steelmaking, for example, because of the geometry of the vessel in which the steel is made, splashing is not usually considered to be a major problem. In this process therefore it is not uncommon to employ metallurgical lances discharging an oxygen stream from heights of inches or more above the molten bath surface. Penetration, however, is still believed by many skilled in the art to be an important factor as it is in most other processes in which a gaseous treating stream is introduced into a molten metal bath. Penetration in the basic oxygen process accomplishes two primary purposes. It causes a stirring action within the bath which is believed by many skilled in the art to promote the speed of the reaction between the many ingredients within the bath. It also is believed to be a factor which affects the rate at which the carbon in the metal is oxidized by the oxygen stream per unit of oxygen introduced. Thus, it is believed that less oxygen is required in the process when deep penetration is achieved than if only a limited quantity of the oxygen stream penetrated the metal surface sufliciently.

The primary reason for operating the lance 30 inches It is believed that the percentage of oxygen which reacts with the metal when the present type lances are operated so as to discharge a gaseous oxygen stream from heights of 30 inches or more above the metal surface, is far below its most efficient level. Accordingly, a substantial amount of the oxygen introduced into the vessel is wasted. Moreover, even to achieve the rate of penetration presently attained, it has been current practice to have the gaseous oxygen stream supplied to the lance at a pressure on the order of 110 p.s.i.g. This may be compared to a pressure of about 50 p.s.i.g. for lance operation in the open hearth process.

It is therefore the main object of the present invention to provide a method and apparatus for introducing a gaseous treating stream into a molten mass consisting of molten metal covered by a slag layer, in such a manner as to enable the treating stream to pierce through the slag layer and deeply penetrate into the molten metal without the occurrence of substantial splashing.

Another object of this invention is to provide a method and apparatus for introducing a gaseous treating stream into a molten metal bath in such a manner that deep penetration of the treating stream into the metal bath is achieved with only nominal metal and slag splashing being induced when the treating stream is discharged from heights above the metal bath surface which were heretofore commercially unfeasable.

A further object of this invention is to provide a method and apparatus for introducing one or more gaseous treating streams into a molten metal bath in such a manner as to limit the amount of metal splash resulting from such introduction, and thereby extend the useful life of the exposed furnace refractory and the introduction apparatus.

A still further object is to provide a method and apparatus for introducing a gaseous treating stream to deeply penetrate the surface of a molten metal bath when the treating stream is discharged from the apparatus at a pressure on the order of to 70 p.s.i.g. and from a height on the order of 4 to 40 inches above the molten metal surface.

In accordance with these objects, our invention contemplates an improvement in the refining of metal wherein a gaseous treating stream is blown into a molten metal mass, the improvement comprising surrounding said gaseous treating stream, for substantially its entire length, with heated gases formed by the combustion of fuel and oxidant, to confine the gaseous treating stream in such a manner as to enable it to react with said molten metal without inducing substantial splashing.

More specifically, in accordance with our invention, a process is provided for treating a molten metal bath with a gaseous treating stream which comprises positioning a lance above the bath surface and disposed to discharge thereinto, supplying a stream of fuel and a stream of combustion supporting gas to said lance, discharging said streams at low velocity to form a hollow combustible mixture, which upon ignition forms a hollow shroud of flame extending to about the surface of said bath, supplying a gaseous treating stream to said lance and discharging said treating stream at high velocity within said hollow shroud of flame, into said molten metal bath.

In the drawings:

FIG. 1 is an elevational sectional view of a metallurgical vessel, illustrating a preferred embodiment of the present invention;

FIG. 2 is an enlarged longitudinal sectional View of the lance shown in FIG. 1;

-FIG. 3 is a front end view looking at the discharge nozzle face of the lance shown in FIG. 2;

FIG. 4 is a longitudinal sectional view of an alternative lance to be used in accordance with our invention;

FIG. 5 is a front end view looking at the discharge nozzle face of the lance shown in FIG. 4; and

FIG. 6 is an enlarged sectional view of the discharge opening shown in FIG. 4.

Referring to FIG. 1, our process may be shown in connection with a basic oxygen steelmaking process, often termed an L-D process. The vessel 10 consists of a steel shell 11 having refractory lined walls 12 and a bottom 13. The steelmaking raw materials such as pig iron, scrap, limestone, alloys, etc. may be charged into the mouth 14 of the vessel to form a bath 15. A lance 16 is then positioned above the bath and is disposed to discharge a stream of treating gas into the bath to refine the metal. The height of the lance discharge end above the bath surface is preferably held constant throughout the period of lance operation at a height between 4 and 40 inches depending upon the depth of the bath, the temperature of the bath, and the oxygen flow rate into the vessel. The gaseous treating stream will generally consist of oxygen, although other treating streams may be used, for example, powdered lime may be introduced through the lance in an oxygen gas carrier.

A stream of fuel, such as for example, methane is supplied to the manifold 17 at the upper end of the lance. A stream of combustion supporting gas such as air or oxygen is also supplied to inner tube 24 which passes through manifold 17. The streams are discharged at lowvelocity from the lance lower end to form a post-mixed combustible mixture having a hollow center portion, which upon ignition will form a shroud of flame 18 extending from about the lower end of the lance to about the surface of the slag bath. It is essential that the streams forming the combustible mixture leave the lance in such a manner as to form when ignited, a hollow shroud of flame extending to about the surface of the slag covering the bath. The main stream of treating gas 19 is then supplied to inner tube 24 which passes through lance manifold 17 and is discharged through a separate passage 20 at high velocity, within the established hollow shroud of flame 18. The hollow shroud of flame 18 formed by combustion of the mixed fuel and oxidant streams, produces heated gases which act to confine the gaseous treating stream in such manner as to enable it to pierce through a slag layer and deeply penetrate into a molten metal bath. The purpose therefore of the hollow shroud of flame is to confine the gaseous treating stream such that it is substantially prevented from expanding in cross-sectional area as it passes from the lance discharge end into the metal bath. It has been found essential that the shroud of flame surround the gaseous treating stream for substantially its entire length.

It is believed that the basic oxygen or LD process will be improved by practicing our invention since eflicient oxygen utilization will be realized.

When practicing our invention it should be possible to obtain deep penetration into a molten metal bath at low supply pressure whenoperating at discharge heights in the range of 4 to 40 inches above the metal bath surface.

Deep penetration generally creates a desirable stirring action within the bath which in turn promotes faster reactions between the molten metal and the gaseous treating stream being introduced thereinto.

It is to be understood at this point that although our process has been illustrated in connection with a basic oxygen process for steelmaking, we do not wish to limit our invention to this particular application of our invention. Our process can be used effectively in connection with any metallurgical process in which a gaseous stream is required to be introduced into a molten metal bath. Examples of several alternative applications of our invention would be the injection of chlorine or fluorine into an aluminum bath; the injection of partially oxidized hydrocarbons into a copper bath; the injection of powdered nickel magnesium alloy in an inert gas carrier stream into cupola iron in order to produce nodular iron; and the injection of powdered lime in an oxygen carrier into a steel bath.

Referring now to FIGS. 2 and 3, a preferred lance apparatus for use with our process is shown and comprises a centrally located inner tube 20, the forward end of which terminates in a discharge opening 21 at the exposed face. The inner tube forms the conduit for passing the main gaseous treating stream into the molten metal bath. A second conduit 23 surrounds tube 20, forming annular passage 22 therebetween for the flow of combustion supporting gas. Tubes 20 and 23 are connected to main supply passage 24, however, this common supply connection is used only because we usually desire to use oxygen as the main gaseous treating stream as well as for the combustion supporting gas. If it were desirable to introduce another gaseous treating stream into a molten bath, for example fluorine, it would become necessary to have the tube 20 continuous for the length of the lance, to connect with a fluorine supply, and have conduit 23 similarly continuously spaced apart therefrom to form a continuous longitudinal annular passage for the flow of combustion supporting gas.

A conduit 26 surrounds tube 23 forming annular passage 25 therebetween for the flow of fuel such as, for example, methane. Outer conduits 28 and may surround conduit 26 to form annular passages 27 and 29 through which a flow of cooling water may be passed. All of the spaced conduits connect to a manifold 31 at the upper end of the lance. In operation, fuel is supplied to manifold 31 through port 32 whereupon it flows through annular passage 25 to the forward face of the lance. Oxygen is supplied to the manifold 31 through port 33 and flows through passage 24. A small percentage of the main oxygen stream is diverted into annular passage 22 by passing through annularly spaced circularly arranged ports 34 in cap 35. The substantially larger amount of the main stream oxygen continues to flow through central passage 20 until it is discharged from the lance lower end.

The fuel gas leaving the lance through annular passage 25 and that portion of the mainstream oxygen leaving the lance through annular passage 22 form a post-mixed hollow combustible mixture forward, or downstream of the lance which upon ignition forms a circumferentially continuous hollow shroud of flame. The main supply of oxygen flowing through tube 20 is discharged at high velocity centrally within the established shroud of flame.

To establish the proper shroud of flame it has been found necessary to discharge the fuel and oxygen streams forming the combustible mixture, at low discharge 'velocity with respect to the discharge velocity of the main oxygen stream. Hence, upon ignition, the average downstream velocity of the shroud approaches that of the mainstream because of the expansion of the gases resulting from the combustion.

For purposes of cooling the lance, a continuous flow of cooling water may be maintained by means of annular water in passage 27 and annular water out passage 29.

Referring now to FIGS. 4, 5 and 6, an alternate lance apparatus for introducing a gaseous treating stream, in this case oxygen, into a molten metal bath is shown and comprises an inner tube 40 which forms a central coolant passage 41 in the lance. A second conduit 42 surrounds tube 40 and forms annular passageway 43 therebetween for the flow of oxygen. A third conduit 44 surrounds conduit 42 and forms annular passageway 45 therebetween for the flow of fuel gas. A fourth conduit 46 surrounds conduit 44 and forms annular passageway 47 for the flow of return coolant supplied through tube 40.

The conduits 42, 44 and 46 are closed on the upper end by manifold 48 and are closed on the lower end by a nozzle 50. The nozzle has shoulders 52, 54, 56 and 58 for receiving the respective ends of the circular conduits which are attached thereto by welding or brazing.

The nozzle is preferably a suitably shaped block of a high conductivity metal such as copper. The nozzle 50 has a large central bore 51 therein which terminates short of the front face 60 of the nozzle. The shoulder 52 at the upper edge of the bore 51 receives the inner tube 40. Extending between the shoulders 52 and 54 is an annular surface 53 serving to close the first annular passageway 43. Similarly annular surface 55 extending between shoulders 54 and 56 serves to close the second annular passageway 45. Main oxygen orifices 57 extend from the surface 53 to within a fraction of an inch of the exterior face 60 of the nozzle 50. Six main oxygen orifices 57 are shown in the drawings but a greater or lesser number can be employed. Drillings 59 are provided to form a plurality of spaced oxygen orifices 61 surrounding each main oxygen orifice 57. The drillings are arranged so as to be supplied with oxygen bled from each main oxygen orifice '57. It is preferable to provide enough orifices 61 so as to completely surround each main orifice 57. Fuel gas orifices '63 extend from the surface 55 to within a fraction of an inch of the exterior face 60 of the nozzle 50. Cooling water passages 65 extend substantially radially from the central bore 51 to return water passage 47. As seen in FIG. 5, there is a cooling water passageway (shown in broken lines) between each adjacent pair of main oxygen orifices.

In operation, fuel gas discharged from orifices '63 forms a combustible mixture with oxygen discharged from orifices 61 which upon ignition forms a plurality of circumferentially continuous hollow shrouds of flame. The main oxygen streams issuing from orifices 57 are thus completely surrounded and confined by each shroud of flame.

'It has been found that a properly established circumferentially continuous hollow flame can confine a gaseous stream introduced therethrough such that the cross-sectional area of said gaseous stream will remain substantially constant from its point of discharge through a vertical distance of as much as 48 inches. When introducing a confined gaseous treating stream into a molten metal bath it is possible to achieve deep penetration into the bath with an absolute mini-mum of splashing produced. This has been found to hold true when the gaseous treating stream has been discharged from a range of heights above the molten bath surface. The effect of the flame and the hot combustion products produced thereby is to shroud or envelope the gaseous treating stream being introduced into the molten metal bath such that the gaseous treating stream is substantially prevented from diverging after it has been discharged from the' forward end of the lance.

In order to form a properly established confining shroud, it has been found necessary to closely control the amount of fuel and combustion supporting gas used. In determining the necessary flows, it will be preferable to employ just enough of each to form an axially continuous flame; that is, a flame extending from the lance discharge end to about the slag surface covering the molten metal. If a greater quantity of fuel or combustion supporting gas is discharged, it will create excess turbulence around the main gaseous treating stream being confined such that increased slag and metal splashing will occur. In all cases, the quantity of fuel and combustion supporting gas used to properly establish the shroud is nominal when compared to the amount of the gaseous treating stream which can be confined or shrouded thereby. For example, when operating a lance at a height 9 inches above the metal bath surface (distance measured from the bath surface to the discharge nozzle face of the lance) a shroud ample to confine 1200 s.c.f.h. of main stream argon was established with 40 s.c.f.h. of methane and s.c.f.h. of oxygen. In another instance, when operating a lance at a height 18 inches above the bath a flame shroud ample to confine 8400 s.c.f.h. of main stream oxygen was established with 950 s.c.f.h. of methane and 250 s.c.f.h. of oxygen. It has been found that the optimum desirable flow rate of fuel gas does not vary in direct proportion with the flow rate of the main treating fluid stream, as one might expect. For any given size nozzle, the amount of fuel gas required will be a function of the height above the slag at which the lance is operated. The height is measured along the longitudinal axis of the lance and is the distance along this axis from the discharge face of the lance to the surface of the molten slag.

We have also found it necessary when carrying out our process to discharge the main gaseous treating stream at high velocity, preferably sonic, and conversely to discharge the fuel gas and combustion supporting gas stream at velocities which are lower than the velocity of said main gaseous treating stream.

In forming a proper shroud for the gaseous treating stream, it is preferably to discharge the fuel and oxidant streams in such manner as to form a circumferentially continuous shroud of heated combustion products about the treating stream. In other words, it is necessary to completely surround the treating stream with an envelope of confining gases. Thus, if the discharged gaseous treating stream was elliptical in shape, the shroud of confining gases may also be formed into a elliptical shape.

We have found that an excellent shroud of confining gases may be formed by the combustion of fuel and oxygen. We have described this type of shroud throughout our specification as a flame shroud or shroud of flame. It should be understood, however, that the shroud may be produced by separately burning the fuel and oxidant and utilizing the resulting hot combustion gases to confine the main treating stream.

In establishing a proper flame shroud in accordance with our invention, we have found it preferable to operate with oxygen to hydrocarbon fuel gas ratios by volume at S.T.'P. in the range of 7 /2% to 62 /2% of the stoichiometric requirements, depending upon the diameter of the main gaseous treating stream and the discharge height above the metal bath surface. In this connection, it should be noted that any heating effect produced by the flaming shroud would be purely incidental. It is not an object of our invention to provide a burner apparatus, in fact the ratios of oxygen to fuel gas used in establishing the flame shroud would not be suitable for efiicient combustion practice. Modern combustion theory calls for the use of oxy-fuel gas ratios of about 2.0 to 1 when using methane as the fuel gas. This may be increased, to provide a more oxidizing flame, to about 3.0 to 1 or may be lowered, to produce a more reducing flame, to about 1.7 to 1. In any event, it would be considered extremely poor practice to operate a burner at any oxy-methane ratio substantially below 1.7 since fuel would be incompletely burned and therefore wasted. Moreover, lower flame temperatures would be produced with such flames and thus the rate of heat transfer therefrom would be much slower than with higher temperature flames. We have found the proper 8 oxygen-methane ratio to form our shroud to be in the range of 0.15 to 1.25.

We have found that whenever ratios of oxygen to methane in excess of 1.0 are employed, such turbulence is caused as to promote the breaking up of the shroud and therefore a substantial increase in the amount of splashing produced by the gaseous treating stream contacting the metal.

As aforementioned, the extreme temperatures within metallurgical furnaces, particularly steelmaking furnaces, has an adverse affect upon the discharge end of lances suspended therein. It has been found that when a lance is operated with its discharge end in the slag layer, only a few inches above the molten metal surface, its service life is very short; perhaps an average of only 25 heats or less. On the other hand, whenever the lance has been operated at greater heights above the bath, there has been a substantial increase in its service life. The problems occurring when conventional lances are operated at the greater heights above the bath, are: 1) substantial increase in molten metal splashing resulting in increased refractory damage: (2) penetration into the slag and metal decreases, causing increased damage to the furnace roof refractory; and (3) lower utilization efliciency of the gaseous treating stream employed.

Laboratory testing has indicated that deeper penetration into a bath occurs per unit height of the lance nozzle above the bath, with substantially less splashing, when operating in accordance with our invention. The results were compared with operation according to present-day conventional practice. The results of a typical comparison test are indicated below in tabular form. In each case the main gaseous treating stream flow conditions were identical, the only difference being that in one case the main stream was provided with a properly established confining shroud while in the other, a confining shroud was not provided. Each of the lances was suspended at the same height above a water bath; the height was taken as the perpendicular distance from the water bath surface to the discharge nozzle face of each lance. A tank having a transparent wall was used to facilitate measurement of the gaseous penetration into the water.

SHROUDED VS. UNSHROUDED PENETRATION OF XYGEN STREA NoTE.Constant mainstream oxygen flow rate ,400 e.f.h. through 2.

%-inch diameter orifice.

The affect of using various gases for the main stream conclusively established that a properly established confining shroud will provide benefits regardless of the main gaseous treating stream employed.

What is claimed is:

1. In a process for refining molten metal wherein a high velocity gaseous treating stream is blown into the molten metal, the improvement comprising confining the gaseous treating stream for substantially its entire length above the surface of the molten metal to substantially prevent its normal expansion by the step of directing a stream of heated combustion products at a velocity substantially less than the velocity of the gaseous treating stream in surrounding relationship about the gaseous treating stream and for substantially its entire length above the molten metal surface, said combustion products being formed by directing a combustible mixture of oxy gen and gaseous hydrocarbon fuel supplied in a ratio by volume at S.T.'P. of oxygen to fuel in a range of from 7 /2% to 62 /2% of the stoichiometric requirements, whereby the gaseous treating stream will penetrate into the molten metal without the occurrence of substantial metal splashing.

2. A proces as claimed in claim 1 wherein the process is a basic oxygen steel making process, wherein the molten metal bath is a ferrous bath, wherein the stream of heated combustion products is discharged at a low subsonic velocity, and wherein said gaseous treating stream is composed of oxygen and is discharged at about sonic velocity.

3. A lance for use in a metallurgical furnace to direct a plurality of oxygen streams into a slag covered molten steel bath without inducing substantial metal splashing when the lance is operated with its discharge face above the slag surface said lance comprising: means for directing a plurality of high velocity oxygen streams into said bath, means for directing a low velocity flow of combustion supporting gas in a plurality of streams outerly concentric with respect to said oxygen streams, and means for directing a low velocity flow of fuel gas in a plurality of streams outerly concentric with respect to said oxygen streams to provide, when ignited, a hollow flame surrounding each high velocity stream of oxygen directed into said molten metal bath.-

4. A lance as claimed in claim 3 wherein means are provided for establishing and maintaining a continuous flow of coolant in order to cool said lance.

5. A process as claimed in claim 1 wherein the gaseous treating stream is argon.

6. A process as claimed in claim 1 wherein the molten metal is aluminum and the gaseous treating stream is a member selected from the group consisting of chlorine and fluorine.-

7. A process as claimed in claim 1 wherein the molten metal is copper and the gaseous treating stream comprises partially oxidized hydrocarbons.

8. A process as claimed in claim -1 wherein the molten metal is cupola iron and the gaseous treating stream comprises an inert carrier gas containing powdered nickel magnesium alloy.

9. A process for treating a slag covered molten metal bath with a gaseous treating stream which comprises positioning a lance above the surface of the bath and disposed to discharge thereinto, supplying gaseous streams of methane fuel gas and oxygen to said lance, discharging said streams in a ratio by the volume at S.T.P. of oxygen to fuel in a range between 0.15 and 1.25 to form a circumferentially continuous combustible mixture having a hollow center portion, igniting said mixture to form a circumferentially continuous shroud of flame having a hollow center portion and extending from about the discharge end of said lance to about the surface of said slag covering, supplying a gaseous treating stream to said lance and discharging it centrally within the hollow portion of said shroud of flame, and into said bath.

10. A process as claimed in claim 9 in which the low velocity reducing mixture is formed by a plurality of a1- ternately spaced individual streams of fuel and oxidant.

11. In a process as claimed in claim 2, the improvement which comprises discharging the fuel and oxidant streams to form a plurality of individual shrouds of flame, each having a hollow center portion, and discharging the oxygen stream supplied to the lance, in subdivided streams within the hollow center portion of each individually formed shroud of flame.

References Cited UNITED STATES PATENTS 2,991,173 7/1961 Trentini et al 75-52 3,115,405 12/1963 Boyd 7560 3,216,714 11/1965 Eibl et a1. 26634 3,304,173 2/1967 Smith 7552 RICHARD O. DEAN, Primary Examiner.

11.3. C1. X.R.

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