US3347660A - Method for refining metals - Google Patents

Description

Oct. 17, 1967 G. H. SMITH ET A1.

METHOD FVOR REFINING METALS 2 Sheets-Sheet 1 Original Filed Nov. 28, 1960 oct. 17, 1967 G. H. SMITH ETAL METHOD FOR REFINING METALS Original Filed Nov. 28, 1960 2 Sheets-Sheet 2 w w mi 1MM N 4 we; my w mm i QQ if 5 n/ w v Nw l/ r Q /V iN@ QQ @ce n um United States Patent Cfiiice 3,347,660 Patented Get. 1 7, 1967 3,347,660 METHD FR REFiNiNG METALS George H. Smith, Berkeley Heights, and Raymond E. Armstrong, Jr., Clark, NJ., assignors to Union Carbide Corporation, a corporation of New York @riginal application Nov. 28, 1960, Ser. No. 72,034, now Patent No. 3,175,817, dated Mar. 30, 1965. Divided and this appiieation July 1, 1964, Ser. No. 379,654 7 Claims. (Cl. 75-43) This is a divisional application of Serial No. 72,034, filed Nov. 28, 1960, now Patent No. 3,175,817.

The present invention relates to an improved jet device and process for directing separate ows of a treating uid and a combustible gas mixture toward the charge in a metallurgical furnace. It further relates more particularly to a novel construction and method for cooling such a device when exposed to the hot molten bath formed there- 1n.

The use of oxygen by the steel industry to speed up production is increasing every year. Not only are oxygen and other treating gases used extensively in the final stages of the open hearth method to refine the steel, but they are used also in the initial stages of the process to speed up melting of the charges by flame enrichment with oxygen. It has also been found that refining periods may be greatly reduced especially in the open hearth type of furnace, by supplementing the normally present end positioned burners, with burners which may be suspended from the furnace roof thereby permitting heating flames to be directed at close range upon the upper surface of hehfurnace charge and on the subsequently formed molten In order to fully and most economically utilize the lances which conduct the treating fluids, or direct the heating flames onto the molten bath surface, it is necessary to provide such lances with adequate means for countering the effects of high temperatures, furnace atmospheres, and molten material splash. Generally such lances, or jets as they are frequently referred to, consist of a plurality of vertically and concentrically disposed elongated tubes which are so associated as to provide a ow of the treating material from the lance lower face, which face is normally spaced within the range of a few inches to a few feet from the bath surface. It is of course necessary to incorporate into such devices a cooling system of some sort which most generally embodies a passage for conducting a flow of coolant liquid toward the lance face, and a return channel which brings the liquid into contact with the heated outer casing of the lance. This method of removing heat, by a circulatory coolant ow, is found to be satisfactory up to a certain point after which it is impossible to achieve a sufficiently high coolant rate of flow to overcome the damages resulting from exposure to the furnace heat and from metal slag buildup on the lance outer surface due to furnace splash.

In the instance of roof burners used in open hearth installations for the purpose of increasing the scrap melt down rate, the prior art has proposed devices in which the fuel gas composition is premixed within some portion of the burner end thence ignited at the discharge face to form heating flames. A notable disadvantage to this methd of flame generation is the susceptibility of the combustible mixture to being ignited Within the confines of the burner thereby resulting in flash back or burn back of the gas. Since ashback often results in damage to the burner itself, or parts associated therewith, it is highly desirable to prevent such a reaction.

It is therefore a primary object of the present invention to provide an apparatus for treating the charge in a metallurgical furnace, said apparatus being particularly adapted to resist the detrimental effects of excessive furnace temperatures and molten splatter.

A further object is to provide a device of the type described in which a liquid coolant material is provided as a heat transfer medium for protecting the surfaces of said device which are exposed to the molten metal bath.

Still another object is to provide a combination oxygen roof jet and roof burner of the postmixed gas ame type, including means for protecting the forward exposed surface thereof with a flow of coolant fiuid.

In the drawings:

FIG. 1 is a longitudinal view in cross section of a combination oxygen jet and roof burner apparatus embodying the novel features of the invention;

FIG. 2 is a plan view of the apparatus shown in FIG. 1;

FIG. 3 is an enlarged cross sectional view illustrating the lower portion of the apparatus shown in FIG. 1; and

FIG. 4 is an enlarged View of the front end discharge face of the apparatus shown in FIG. 1.

In brief, the device contemplated by the present invention includes the combination of a roof lance for introducing flows of a treating gas such as oxygen to a molten bath, and a roof burner for impinging heating ames onto the unmelted furnace charge and against the bath surface in a single apparatus. The combustion jet, as the device will be hereinafter referred to, consists of an inner elongated tube extending the burner length, the forward end of said tube being terminated at the burner face in a nozzle portion. A plurality of concentrically disposed tubes surrounding the inner tube, define annular passages for separately conducting flows of the treating gas, a fuel gas, and a coolant fluid respectively to the nozzle portion which fixedly positions the lower end of said tubes relative to each other. A manifold engaging the tube upper ends provides a closure thereto and also affords means for communicating with the said annular passages. The burner inner tube is provided at the upper end with means for simultaneously introducing at a high pressure, a fuel gas, and a non-combustible, heat vaporizable fluid additive substance; a deector interposed at the lower end of said inner tube deliects the high velocity composite stream of said fuel gas and additive, outwardly toward the burner Wall where the latter may adhere to and flow toward the exposed burner face. The fuel gas thereafter is discharged from the burner face, to mix with an oxygen stream and thence burn as a heating fiame.

Referring to FIG. 1, a preferred embodiment of the present combustion jet is shown at 10 and comprises a centrally located inner tube 12, the forward end of which terminates in a discharge opening 14 at the exposed burner face. The upper end of said tube is slidably enclosed by a cap 16 which constitutes a removable segment of the manifold 18. A resiliently sealed opening in said cap 16, including the O ring 20 retained in a groove therefore, provides a uid tight connection with the outer surface of tube 12 in spite of relative movement between the sealing surface of said tube and cap due to thermal expansion and contraction of 4the respective burner parts in the course of operation. The cap 16 is provided with a port 22 for introducing to the inner tube 12 a flow of fuel gas such as methane, or natural gas. According to the invention, this gas is ordinarily delivered to the inner conduit 12 a-t a sufiiciently high pressure to achieve a rate of delivery to the furnace of about 20,000 to 60,000 cubic feet per hour. Such a volume of gas in passing through the relatively small diameter of the inner conduit 12 will of course form a high velocity stream.

Into the high velocity gas stream thus formed, there is injected a relatively small amount of vaporizable coolant fluid preferably water or steam, which is introduced through a second port 24 positioned down stream of port '3 r3 22, so that` the injected fluid will be aspirated, substantially atomized, and conveyed as minute droplets in the gas stream toward the burner discharge opening 14. While not presently shown in the drawings, the port 24 may be provided with suitable flow metering means such as a valve, for proportioning the proper amount of liquid or steam into the gas stream.

The lower or discharge end of tube 12 as previously noted, is generally positionedin an open hearth or other type of furnace, a matter of a few inches above the molten bath or scrap charge surface and therefore subject to severe abuse both from the bath heatand from i molten splatter. In addition, as the stream of fuel gas emerges from the discharge port 14, it willthen mix with a stream of oxygen also emitting from thefburner to form a combustible mixture and be ignited into an intensely hot flame which tends to further heat the burnerface.

Also, since it has been found desirable to introduce the oxygen to a molten bath in the form of a large number of high velocity jets, a further problem has often been encountered. Since the orifices which form the high velocity jets are positioned at the lance face, they are subjected to particular abuse from molten splatter, as are the web sections 85 which separate the respective oriiices. In order to obtain the maximum number of oxygen streams, the lateral spacing therebetween is usually quite limited and consists in many instances of no more than a thin web 85. Since it is quite difficult to adequately cool the web section, burning out at this vital point is one of the most common causes fory lance failure.

In accordance with the invention, much of the heretofore frequently occurring damage to roof lances of the type described has been overcome by interposing in the lower end of tube 12, at a point slightly to the rear of the discharge opening 14, a fuel stream diffuser element 26. This diffuser in effect separates the tube 12 into respective upper and lower portions. The primary purpose of the deflector is to intercept the downwardly iiowing composite fluid stream and urge said stream laterally toward the conduitswall. As illustrated in FIG. 3, a preferred embodiment of said element 26 is providedwith a generally helicoid configuration characterized by gradually sloping surfaces disposed to meet the high velocity, composite fuel gas and coolant stream, and to redirect said stream into a substantially lateral direction with respect to the burner center axis.

The centrifugal force thereby imparted to the iiuid particles making up the composite stream, will impinge said particles against the smooth inner wall of the conduit 12 at a glancing angle with the` result that the heavier liquid particles of water will tend to cling to the wall while the lighter gas particles will merely be guided into a swirling path. When steam is employed in lieu of entrained water, the steam will be guided into a swirling path along with the fuel gas but since the inner wall surfaces are maintained at -a temperature below the condensing point of steam, the steam will condense on the wall surfaces forming droplets of water whereas the fuel gas will leave the jet as aforementioned. During the decar-` burizing phase of the steelmaking process, the use of steam without fuel gas is employed, as the fuel gas would create a reducing atmosphere. Referring to FIG. 3, an embodiment of the novel deiiecting element 26` consists of a screw-like member having a peripheral channel 28 formed thereon defined by a spiral land 30. This land is provided withan outer diameter approximating theinside diameter of the tube 12 so as to contactthe inner wall of said tube or be contiguous thereto. A smoothly tapered rearwardly projecting portion 32 of the dcflector 26, minimizes the actual blocking force exerted by said member against the rapidly moving composite stream so that the high forward velocity component of the gas stream will be maintained along with the swirling component.

The deflector axial length is preferably minimized in order to reduce back drag on the swirling stream and also to permit the formation of a forwardly advancing thin liquid film on the conduit wall. We have found that in a tube `having a diameter of about 2 inches, a suitable length for the deector from forward to rear end would be about 4 inches. Said member 26 may be positioned by welding or other suitable means at the desired location in conduit 12 or it may be adjustably disposed. It has been determined that a high degree of cooling is effected when the deiiector is positioned about 6 inches in from the burner lower face.

As illustrated in the figures, the centrifuging effect on the composite fuel gas stream will cause a thin film of water to form along the cylindrical wall of tube 12 from the downstream end `of deiiector 26 to the forward opening 14. The high velocity swirling gas stream, to.- gether with the gravitational force acting thereon, then will continue to urge the water film forward along the outwardly (divergent) throat 40` and thence in a lateral direction onto the recessed plane face portion 42 of the burner. It has been found that not only does the thin water layer cool the exposed burner surfaces by an evaporation process, but said layer also serves to prevent metallic particles ejected from the bath, from clinging to said surfaces. Actually, there is both a wetting of the exposed surfaces for cooling purposes and also a slight explosive effect when the hot bath particles form steam on striking` the liquid nlm. Such cooling is particularly effective for protecting the previously mentioned web sections intermediate the oxygen orifices.

Under actual operating conditions, we have found that when the burner is operated as a heating device, with natural gas as the fuel, a proper mixture would con-` stitute 60,000 to 160,000 c.f.h. of oxygen to 30,000 to 80,000 c.f.h, of fuel gas, with about 10 to 5() gallons per hour of water entraincd in the fuel stream.y In the subsequent refining step where only oxygen was introduced to the bath, about 80,000 c.f.h. of oxygen was injected while l0 to 70 gallons per hour of water was carried through the burner by a nominal iiow` of fuel gas. When steam rather than water is utilized as the cooling medium, for the above-noted fuel and coolant mixtures, about 30 to 100 pounds per hour of steam are required.

gain referring to FIGS. 1 and 3 of the drawings the inner tube 12 is surrounded by a second tube 44 outwardly spaced vtherefrom to define an annular passage 45 for conducting a treating gas such as oxygen toward the burner forward end. The lower end of said tube engages the burner nozzle in a gas tight seal and the upper end is enclosed by a cylindrical ring portion 46 of the manifold 18 to deiinean annular chamber 48. Said chamber is maintained iiuid tight with respect to tube 44 and with the adjacent manifold chambers, by resilient seal rings 20,;

50 and 52 respectively, which are confined in grooves therefor at the respective ends of said ring 46. As noted previously with respect to seal ring 20; the sliding joints so formed by the companionate surfaces of the tubes and resilient seal rings, permits a degree of longitudinal expansion of the burner tubes without the consequence of iiuid leakage.

An inlet 54 communicates with chamber 48 for providing oxygen to therl-ance, and may be coupled to a supply of said gas by a exible hose or other suitable form of conduit. The lower end of passage 45 terminates at the burner nozzle into which a plurality of small bore oxygen orifices 56 are formed. The oxygen orifices as shown in FIG. 3, are disposed in circular fashion about the center opening 14 and yare slightly outwardly biased from the burner longitudinal axis to form divergent streams. On emerging at a relatively high velocity from the circularly spaced orifices the oxygen streams at a point forward of the nozzle face, will impinge against the spiral stream of fuel gas emerging from the center discharge opening 14 and thereby provide a combustible mixture which is immediately ignited to form an elongated conical flame.

It has also been found that, rather than employing the circularly spaced oxygen orifices as presently shown, an annular orifice disposed outwardly of and substantially concentric with opening 14 will also provide an efficient mixing of oxygen and fuel gas Iafter both of said gases leave the burner face. The orifices 56 as shown in FIGS. 1 3 are directed in a generally -divergent pattern not only for the purpose of proper mixing with` the fuel gas stream but also for accomplishing a dispersed treating area on the molten bath surface when the streams of oxygen are being introduced thereto without a heating flame, as for example in a deoxidizing step.

In normal furnace operation, the presently disclosed combined roof lance and burner would first be utilized in a heating capacity by directing Oxy-fuel gas flames onto the unmelted scrap metal charge. As the molten bath is formed, the flow of fuel gas is substantially abated until only the oxygen flow is continued. In order to sustain the above-mentioned wetting of the exposed lower wall portion of the center tube, as well as the exposed burner face, a limited flow of the fuel gas may be provided merely to act as a carrier for the water additive. It should be noted though that when steam rather than water is utilized, the former would not require a carrier and may be introduced alone. Therefore, it is possible to effect the desired burnerprotection lduring all steps of the metal refining process. Especially beneficial in this respect is the distinct advantage realized that there will be absolutely no mixing of the fuel and combustion supporting gases prior to their exiting from the burner. This will of course preclude the possibility of flashback in the burner body or in the gas equipment associated therewith.

Referring to FIGS. 1 and 3 of the drawings, the internal cooling system employedin the present burner consists of a pair of elongated cylindrical conduits 60 and 62 which are disposed outwardly of tube 44 in substantially concentric relationship therewith to define respective coolant inlet passage 63 and coolant return passage 64. As illustrated in the figures, said conduits extend substantially the length of the burner and are engaged at the upper end with a circumferential collar 66 which forms an integral portion of the manifold 18. The lower end of conduit 60 terminates at the burner nozzle, at a point rearwardly adjacent to an annular coolant chamber 67 formed therein. Said chamber 67 is provided with a curved forward surface which constitutes the rear wall of the exposed nozzle face 42 such that circulating coolant liquid, which is generally water, will be received from the water inlet passage 63 and then redirected into the outer coolant return passage 64.

It has been found that a more efficient cooling of the burner may be Iachieved by the provision of a baffle member 68 disposed in passage 63, and a similar baffle member 70 positioned in passage `64. The respective bafiies as shown comprise a spiral shaped member which, when interposed in the annular coolant passages, urge the coolant stream into a confined spiral channel. By so doing, the velocity of the water is increased and a smooth flow is obtained, both of which characteristics improve the rate of heat transfer from the burner. These baffles are so constructed and arranged that cooling water passing downwardly through passage `63 will be given a swirling motion in, for instance, a clockwise direction. On passing through the annular chamber 67, the swirling motion will be continued and the stream will be thence directed into the channels formed in passage 64. These latter channels are likewise arranged to continue the stream in a swirling path so as to maintain a rapid velocity through out the lance.

As mentioned above, collar 66 engages the respective upper ends of conduits 60 and 62, said collar is adapted to threadably engage the outermost conduit 62 and to slideably, fluid tightly engage conduit 60 and tube 44 respectively. A water hose, or similar fiexible conduit not shown on the drawings, but connected to a suitable water supply, may be coupled at inlet port 72 to provide a fiow of the coolant liquid to an annular chamber 74 and thence to the cool-ant inlet passage 63. Likewise, the outer coolant return passage 64 terminates in an annular passage 76 which is provided with a port 78 for communication with a second hose for coolant fluid.

The nozzle or discharge end of the burner is provided as shown in FIG. 3 with a smooth outer surface which terminates at the forward end in the recessed face 42. It has been found that much of the burner damage, usually caused by blocking of the oxygen orifices with splashed molten metal particles, may be avoided by preventing said molten particles from flowing down the burner exposed outer wall and thence being aspirated into the high velocity gas stream. In this respect, a peripheral lip or ring "80 formed on said face and spaced radially outwardly of the circularly disposed orifice 56, permits the down flowing molten metal on the lance outer surface to drip back into the bath.

A circumferential plate 82 fixed to the outer surface vof conduit 62 immediately below the manifold 118, provides means for supporting the burner in operating position, within a furnace. A metal bail 84 formed to be positioned above cap 22, support-ably engages said plate 82. Normally the burner may be transported and positioned in an open hearth furnace by an overhead traveling crane of the type peculiar to steel mills, which crane is provided with la downward extending hook for engaging the burner bail.

In view of the operating hazards which normally accompany any metal refining process, it will be readily appreciated that the construction of the present burner which obviates the necessity for flashback precautions is highly desirable. Furthermore, not only is the lance a safe working tool, but by virtue of' the external cooling feature, it has exhibited a useful life that is prolonged considerably over similar jets or burners utilizing the conventional circulatory cooling means.

Of particular advantage are means by which oxygen may be introduced to the bath. As suggested by prior art devices, the web portion of the nozzle between oxygen orifices had to be maintained at -a certain thickness. The greater this thickness, the less would be the number of orifices which could be formed into any particular lance nozzle. The unique cooling method presently disclosed permits a greatly reduced web thickness limited only by machining tolerances. Therefore, with a greater number of orifices, met-al and slag splash is substantially reduced for a given oxygen fiow.

It is understood that the presently disclosed combination treating lance and roof burner constitutes a preferred embodiment of the novel apparatus, and that certain changes and alterations may be made by one skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. In a process of refining a metal bath in a metallurgical furnace by injecting streams of a treating gas into said bath from the exposed face of a discharge nozzle positioned at the forward end of an injection lance, the improvement for protecting said nozzle from the thermal and chemical effects of said bath during such injection which comprises introducing a high velocity ow of treating gas into said lance, aspirating into said gas fiow, a coolant fiuid to form a composite stream therewith, deflecting said stream near the forward end of said lance into a swirling path to cause said coolant fluid to be deposited against the forward wall of said lance and thence be urged along said wall and onto said exposed face of said injection nozzle, while the stream of treating gas is directed toward the metal bath, whereby said coolant will effect a cooling and wetting of the nozzle face exposed to the high temperature metal bath.

2. In a process as claimed in claim 1 wherein the coolant fluid is water.

3. In a process of refining a metal ybath in a metallurgicalfurnace `by injecting streams of a treating gas into the bath from the exposed face of a nozzle ,positioned at the forward end of an injection lance, the improvement for protecting said lance nozzle face from the thermal and chemical effects of said bath during injection which comprises; introducing a pressurized ow of steam into said lance, guiding said steam ow toward the nozzle face, deflecting said flow into a spiral path at a point upstream of said nozzle face to cause said steam fiow to contact the wall of said lance, condensing said steam to f form water droplets on said lance wall, and urging said water droplets along said wall and onto said exposed nozzle face to effect a cooling and wetting of said nozzle face.

4. In a process for refining a metalcharge in a metallurgical furnace by directing toward said charge a high temperature heating fiarne from the discharge end of a burner adapted to direct said flame; the improvement which comprises, forming in said burner a first high velocity stream of fuel gas having intermixed therewith particles of a heat vaporizable coolant fluid, directing said first stream toward the burner discharge end, interrupting said stream and urging said stream outwardly toward the burner walls to impinge the heavier fluid particles thereof against said wall, guiding the -stream of gas toward the burner discharge end, forming in said burnerv a second stream consisting of a combustion supporting gas, discharging said second stream from` said discharge end in a direction to impinge against said first stream and form a combustible gas mixture, and igniting said mixture to provide a heating flame.`

5. In the process of refining a metal charge ina metallurgical furnace bydirecting, toward said charge a high temperature heating ame from theY discharge end of a burner 'adapted to direct said ame; the improvement which comprises; forming in said burner a high velocity stream of fuel gas having intermixed therewith particles of a heat vaporizable coolant fluid, directing said stream toward the burner discharge end, guiding said stream into a swirling path to impinge said liquid particles against the burner wall, discharging the swirling fuel gas stream toward the furnace charge, forming in said burner a stream of combustion supporting gas, discharging said stream of combustion supporting gas from said burner in a direction to impinge against said swirling stream of fuel gas to form a combustible gas mixture external to said burner, and igniting said mixture to provide a heating flame.

6. In a process as claimed in claim 1 wherein water comprises said coolant uid and is aspiratedvinto said gas flow at a rate between l0 and 70 gallons per hour.

7. In a process` as claimed in claim 3 wherein said steam flow is supplied at a rate between 30 and 100 pounds per hour.

References Cited UNITED STATES PATENTS 754,103 3/1904 Thomley 15s- 73 1,518,854 12/1924 v Kirby 75-41 2,175,182 10/1939 Dino 26a-34x 2,732,257 1/1956 Cress 158-73 2,905,234 9/1959 Scholz 15s-73 3,112,194 11/1963 De vries 75-60X DAVID L. RECK, Primary Examiner.

W. H, TARRING, Assistant Examiner.

Claims (1)

1. IN A PROCESS OF REFINING A METAL BATH IN A METALLURGICAL FURNACE BY INJECTING STREAMS OF A TREATING GAS INTO SAID BATH FROM THE EXPOSED FACE OF A DISCHARGE NOZZLE POSITIONED AS THE FORWARD END OF AN INJECTION LANCE, THE IMPROVEMENT FOR PROTECTING SAID NOZZLE FROM THE THERMAL AND CHEMICAL EFFECTS OF SAID BATH DURING SUCH INJECTION WHICH COMPRISES INTRODUCING A HIGH VELOCITY FLOW OF TREATING GAS INTO SAID LANCE, ASPIRATING INTO SAID GAS FLOW, A COOLANT FLUID TO FORM A COMPOSITE STREAM THEREWITH, DEFLECTING SAID STREAM NEAR THE FORWARD END OF SAID LANCE INTO A SWIRLING PATH TO CAUSE SAID COOLANT FLUID TO BE DEPOSITED AGAINST THE FORWARD WALL OF SAID LANCE AND THENCE BE URGED ALONG SAID WALL AND ONTO SAID EXPOSED FACE OF SAID INJECTION NOZZLE, WHILE THE STREAM OF TREATING GAS IS DIRECTED TWOARD THE METAL BATH, WHEREBY SAID COOLANT WILL EFFECT A COOLING AND WETTING OF THE NOZZLE FACE EXPOSED TO THE HIGH TEMPERATURE METAL BATH.

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