MXPA98002064A - Launch / burner for metal fund oven - Google Patents

Abstract

The present invention relates to a method for injecting gas into, and penetrating the surface of, a bath of molten metal in an oven, from an injection point in the furnace at a significant distance above the surface of the molten metal bath, wherein the molten metal bath has a slag layer on its upper surface, said method comprising: (A) forming a coherent supersonic gas flow in the furnace, by (1) injecting in the furnace, above the molten metal bath through a nozzle directed towards the surface of the bath, (a) a main gas stream whose initial flow axis speed is supersonic and (b) a fuel and secondary oxygen coaxially with the supersonic main gas stream, and ( 2) surrounding the supersonic main gas stream with a phlegm coating that is formed by combustion of the fuel with the secondary oxygen and extending substantially the entire length of the stream supersonic main gas in the kiln, from the outlet of the nozzle to the molten metal bath, where the nozzle has an outlet diameter d, and where the length of the supersonic main gas stream inside the furnace is, at least 20 d, and (B) penetrate the surface of the molten bath with the main gas stream, whose flow axis velocity at that point is still supersonic.

Description

LAUNCH / BURNER FOR CASTED METAL OVEN Technical Field This invention relates generally to the injection of gas such as oxygen into an oven containing a melt bath of molten metal and is particularly advantageous for use in an electric arc furnace.

Previous Technique In the processing of molten metal in a furnace it is frequently desired to provide gas such as oxygen within the molten metal. A recent significant advance for the processing of molten metal in an electric arc furnace is the post-combustion method described and claimed in U.S. Pat. 5, 572,544 - Mathur et al. , wherein the main oxygen is provided within the molten metal from above the surface of the melt bath of molten metal and the post-combustion oxygen is provided inside the furnace above while closing the surface of the molten metal bath. In such a system, because the main oxygen must penetrate into the molten metal bath, it must be injected into the furnace very close to the surface of the molten metal using one or more lances cooled with water or injected into the molten metal at the point below the surface of the molten metal bath using one or more pipes. However, this speed is still not satisfactory since the proximity of the tip of the gas injection device to the surface of the liquid causes excessive but inevitable wear of the lance-type oxygen injector cooled with water. The pipes must be continuously advanced to compensate for melting and oxidation at the submerged end in the molten steel bath which not only requires the pipe handling equipment but is also expensive due to the continuous loss of pipe. In addition, since the surface of the molten metal is not stationary, the oxygen injector must be moved continuously to ensure that the oxygen injection is made in the proper location and with the appropriate nozzle for the distance of the surface of the molten metal bath. . Accordingly, it is an object of this invention to provide a system for providing gas such that oxygen within a furnace containing a molten metal bath where the gas passes into the molten metal bath, although excessive wear of the gas is prevented. gas injection system. There are occasions when it is desired to provide heat within the molten metal furnace, for example to melt waste, in addition to providing gas within the molten metal bath. Accordingly, it is another object of this invention to provide a system for supplying gas within a furnace so that the gas can be effectively passed into the molten metal within the furnace while heat is also provided inside the furnace. In the operation of an electric arc furnace it is desirable to generate a foamed slag layer on the molten metal bath. Accordingly, it is a further object of this invention to provide a system for supplying gas within an electric arc furnace so that the gas can be effectively passed into the molten metal inside the furnace while a foaming scum is also generated. on the molten metal. In the operation of an electric arc furnace it is desirable to reduce the amount of smoke that is generated. Accordingly, it is a further object of this invention to provide a system for supplying gas within an electric arc furnace which minimizes the creation of splashing and also provides a reducing atmosphere that is formed in the vicinity of the splash to reduce the amount of smoke formation. In the operation of an electric arc furnace it is desirable to inject reagents such as carbon, quicklime, alloys, etc. , in the form of powder inside the bathroom. Accordingly, it is an object of this invention to provide a system for supplying gas within an electric arc furnace so that the gas can be effectively passed into the molten metal inside the furnace while also introducing powder reagents into the molten metal.

Brief description of the I nvention The above and other objects, which will become apparent to those skilled in the art, are achieved by the present invention which is: A method for providing gas within an oven containing a bath that is comprised of a metal bath fused with a slag layer on its upper surface, the method comprising: (A) injecting a main gas stream at high speed into the furnace above the bath and injecting it into the furnace fuel and secondary oxygen coaxially with the stream of main gas at high speed; (B) burn the fuel with secondary oxygen to form a flame cover around the main gas stream at high speed; and (C) passing the main gas stream at high speed into the bath. As used herein, the term "oxygen" means a fluid having an oxygen concentration exceeding that of air, preferably having an oxygen concentration of at least 30 mol%, more preferably at least 80 mol% . The oxygen may be commercially pure oxygen having an oxygen concentration of 99.5 mol% or more.

As used herein the term "flame cover" means a combustion current substantially coaxial with the main gas stream and annular therewith. As used herein, the term "slag" means a fused or solid layer of oxides generally comprising one or more of calcium oxide, silicon dioxide, magnesium oxide, aluminum dioxide and iron oxide. As used herein, the term "foamy slag" means a slag which also contains a high volume fraction of gas bubbles such as carbon monoxide which greatly reduces the density of the slag layer and imparts an appearance and behavior similar to that of the slag layer. foam to the slag layer.

Brief Description of the Drawings Figure 1 is a cross-sectional elevational view of a lance / burner embodiment of this invention in operation in an electric arc furnace. Figures 2 and 3 are detailed views of one embodiment, Figure 2 being a cross-sectional view and Figure 3 being a front view, of the injection end of the lance / burner useful in the practice of this invention. Figure 4 is a representation of a preferred embodiment of the gas streams emitted from the lance / burner and the flame shell formed around the main gas stream in the practice of this invention. The numbers in the Figures are the same for the common elements.

Detailed description In general, the invention comprises the creation and use of a high velocity main gas jet such as oxygen that is held coherent by a flame cover around the high velocity jet. The coherence of the jet allows the injection point of the jet inside the furnace to be placed at a significant distance on the surface of the molten metal bath while allowing the jet to penetrate the surface of the molten metal bath so that the gas Main at high speed can pass inside the molten metal bath. The flame cover is formed by the combustion fluid, preferably injected into the furnace in two fluid streams which are each annularly coaxial with the high velocity gas stream. One of the fluid streams is a fuel stream and the other is a secondary oxygen stream. The slower movement of the flame cover resulting from the combustion of the two ring currents forms a fluid or barrier shield around the gas stream at high speed greatly reducing the gases from the outside of the gas stream to high speed that is entering into the high-speed gas stream. UsuallyAs a high velocity fluid stream passes through the air or some other atmosphere, the gases are introduced into the high velocity gas stream causing it to expand in a characteristic cone pattern. By the action of the flame cover barrier, this entry is greatly reduced for a significant distance from the point of injection into the furnace, and the high velocity gas jet retains substantially its original diameter through this distance, i.e. It is coherent through this distance. This coherence allows the jet to retain its ability to penetrate the molten metal bath and consequently the jet injection point can be separated from the molten metal surface while still achieving adequate penetration of the molten metal. In addition, if desired, the jet may contain powder or other additives that can be injected into the molten metal with the main gas. A particularly advantageous application of this invention is the use of an electric arc furnace. In such a practice the main gas jet comprises oxygen which reacts with carbon in the molten metal to form carbon monoxide which bubbles out of the molten metal. The afterburning oxygen reacts with this carbon monoxide on the surface of the molten metal bath that provides additional heat inside the furnace improving energy efficiency and productivity and reducing the level of harmful carbon monoxide that is emitted into the atmosphere from the oven. The invention will be described in greater detail with reference to the drawings and also with reference to the application of electric arc furnace for the invention. Referring to Figures 2 and 3, there is illustrated a lance 1 having a central duct 2, a first annular passage 3 and a second annular passage 4, each of the annular passages being coaxial with the central duct 2. The central duct 2 ends at the injection end 5 of the lance 1 to form the main orifice 6. The first and second annular passages also terminate at the injection end, preferably, as illustrated in the Figures, substantially in the same plane as the orifice 6. The first and second ring passages can each form annular holes around the main orifice 6. Preferably, as illustrated in Figure 3, the first annular passage 3 ends at the injection end 5 in a set of first holes. of injection 7 placed in a circle around the main orifice 6 and, the second annular passage 4 ends at the injection end 5 in a set of second injection orifices 8 placed in a circle around the main orifice 6 and the first injection orifices 7. Each of the central conduit 2 and the second annular passage 4 communicate with an oxygen source (not shown). The oxygen used in the central conduit 2 and the second annular passage 4 may be the same oxygen fluid, or an oxygen fluid may be used in the second annular passage 4 different from that used in the central conduit 2. The first annular passage 3 communicates with a fuel source (not shown). The fuel can be any fuel, preferably it is a gaseous fuel and more preferably it is natural gas or hydrogen. In an alternative mode the fuel can be passed through the lance into the outermost annular passage and the secondary oxygen can be passed through the lance into the innermost annular passage. In another alternative embodiment the fuel and the secondary oxidant can be passed through the lance as a mixture through an annular passage. Referring to the figure, the electric arc furnace 20 having the side wall 21 and the bottom wall 22 and containing a bath comprising a bath of molten metal 23. Generally the metal will comprise iron or steel. In FIG. 1 a slag layer 24 is also illustrated., which may be fused or solid, on the molten metal bath and a layer of metal in lump 25 on the slag layer 24. The slag layer generally comprises one or more of calcium oxide, silicon dioxide, magnesium, aluminum dioxide and iron oxide. The chunk layer, if present, is melted by the heat provided by the electrodes 26 to form the bath of molten metal 23. The molten metal bath comprises, in addition to the metal, oxidizable material such as carbon and / or hydrocarbons.

The lance / burner is positioned so that it passes through the side wall 21 with its injection end 5 above and spaced from the upper surface of the bath by a distance along the jet axis of at least 20d, and it can be separated from the bath by a distance along the axis of the jet of up to 100d or more, where d is the external diameter of the nozzle through which the main gas is expelled from the lance / burner. The jet axis is the imaginary line that runs through the center of the jet along its length. Typically this spacing along the shaft jet is within the range from 30d to 60d. Figure 1, for illustrative purposes, shows a lance used with the furnace. In commercial practice it may be preferable to use more than one lance. Preferably, three or four lances are used, and their locations are selected to provide heat to the normally colder regions of the furnace, as between the electrodes and the nearby openings in the side wall or the roof of the furnace. The main oxygen is injected into the furnace 20 through the nozzle orifice 6 of the lance 1 into the bath comprising the molten metal bath 23 at an initial jet axis velocity, generally at least 304 meters per second and preferably at least 456 meters per second, to form a main oxygen stream at a high velocity 30 as illustrated in Figure 4. The jet axis velocity is the velocity of the gas stream at its jet axis. The main oxygen will contact the bath at a rate of at least 50%, preferably at least 75% of the initial jet axis velocity of the main oxygen stream. Preferably the main oxygen has a supersonic velocity from the lance and also has a supersonic velocity when it makes contact with the bath. Simultaneously with the main oxygen injection, the fuel is injected into the furnace 20 through the first injection holes 7 and the secondary oxygen is injected into the furnace 20 through the second injection holes 8 to form a fuel stream and a secondary oxygen stream, each of those currents being concentric with and coaxial with the current 30. The secondary oxygen burns the fuel to form the flame cover 33 which has a velocity that is lower than that of the oxygen stream. main 30 and is generally within the range from 15.2 to 152 meters per second. The flame cover forms a or very close to, for example, 2.54 cm, towards the tip of the lance and extends substantially, that is to say at least 75% of, the full length of the main gas stream into the furnace towards bathroom. Preferably the flame cover extends the full length of the main gas stream into the furnace into the bath. The flare cover 33 forms a barrier or protection around the oxygen stream 30 greatly reducing in this way the amount of gas outside the stream 30 that is introduced into the stream 30. Therefore, the stream 30 does not expand significantly from the point where it is injected into the furnace through the lance 1 to the point where the bath comprising the * molten metal bath 23 impacts. Generally the diameter of the current 30 when it hits the bath comprising the molten metal bath 23 will be essentially the same as when injected into the furnace 20 through the lance 1. Since the stream 30 remains substantially coherent as it passes from the lance injection end towards the surface of the bath, the injection end may have a large distance from the molten metal while still allowing the high velocity oxygen stream 30 to impact the surface of the molten metal bath With sufficient force so that the high velocity oxygen stream penetrates the surface of the bath and passes into the molten metal bath. Inside the molten metal bath 23, the main oxygen in the high-speed stream 30 reacts with the oxidizable material inside the molten metal bath. For example, the main oxygen can react with the carbon in the molten metal bath to generate carbon monoxide in an exothermic reaction that provides additional heat to the furnace and agitates the molten metal to improve heat transfer. The gas generated by the reaction of the main oxygen with the oxidizable material inside the molten metal bath bubbling out of the molten metal bath. In many cases such gas or gases are in the form of incompletely burned species, such as the aforementioned carbon monoxide. Such incompletely burned species are harmful to the environment and also represent a loss of energy if they are allowed to pass unreacted out of the furnace. The post-combustion oxygen provided inside the furnace above the molten metal reacts with those incompletely burned species as previously described. In an embodiment of this invention in the lance mode, the amount of fuel and secondary oxidant used is not significantly greater than that required to form the flame cover. However, in some situations, it may be desirable to provide a large amount of heat inside the oven, such as, for example, melting the pieces in the oven. In such situations a high oxidant flow rate may be provided inside the furnace and the fuel and oxidant, which may be the secondary oxidant and / or the main oxidant, is used to burn the fuel to generate heat for the furnace. That is, the lance used in the practice of this invention can, if desired, also function as a burner, that is, in the lance / burner mode. In this way a very intense flame is provided which can be used to penetrate and melt the piece metal to provide an unobstructed passage through which the oxygen jet can pass to reach the surface of the molten metal bath. Simultaneously, the flame can melt any piece that may remain in front of the burner due to the progression of the piece fusion and the subsidence, thus maintaining the passage for the bath injection. The high flow rate of natural gas can also provide a natural gas pattern around the coherent jet as the molten metal bath penetrates. When the coherent jet penetrates the metal bath, a small localized cavity is formed and there is little deflection of the gas stream and little splash of the bath. However, some spraying may occur around the bathroom. The spray may be contained in a fuel gas pattern. This will prevent oxidation of the metal droplets that lead to smoke formation. The formation of smoke during the injection is suppressed in two ways: (a) the amount of the spray is greatly reduced by the injection of a coherent jet instead of a normal jet; and (b) the fuel gas pattern will prevent oxidation of the metal droplets on the surface of the bath. In addition, in some situations it may be desirable to use the excess fuel and provide the fuel within the molten bath with the high velocity gas. Such a situation would be to help generate a foamy slag in the practice of the electric arc furnace. Foamy slag is very desirable in reducing energy losses from the electric arc and in reducing refractory wear on the furnace wall. In this situation, excess fuel such as natural gas is introduced into the slag layer where it undergoes decomposition and reaction to produce gases such as carbon monoxide, hydrogen and carbon dioxide which subsequently generates the desirable foam scum. Furthermore, in some situations it may be desirable to introduce reactants in the powder form into the gas stream so that it can be effectively injected into the molten metal bath. Among such reagents can be named carbon, various lime compositions, alloy additions, iron oxide and powder produced by electric arc furnaces. Once the spear / burner of the invention is in place, it can only function as a burner at times when high velocity gas injection into the molten metal bath is not desired. The following guidance pertains to the design and operation of the invention as illustrated in Figures 2 and 3: 1) It is important to have some oxygen flow in the outer ring of the holes for all modes of operation to stabilize the flares around of the central jet. When operating in the lance and lance / burner modes, the oxygen flow through the center rings of the holes should be at least 1% of the total oxygen flow and preferably on the scale of about 5% to 10%. %. 2) When operating in the lance and spear / burner modes, the flow velocity of combustible gas through the inner ring of the holes must be greater than that required to stoichiometrically burn with the oxygen in the outer ring of the holes. 3) When operating in the spear and spear / burner modes, the velocity of the center jet should be greater than about 152 meters per second and preferably greater than 364.8 meters per second. 4) when operating as a burner to preheat and melt cold metal pieces, the portion of the oxygen flow rate for the outer ring of the holes should be between 25 and 75% of the total oxygen flow rate, preferably between 40 and 60% of the total oxygen flow rate and total oxygen must be between 100 and 200% of the stoichiometric oxygen required to burn the fuel gas to completion. 5) When operating in the lance / burner mode to penetrate the partially molten piece, the portion of the oxygen flow rate to the central jet must be greater than 50% and preferably between 75 to 99% of the flow rate of total oxygen and total oxygen must be greater than 100% of the stoichiometric oxygen required to burn the fuel gas to completion and preferably greater than 150%. The following example of the invention is presented for illustrative purposes and is not intended to be limiting. Using a system similar to that illustrated in Fig. 1, oxygen was injected into a bath of molten metal. Oxygen was expelled from the tip of the lance through a nozzle that has an exit diameter of 2,049 cm. The tip of the lance was placed at 71 .12 cm on the surface of the bath and at an angle of 40 degrees towards the horizontal so that the oxygen jet passed through a distance of 109.22 cm or 53 nozzle diameters from the tip of the spear to the surface of the bathroom. The main oxygen gas was covered in a flame cover from the tip of the lance to the surface of the bath and has an initial jet axis velocity of 486.4 meters per second and maintained this jet axis velocity of 486.4 meters per second when it hit the surface. Approximately 85% of the oxygen expelled from the lance entered the molten metal bath and became available to react with the components of the molten metal. Approximately 10.27 m3 standard (MCS) of oxygen per ton of molten metal were needed to burn approximately 9.06 kg of carbon per ton of molten metal compared to approximately 15.62 m3 of oxygen per ton of molten metal that were required for the same metallurgical operation although using the practice of conventional gas provision. Now by the use of this invention, gas can be effectively provided within a molten metal furnace such as an electric arc furnace. Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that other embodiments of the invention exist within the spirit and scope of the invention.

Claims (10)

1. A method for providing gas within a furnace containing a bath that is comprised of a bath of molten metal with a slag layer on its top surface, the method comprising: (A) injecting a main gas stream at high velocity within of the furnace above the bath and injecting it into the furnace fuel and the secondary oxygen coaxially with the main gas stream at high speed; (B) burning the fuel with the secondary oxygen to form a flame cover around the main gas stream at high speed; and (C) passing the main gas stream at high speed into the bath where the flame cover extends substantially the entire length of the main gas stream into the furnace into the bath.

2. The method of claim 1, wherein the main gas comprises oxygen. The method of claim 2, wherein the molten metal bath contains carbon and further comprising reacting the main oxygen with the carbon within the molten metal bath to form carbon monoxide, bubbling the carbon monoxide out of the bath of molten metal and injecting additional oxygen into the furnace above the molten metal bath to oxidize the bubbling carbon monoxide out of the molten metal bath. The method of claim 1, wherein the fuel and secondary oxygen are injected into the furnace in two streams, each of the two streams being concentric with the main gas stream at high velocity. The method of claim 1, wherein the main gas stream comprises an inert gas. 6. The method of claim 1, wherein part of the fuel is not burned and is passed into the slag layer where it reacts to form gas that serves to create a foamed slag layer. The method of claim 1, wherein the flame cover extends the full length of the main gas stream into the furnace into the bath. The method of claim 1, wherein the main gas stream passes into the molten metal bath containing powder. The method of claim 2, wherein the secondary oxygen is injected into the furnace at a flow rate that is within the range of 25 to 75 percent of the total oxygen flow rate of the secondary oxygen and oxygen main injected into the furnace, and the total oxygen flow rate is within the range of 100 to 150 percent of that required to burn stoichiometrically with the fuel injected into the furnace. The method of claim 2, wherein the main gas oxygen is injected into the furnace at a flow rate that is within the range of 75 to 99 percent of the total oxygen flow rate of the secondary oxygen and the main gas oxygen injected into the furnace, and the total oxygen flow rate is greater than 100 percent of that required to stoichiometrically burn with the fuel injected into the furnace. SUMMARY A method for providing main gas effectively within a molten metal bath, which is particularly useful for use in an electric metal furnace. The method employs the combustion of secondary oxygen with the fuel to form a flame cover around a main gas stream that protects the main gas from the ingress of natural gases as it passes through the upper space of the furnace. This allows the gas to retain its original force to injection to a substantial degree within the headspace and therefore can be injected into the furnace at a safe distance from the surface of the molten metal while full penetration into the furnace is still achieved. molten metal.