Patent Number: 063226103
Section: summary

FIELD OF THE INVENTION This invention concerns an integrated device to inject oxygen and technological gases in general, and also solid material in powder form, as set forth in the relative main claim. The invention also concerns the method to use the integrated device for the metallurgical processing of a bath of molten metal. In the following description we shall refer principally to oxygen, but it is implicit that the device according to the invention can be used also for the injection of any other technological gas, for example air, argon, nitrogen or others, or a mixture thereof, in a metallurgical process which includes a bath of molten metal. The device according to the invention is suitable to inject, together with the gassy jet of oxygen or other technological gases, a jet of solid material in powder form, such as for example lime powder, carbon powder or similar. The invention is applied, preferably but not exclusively, in steel working industries and is particularly indicated to be applied in processes to melt steel, for example in electric arc furnaces. BACKGROUND OF THE INVENTION It is common practice in electric arc furnaces, and in other applications in steel and metallurgical industries, to inject technological gases and solid material in powder form above and inside the bath of melting metal. Generally speaking, technological gases should be taken to mean oxygen, nitrogen, argon, methane, propane, air or other gases with like characteristics. Generally speaking, solid material in powder form should be taken to mean the powders of coke, carbon, iron alloys, lime, dolomite or other materials with like characteristics. There are many purposes for this injection, among the most important being: to provide an energy input for melting; PA1 to activate the oxidation step and influence the dephosphorization and the desulphurization of the liquid metal; PA1 to encourage slag foaming; PA1 to facilitate the melting and shearing of the scrap; PA1 to encourage the stirring of the bath, thus accelerating the time taken to activate the chemical reactions; PA1 to actuate decarburation, that is to say, the regulation of the carbon content, and to control the tapping temperature; PA1 to obtain the burner functioning mode, wherein the oxygen or air enriched with oxygen act as comburents of natural gas, methane, oil, propane, butane, carbon or other solid or gassy fuels. PA1 a) by means of water-cooled lances equipped at the ends with a nozzle, for example of the convergent/divergent type, suitable to produce a supersonic jet at outlet; PA1 b) by using lances of the consumable type. PA1 the need for manipulation; PA1 the gassy jet loses energy due to the distance from the bath, which often implies it is impossible for the jet to penetrate inside the bath; PA1 large quantities of cooling water are needed to prevent the tip of the lance from being destroyed due to the heat and the mechanical stresses; PA1 danger of explosions caused by possible water leakages; PA1 if the lance is very close to the bath there is a risk of damage due to the heat, the tip may be washed, encrustations of steel may form and there is a risk of erosion; PA1 if the lance is very close to the scrap, the gassy jet may be deflected and even reflected against the end or the side of the lance and therefore cause damage thereto; PA1 another lance is needed for the combustion of the CO which escapes from the bath; PA1 other devices are needed to inject the solid material in powder form. PA1 high cost of the parts which are consumed; PA1 it is difficult to determine the exact positioning of the tip of the lance; PA1 the method is not very efficient at distributing the point of impact of the jet; PA1 due to overheating the lance may bend; PA1 it is necessary to add new segments of lance as it is gradually consumed; this requires a wide use of equipment and manipulators which are costly and bulky; PA1 further devices are needed for the post-combustion and injection of the solid material in powder form. PA1 reduction of tap-to-tap time; PA1 reduction of electric energy consumed; PA1 reduction of electrode consumption; PA1 improved penetration of the gassy jet into the bath of metal; PA1 more accentuated turbulence in the bath, which entails a more uniform temperature and a quicker melting of the scrap; PA1 greater melting intensity; PA1 greater productivity and greater efficiency in the use of the oxygen in the bath; PA1 reduced concentration of oxygen in the liquid bath and therefore better quality of steel; PA1 when coupled with electromagnetic stirrers, in some cases it allows to eliminate the function of the bottom tuyeres; PA1 reduction of erosion of the refractory; PA1 greater efficiency in post-combustion and reduction of the carbon oxide in the gases discharged from the furnace; PA1 reduction of the water cooling of the injection means; PA1 more efficient use of foamy slag technique. In the state of the art two main solutions are adopted to inject oxygen or other gases inside a liquid bath: Using water-cooled lances entails the following disadvantages: The disadvantages of consumable lances are as follows: Of the two solutions, in recent years the use of supersonic lances has particularly developed; with these it is possible to inject the necessary quantity of oxygen by means of a jet with a speed higher than that of the sonic speed of the fluid in the relevant conditions of supply temperature and pressure. However, with present-day technology, the oxygen is not injected an optimum manner of functional to the melting process. In fact, in systems known to the stat of the art, the impulse of the jet of oxygen is insufficient to penetrate the bath of liquid metal to a depth sufficient to ensure that the oxygen is adequately distributed throughout the bath (for example equal to half the overall height of the bath). At the moment of impact with the surface of the bath, the jet generates impact waves of compression of very high intensity, which cause a dissipation of the jet and a dispersion of the gas on the surface of the bath, so that only a minimum part of the gas penetrates into the liquid bath of molten metal. This impact against the surface of the bath also causes a loss of coherence and parallelism in the fluid threads in the jet, with a resultant loss in its penetrative ability. Moreover, the system makes it necessary to mount the supersonic lance on a manipulator, or another mechanical organ which allows the lance to be moved, in order to adjust the outlet distance with respect to the surface of the bath, since the jet of oxygen tends to disperse after a few centimeters, in the order of a few dozen cm, from the outlet of the supersonic nozzle. For this reason, consolidated practice provides to insert the end part of the supersonic lance inside the layer of slag above the bath to ensure that the oxygen is introduced inside the liquid bath in a sufficiently efficient manner, but in any case this is not an optimum solution. EP-A-874.194, which discloses the pre-characterizing part of claim 1, describes a burner which can be used on electric arc furnaces comprising a first, inner nozzle with a convergent-divergent development (Laval nozzle) which emits a mixture of oxygen and natural gas, and a second nozzle, coaxial to and outside the first, which emits particulate material. In this document, the purpose is substantially to allow the flow of particulate material to mix with the primary flow of oxygen and fuel, so that the material can be distributed uniformly in the flame produced by the burner and can be projected as far as possible inside the furnace. The outer nozzle defines a straight flow path for the particulate material in order to prevent abrasions on the wall due to the passage of said material. In this document, the flow delivered by the outer nozzle does not form a protective crown for the primary flow delivered by the inner nozzle, but mixes immediately therewith, already inside the burner itself, since it is drawn by the high increase in pressure created by the supersonic acceleration of the oxygen and fuel. Moreover, this document does not provide variable working options to modify the composition and the development of the flame according to the various steps of the melting process, so that the regulation of the working of the burner is not correlated to the development of the melting cycle and to the different technological requirements which gradually occur. The present Applicant has designed, tested and embodied this invention to overcome all these shortcomings and to obtain further advantages. SUMMARY OF THE INVENTION This invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the main embodiment. The purpose of the invention is to achieve an integrated device to inject oxygen and technological gases into a bath of liquid metal which will ensure maximum efficiency and yield, minimum wear and minimum difficulty in use and manipulation. Another purpose of the invention is to integrate in a single device the following functions: to inject gases, to inject solid fuel in powder form or in particles, to add comburent in the post-combustion process, to inject powders to passivate the slag, and also to function as a burner; these various functions may be carried out in succession by the same device according to the progress of the melting cycle. With the device according to the invention, in fact, a single module allows to achieve all the steps of the melting process, that is to say, heating the material to be melted, melting and shearing the scrap by injecting high density oxygen, decarburation, slag foaming, injecting solid fuel in powder form or in particles, post-combustion and energy input in the decarburation step. All or part of the above-mentioned functions can be performed at the same time. In other words, according to the needs and the specific step of the cycle, the device according to the invention can be made to function either as a burner with a variable stechiometric ratio and a variable flame length, or also as an injector of oxygen only or other technological gas with a high rate of distribution of the gassy flow into the liquid bath, or also as a simultaneous injector of technological gases and powdered fuel, for example to obtain the production of foamy slag or to obtain the passivation of the slag itself. The device according to the invention therefore allows, in a single body, to integrate the function which in the state of the art are normally performed by three different devices: a supersonic lance to inject a gassy jet, a subsonic lance or burner for post-combustion, and a lance to inject solid fuel such as carbon powder or combustible powders in general. Using the device according to the invention allows to obtain substantially operating advantages, such as for example the reduction of the work force required, greater safety for the workers, improved working conditions and a greater control over the process. In terms of the process, using the device according to the invention allows to obtain the following improvements: The device according to the invention allows the simultaneous emission of two jets substantially autonomous and independent, which ensures a good working flexibility and versatility. The device according to the invention is mounted in an axially fixed manner on the wall of the furnace, and therefore does not need any manipulation, replacement of tubes, insertion of equipment through apertures in the furnace, with the consequent need of keeping the slag door open. The device is mounted in such a way that its angle of inclination with respect to the surface of the liquid bath can be varied so as to adapt it to the changing conditions which occur inside the furnace during the cycle. For example, the inclination of the device can be varied during the process in order to reduce the level of the liquid bath so as to maintain substantially constant the angle of incidence of the jet, thus preventing the unwanted phenomenon of the jet itself being reflected. The device according to the invention can be used in a modular system which provides a plurality of injection points distributed on the periphery of the furnace, which makes the injection system extremely flexible and versatile and reduces the risks of splashes of liquid metal against the walls of the furnace thanks to the fact that it is possible to use lesser smaller amounts of gas for each device. The device according to the invention allows to emit an extremely energetic gassy jet with a high specific density, which encourages the penetration into the liquid metal and increases efficiency also when there is a smaller quantity of gas introduced.