Metallurgical apparatus – Process – Cooling
Reexamination Certificate
1999-11-09
2001-09-04
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Process
Cooling
C266S217000, C266S265000, C239S601000
Reexamination Certificate
active
06284189
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a nozzle for a device to inject oxygen and technological gases, and also the relative dimensioning method.
The device is used to inject at supersonic velocity a gassy flow of oxygen or other technological gases used in metallurgical processes of metal melting.
The nozzle according to the invention can be used advantageously, though not exclusively, in an integrated injection device suitable to emit, with the supersonic gassy flow, another flow, at subsonic velocity, either gassy, liquid or consisting of solid fuels in powder form or in little particles.
BACKGROUND OF THE INVENTION
It is common practice in electric arc furnaces, and in other applications of steel and metal working industries, to inject, by means of lances or other types of devices, technological gases and liquid and solid fuels above and inside the bath of melting metal.
The purposes of this injection are manifold and known to anyone operating in this field
One problem which operators in this field particularly complain of is how to achieve a nozzle which will make it possible to obtain the maximum productivity in injection operations at supersonic velocity of a gassy flow of oxygen or other technological gases.
In the dimensioning of the supersonic nozzles of the injection devices, from the fluido-dynamic point of view there are two fundamental parameters to take into account in order to ensure maximum performance:
outlet velocity of the gassy jet;
density of the penetrating jet, defined as the ratio between the momentum and the area of the section penetrated.
From the operating point of view, the optimum solution would suggest mounting the injection device on the walls of the furnace, putting the end, or emission nozzle, far from the bath of metal, in such a way as to preserve it from such damaging elements as the extremely high temperature, the splashes of molten metal, corrosion and impacts with the scrap.
This also allows to reduce the cooling requirements of the head of the device.
This operating constraint contrasts with the technological aspects linked to the fluido-dynamic performance of the gassy jet, since it requires a considerable increase in the outlet velocity of the flow to keep density high as it passes through the layer of slag to the point of entry into the bath of metal.
It is also obvious that the farther the emission point of the injection device is from the zone of impact in the bath of metal, the more risk there is of weakening and dispersing the jet, and therefore of loss of performance and precision in the injection.
At present there are no solutions known to the state of the art wherein the problem of dimensioning the nozzles has been faced in the light of satisfying all these contrasting requirements.
Until now, the dimensioning of devices with nozzles of a constant section has been achieved according to conventional criteria of one-dimension calculation, which limit the outlet velocity of the gassy jet to values of not more than 1 Mach.
Moreover, these dimensioning criteria have the disadvantage that, in order to obtain the desired outlet velocity for a given diameter of the injection device and for a given surface roughness, the length of the device must be increased; consequently, to prevent choking, high stagnation pressures have to be used, which often cannot be obtained in practical applications in steel working plants.
By exploiting the geometry of the nozzles with a convergent/divergent development, it has been possible to obtain higher outlet velocities; however, due to the inaccuracies of present dimensioning criteria, based on empirical data or on simplified analytical methods, the velocity and pressure profiles obtained along the nozzle and in correspondence with the outlet thereof often have a high level of instability and therefore limited performance.
When the emergent gassy jet interacts with the surrounding atmosphere of the furnace, high and irreversible pressure losses therefore occur which impede and prevent high performance and operating efficiency being obtained.
Even when more evolved and sophisticated methods have been proposed for dimensioning the nozzles of the lances, (see for example the document by J. D. Anderson Jr. “Fundamentals of Aerodynamics”, McGraw-Hill, 1991), these methods have shown themselves to be applicable for dimensioning only the divergent part of the nozzle.
To obtain a complete dimensioning of the entire convergent/divergent development of the nozzle it is necessary to combine that method with a conventional method.
However, adopting that dimensioning method there is the problem of combining the resolution of a field of subsonic motion of an elliptic type with the solution of a field of supersonic motion of a hyperbolic type.
The transition between these two regions of flow gives a field of motion of a parabolic type which is very susceptible to instability.
The present Applicant, in the light of the shortcomings of the state of the art, and taking into account the technological requirements of preparing injection devices with high performance and high functionality, has developed an algorithm of dimensioning and calculation which allows to design nozzles suitable to satisfy all the operational and technological requirements.
The principle of the invention is based on the concept of optimising the conversion of potential energy into kinetic energy, so that the potential energy varies with respect to the axial coordinate of the nozzle following a law of the type with a hyperbolic tangent.
This invention is therefore achieved in a method of dimensioning and calculation which exploits the algorithm mentioned above and allows to obtain many advantages, overcoming the shortcomings of the state of the art.
SUMMARY OF THE INVENTION
The purpose of the invention is to define an inverse method of three-dimensional axi-symmetric dimensioning for nozzles with a convergent/divergent development applied on supersonic injection devices, hereinafter called simply lances, which allows to obtain a plurality of advantages with respect to traditional methods adopted until now.
A first advantage is that it is possible to achieve a nozzle with a geometry which develops in such a way as to adapt to the natural profile of the fall in pressure of the low delivered.
A second advantage is that the method according to the invention allows to obtain the profile of the whole nozzle without dividing it into a supersonic zone, a subsonic zone and a transit zone between the two.
Another advantage is that it is possible to obtain a great homogeneity of the profile of velocity and pressure along the nozzle, and particularly in correspondence with the outlet of the relative lance; this allows to obtain greater distances from the outlet along which the density of the jet can be maintained.
Moreover, a further advantage is that the operation to dimension the nozzle is considerably simplified.
The method according to the invention allows to achieve a nozzle with a convergent/divergent development, obtaining velocity and pressure profiles which are highly stable inside the nozzle itself in its different transverse sections; it also obtains a very limited sublayer, and extremely uniform values of pressure/temperature/velocity at the outlet, throughout the field of application of the technology.
According to the invention, the characteristics as above are obtained by optimising the fall in pressure along the convergent/divergent nozzle (Laval nozzle) in such a way that the fall in pressure follows a hyperbolic tangent development.
In other words, the approach adopted to obtain the dimensioning of the nozzle is an inverse approach, in the sense that the geometric development of the nozzle adapts to the natural profile of the fall in pressure of the gas, instead of imposing it arbitrarily with its geometric configuration
In this way, the geometry of the nozzle is adapted to the natural fall in pressure of the gassy flow which travels through the nozzle and therefore we obtain an optimum variation of the thermodynamic parameters, acco
Morsut Stefano
Pavlicevic Milorad
Poloni Alfredo
Danieli & C. Officine Meccaniche S.p.A.
Kastler Scott
Stevens Davis Miller & Mosher LLP
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