Method and equipment for the intensive use of oxygen in open hearth furnaces for the production of steel

Feb. 19, 1963 m. foresi etal 3,078,084

METHOD AND EQUIPMENT FOR THE INTENSIVE USE OF OXYGEN IN OPEN HEARTH FURNACES FOR THE PRODUCTION OF STEEL

Filed Oct. 9, 1959

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3,978,084

Patented Feb. 19, 1963

United States Patent Office

3,078,034

METHOD AND EQUIPMENT FOR THE INTENSIVE USE OF OXYGEN IN OPEN HEARTH FURNACES FOR THE PRODUCTION OF STEEL

Mario Foresi, Genoa-Pegli, and Salvatore Ungaro, Genoa, Italy, assignors to “CornigUano” Societa per Azioni, Genoa, Italy

Filed Oct. 9, 1959, Ser. No. 845,529 Claims priority, application Italy Nov. 12, 1958

Claims. (Cl. 266—33)

In open hearth furnaces, in the production of steel, it is a known practice to use oxygen which is introduced into the flame or on to the bath with the aim of accelerating the siderurgical process; also known are the difficulties of suitably subdividing the oxygen between the flame and the bath, and of avoiding dangerous concentrations of heat which reflect themselves in a limitat'on in the employment of the oxygen, in a wearing action on the fireproof bricks, and in a heavy formation of red iron oxide fumes.

The method and equipment in accordance with the present invention successfully permit, simultaneously and in a variable manner, of either the insufflation of oxygen in the flame, in a quantity and a position such as are likely to achieve its highest efficiency in the whole of the operation while at the same time preventing the flame, which is enriched in oxygen, from developing a wearing action on the refractory bricks, or the sending of a controlled jet of oxygen, at a very high speed, on to the charge, with the aim of activating the thermal exchange between the flame and the charge for the purpose of accelerating the transformation processes of the metal without dangerous concentrations of heat, and for the purpose of completely burning up the reaction gases.

The method for the intensive use of oxygen in an open hearth furnace, for the production of steel, is characterized by the fact that the oxygen is insufflated into the furnace at a very high velocity below the lighted fuel, and the jet of oxygen, in the shape of a cone, is regulated in such a manner that a part of the said jet shall reach the cone of lighted fuel with a view to activating the flame, and another part of the jet, which is appropriately distributed for the purpose of preventing a concentration of heat, shall reach the charge so as to act physically and chemically on the charge and on the reaction gases.

The afore-mentioned method is also characterized by the fact that the ccne of the lighted fuel, with its bottom portion, comes into contact with the oxygen’s cone-shaped jet, and the flame reaches a higher temperature whereas, with its upper portion, which is not in contact with the oxygen but with the air originating from the regenerator, it protects the furnace’s refractory lining from the high temperature reached by the flame, which is underneath, and by the bath.

The equipment for carrying into effect the afore-mentioned method is characterized by the fact that it has at least two conduits, which are suitably arranged and separately movable, the first for the purpose of conveying the fuel and the second for conveying the fuel and the second for coinveying the oxygen, both being equipped with means of regulation.

The afore-mentioned equipment is also characterized by the fact that it has:

At least three conduits, arranged one on the other, and being separately movable; the first and the second for the purpose of conveying the gaseous fuel or fuels, the liquid fuel or fuels, and the bottommost one for the purpose of conveying the oxygen, all of them being equipped with means of regulation;

A burner which is movable in the vertical and horizontal planes, and containing three or more pipes arranged on superposed planes; the top ones for the purpose of conveying the gaseous fuels or fuel and the liquid fuel or fuels; the bottom one for the purpose of convey5 ing the oxygen; they are all equipped with means of regulation and are protected by an empty space through which a cooling fluid flows;

The terminal portion of the nozzle conveying the oxygen being equipped with a convergent-divergent nozzle func10 tioning as a diffuser for the purpose of transforming, at the end of the flow, a very high pressure there available so as to increase its velocity which, in the minimum section of the piping already reaches the velocity of sound;

A pipe for the central feeding of solid, liquid or gaseous substances, which enters the pipe which carries the oxygen and which has a flow orifice which is arranged so as to correspond to the minimum section of the nozzle in such a way that the said substances are carried to the 20 centre of the jet of oxygen and carried along by same;

At least two pipes for the peripheral supply of solid, liquid or gaseous substances which make their way obliquely into the pipe which supplies the oxygen, and having flow orifices which connect with the nozzle’s di25 vergent surface; in such a way that the substances are carried to the outside of the jet of oxygen carried along by the latter.

The invention will now be further described with reference to the accompanying drawings which illustrate, in 30 diagrammatic form and solely for the purpose of example, a piece of equipment in accordance with the invention, two particularities of the nozzle prefitted on the oxygen flow orifice, and one application of the equipment. In these drawings:

FIG. 1 is the longitudinal section of a burner,

FIGURES 2 and 3 are longitudinal sections of two types of convergent-divergent nozzle to be fitted so that they communicate with the end of the oxygen flow and designed for the introduction of substances into the ac40 tual jet,

FIG. 4 is vertical section of an end of the open hearth, furnace, with a burner fitted.

As regards FIGURE 1, reference 1 denotes the outer body of the burner, the outer surface of which is in 45 contact with the combustion’s hot gases, and the inner . surface of which is washed by the cooling water; 2 is the inner body of the burner, the outer and inner surfaces of which are washed by the cooling water; 3 is the space which subsists between the outer body 1 and the inner ⁵⁰ body 2 and which forms the empty space between the two bodies inside which the cooling water flows; 4 is the pipe for the gaseous fuel which is built into the top portion of the inner body 2; 5 is the regulating valve for the gaseous fuel, and 6 is the gases’ flow end fitted °5 on the head of the outer body 1; 7 is the pipe for the liquid fuel, which is built into the inner body 2, below the pipe 4; 8 is the regulating valve for the liquid fuel, and 9 is the liquid fuel’s flow end fitted on the head of the outer body 1; 10 is the oxygen pipe, which is built into ⁶⁰ the inner body 2, below the pipe 7; at the end 12 of the pipe 7 is fitted a convergent piping 13 and divergent piping 14, acting as a nozzle fitted on the head of the outer body 1; 11 is the valve for regulating the oxygen; 15 is the bottom closure of the outer end of the body 65 2 which is traversed by the three pipes 4, 7 and 10; 16 is the connection for the intake of the cooling water which is connected to the outer portion of the inner body 2, and 17 is the connection for the cooling water outlet, which is connected to the outer portion of the outer ⁷⁰ body 1.

As regards FIGURES 2 and 3, reference 18 denotes the oxygen feed pipe which terminates at 12; 19 is the

3,078,084 convergent-divergent piping, or nozzle, fitted at the end of the pipe 13; Si is the intake section, Sc is the critical section, and Sr is the end section of the nozzle 19; 20 is the pipe for the central supply of solid, liquid or gaseous substances, which enters the pipe 10, having the flow orifice 21 communicating with the critical section Sc of the nozzle 19 and located on the axis of this same nozzle; 22 are the two pipes for the peripheral supply of solid, liquid or gaseous substances which enter the nozzle 19 obliquely and have flow orifices 23 communicating with the divergent surface 14.

As regards FIGURE 4, reference 24 is the head of an open hearth furnace; 25 is the sole of the said furnace, and 26 is the vaulted roof of the same furnace; 27 is the upper level of the bath; 28 shows the highest position, and 29 the lowest position which may be assumed by the axis of the burner; 3® are the two generatrixes of the cone formed by the lighted fuel, and 31 are the two generatrixes of the cone formed by the oxgen; 32 is the axis about which the burner turns on the vertical plane; the arrows indicate the path followed by the air which is pre-heated by the regenerator.

The manner in which the equipment functions is as follows: The jet of the ignited liquid fuels, with the jets of the gaseous fuels, forms a flame which is substantially in the shape of a cone; below the said flame the oxygen is distributed at a velocity exceeding that of sound, the said oxygen, as it emerges from the nozzle 19 also forming a jet which is substantially in the shape of a cone, the upper portion of which enters the cone of ignited fuels located above, whilst the lower portion of the jet of oxygen reaches the charge.

If, by means of the regulating valves’ being adjusted singly or jointly, the supply of fuel and oxygen is varied, it will be possible to obtain automatically the interference required by the cone of oxygen with that of the flame, and the action of the oxygen on the charge.

Distributed in this manner, the oxygen, by combined action (mass, velocity and oxidation) acts on the flame, the charge, and on their heat exchange. In particular, the oxygen improves the flame’s characteristics, accelerates, first of all, the fusion, and then the transformation of the charge, and it acts direct on the molten metal after first having removed from the latter the layer of slag floating on top.

Moreover, the oxygen succeeds in burning, near the bath, the gases which are set up by the latter, producing a better yield from the operation and preventing the combustion of the said gases from spreading to places where it would be of no value for the operation as such and indeed dangerous for the refractory lining. With this better distribution of oxygen there is obtained a more uniform action on the charge without excessive concentrations of heat and without the consequent development of red iron oxide fumes.

Using the equipment which is the subject of the present invention it is possible to distribute appropriately quantities of 2500 Nmc./h. of oxygen * (with an average consumption of 40 Nmc./t.) resulting in a doubling of the production (average hourly production 60 t./h. in an open hearth furnace with a capacity of 250 tons) at a smaller prime cost and lower specific consumption of fuel and refractories.

In FIGURE 4 is shown, for the purpose of example, the mounting of a burner in accordance with the invention on one of the two heads of an open hearth furnace, though the mounting is made on the two heads with the aim of utilising the air which has been pre-heated again by the regenerator; the operation of the two burners takes place consecutively and alternately.

The burner in accordance with the invention may also be used with any other type of open hearth furnace and with any other type of charge and fuel. The pipe which * Nme. = normal cubic meter.

conducts the oxygen may also be fitted separate from the burner in cases where an independent movement on the part of the burner is desired.

With the convergent-divergent pipings cf the kind shown in FIGURES 2 and 3 it is possible to introduce, into the jet of oxygen, solid, liquid or gaseous substances such as are suitable for the performance of tire siderurgical operation or for the protection of the fireproof lining.

The said substances come in respectively either centrally or peripherally, in suitable positions, for the purpose of being swept along in the jet of oxygen while remaining, respectively, in the desired zone, be it central or peripheral.

Depending on the requirements of the particular siderurgical operation, use will be made, for example, of the following substances: iron alloys, coal, deoxidizers, lime, water, steam, inert gases, etc.

Although, for descriptive reasons, the present invention has been illustrated on the basis of what has previously been described, many modifications and variations may be made in the execution of the equipment, particularly as regards: the structure of the divergent portion of the nozzle for the oxygen, the reciprocal position of the pipes which carry the fuels, the positions and structure of the flow orifices of the substances which are injected into the jet of oxygen, all these modifications and variations being nevertheless based on the fundamental ideas of the invention as summarized in the following claims.