US3446494A

US3446494A - Method and device for the protection of the refractory masonries

Info

Publication number: US3446494A
Application number: US618747A
Authority: US
Inventors: Giancarlo Consogno
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-03-01
Filing date: 1967-02-27
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27
Also published as: FR1511860A; BE694367A; GB1157848A; NL6703143A; LU52984A1

Description

G. CONQS'OGNO May 27, 1969 METHOD AND DEVICE FOR THE PROTECTION OF THE REFRACTORY MASQNRIES Sheet I z of 3 Filed Feb. 27. 1967 y 7, 1969 ca. CONSOGNO 3,446,494

METHOD AND DEVICE FOR THE PROTECTION OF THE REFRACTORY MASONRIES Sheet Z of 3 Filed Feb. 27, 1967 FIG. 3

FIG.4

FIG.5

FIG.6

y 27, 1969 G. CONSOGNO 3,446,494 I METHOD AND DEVICE FOR THE PROTECTION OF THE REFRACTORY MASONRIES Filed Feb. 27, 1967 Sheet 3 of 5 FIG.8

United States Patent U.S. Cl. 263-44 14 Claims ABSTRACT OF THE DISCLOSURE The invention relates to method and apparatus for the protection of refractory masonries and in particular the crowns of open hearth furnaces. In accordance with the invention, nitrogen is insulflated under pressure against the furnace crown so that between the crown itself and the atmosphere of the furnace there is formed a cushion of nitrogen under pressure which is continuously renewed. Preferably, the nitrogen is introduced under pressure in a direction substantially tangent to the crown to be protected. The pressure of the nitrogen insufllation is preferably kept between 4 and 12 atmospheres and the nitrogen delivery is controlled so that its cooling action on the masonries to be protected keeps the masonries at a selected temperature which may, for example, vary between 1,400 C. and 1,600 C.

Apparatus for carrying out the method comprises a set of nozzles for blowing the nitrogen under pressure just under the crown of an open hearth furnace through a series of blowing heads fed through suitable conduits. Each blowing head is preferably provided with a set of nozzles and axial conduit for supplying cooling liquid under pressure, an outer jacket providing an annular ai cavity for return of the cooling liquid and a cylindrical chamber placed at the end of the head to receive the cooling liquid. A suitable set of conduits puts the chamber in communication with the lower zone of the annular air cavity. The nozzles for the nitrogen are preferably radially disposed in a sector of the blowing head.

Object of the present invention is the utilization of an inert gas to protect the inner walls of the crowns in the open hearth furnaces and the cooled lance by means of Which the maintenance of the defensive shield is possible.

The recently developed technique of the direct insufflation of oxygen during the steel refining process, has the serious disadvantage of causing an excessive wearing to the refractory material of the crowns with consequent shorter life of the furnace life.

Object of the invention is to prevent this disadvantage in order to extend the life of the refractory material by keeping it out of direct contact and by diluting the con centration of the oxygen in excess in the laboratory atmosphere.

Besides a purely chemical protection effect, object of the present invention is to protect mechanically the refractory crown of the furnace against the bath sprinkles and the powders dragged by the fumes, and to obtain, by means of nitrogen, a cooling effect which reduces the thermal stress of the refractory materials.

The method for the protection of the refractory masonries, particularly of the crowns, in the open hearth furnaces, is characterized in that it provides the insufllation of nitrogen under pressure towards the furnace crown, so that a cushion of nitrogen under pressure continuously renewed is formed between the crown itself and the furnace atmosphere, this cushion finds its way out from the furnace also through the interstices existing among the bricks.

The insufllation of nitrogen is effected right under the furnace crown, by means of blasts of nitrogen under pressure, the axis of which is preferably substantially tangent to the crown to be protected, so that the insufllated nitrogen expands tangentially to the crown to be protected, remaining adjacent to it, without being violently reflected against the surface of the underlaying bath. The nitrogen insufliation pressure is preferably kept between 4 and 12 atmospheres.

The nitrogen delivery is arranged in function of the delivery of oxygen insufilated against the bath surface.

At present, according to the necessity, from 1,400+ 1,800 Nmc/h (cubic meters of nitrogen per hour) of oxygen are blown in.

The range may vary in the time according to the availability of 0 A minimum constant nitrogen delivery of about Nmc/h. 200 is provided. Upon the insufllation of 0 said delivery should vary between 300 and 500 Nmc/h. (maximum availability of nitrogen in the present equipment conditions).

Consequently it is possible in the future to vary, according to the availability, the delivery of both fluids in order to speed up the charge refining times.

The delivery of nitrogen is controlled in a different solution so that its cooling action on the masonries to be protected keeps them at a temperature lower than a prefixed one.

In function of the crown temperature with a lance considered for a delivery of 10 atm. of nitrogen, the following value range will be used:

Degrees C.: Delivery Nmc./h.

The equipment for embodying the above process is characterized in that it comprises a set of nozzles, for blowing nitrogen under pressure, suitably placed just under the crown of an open hearth furnace, through a series of blowmg heads fed through suitable conduits preferably crossing the crown itself.

The cited nozzles have their axis substantially parallel to the furnace crown or anyhow slightly inclined towards the crown.

Each blowing head is provided with a set of nozzles distributed according to a sector of suitable width.

Each blowing head is provided with an axial conduit for the supply of a cooling liquid under pressure, like water; an outer jacket providing an annular air cavity for the return of the cooling liquid; a cylindrical chamber placed correspondingly to the end of the cited head, into which the cooling liquid flows; a suitable set of conduits puts the said chamber in communication with the lower zone of the cited annular air cavity; at least a conduit for the supply of the nitrogen under pressure, comprised between the cited axial conduit and the cited annular air cavity; a series of radial nozzles distributed according to a sector of suitable width, with their axes substantially perpendicular to the axis of the cited head, said nozzles putting into communication the lower end of the inflow conduit of nitrogen with the outer part of the cited head.

Right above the port of the nitrogen outlet nozzles, the cited blowing head is provided with a sharp constriction so as to have a free surface for the nitrogen flow obtained over said nozzles. Also the length and diameter of each nozzle can be varied as a function of the feeding pressure of the nitrogen, in this way the outer diameter of the lance is varied accordingly.

The objects, advantages and characteristics of the invention will further result from the following description, referring to embodiments chosen by way of example only with reference to the accompanying drawings, wherein:

FIG. 1 shows the plan from the bottom of the standard crown of an open hearth furnace; FIG. 2 shows the same crown in the same projection illustrated in FIG. 1, the positions of the lances for nitrogen blowing and further the direction to which the relative nozzles must be arranged; FIGS. 3 and 4 show in section, according to a horizontal plane and a vertical one respectively, the distribution area of a flow of nitrogen coming out from a nozzle at a pressure of 8 atm.; FIGS. 5 and 6 are similar to the preceding FIGURES 3 and 4, in the case the nitrogen feeding pressure is at atm.; said diagrams have been obtained experimentally; FIG. 7 is a plan from above of a head for blowing nitrogen under pressure; in a preferred embodiment; FIG. 8 is a section according to the lines VIII-VIII of the preceding FIG. 7.

With particular reference to FIGS. 1 and 2: 1 is the section of the plan from above of the standard crown of an open hearth furnace; the dotted line 2 is the outline of the zone 3 of greater wearing of the furnace crown; 4 are the holes through which pass the lances for blowing oxygen under pressure, the position thereof being directly connected with the extension of the zone 3; 5, 6, 7 and 8 are the positions of four heads for blowing nitrogen under pressure; while the heads for the lances for blowing oxygen project under the furnace crown towards the bath surface, the heads 5 to 8 for blowing nitrogen are practically adjacent to the lower surface of the furnace crown; the curves 9 to 12 are the areas for the distribution of the nitrogen coming out from the heads 5 to 8 respectively, when it is fed at the pressure of 12 atmospheres; the curves 13 to 16, similar to the preceding ones, refer to the case when the nitrogen is fed at a pressure of 10 atmospheres; the arrows 17 to 20 are the intermediate positions to which the sets of nozzles of the outflow heads 5 to 8 are directed.

As clearly seen in FIG. 2, the zone 3 limited by the dotted line 2 is substantially wholly covered by the distribution area of the nitrogen flow coming out from the set of nozzles which each outflow head 5 to 8 is provided with; in the vertical sense, said area of nitrogen distribution has the course indicated in FIGS. 4 to 6; that is, the nitrogen is practically directed to a direction tangential to the furnace crown, so that a protecting cushion is formed between the crown and the underlaying laboratory atmosphere, said cushion however, does not mix with said underlying atmosphere and therefore it does not interfere with the flow of oxygen coming out from the corresponding lance at a lower level. Consequently, the effectiveness of the oxygen action is not reduced by the presence of the outflow of nitrogen.

With particular reference to FIGS. 3 to 6, the values denoted on the axis of the abscissas and of the ordinates of the four diagrams illustrated in FIGS. 3 to 6, are, in millimetres, the distances in the two orthogonal directions, from the centre of a generic inflow head for the nitrogen; as indicated in FIGS. 4 to 6, at a distance of about 4 metres from the corresponding outflow head, the thickness of the outflow area of nitrogen, measured in a vertical sense, is till lower than 500 mm., which assures both the eificiency of a nitrogen cushion sufliciently compact and the non-interference with the underlying outflow Zone of the oxygen.

Anyhow, the distribution areas of the nitrogen outflow may he obviously modified each time by acting, according to the necessities, on the number of nozzles provided in each head, on their diameter and shape, on the feeding pressure, on the distribution of the nitrogen outflow heads and the like.

With particular reference to FIGS. 7 and 8: the outfiow head 21 comprises substantially two

cylindrical bodies

22 and 23 coaxial and overlapped, the side surfaces of which are connected by means of a cone-shaped surface 24; on the cylindrical surface 22, right under the surface 24, the outflow nozzles 25 for the nitrogen are placed; as shown in FIG. 8 the nozzles 25 have their axes 26 substantially horizontal; as shown in FIG. 7, the axes of the set of nozzles of each head 21 are placed radially wtih respect to the axis of head 21 and they are substantially distributed in a single practically horizontal plane; the series of nozzles 25 embraces a sector which, in the shown preferred case, corresponds to about in such a way, the four outflow heads 5 to 8 can cover with the nitrogen flow the whole zone 3 as shown in MG. 2; it is obvious that, with a different distribution of the outflow heads, the cited angle could be different from 90 as indicated in the figure.

Each one of the heads 21 is provided with a central conduit 27 for the inflow of a cooling liquid constituted, for instance, by water; said conduit flows into a cylindrical cavity 28 and herefrom, through a set of inclined ducts 29, reaches an air cavity 30 constituting the back duct of the cited cooling liquid; 31 is a duct asymmetric with respect to the axis of the lance 21 necessary for carrying the nitrogen under pressure and ending correspondingly to the inflow inlet of the nozzles 25.

As already said, the delivery of nitrogen may be regulated according to the temperature of the furnace crown, so that said temperature is always kept under a prefixed value; said delivery may also be regulated in function with the delivery of oxygen insufflated into the furnace, being the quantity of insufflated oxygen the governing factor on which the crown temperature depends.

In the first case the valve which regulates the delivery of nitrogen will be directed through one or more thermocouples measuring constantly the temperature of the furnace crown; in the second case said valve will be suitably coupled with the valve which regulates the oxygen delivery, so that the deliveries of the two gaseous fluids are therebetween arranged according to the values of a prefixed ratio possibly variable according to a prefixed rule.

Although for describing reasons, the present invention has been based on that described and illustrated above by way of example only, many modifications and variations may be made in embodying the invention.

I claim:

1. A method for the protection of the refractory masonry, and particularly the crown of a furnace in which steel is refined by insufliation of oxygen, which comprises blowing nitrogen under pressure along the lower face of the furnace crown and substantially tangentially thereto, to form a cushion of nitrogen between said crown and the atmosphere of said furnace, permitting said nitrogen to exit from said furnace and through the interstices existing in the furnace masonry, and continuously renewing said cushion of nitrogen.

2. A method according to claim 1 in which said nitrogen is blown directly under said furnace crown by means of blasts of pressurized nitrogen which have axes substantially tangent to said crown whereby said nitrogen expands tangentially to said crown, and remains adjacent thereto without being violently reflected against the surface of the underlying bath contained in said furnace.

3. A method according to claim 1 in whcih said nitrogen is blown under a pressure of 4 to 12 atmospheres.

4. A method according to claim 1 in which the amount of nitrogen blown into said furnace is adjusted as a function of the amount of oxygen blown into said furnace, and in which oxygen is blown into said furnace in an amount of about 1,400 to 1,800 times the amount nitrogen blown into said furnace.

5. A method according to claim 4 in which the amount of said nitrogen blown into said furnace is about 300 to 500 cubic meters per hour.

6. A method according to claim 1 in which said nitrogen is cooled prior to its entry into said furnace.

7. A method according to claim 1 in which the amount of said nitrogen blown into said furnace is adjusted so as to maintain said masonries being protected under a predetermined temperature and in which at a crown temperature of l,400 to 1,600 C. the amount of nitrogen blown into said furnace is from about 200 to 400 cubic meters per hour while the feeding pressure of said nitrogen correspondingly varies from about 4 to about 12 atmospheres.

8. In a furnace for refining steel by insufllation of oxygen, a crown and means for protecting said crown from the atmosphere and bath of the furnace and also from heat, said means comprising a series of blowing heads fed through ducts in said crown and a set of nozzles in said blowing heads for blowing nitrogen just under said crown.

9. A furnace according to claim 8 in which said furnace is an open-hearth furnace.

10. A furnace according to claim 8 in which said nozzles have axes which are substantially parallel to or slightly inclined toward said crown.

11. A furnace according to claim 8 in which a series of said nozzles is distributed along a sector of each of said blowing heads, in which the axes of said nozzles are parallel to or slightly inclined toward said crown and in which said blowing heads are positioned across said crown so that nitrogen flowing through said nozzles forms a cushion of nitrogen just under the lower face of said crown.

12. A furnace according to claim 8 in which each blowing head is provided with a duct for the inflow of cooling fluid, a chamber in communication with said duct for the inflow of cooling fluid and positioned at the end of said blowing head which projects farthest into said furnace and means for the return of said cooling fluid from said chamber.

13. A furnace according to claim 8 in whicheach blowing head is provided with an axial duct for the inflow of cooling fluid, a fluid chamber in communication with said axial duct and positioned at the end of said blowing head which projects farthest into said furnace, an outer jacket creating an annular air cavity for the return of said cooling fluids, ducts in communication with said fluid chamber and said outer jacket, and at least one duct for the inflow of pressurized nitrogen in communication with said nozzles and positioned between said axial duct and said outer jacket.

14. A furnace according to claim 8 in which the outer surface of said blowing head is provided with a sharp constriction above the outlet of said nozzles so as to have a free surface for forming the flow of nitrogen above said nozzles and in which said nozzles are variable in length and diameter.

References Cited UNITED STATES PATENTS 1,665,205 4/1928 Getz 26344 1,783,284 12/1930 Easter 26344 2,186,740 1/1940 Teeters 26344 2,293,332 8/1942 Dow et a1. 26344 X 3,165,301 1/1965 Riviere 26315 JOHN J. CAMBY, Primary Examiner.

Us. 01. X.R-. 266 -33