US3621104A

US3621104A - Sealing device for electrode holes in electric arc furnaces

Info

Publication number: US3621104A
Application number: US73204A
Authority: US
Inventors: Alexander Yordanov Valchev; Kyril Hristov Tashev
Original assignee: DMZ LENIN
Current assignee: DMZ LENIN
Priority date: 1969-09-19
Filing date: 1970-09-17
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: FR2062396A5; DE2045133C3; DE2045133A1; DE2045133B2; ES383571A1; GB1263015A; SE373261B

Abstract

Sealing device for electrode holes in electric arc furnaces; the device includes means creating a chamber around the electrode, and means for creating in the chamber a gas pressure exceeding the pressure in the furnace space. A diffuser is placed in the access duct of the chamber and a nozzle is located in the axis of the diffuser, this nozzle delivering gas under pressure which entrains additional quantities of gas. Preferably the gas is air. The chamber of the sealing device may have two or more access ducts, diffusers being placed in all access ducts, and a nozzle being located in the axis of each diffuser, each such nozzle delivering gas under pressure. The cross section of the diffuser may have a reduced height and an increased width, and may be shaped as an oval, an ellipse, a rectangle, or another similar geometrical figure; there may be two or more nozzles located in the diffuser, such nozzles delivering gas under pressure.

Description

United States Patent SEALING DEVICE FOR ELECTRODE HOLES IN ELECTRIC ARC FURNACES 5 Claims, 7 Drawing Figs.

U.S. Cl. 13/9, 98/115 R, 13/17 Int. Cl 1105b 7/12 Field of Search 13/1, 9. l4,

Primary Examiner-Bernard A. Gilheany Assistant Examinen-R. N. Envall. Jr. A!IurneyArthur O. Klein ABSTRACT: Sealing device for electrode holes in electric arc furnaces; the device includes means creating a chamber around the electrode, and means for creating in the chamber a gas pressure exceeding the pressure in the furnace space. A diffuser is placed in the access duct of the chamber and a nozzle is located in the axis of the diffuser, this nozzle delivering gas under pressure which entrains additional quantities of gas. Preferably the gas is air. The chamber of the sealing device may have two or more access ducts. diffusers being placed in all access ducts. and a nozzle being located in the axis ofeach diffuser, each such nozzle delivering gas under pressure. The cross section ofthe diffuser may have a reduced height and an increased width, and may be shaped as an oval. an ellipse, a rectangle, or another similar geometrical figure; there may be two or more nozzles located in the diffuser, such nozzles delivering gas under pressure.

PATENTEMuv 16 mn 3,621,104

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ALEXANDER YORDANOV VALCHEV KEQL HRISTOV TASHEV Attorney PATENTEDuuv 16 men 3.621.104

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2 or 2 ALEXANDER YORDANOV \ALCHEV KYRIL.HRISTOV TASHEV Attorney SEALING DEVICE FOR ELECTRODE HOLES IN ELECTRIC ARC FURNACES This invention relates to a sealing device for electrode holes in electric arc furnaces.

At the present time various sealing devices for electrode holes are used in electric arc furnaces. Among the known types of sealing devices, the ones with the best operational properties are those sealing devices of the air-cushion" type. This type of sealing device creates a chamber around the electrode, into which such a quantity of air is delivered that, when the air flows out through the clear section area upwards along the electrode, a pressure is maintained in the chamber which slightly exceeds the pressure in the furnace space (by 0.5 mm.

water column, for example). In order to provide a good sealing action, a large volume of air must be delivered to these sealing devices.

The required air volume is proportional to the area of the clearance between the seal and the electrode. Usually, in large electric arc furnaces, each seal has a clear area of 200 to 400 cm?; hence, to obtain a good sealing, 800 to 1,600 m. of air per hour must be delivered to each seal. The aforementioned size of the clear area is equally valid for electrodes without a protective coating, as well as for electrodes with a protective coating. In the case of electrodes without a protective coating, at the beginning of the casts the clear area is smaller, but increases as a result of the intensive oxidation of the graphite in the seal. In the case of electrodes with a protective coating, such oxidation does not take place, and the clear area does not change; however, this area is, as a rule, larger, because slag drops stick to the coating, whereby the size of the electrode is increased.

The delivery of large volumes of air in the aforementioned sealing devices creates considerable difficulties in operation. The air for sealing may be delivered by a fan, which is attached to the roof ring of the furnace. Such a solution has the advantage that the fan air is very cheap, but it possesses at the same time great disadvantages.

It is difiicult in practice separately to regulate the air delivered to each seal. Furthermore, it is not possible to regulate during a cast the total volume of air for the three seals ofa three-phase furnace, this volume being different for the different periods of the cast.

An important disadvantage is the fact that it is not possible, in the case in which it is necessary to increase considerably (several times) the volume of air delivered to one of the seals which is undergoing severe working conditions or works with a greatly increased free area between seal and electrode. This disadvantage results from the fact that, in most contemporary furnaces, the distances between the roof and the arms, or between the roof and the electrode holders are small and do not permit the mounting oflarge air ducts and of seals of great height. For this reason, the air ducts are usually dimensioned in such a way that only a small reserve for increasing the volume of the delivered air exists percent, for example. Consequently, each significant worsening of the working conditions of one of the seals leads first to the elimination of the sealing action, and in short time also to a total destruction, by oxidation and melting, ofthe seal.

An important disadvantage of such prior construction are the large-sized air ducts on the roof of the furnace, which require a reliable electrical insulation between the air ducts of the separate phases of the multiphase electric current supply. As a result of the severe working conditions of the roof of the electric furnace, such as high temperature, deposition of electrically conductive powder, vibrations, etc., short circuits may occur; these can interrupt the air duct for one of the phases. However, the repair of damages in the roof of the electric furnace is dangerous, and in many cases, even impossible. Furthermore, the mounting of air ducts to each new roof is labor and material consuming.

A further drawback of the aforementioned solution of the problem is the frequent burning of the electric motor of the fan in the case of worsening of the sealing between the roof ring and the furnace. It is true that there exist solutions wherein the fan is mounted on the platform of the furnace and is connected in a convenient way to the air duct on the roof. However, such solutions have the disadvantage during operation that the movable connection between both air ducts can easily shift out of center and create additional operating difficulties.

It has been attempted to deliver compressed air in the aircushion type of sealing devices. Such a solution eliminates all the aforementioned drawbacks, but is not used in practice because for this specific use the cost of the compressed air is unacceptably high and exceeds all profits due to the sealing.

There are, nevertheless, sealing devices of the air-cushion type which operate with compressed air; however, in this case, auxiliary mechanical seals are fitted on the air seals in order to reduce the clear area between electrode and seal, i.e., to reduce many times (10 times, for example) the required volume of compressed air. Such sealing devices have been used in practice, but their important drawback is their complex design; they also require a more careful and expensive maintenance.

The sealing devices of the air-cushion type have better operating properties than the other known types of sealing devices; however, because of the aforementioned drawbacks, they are used only in a limited number of metallurgical works and have not found a wide industrial application.

It is, therefore, a general object of the present invention to provide such a delivery of air to the sealing devices creating a chamber around the electrode that the sealing action of each separate seal may be regulated easily within broad limits. The sealing action of the three seals altogether is also readily controlled.

It is a further object of the present invention to avoid the necessity oflarge-sized air ducts on the roof of the furnace and of electric insulation between them.

According to the present invention, these objects are achieved by placing a diffuser in the access duct of the seal creating a chamber around the electrode, and locating a nozzle in the axis of the diffuser, the nozzle delivering compressed gas in such a way that the gas stream from the nozzle sucks into the diffuser the required air volume from the atmosphere and forces it into the chamber.

The design of the injector incorporating such diffuser and nozzle takes into consideration the existing conditions in the different types of electric furnaces. In the case of a sufficient available height on the roof of the furnace, a simplified design ofa gas injector is useda cylindrical diffuser with a nozzle.

In the case of an insufficient height of the roof of the furnace, i.e., of a small height of the chambers, it is possible to mount several injectors along the periphery of each chamber. However, such a design is usually unfavorable for most electric arc furnaces because of the small distance between the electrodes.

In the case of a small height of the chambers, it is more advantageous to use a diffuser of reduced height and increased width, i.e., the cross section of the diffuser being then an oval, an ellipse, a rectangle or another similar geometric figure, and placing on the diffuser two or more nozzles delivering gas under pressure.

Combinations between the aforedescribed solutions are also possible.

It is also possible to use a cylindrical diffuser with one nozzle if the height of the roof is insufficient. In such a case, the diffuser can be located on the lower part of the roof and connected with the chamber by means ofa suitably shaped duct.

Any suitable gas under pressure can be used as an injecting gas. It is evident that, in practice, the cheapest compressed gases are used, namely air and steam, as well as industrial exhaust gases, such as commercial nitrogen, and the like. In applying the main feature of the present invention, namely that a sealing device, creating a chamber around the electrode, is supplied with air by means of a gas injector, it is usually of no importance in which place the air stream will enter the chamber. It is possible to direct the air stream frontally against the electrode axis with or without the use of diverting partitions, to direct the stream tangentially, or to use other intermediate solutions. The shape of the chambers can also be different, since it depends to a certain degree on the availability or presence of distributing ducts or diverting partitions. It is easy to choose for each shape of the chamber a suitable way of directionalizing the air stream, or it is easily possible to choose for each way of directionalizing the air stream a suitable shape of the chamber.

The use of a gas injector to deliver air into the chamber avoids substantial drawbacks of the air-cushion type sealing devices, preserving at the same time all their advantages.

If the gas injector is adequately dimensioned, the injecting gas is delivered in the nozzle at a comparatively low overpressure, 0.5 atm., for example. Usually the pressure in the mains for compressed air and steam is in the order of 6 to l2 atmospheres, which permits to increase many times the volume of the delivered air in the case of an aggravation of the condition of one of the seals, i.e., the sealing action is preserved in the case of aggravated conditions.

When using gas injectors, only a small quantity of injecting gas is necessary, and because of this the gas ducts, which deliver the gas to the seals, are of small size-20 mm. diameter, for example. For this reason, the regulation ofthe pressure of the injecting gas for each seal, as well as for the three seals as a whole, is carried out in practice easily from the control desk or console of the electric furnace.

It is evident, that in the injector sealing devices there is no need of large-sized air ducts on the roof and of an electric insulation between them.

The injector sealing devices provide an adequate sealing action during the whole duration of use of the roof, which protects the seals from destruction and increases many times the period of their use. The reliable sealing action permits the full usage (not only for a limited time) of the advantages resulting from the operation of the furnace at a positive pressure.

In the injector-type sealing devices the volume of the injecting gas is only about percent of the total volume of the injected air. Although in this case the value of the air for sealing is 3 to 4 times higher than in the case of the use of fan air, this value is negligibly small, and is compensated many times by the increased period of use of the air seals only. The remaining advantages resulting from sealing the electrode holes are a pure profit.

The invention will be more readily understood upon consideration of the accompanying drawings, in which:

FIG. 1 is a view in plan ofa first embodiment of an injectortype sealing device in accordance with the invention, an electrode which passes through the sealing device being shown in horizontal section;

FIG. 2 is a view in elevation of the sealing device of FIG. I, a fragment of the respective electrode being shown;

FIG. 3 is a view in plan ofa second embodiment of an injector-type sealing device in accordance with the invention;

FIG. 4 is a view in elevation of the sealing device of FIG. 3;

FIG. 5 is a view in plan ofa third embodiment of an injectortype sealing device in accordance with the invention;

FIG. 6 is a view in elevation of the sealing device of FIG. 5; and

FIG. 7 is a view in vertical section through the diffuser of the third embodiment of sealing device, the section being taken along line 77 ofFIG. 6.

As will be evident from the above, three embodiments of the injector-type sealing device of the invention are shown herein. The first embodiment is shown in FIGS. I and 2, the second in FIGS. 3 and 4, and the third in FIGS. 5, 6, and 7. The same reference characters are employed to designate the same parts throughout the several embodiments.

In FIGS. 1 and 2 in jector-type is shown an in jector-type sealing device for an electrode hole in an electric arc furnace roof, the furnace having an available height on the roof exceeding 200 mm. The sealing device is composed of a chamber I, a diffuser 2, and venturi nozzle 3. Nozzle 3 discharges air at high speed in the flared outer end 2a of diffuser 2. The chamber 1 is formed of upper and

lower ringshaped members

5 and 6, and a peripheral wall formed in part by spiral 4 and an arcuate member 7. The member 4 extends from the radially outer edge of the entrance port to which the diffuser 2 is attached around the axis of the chamber to the inner edge of such port, as shown in FIG. I. An arcuate partition member 4a, one end of which bisects the entrance port, extends about around the axis of the chamber. The outer arcuate member 7 extends from an edge 7' partially around the chamber to be sealed to the diffuser 2. All of such members are fixedly secured and sealed together, as by being welded. It will be seen that the members 4 and 4a, not only reinforce the chamber structure against deformations, but guide the air fed into the chamber through the diffuser 2 so that a portion of the air enters the annular space 9 between an electrode passing through the chamber and the inner periphery of the chamber at a zone located adjacent the air entrance port, whereas the remainder of the air passes between the members 4 and 4a to be distributed throughout the remainder of such annular space 9.

The diffuser 2 is in the form of a tube connected to the chamber 1 tangentially thereof at a location where the larger diametered end of member 4 is located. When gas is delivered under pressure through the nozzle 3, the required volume of air is sucked from the atmosphere and enters the chamber I through the diffuser 2.

The injector-type sealing device shown in FIGS. 3 and 4 is adapted for use with electrode holes in electric arc furnaces which have a limited available height on the roof, such as mm. only. In such cases the total height of the seal must not exceed 70 mm. The injector-type sealing device is composed of a chamber Ia, three diffusers 2 spaced equally angularly about the axis of the chamber la, a nozzle 3 for each diffuser 2, and spiral chamber-strengthening and air-directing partitions 4b disposed between and permanently secured to the

annular members

5 and 6 as shown. The air-directing partitions 4b direct the air flowing inwardly to the chamber In so that the air from each diffuser 2 impinges directly upon the electrode at a zone which is spaced equally angularly from the similar zones supplied by the other two diffusers.

In the embodiment of the injector-type sealing device shown in FIGS. 5, 6, and 7, the chamber lb is formed by upper and lower

annular members

5b and 6b which are permanently connected and sealed together by a peripheral wall 71;. The diffuser 2b in this case is of oval cross section, there being three nozzles 3 located horizontally one beside the other and directed to discharge air streams into the flared outer end 2a of the diffuser 2b. Arcuate partition members 4c which are mirror images of each other are disposed at equal distances on opposite sides of the longitudinal vertical plane through the diffusers 2b and the chamber 1b. Members 4c deflect the outer portions of the stream of air passing through the diffuser 212 so that such portions flow around the chamber lb in contact with the outer wall 7b, whereby to distribute air substantially uniformly to the annular space existing between an electrode (not shown) and the central openings through the

members

5 b and 6!).

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

What is claimed is:

1. A device for sealing the space between an electrode and a hole in a wall of an electric arc furnace, comprising means forming a chamber around the electrode, and means for creating in the chamber a gas pressure exceeding the gas pressure in the furnace space, said last-named means comprising an access duct including a diffuser connected to the chamber, a nozzle disposed at the entrance end of the access duct so that gas issuing under pressure from the nozzle entrains additional quantities of gas and impels them into the access duct, and a source of gas under pressure connected to the nozzle.

2. A sealing device according to claim I, wherein the gas under pressure is air, and the air issuing from the nozzle entrains ambient air into the air stream entering the access duct.

3. A sealing device according to claim 1, wherein the means creating a chamber includes partition means which distributes air delivered by the access duct around the annular space between an electrode passing through the compartment and the radially inner edge of the compartment forming means.

4. A sealing device according to claim 1. wherein the chamber has a plurality of access ducts spaced substantially equally about the axis of the chamber. each access duct having a diffuser and a nozzle, and each nozzle being connected to a source of gas under pressure.

5. A sealing device according to claim 1, wherein the diffuser has a cross section with a height substantially less than its width, and comprising a plurality of nozzles disposed side by side at the entrance end of the access duct such as simultaneously to deliver jets of gas thereinto.

k -lw

Claims

2. A sealing device according to claim 1, wherein the gas under pressure is air, and the air issuing from the nozzle entrains ambient air into the air stream entering the access duct.

4. A sealing device according to claim 1, wherein the chamber has a plurality of access ducts spaced substantially equally about the axis of the chamber, each access duct having a diffuser and a nozzle, and each nozzle being connected to a source of gas under pressure.