US3416779A - Composite refractory lining for basic oxygen furnace - Google Patents

Description

Dec 17 1958 F. CAMPBELL, JR

COMPOSITE REFRACTORY LNING FOR BASIC OXYGEN FURNACE Filed March l5, 1966 lll/ll ll Fra/7K Cam/abe# z/r.

I NVENTOR United States Patent O 3,416,779 COMPOSITE REFRACTORY LINING FOR BASIC OXYGEN FURNACE Frank Campbell, Jr., Bethlehem, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware Continuation-impart of application Ser. No. 482,680,

Aug. 26, 1965. This application Mar. 1S, 1966, Ser.

2 Claims. (Cl. 266-36) ABSTRACT OF THE DISCLQSURE A composite working lining for va basic oxygen furnace including a first layer of sprayable :basic refractory bricks which may be one of the following types of basic refractory bricks: tempered tar-bonded, resin-bonded or coked, carbon-bonded tar impregnated; laid up against a layer of refractory material protecting the shell of the vessel and a second layer of nonsprayable basic refractory bricks which are burned and tar-impregnated laid up inwardly of said first layer of basic refractory bricks.

This invention in general relates to linings for metallurgical furnaces and in particular to llinings of furnaces utilizing oxygen as a means of melting and refining steel such as the basic oxygen furnace and is a continuationin-part of my application Ser. No. 482,680, led Aug 26, 1965, now abandoned.

A basic oxygen furnace shop usually consists of at least two furnaces. Economically, a one furnace shop is not feasible because of the excessive down-time required to reline the furnace with refractory brick decreasing the furnace availability of the shop. Relinng a furnace requires at least three days and may require as much as seven days. On the other hand, theoretically, a two furnace shop will maintain a continuous production of refined steel because of furnace availability. While one furnace is down for relining, the second furnace is available to produce steel. When the down furnace has been relined and the lining burned-in, it is ready for operation and the operating furnace can be taken out of service for relining. The down furnace now becomes the operating furnace and the operating furnace is now the down furnace. Alternating furnaces in this manner results in an economical, eiiicient, continuous operation. Unfortunately, this mode of operation is not often achieved because of early failure of the refractory brick lining in the operating furnace resulting in downtime while waiting for the down furnace to be relined and burned-in thus decreasing the furnace availability in the shop.

The basic oxygen furnace generally comprises a steel shell and the basic refractory lining. The basic refractory lining includes a safety lining, usually burned magnesite brick laid-up against the shell of the furnace, an inner working lining of a tar-containing dolomite or magnesite brick and a rammed tar-containing magnesite mix between the safety lining and the working lining.

The refractory brick lining in the basic oxygen furnace fails because the brick cannot withstand the severe varying conditions, for example, excessively high temperatures caused by reaction of the metal with high velocity, gaseous oxygen, changing slag compositions, splashing caused by the introduction of oxygen at supersonic velocities, and erosion caused by the impact of heavy raw materials during charging, which exist in the furnace.

Because the basic oxygen process utilizes basic slags, the working linings, that is, the refractory brick lining which is exposed to the hot metal, are made of basic refractory materials, such as stabilized dolomite, mag- ICC nesite or combinations thereof. In the prior art each particular lining of a furnace is made of one particular basic refractory material. In an effort to increase the service life of the working lining and to improve the efficiency of the multi-furnace shop by increasing furnace availability, attempts have been made to spray the exposed surface of the Working lining with a basic refractory mix of high purity magnesite bonded with tar, pitch, or resin materials, while the furnace is being tilted after tapping. This has not always been successful because the sprayed material does not adhere to all types of brick used in the working lining. Then too, the sprayed material may cause thermal shock in the brick of the working lining resulting in spalling of the face of the brick reducing the service life thereof. Also, because of the high heat of the furnace, it is difficult to locate the areas which require spraying. As a result, areas which should be sprayed may not be properly sprayed resulting in premature failure of the lining.

Other types of Ibasic refractory brick may not be sufficiently resistant chemically and physically to the varying compositions of the slags formed by the reactions in the basic oxygen furnace. Premature failure of the working lining occurs. These brick do not have a service life sufficiently long to allow relining of the down furnace while the second furnace is in operation, resulting in reduced furnace availability.

It is, therefore, the object of this invention to provide a metallurgical furnace with a working lining having improved service life, thereby increasing the furnace availability of the shop.

It is another object of this invention to Iprovide a metallurgical furnace with a composite working lining, one component of which will resist erosion at the high temperatures existing in the furnace and the other component of which will resist spalling when sprayed with a refractory mix.

These and other objects are attained by providing a basic oxygen furnace wih a working lining comprising several types of brick, each type of brick being selected for its physical and chemical properties according to the lconditions each type must meet.

In a multi-furnace shop, it is advantageous to use a spray maintenance program. In this type of program, one furnace operates while the other furnace or furnaces are being relined or being sprayed. To make use of a spray maintenance program, it is necessary that the operating furnace have a working lining which will wear a suliicient length of time to allow the relining and burning-in of the said working lining in the second furnace. It is further necessary that a sucient amount of the working lining of the operating furnace remain so that by spraying the said working lining, the furnaces may be operated alternately thereby increasing furnace availability which might thereby increase shop productivity. The lining life of the operating furnace is prolonged by spraying it with basic refractory materials which Imust adhere to the brick in the working lining without causing thermal shock and spalling in the lining.

The single gure of the drawing shows the general arrangement of the refractory working lining in a basic oxygen furnace contemplated in the instant invention.

In the drawing, the basic oxygen furnace is shown generally at 10. The shell of the furnace is designated by 11. Immediately adjacent to and laid-up against the shell of the furnace is a basic refractory brick safety lining 18 made from basic refractory brick such as burned magnesite, stabilized dolomite and the like. The dished bottom or center dome shown at 12 is lined with a tar-containing refractory brick such as dead burned dolomite, dead burned lime, stabilized dolomite, magnesite and the like either alone or combinations thereof. The stadium and operating slag line area of the furnace shown at 13 is lined with a tar-impregnated basic refractory brick such as magnesite and the like. Itis preferred to use a magnesite brick having a high percentage of magnesia, that is, up to 97% magnesia. The barrel or splash area shown generally at 14 extends from the stadium and operating slag line 13 of the furnace up to the charging pad 15 at the base of the cone 21 of the furnace. In this area, a layer of tempered tar-bonded or resin-bonded or a coked carbon-bonded tar impregnated basic refractory brick 17 of the magnesia or dolomite type is laid-up against the safety lining of the furnace. An inner layer of basic refractory brick 16 which is exposed to the molten metal and to the atmosphere within the furnace is laid-up against the basic refractory brick 17. The inner layer of basic refractoiy brick 16 may be of the burned tar-impregnated type, such as magnesite or stabilized dolomite but it is preferred to use the pure magnesite type of brick having up to 97% magnesia. The high purity magnesia refractory brick is more highly resistant to the varying compositions of the slag and to d the FeO content of the slag than are the dolomite refractory brick or the refractory brick containing less than 97% magnesite. Because this type of basic refractory brick is resistant to the slag compositions, has greater resistance to abrasion and erosion and has higher hot strength due to the ceramic bonding therein than other types of basic refractory brick, the service life is longer than the other types of basic refractory brick.

The charging pad 15 of the furnace, so-called because the raw materials impinge on this area of the furnace wall when they are charged into the furnace, is lined with burned tar-impregnated magnesite refractory brick having a high resistance to abrasion and erosion and high hot strength.

The upper zone 20 of the cone section 21 may be of tempered tar-bonded or resin-bonded basic refractory brick such as dead burned magnesite or dead burned dolomite or stabilized dolomite and the like, although it it preferred to use a magnesite brick having at least 80% magnesia. The furnace is provided with a conventional refractory lined tab hole 19 in the cone section 21.

When the burned tar-impregnated brick 16 wear down to expose the layer of tempered tar-bonded or resinbonded or a coked carbon-bonded tar impregnated brick 17, the exposed surface of the tempered tar-bonded or resin-bonded or a coked carbon-bonded tar impregnated brick is coated with a layer of the aforementioned basic refractory spray mix. The operating sprayed furnace is then used alternately with the newly relined burned-in furnace. When the tempered tarabonded or resin-bonded or a coked carbon-bonded tar impregnated portion of the working lining of the operating furnace has been worn down to the safety lining, it is removed from service for relining. A sucient portion of the burned tar-impregnated basic refractory brick remains in the one furnace now operating, to allow the relining and the burning-in of the lining in the inoperative or down furnace. By using the spray maintenance program, it is therefore, possible to increase the service life of a working lining and thereby increase furnace availability of the Shop.

In a specific example of the invention, a 250 ton basic oxygen furnace was lined with a safety lining of burned magnesite brick. The working lining was made up of various tar-containing types of brick each brick being best adapted to be used in the particular area of the furnace. The center dome is laid up with 24 x (6 to 51/2 and 6 to 5 and 6" to 4") x 3 tar-bonded magnesia brick. The stadium and operating slag line area has ten rings of high purity magnesite, at least 97% magnesia brick each being 27 x (6 to 51/2" and 6 to 4) x 3". The splash or wear area has 43 to 47 courses of two types of brick. The layer of brick exposed to the slag splash are of burned tar-impregnated high purity magnesite composition, alternate courses of brick being l2" x (6" to 5]/2 and 6" to 5) x 3 and 15I x (6 to 51/2 and 6" to 5) x 3". The

intermediate layer of brick between the burned tar-impregnated brick above and the safety lining is made of tempered tar-bonded magnesite brick, alternate layers of which are 12 x (6'l to 51/2" and 6" to 5) x 3 and l5 x (6 to 51/2 and 6 to 5) x 3". The brick in the splash area are laid-up in overlapping relationship to each other. The base cone or charge pad brick are burned tarimpregnated hmagnesite having a high resistance to abrasion and high hot strength. Each brick is 24" x (6 to 51/2 and 6 to 4") x 3". The cone section ofthe furnace is lined with tempered and tar-bonded brick two sizes of brick being used, the lower portion of the cone having brick 21 x (6 to 5%." and 6 to 5" and 6" to 4) x 3" and the upper portion of the cone section having brick 18 x (6 to 51/2 and 6 to 5" and 6l to 4) x 3".

The furnace was burned-in, and operated continuously to make 164 heats. A small wear area in the upper portion of the slag splash area was noted, that is, the burned tar-impregnated magnesite refractory brick had worn through to the tempered tar-bonded brick. Because of an unavoidable delay in relining the down furnace which stretched the relining and burning-in of the down furnace to seven days or approximately 4 days longer than normal time required, necessitating a one furnace operation, the spray program could not be started until 194 heats had been made. At this time, the small wear area had enlarged and several other Wear areas were noted at the operating slag line and the turneddown slag lines. The wear areas were sprayed with approximately 2600 pounds of Quigley type BOF guntapite (an 87% magnesia mix having borate and phosphate bonding agents added). The furnace lining was sprayed intermittently until 255 heats had been made. At this point, the down furnace was burnedin and operated alternately with the sprayed furnace. At 255 heats the operating furnace was sprayed with approximately 5200 pounds of the 87% magnesia mix. The operating furnace was sprayed at 268 heats, 275 heats, 289 heats and 294 heats. The wear area at the operating slag line was noticeably larger and deeper and it was noted that several brick from this area were dislodged and fell into the molten metal. The furnace was sprayed after 298 heats, 308 heats, 311 heats and 319 heats respectively. It was then noted that the safety lining was being eroded. The furnace was taken off operations for relining.

By comparison, in a furnace having a working lining of tempered tar-bonded refractory brick only, a wear area at the operating slag line was noted and sprayed after heats. The spraying technique allowed the furnace to be used to make an additional 33 heats or a total of 213 heats.

Since the composite lining and the spraying technique were responsible for increasing the production of the furnace from 194 heats to 319 heats whereas an increase of only 33 heats was obtained by using the spray technique wtih a lining composed of only one type of brick, namely, tempered tar-bonded, it is evident that the use of the composite lining will increase the efliciency of a multi-furnace basic oxygen shop by increasing the furnace availability of that shop.

The wear of the basic refractory brick in the working lining is not even throughout the furnace. It has been found that areas of the Working lining exposed to the more severe conditions wear more rapidly than other areas. The brick in the Operating slag line, tapping slag line, splash area and charging areas wear more rapidly than the brick in other areas of the working lining. The wear occurs as a crater or hole in the lining. These areas are usually difcult to observe because of the intense heat in the furnace. It has been found that the uneven wear of the burned tar-impregnated refractory brick of the composite lining of the invention creates a washboard like pattern which is readily discernible when the furnace is tilted for pouring or charging. The appearance of the Washboard pattern indicates that spraying is required a group consisting of tempered and tar-bonded basil and pinpoints the areas which should be sprayed. When refractory bricks, resin-bonded basic refractorj the wear surface becomes smooth and the washboard bricks, and coked carbon-bonded tar impregnatec pattern can no longer be seen, the burned tar-impregnated basic refractory bricks, and refractory brick have been worn away and the remaining 5 (b) a second layer of burned tar-impregnated basic refractory lining is tempered tar-bonded refractory brick. refractory bricks laid inwardly of said first layer oi Although I have shown the splash area of the working basic refractory bricks. lining in the furnace, laidup wtih overlapping courses 2. A combination as claimed in claim 1 in which said 0f brick, it is within the scope of this invention to laysecond layer of basic refractory bricks is in alternate up this area with the faces of the brick in abutting relalo course-overlapping relationship with said first layer of tionship. It is also within the scope of this invention to basic refractory bricks. use a Working lining of greater or lesser thickness than disclos-ed in this specification depending upon the severity References Cited OfIthle praatten. UNITED STATES PATENTS c aim: 1

1. A basic oxygen vessel having a metal shell, gen- 5 248-0359 8/1949 Debnham 26643 erally dening a bottom zone a barrel zone and a cone 3141790 7/1964 D iwles et al' 266`43 3,294,386 12/1966 Wlllenbrock 266`43 Zone, a shell protective lining in contact with the inside surface of the shell and an improved composite working J SPENCER OVERHOLSER Pfl-mary Emmi-nPr lining substantially throughout said barrel zone in contact 20 v with and subjected to attack by the environment in said R- D BALDWIN, Assistant Examine"- basic oxygen vessel, said working lining comprising:

(a) a first layer of bricks capable of being sprayed U-S- Cl- XR- with a basic refractory material, laid against the 266-43 shell protective lining, said bricks being selected from 25

Images