WO2006040393A1

WO2006040393A1 - Metallurgical furnace

Info

Publication number: WO2006040393A1
Application number: PCT/FI2005/000431
Authority: WO
Inventors: Risto Saarinen; Ilkka Kojo; Eero Hugg
Original assignee: Outokumpu Technology Oyj
Priority date: 2004-10-14
Filing date: 2005-10-11
Publication date: 2006-04-20
Also published as: PE20060787A1; CA2581978C; CA2581978A1; FI20041330A0; EA011183B1; FI20041330A; EA200700586A1; CN101040160B; FI118437B; ZA200702958B; CN101040160A

Abstract

The invention relates to the structure of the bottom area of a metallurgical furnace (1), comprising a bottom part (2) and a wall (3), both of which include a steel structure (6, 21) forming the external surface, and a refractory inner brick lining (12), the bottom part (2) and the wall (3) being joined together; the wall (3) of the furnace (1) is divided into a lower part (4) and an upper part (30), whereby the steel structure (21) of the lower part (4) is a separate ring consisting of parts (23), joints (19) being provided between the parts (23) and arranged to expand. The invention further relates to a method for controlling the expansion of the furnace (1).

Description

METALLURGICAL FURNACE

The invention relates to a metallurgical furnace that is provided with a refractory lining and an external furnace armour plate. To be more precise, the invention relates to the construction of the metallurgical furnace bottom area and a method for controlling the expansion of the furnace.

Generally, the bottom construction of metallurgical furnaces, such as arc fur¬ naces or flash smelting furnaces consists of bricks that are stacked in layers on top of a concreting or a steel bottom, the number of brick layers typically being about 3 to 5. The construction of the furnace wall consists of a firm steel plate on the outside and a brick lining inside the same, comprising one or more lay¬ ers of bricks in the direction of the thickness of the furnace wall. Typically, the temperatures in such furnaces rise to well over one thousand degrees Celsius. In the case of copper or nickel, the temperature of the melt is about 1250 to 1300⁹C and that of iron is about 1500⁹C. Because of the high temperatures, it is necessary to arrange extra cooling in the furnaces. By cooling the furnace walls at a suitable efficiency, it is possible to make the molten material inside the furnace form an autogenous protective layer on the inner surface of the fur- nace wall. This protective autogenous layer extends the service life of the fur¬ nace by protecting the inner brick lining of the furnace against wear.

In prior art solutions, there is the problem of circular furnaces expanding during use. Expansion takes places in the area of the furnace bottom in particular, causing buoyancy in the vaulted bottom structure. This developing buoyancy also causes displacements in the brick lining of the wall, which tends to rise upwards. This movement may cause the collapse of the brick lining and flaws in the steel mantle. Efforts have been made to compensate for the movement by placing a layer of mass between the brick lining and the steel mantle, among others. The expansion is caused by the molten material penetrating inside the brick lining of the bottom, especially by its components that solidify at low tem¬ peratures, such as nickel or copper sulphide. The bottom continues to expand throughout the entire service life of the furnace and, finally, results in removing the furnace from service.

The purpose of the solution according to the invention is to prevent or at least decrease the expansion of the bottom after the first warm-up of the furnace and the associated delivery of molten material, and to prevent the adverse effect of the displacements on the wall structure caused by the expansion.

The set task is solved by the construction of the furnace bottom area and the method for controlling the expansion described in the independent claims.

In the following, the invention is described in detail with reference to the ap¬ pended drawings, wherein:

Fig. 1 shows a partial cross-sectional view of the structure of the furnace bot¬ tom area,

Fig. 2 shows the junction of the lower part of the furnace wall before the furnace is heated, and Fig. 3 shows the junction of the lower part of the furnace wall after the furnace has been heated.

Fig. 1 shows the structure of the bottom area of a metallurgical furnace 1 as a partial view. Fig. 1 is from an area, where the bottom part 2 joins the cylindrical wall 3 of the furnace 1. The wall 3 of the furnace 1 consists of an annular lower part 4 and a cylindrical upper part 30 on top of it. The furnace 1 is installed on a tier of steel beams 5 on top of a concrete foundation 6. The brick lining 12 of the bottom part 2 is made by laying four brick courses on top of the steel bot¬ tom plate 7 of the furnace 1. Typically, the thickness of the brick lining 12 is from two to six brick courses. The brick lining 12 in the area of the wall 3 is typi- cally slightly thinner than in the area of the bottom part 2. Under the steel bottom plate 7, there is provided a false bottom 13, enabling an effective air change and air cooling in the area of the bottom part 2. A channel system 14 is built between the false bottom 13 and the steel bottom plate 7 for an effective air flow, air being blown into the channel system by one or more blowers (not shown in the figure) to enhance the cooling. The cooling air current flows between the bottom plate 7 and the false bottom 13 according to the ar¬ row 15. The amount of blast is used to directly affect the efficiency of the cool¬ ing and, through that, the prevailing temperature distribution inside the brick lin¬ ing 12 of the bottom.

During use, compounds that solidify at low temperatures, such as nickel and copper sulphides, accumulate at the bottom of the furnace 1 in the lower part of the melt. These components tend to penetrate inside the brick lining 12 of the bottom of the furnace 1 in accordance with the arrows 16. In prior art furnaces, these components continuously expand the structure of the bottom during use, as the molten components are able to fully penetrate the first brick layer, be¬ tween the first and the second brick layers, and even deeper before solidifying, causing a continuous expansion during the entire service life of the furnace. In the solution according to the invention, air cooling controlled by the blower makes it possible to lower the temperature of the brick lining 12 to a sufficiently low level and, the metal compounds that solidify at low temperatures can be made to solidify as early as inside the first and innermost brick layer 8, whereby the molten material cannot penetrate all the way between 17 the first and the second brick layers 8 and 9 or deeper. In that case, the continuous expansion of the bottom part 2 of the furnace in connection with the use of the furnace 1 is avoided, as expansion essentially takes place in connection with the first warm- up and the delivery of the molten material only. In future, the material that has solidified inside the first brick layer 8 prevents more molten material from pene¬ trating the brick lining 12 of the bottom.

Air cooling enhanced by the blower is used to lower the temperature inside the first brick layer 8 from a temperature of about 1250 to 1300°C of the molten material inside the furnace 1 to about 650°C, which is the solidification tem¬ perature of the nickel component that solidifies at a low temperature, for exam¬ ple. The temperature needed is dependent on the material in the furnace and the portions of its melt that solidify at the lowest temperatures. It is preferable to reach a temperature of 650°C or a corresponding temperature required, which is dependent on the material, near the midpoint of the first brick layer 8 in order to reach the needed marginal for the solidification. The cooling power is case- specifically selected on the basis of the temperature prevailing inside the fur¬ nace 1 and the solidification temperature of the components of the melt that so- lidify at low temperatures, so that the solidification always takes place inside the first brick layer 8.

Penetrating the brick lining 12, the molten material makes the brick lining ex¬ pand in the direction of the bottom of the furnace 1 according to the arrow 18. However, in the solution according to the invention, this expansion is limited, with the aid of cooling, to mainly take place in connection with the first warm-up of the furnace 1 and the associated delivery of melt. This expansion of the bot¬ tom part 2 caused by the first heating is compensated for by means of the joints 19 of the annular lower part 4 of the wall 3 of the furnace 1 , as is shown in Figs. 2 and 3 below. Partial compensation for the thermal expansion also takes place by means of the mortar joints of the bricks, which gradually burn off from be¬ tween the bricks when the furnace is heated. However, it is important that some thermal expansion also remains for the annular lower part 4 of the bottom part 2 to compensate for by virtue of the elastic elongation exerted on it, so that compression can be exerted on the brickwork. Then, the molten material can¬ not penetrate the gaps of the bricks that have been left open.

The cylindrical upper part 30 of the wall is installed directly on top of the struc¬ ture of the annular lower part 4 that is coupled to the bottom part 2, and there is a sliding joint 20 between them, whereby the expansion of the bottom part in connection with the first heating causes no, or very small deformations only, to the upper part 30 of the cylindrical wall 3. Because of such a solution, only the lower parts of the furnace 1 (the bottom part 2 and the lower part 4 of the wall) expand, and the upper part 30 of the wall remains approximately unchanged. This prevents any movements and fractures in the brick lining of the wall 3 brought about by the buoyancy caused by the expansion of the bottom part 2, which is a typical problem in prior art furnaces. Liquid-circulation cooling ele¬ ments 22 are also arranged inside the steel structure 21 of the lower part 4 of the wall of the furnace 1 to enhance cooling in this area of the furnace. The Cu- Cu surface between the two cooling elements, which is produced at the same time, effectively seals the sliding joint. Furthermore, the effective cooling di- rected at the area guarantees that the molten material solidifies in time in the sliding joint 20 and cannot penetrate out through the wall of the furnace 1.

Fig. 1 further shows a small circular cut-away drawing, which shows the joint 19 of the steel structure 21 of the lower part 4 of the furnace. On top of the joint on the outer side of the furnace 1 , there is provided a connection piece 24, by means of which the doughnut is pulled together. In the following, the joint 19 is described in detail in connection with Figs. 2 and 3.

Fig. 2 shows the joint 19 between the two parts of the annular lower part 4 of the furnace 1 , which consists of parts 23, before the first warm-up of the fur¬ nace. The joint 19 is a flexible joint, such as a friction joint (or a spring joint), which, in this example, consists of a connection piece 24, a supporting part 25 and twelve fastening devices 26. The fastening devices 26 are preferably bolt and nut assemblies or the like. The parts 23 stand tightly against one another at the dashed line 27. The connection piece 24 extends on top of both parts 23 and it is permanently fixed to the other part, for example, by bolt and nut as¬ semblies, welding or a corresponding means. The connection part 24 is at¬ tached to the other part 23 by means of the fastening devices 26 so that the connection part is allowed to slide on its surface and open the seam at the dashed line 27 between the parts 23. Fig. 3 shows the joint 19 of Fig. 2 after the first warm-up of the furnace 1 and the delivery of melt. The joint 19 has opened and the annular lower part 4 of the furnace 1 has expanded to the required extent to compensate for the expansion of the brick lining 12. There are a sufficient number of such joints 19 in the an- nular lower part 4 around the entire furnace 1 , so that it is possible to compen¬ sate for the required part of the expansion. Typically, the furnace 1 has from 5 to 10 parts 23, whereby the expansion takes place in a controlled manner. Part of the expansion is compensated for by stretching the annular lower part 4, which takes place in the elastic section of the steel to provide the required compression in the bottom structure.

Some preferred embodiments of the invention are described above by way of an example. By no means are these examples limiting and it is obvious to those skilled in the art that the preferred embodiments of the invention can vary within the scope of the claims below. It is essential that the components of the molten material that solidify at the lowest temperatures are made to solidify inside the innermost layer of bricks of the furnace bottom, whereby continuous expansion is prevented.

Claims

CLAIMS:

1. The structure of the bottom area of a metallurgical furnace (1), comprising a bottom part (2) and a wall (3), both comprising a steel structure (6, 21), which constitutes the external surface, and an inner refractory brick lining (12), the bottom part (2) and the wall (3) being joined to one another, characterized in that the wall (3) of the furnace (1) is divided into a lower part (4) and an upper part, whereby the steel structure (21) of the lower part (4) is a separate ring consisting of parts (23), joints (19) being provided between the parts (23) and arranged to expand.

2. A structure according to Claim 1 , characterized in that the joints (19) of the parts (23) are flexible joints, such as friction joints, spring joints or the like.

3. A structure according to Claim 2, characterized in that there is a sliding joint (20) provided between the lower part (4) of the wall (3) and the upper part (30) of the wall (3).

4. A structure according to Claim 3, characterized in that cooling elements (22) are provided between the lower part (4) of the wall (3) and the inner brick lining for at least part of the way.

5. A structure according to any of Claims 1 to 4, characterized in that there is a false bottom (13) provided below the bottom part (2) of the furnace (1), between of which false bottom (13) and a steel bottom plate (7) of the furnace there is a channel system (14).

6. A furnace (1) according to Claim 5, characterized in that at least one blower is connected to the channel system (14).

7. A method for controlling the expansion of a metallurgical furnace (1), charac¬ terized in that the annular lower part (4) of the wall (3) is divided into parts (23) in the circumferential direction of the furnace (1) and the annular lower part (4) is allowed to expand by means of the joints (19) between the parts (23), when the furnace (1) is heated.

8. A method according to Claim 7, characterized in that a channel system (14) is formed between the bottom part (2) of the furnace (1) and the false bottom (13), air being blown into the channel system by at least one blower for control¬ ling the temperature of the brick lining (12) of the bottom part (2).

9. A method according to Claim 8, characterized in that the temperature inside the innermost brick layer (8) of the bottom part (2) of the furnace (1) is prefera¬ bly lowered by means of cooling to a temperature, at which the particles of the melt that solidify at low temperatures solidify inside the innermost brick layer (8) of the bottom part (2).

10. A method according to Claim 9, characterized in that the temperature in¬ side the innermost brick layer (8) of the bottom part (2) of the furnace (1) is preferably lowered by means of cooling to about 650 to 800°C depending on the components of the molten material.

11. A method according to any of the preceding Claims 7 to 10, characterized in that the annular lower part (4) of the wall (3), which is integral with the bottom part (2) of the furnace (1), is joined to the cylindrical upper part (30) of the wall (3) of the furnace (1) by a sliding joint (20).