Blast furnace

Abstract

A blast furnace of the shaft furnace type for continuously smelting treated iron ores into liquid pig iron includes a furnace wall of refractory materials. The furnace wall is surrounded by a metal jacket particularly in the lower portion of the blast furnace, the bosh and the hearth arranged underneath the bosh. The blast furnace further includes water-cooled cooling elements, for example, plate-type cooling elements arranged between the refractory furnace wall and the metal jacket. At least those of the water-cooled cooling elements arranged in the hearth area of the blast furnace and between the hearth furnace wall and the metal jacket surrounding the hearth furnace wall are made of a material of high thermal conductivity, such as copper, wherein the thermal conductivity is at least five times the thermal conductivity of cast iron.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a blast furnace of the shaft furnace type for continuously smelting treated iron ores into liquid pig iron. The blast furnace includes a furnace wall of refractory materials. The furnace wall is surrounded by a metal jacket particularly in the lower portion of the blast furnace, the bosh and the hearth arranged underneath the bosh. The blast furnace further includes water-cooled cooling elements, for example, plate-type cooling elements arranged between the refractory furnace wall and the metal jacket.

[0003] 2. Description of the Related Art

[0004] When smelting treated iron ores in the blast furnace by reduction and partial combustion of the reducing agents, high temperatures which may be up to 1,600° C. and more are reached in the lower portion of the blast furnace. The pig iron obtained by reduction at these high temperatures is present in liquid form and collects at the bottom in the lowermost portion of the blast furnace, i.e., the hearth, with layers of molten slag above the pig iron.

[0005] The pig iron collecting in the hearth and the liquid slag are withdrawn or tapped from time to time through appropriate openings and are supplied to their further use.

[0006] In order to keep the blast furnace mechanically stable at these high temperatures and the reducing conditions prevailing in the blast furnace, the furnace wall is made of a refractory material which is suitable for these conditions, wherein the furnace wall is at least in the lower portion thereof surrounded by a metal jacket or casing.

[0007] While alkali vapors and carbon monoxide attack and destroy the refractory materials in the upper zones, wherein carbon is deposited within the refractory materials, an infiltration of liquid metals, metal oxides and slags, which also leads to a disruption of the refractory materials, takes place in the lower zones of the blast furnace.

[0008] In order to minimize and avoid as much as possible these undesirable infiltrations, a principal requirement of these refractory materials, in addition to a high refractoriness under load, is a high apparent density with an appropriately low open porosity. However, a sufficient durability of the refractory materials can only be achieved if they are additionally cooled from outside, usually by a water cooling system.

[0009] For the area of the blast furnace hearth or the lower portion of the blast furnace, in which the liquid pig iron collects and the liquid slag collects above the pig iron, basically different cooling systems are known in the art, namely, those that are effective outside of the slag furnace casing and those that are effective within the blast furnace casing, as extensively described in “Hutte”, Taschenbuch fur Eisenhüttenleute, Verlag Stahleisen mbH, Düsseldorf 1961, pages 530 and 531.

[0010] The external cooling is realized either by an open sprinkling of the hearth casing with water or by guiding the cooling water by means of cooling cassettes welded parallel onto the metal casing.

[0011] Used for the internal cooling are water-cooled, plate-type cooling units of cast iron which are arranged between the refractory furnace wall and the blast furnace casing and extend parallel to the casing. The cooling water is conducted in steel pipes which are cast into the body of the plate-cooling unit. The pipes extend to the outside through appropriate openings in the blast furnace casing where they are connected to a cooling supply line and a cooling water discharge line.

[0012] In spite of these known intensive cooling devices, it frequently occurs after a failure of the refractory hearth wall under the influence of the liquid phases which act from the inside on the refractory materials, that the blast furnace casing melts through in the area of the hearth wall, which causes an uncontrolled discharge of liquid phases, i.e., slags, pig iron, solid components, i.e., coke, charge, and, until the blast furnace is without pressure, even gases.

[0013] In this connection, even the known hearth wall cooling systems fail when a direct contact occurs with the liquid pig iron because, due to their low thermal conductivity, they are not capable of removing great quantities of heat from the liquid pig iron so rapidly that the pig iron solidifies before the material of the cooling elements or the hearth casing melts.

[0014] Both cooling systems described above are not capable of containing pig iron within the hearth if the refractory brick lining of the casing fails. A break-out is unavoidable in such a case.

[0015] Break-outs cause disruption in the entire furnace area because of the direct influence of emerging materials, by irradiation heat and by oxyhydrogen gas explosions which may occur when water from defective cooling elements comes into contact with pig iron. As a consequence of such damage, the blast furnace is frequently not usable for a longer period of time which may be days to weeks. A characterizing feature of many break-outs is the fact that they occur suddenly and without any warning indications. The cause of the break-out can in most cases not be reconstructed or traced because of the destruction in the area of the break-out point.

[0016] Therefore, in addition to the costs of the actual repair, especially the losses due to production interruption must be mentioned. Since the production is today concentrated in a few blast furnaces of the highest capacity and, thus, due to lacking replacement capacities, these losses have become increasingly important.

SUMMARY OF THE INVENTION

[0017] Therefore, it is the primary object of the present invention to improve cooling of the blast furnace hearth in such a way that the liquid phases can no longer melt through the blast furnace casing when the refractory brick lining of the hearth fails for any reason.

[0018] In accordance with the present invention, the water-cooled cooling elements arranged in the hearth area of the blast furnace between the hearth furnace wall and the metal jacket surrounding the hearth furnace wall, i.e., the hearth casing, are made of a material of high thermal conductivity, wherein the thermal conductivity is at least five times the thermal conductivity of cast iron; for example, the material of the cooling elements is copper.

[0019] The measure according to the present invention makes it possible that in the case of a break-out through the refractory brick lining, the liquid pig iron solidifies into a solid layer on the plate-type cooling elements or already on the other side of the refractory hearth wall. Consequently, the cooling system has a self-protective mechanism because the solidified layer protects against another attack by liquid pig iron or liquid slag. In addition, time is gained and it is made possible to stop operation of the blast furnace in a planned manner and to prepare for the necessary repair work.

[0020] The measures according to the present invention are limited to the system of internal cooling because the thermal resistance of the hearth casing proper is not significantly reduced if the external cooling elements are made of a material of high thermal conductivity.

[0021] If, in accordance with the present invention, copper is used as the material of high thermal conductivity, wherein the thermal conductivity of copper at 20° C. with lambda=370 W/m.K is almost ten times greater than that of the normally used iron in the form of cast iron, the possible danger of a break-out is significantly reduced when an appropriately large quantity of cooling medium in the form of water is used.

[0022] In accordance with another advantageous feature of the present invention, the material of high thermal conductivity can also be used in the form of appropriately constructed cooling elements for an intensive cooling of the hearth bottom. In this manner, it is also possible to prevent damage to the refractory lining at the hearth bottom which might result in indentations in the bottom (furnace sow) which frequently may reach a depth of several meters during longer periods of operation of the blast furnace.

[0023] The intensive and extremely rapidly acting cooling according to the present invention not only successfully prevents the occurrence of break-outs, but the now substantially more intensive cooling as compared to conventional cooling systems makes it possible to use uniform wall thicknesses of the usually prefabricated refractory material in the hearth. Since the refractory material is cooled more intensively than was the case in the past and, thus, the thermally caused wear as a result of the contact with the liquid phases progresses more slowly and stops more slowly than was the case previously, it is now possible to construct the refractory material at these locations more uniformly, i.e., they can be thinner. This also makes it possible to construct the hearth casing cylindrically in the case of new constructions and the previously used conically widening shape toward the bottom for receiving additional refractory material volume is no longer required. In addition to saving costs of the refractory materials by rendering the wall thicknesses uniform in the hearth area, also eliminated is the previous disadvantage that the internal pressure of the furnace and the thermal expansion of the refractory material in the previous conical configuration produce significant forces perpendicularly of the furnace foundation which had to be absorbed by appropriately dimensioned and expensive anchoring systems.

[0024] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

[0025] In the drawing:

[0026] FIG. 1 is a vertical sectional view of a blast furnace, and

[0027] FIG. 2 is a sectional view, on a larger scale, of a detail of the blast furnace of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] FIG. 1 of the drawing shows in a vertical sectional view an embodiment of a blast furnace 1 substantially of conventional construction in which treated iron ores are smelted in accordance with the counter-current flow principle. The blast furnace 1 is in the known manner essentially divided into four different portions, i.e., the furnace top 2, the shaft 3, the bosh 4 and the hearth 5.

[0029] The charging materials, including the ores, additives and coke as the reducing agent, are added to the blast furnace 1 at its upper portion, i.e., the furnace top or throat 2. Flowing against the charging materials which move downwardly slowly during the travel through the furnace is the air blast which is heated outside of the blast furnace, not shown in the drawing, and is blown into the lower portion of the blast furnace 1 through a ring line 11 and blast tuyeres 6. The charging materials are heated by this air blast and combustion reactions and the reduction of the iron ore take place. These reactions take place in the middle portion of the blast furnace 1, i.e., the shaft 3 and in the bosh 4 therebelow, so that molten pig iron and molten slag are formed which collect in the hearth 5, wherein the liquid pig iron settles because of its higher density underneath the slag. The liquid pig iron is discharged or tapped through outlet openings which are located on the level of arrow 10. Outlet openings for the molten slag are provided above the outlet openings for the pig iron, however, these outlet openings are not shown in FIG. 1.

[0030] The hearth 5 is surrounded by a suitable brick lining of refractory materials 7, 7′ which, when contacted by molten iron and molten slag, is essentially resistant and is not destroyed. The refractory brick lining 7 of the hearth 5 extends upwardly to the level of arrow 9.

[0031] According to the present invention, arranged between this refractory brick lining 7 and the surrounding metal jacket 8, i.e., the hearth casing, are cooling elements 13, for example, plate-type cooling elements, which, according to the present invention, are made of a material of high thermal conductivity. In accordance with the present invention, these cooling elements are also arranged in the hearth bottom 12.

[0032] The intensive cooling action taking place as a result of the measures of the present invention make it possible, particularly in the case of new constructions of blast furnaces, to construct the obliquely outwardly extending portion 7′ of the refractory brick material 7 more uniformly and cylindrically, so that refractory material is saved and the now also cylindrical hearth casing can be installed without the otherwise required cost-intensive anchoring systems.

[0033] FIG. 2 of the drawing shows the feature according to the present invention in a partial sectional view on a larger scale. Specifically, FIG. 2 shows in a simplified illustration the hearth 5, the bosh 4 and the lower portion of the shaft 3 of the blast furnace 1. The hearth 5 and the bosh 4 are constructed of a refractory material, i.e., the brick lining 7, 7′ which is surrounded by a metal jacket 8, i.e., the casing. In the illustrated embodiment, the refractory brick lining 7 extends upwardly to the upper end of the bosh 4.

[0034] Arranged between the metal jacket 8 and the refractory brick lining 7, 7′ are cooling elements 13 which, according to the present invention, are made of a material of high thermal conductivity, for example, copper. As shown in FIG. 2, these cooling elements 13 extend from the hearth bottom 12 past the blast tuyeres 6 up to the level of arrow 9. The cooling elements 13 are connected to a pipe system 14 arranged outside of the metal jacket 8. The pipe system 14 ensures that the cooling elements 13 are supplied with a sufficiently high quantity of cooling water.

[0035] Because of their relative size, the cooling elements 13 are may schematically illustrated in FIGS. 1 and 2 of the drawing. Accordingly, the specific configuration of the cooling elements 13 is not shown in the drawing. However, this is not required because conventional and proven cooling elements, such as plate-type cooling elements, can be used, as long as they are made of a material of high thermal conductivity, for example, copper, as provided by the present invention.

[0036] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

1. A blast furnace of shaft furnace construction for the continuous smelting of treated iron ores into liquid pig iron, the blast furnace comprising a furnace wall of refractory materials, a bosh and a hearth underneath the bosh and a metal jacket surrounding at least a lower portion of the blast furnace, the bosh and the hearth, further comprising water-cooled cooling elements arranged between the refractory furnace wall and the metal jacket, wherein the water-cooled cooling elements arranged in an area of the hearth of the blast furnace are of a material having a high thermal conductivity, and wherein the thermal conductivity is at least five times that of cast iron.

2. The blast furnace according to claim 1, wherein the cooling elements are plate-type cooling elements.

3. The blast furnace according to claim 1, wherein the material of high thermal conductivity is copper.

4. The blast furnace according to claim 1, further comprising additional water-cooled cooling elements of a material of high thermal conductivity arranged in a hearth bottom.

5. The blast furnace according to claim 4, wherein the additional cooling elements are of copper.

6. The blast furnace according to claim 1, wherein the refractory furnace wall has a uniform wall thickness in the area of the hearth, and wherein the metal jacket surrounding the furnace wall in the area of the hearth is of cylindrical construction.