AU738253B2 - Tapping launder for a molten iron - Google Patents

Abstract

The invention relates to a tapping launder for an iron smelt, comprising an outer support structure (10), a fireproof lining (16, 18) and a copper lining (20) with ducted cooling. Said copper lining (20) surrounds the fireproof lining (18) in the support structure (10). Solid ribs (32) on the copper lining (20) project deep into the fireproof lining (18). The main purpose of said ribs is to cool any iron smelt which penetrates through cracks in the fireproof lining (18) to hardening, hereby stopping said smelt before it comes into contact with the solid copper base body. This prevents cracks caused by overheating from forming in the solid copper base body, hereby reducing the risk of coolant leaking into the iron smelt.

Description

P-PWU-380AWO TAPPING LAUNDER FOR A MOLTEN IRON The invention relates to a tapping launder for a molten iron as used e.g.

in a blast furnace for tapping the pig iron.

Tapping launders for molten irons have been known for a long time. They consist essentially of an outer supporting structure a metal trough) with a refractory lining. The lining usually consists of a permanent lining made e.g.

from refractory bricks, which are placed directly in the metal trough, and a wearing lining made from a refractory pourable compound, in which the receiving channel for the molten iron with a temperature of approximately 15000C is formed. In modern large blast furnaces with a production of several thousand tonnes of pig iron per day the tapping launder is subjected to heavy loads. The refractory lining has to be repaired or renewed with corresponding frequency.

It is already known that the life of the refractory lining can be improved by cooling. However, the use of cooling circuits with liquid coolants (usually cooling water) in the tapping launder is not without problems. In fact, if molten iron and cooling water meet, e.g. if the molten iron penetrates the refractory lining, a violent hydrogen explosion may occur. Several solutions have already been proposed to reduce or totally eliminate this explosion hazard.

For example, it was proposed in EP-A-0060239 that the outer supporting structure be designed as a double-walled metal trough, through which compress6d-air is conducted as coolant. However, forced cooling with air is far less effective than forced cooling with a liquid coolant. In addition compressedair cooling of this type is highly energy-intensive. A further disadvantage is that the production cost of the double-walled sheet metal trough is relatively high.

It was proposed in EP-A-0143971 that box-shaped cooling elements or cooling pipes, which are connected to a cooling water circuit, be provided at the side of the casting channel within the refractory lining. An expensive safety system has been provided to reduce the explosion hazard. A copper plate with thermocouples is arranged in front of the cooling elements in the wearing lining.

The thermocouples are connected to a control circuit, which shuts off the water supply if a predetermined maximum temperature or rate of temperature increase is exceeded and connects the cooling elements to a compressed-air system for emergency cooling.

It was proposed in EP-A-0090761 that the permanent lining be covered with a highly conductive layer of graphite, semi-graphite or silicon carbide bricks, which is traversed by cooling pipes, through which a liquid coolant flows.

This highly conductive layer is cooled markedly by the liquid coolant, so that the molten iron, which penetrates through cracks to this outer cooling layer, solidifies immediately. In the same patent application it is likewise indicated that the graphite, semi-graphite or silicon carbide bricks could also be replaced by copper, iron or cast iron plates and that the cooling pipes could be embedded in a highly conductive material.

Because of the high conductivity of the copper copper plates with cooling ducts integrated directly in the copper appear to be a particularly interesting solution. However, a copper lining with forced cooling has so far not been used for tapping launders for molten irons with a temperature of 1500 0 C. Although it is anticipated that the molten iron solidifies immediately in the event of local penetration of the melt as far as the copper lining, it is feared that the direct contact of the molten iron with the force-cooled copper lining leads to overheating cracks, which may cause coolant discharge into the molten iron.

3 The present invention is based on the task of creating a force-cooled tapping launder with a copper lining, in which the risk of coolant discharge into the molten iron is greatly reduced.

A tapping launder according to the invention is a possible solution solution to this problem.

According to a first aspect, the present invention consists in a tapping launder for a s molten iron, comprising an outer supporting structure; a refractory lining in the supporting structure, a channel for the molten iron being formed in this refractory lining; a copper lining, which encloses the refractory lining in the supporting structure, and a cooling device for the forced cooling of the copper lining; 1o wherein solid ribs of the copper lining penetrate into the refractory lining.

A tapping launder of this type comprises an outer supporting structure with a refractory lining, in which a channel for the molten iron is formed. A solid copper lining force-cooled by a cooling •system encloses the refractory lining in the supporting structure. Its function is to cool the inner :refractory lining and thus extend its life. It likewise protects the outer supporting structure against 15 overheating. According to an important feature of the present invention this copper lining has solid ribs, which project to a considerable extent from a solid copper base into the refractory lining. It goes without saying that these ribs improve the cooling effect in the refractory lining and thus its life. However, the main function of these ribs is to protect the solid copper base in the event of penetration of molten iron into the refractory lining. This protective function is fulfilled mainly by the 20 fact that the penetrated molten iron is extensively cooled by the ribs until it solidifies and is thus already stopped before it can come into contact with the solid copper base. Consequently :'*:overheating cracks in the solid copper base are prevented and the risk of coolant discharge into the **.molten iron is thus reduced. It should be noted that although contact between the molten iron and rib may cause local overheating or partial melting of the rib, it usually does not have significant negative effects on the copper base.

The refractory lining is advantageously poured onto the copper lining at least in the area of the ribs. Consequently the heat transfer between the refractory lining and copper lining in the area of the ribs is improved. Cavities and gaps, through which the molten iron could penetrate as far as the copper lining, are more effectively prevented.

The copper lining is preferably formed by solid copper plates, which are advantageously continuously cast. A longitudinal section of the tapping launder [R:\LD3FF]04086.doc:mrr may consist, for example, of a base plate and two side plates made from copper.

In a first embodiment the cooling system comprises cooling ducts in the copper lining, each of the cooling ducts being covered by a rib. The position of the cooling ducts under the solid ribs further reduces the risk of coolant discharge into the molten iron.

The ribs and cooling ducts preferably run parallel with the longitudinal direction of the tapping launder. Consequently the number and length of the outer connections between the cooling ducts are reduced. Furthermore, in the case of continuously cast copper plates this arrangement allows the cooling ducts to be designed as through-ducts in the casting direction by inserts in a continuous casting mould and/or the ribs formed by crenellations in the continuous casting mould.

In a further solution to the specified problem the cooling device may have an external cooling circuit, which cools the copper lining from outside, i.e. from the rear facing the supporting structure, instead of cooling ducts in the copper lining. This solution also permits reduction of the risk of coolant discharge into the molten iron. The solid copper lining in fact forms an extremely effective shield, which certainly prevents contact between cooling liquid and molten iron.

Small cracks in the solid copper lining are hardly a risk in this case.

An outer cooling circuit of this type may, for example, comprise a device for spraying the rear of the copper lining with a cooling liquid. It should be noted that on contact with a molten iron finely sprayed water, for example, constitutes a far smaller hazard than a compact water jet escaping from a leak in a cooling duct. To improve the cooling of the copper lining by the spraying device, its rear side is advantageously enlarged by grooves.

However, an outer cooling circuit of this type may also comprise outer cooling elements, through which a cooling liquid flows and which are connected thermoconductively to the rear of the copper lining. In a first embodiment these cooling elements are designed as solid copper bars with integrated cooling ducts. In an alternative embodiment these cooling elements are designed as turbulence chambers, which are arranged at right angles to the rear of the copper lining.

It should be noted that cooling circuits, which cool the copper lining from outside, i.e. from the rear, can of course be used both with and without ribs on the inside of the copper lining facing the refractory lining).

Further advantages and features of the present invention can be derived from the following description of some exemplified embodiments of tapping launders with reference to the enclosed drawings: Fig. 1 shows a cross-section through a first embodiment of a tapping launder; Fig. 2 a cross-section through a second embodiment of a tapping launder; Fig. 3 a cross-section through a third embodiment of a tapping launder, which is drawn partially in perspective; Fig. 4 a cross-section through a fourth embodiment of a tapping launder, which is drawn partially in perspective, only the right-hand half of the launder being shown; Fig. 5 a cross-section through a fifth embodiment of a tapping launder, which is drawn partially in perspective, only the right-hand half of the launder being shown; Fig. 6 a diagram of the temperature curve in the cross-section of a tapping launder with ribs.

Figs. 1 to 5 show tapping launders for a molten iron, as used e.g. in a blast furnace for tapping the pig iron. They comprise a supporting trough 10, in which a channel 12 for the molten iron 14 at a temperature of approximately 1500 0 C is formed in a refractory lining 16, 18. The latter usually consists of a wearing lining 16, in which the channel 12 is formed, and a permanent lining 18, which encloses the wearing lining 16. A copper lining 20, 120, 320, 420, which is force-cooled by a cooling device, is arranged between the permanent lining 18 and the supporting trough 10. This force-cooled copper lining 20, 120, 320, 420 protects the supporting trough 10 against overheating and thus against thermal deformations. If the tapping launder is arranged in a concrete channel, it also protects the concrete and its fittings against thermal overloading. It likewise cools the refractory lining 16, 18 and thus extends its life. This applies in particular to the refractory permanent lining 18. In the case of a tapping launder in a cast concrete channel, the latter can take over the supporting function of the supporting trough 10, so that the copper lining 120, 320, 420 can be arranged directly between the concrete walls and the permanent lining 18. If necessary thermal insulation can be provided between the copper lining 20, 120 and the supporting structure 10 (see e.g. in Fig. 3 the insulating plates designated 21). It should be noted that the cross-section of the channel, which is formed by the supporting trough 10 (or the concrete channel), determines the shape of the copper lining 20, 120, 220, 320, 420. A preferred form of this cross-section is shown in the figures. However, cross-section shapes other than the one shown are, of course, possible in the embodiment of the invention.

In the embodiment according to Fig. 1 the copper lining 20 consists of essentially vertical side plates 22 and 24 and essentially horizontal base plates 26. These oblong plates 22, 24, 26 are joined in such a way that they form a type of copper trough 20 for the refractory lining 16, 18. The seams between the side plates 22, 24 and base plate 26 are designated 28 and 30 in Fig. 1. As the length of the individual copper plates 22, 24, 26 is generally far shorter than the length of the tapping launder, several side plates 22, 24 and base plates 26 must, of course, be arranged one behind the other to line the supporting trough 10 over its full length.

According to an important feature of the present invention the copper plates 22, 24, 26 have solid ribs 32, which project to a considerable extent into the inner refractory lining 18, on their inner surface, i.e. the surface facing the refractory lining; the ratio of height of the ribs 32 to the thickness of the permanent lining 18 should preferably be between 1:4 and 3:4. The ribs 32 preferably extend over the full length of the copper plates 22, 24, 26 and are separated by grooves 34. They contribute to a significant improvement of the cooling of the refractory lining. In particular the temperatures in the permanent lining 18 are substantially reduced. A no less important function of the ribs 32 is to cool the molten iron to solidification before it comes into contact with the actual copper base and causes deep overheating cracks in the latter in the case of local penetration of the molten iron 14 into the permanent lining 18. It should be noted that although contact between a rib 32 and the molten iron may cause local overheating or even partial melting of the rib 32, it usually does not have significant negative effects on the actual copper base.

To ensure adequate effectiveness of the ribs 32, they must have specific minimum dimensions. In the embodiment shown the ratio of the height of the ribs 32 to the thickness of the copper lining between the ribs 32 is, for example, approximately 2:3. This ratio should be between 1:2 and 1:1 in the normal case. The ratio width of the ribs to width of the grooves 34 as well as the ratio height of the ribs to width of the ribs should both be between 1:3 and 3:1 (in the embodiment shown this ratio is approximately 5:6).

The ratio thickness of the copper lining between the ribs 32 to the mean total thickness of the refractory lining 16 18 should be between 1:10 and when the tapping launder is in its new condition. In Fig. 1 this ratio is 1:3 in the area of the side plates and approximately 3:10 in the area of the base plates.

In the embodiment shown in Fig. 1 the cooling device of the lining comprises cooling ducts 36, which are arranged both in the side plates 22, 24 and in the base plate 26. These cooling ducts 36 advantageously extend under the ribs 32 through the solid body of the plates 22, 24, 26. In other words the solid ribs 32 cover and thus protect the cooling ducts 36. A coolant supply (not shown) provides the cooling ducts 36 with a liquid coolant. This coolant supply is advantageously a low-pressure cooling water supply, i.e. the feed pressure of the cooling water should preferably be less than 1 bar. In the event of cracks in the copper plates the low feed pressure of the cooling water does not cause any large leaks with the result that the explosion hazard is reduced. The coolant supply and cooling ducts 36 are preferably designed in such a way that the temperature of the copper lining does not exceed 100 0 C at any point.

The tapping launder in Fig. 1 is manufactured as follows. The copper plates 22, 24, 26 are first arranged in the supporting trough 10 and secured if necessary. A first refractory compound, which forms the permanent lining 18, is then poured into the copper trough 20. This first refractory compound penetrates the grooves 34 and completely fills the latter. A box-shaped first formwork forms the subsequent interface 38 with the wearing lining 16 above the ribs 32. After hardening of the first refractory compound and after dismantling of the first formwork the wearing lining 16 is constructed. For this purpose a second refractory compound is poured on to the finished permanent lining 18, a second formwork forming the channel 12.

All copper plates for the tapping launders in Figs. 1 to 5 are advantageously continuously cast. During continuous casting of the copper plates 22, 24, 26 for the tapping launders in Fig. 1 inserts in the continuous casting channel can produce through-ducts in the casting direction, which form the cooling ducts 36 in the finished copper plate 22, 24, 26. These throughducts may advantageously have an oblong, e.g. oval, cross-section, as indicated in the copper plate 124 in Fig. 2. Consequently the free cross-section of the cooling ducts 36' is enlarged without reduction of the material thickness of the copper plate in the area of the cooling ducts 36'. The ribs 32 can likewise be produced during continuous casting. For this purpose the continuous casting mould then has, in the continuous casting channel, suitable crenellations, which form the grooves 34. However, the cooling ducts 36 can, of course, also be drilled and/or the grooves 34 cut into a forged or rolled copper ingot. However, continuously cast copper plates 22, 24, 26 with integrally cast cooling ducts can be manufactured at extremely low cost with relatively large lengths. For this purpose it should be noted that copper plates with a large length require fewer coolant connections, which are destroyed in the event of overflow of the tapping launder and could thus cause an explosion.

The tapping launder in Fig. 2 differs from the tapping launder in Fig. 1 essentially by the following features. The base plate 126 has no ribs. It is covered by graphite plates 128, which prevent downward penetration of the molten iron. A further difference is that the copper lining 120 has no cooling ducts in the corner area 121, 122 between the base plate 126 and the side plates 122, 124. Hence these corner areas 121, 122 are cooled exclusively by the base plate 126 and the side plates 122, 124. It has been found in practice that large penetrations of the molten iron always take place in these two corner areas 121, 122. As it is highly probable that large penetrations cannot be solidified in the refractory lining the risk of contact between the cooling liquid and molten iron has been greatly reduced by dispensing with cooling ducts in this area. In other words a preferred "route", via which the molten iron can flow without coming into contact with the coolant in the event of large penetrations from the tapping launder, is incorporated in the latter.

With regard to the embodiments in Figs. 1 and 2 it should be noted that the base plates 26, 126 can also be designed without cooling ducts if necessary. In this case the base plates 26, 126 are cooled by thermal conduction by the side plates 22, 24, 122, 124. In the case of penetration of the molten iron in the base area the risk of contact between the cooling liquid and the molten iron is thus greatly reduced.

The tapping launders in Figs. 3 to 5 differ from the tapping launder in Fig. 1 primarily in that the cooling device in the copper lining 220, 320, 420 in each case has an outer cooling circuit with a liquid coolant, which is arranged behind the rear of the copper lining 220, 320, 420 the surface facing the supporting trough 10). In other words in the event of entry of the molten iron into the permanent lining 18 the copper lining forms a solid protective shield against the outer cooling circuit.

In Fig. 3 the outer cooling circuit comprises a spraying device 240, which sprays a cooling liquid from pipes 242 by spraying nozzles 244 on to the rear of the copper side plates 222 and 224. The cooling liquid running down the surface of the copper side plates 222 and 224 is collected in collecting ducts 246. Grooves 248 in the rear of the copper side plates 222 and 224 enlarge the cooled surface and thus increase the cooling effect. It should be noted that an air/water mixture is advantageously sprayed, viz. in such a way that most of the water evaporates on the surface.

In Figs. 4 and 5 the outer cooling circuit comprises outer cooling elements, through which a cooling liquid flows, which are mounted thermoconductively on the rear of the copper lining.

In Fig. 4 these cooling elements are designed as solid bars 340, which are cast e.g. on to the copper lining 320 or welded or soldered to the latter.

Each of these outer cooling bars 340 has at least one internal cooling duct 342.

If the cooling bars 340 are only welded or soldered to the rear of the copper lining 320, it can be anticipated that they will become detached from the copper lining 320 in the event of a large intrusion of the molten iron into the permanent lining 18. Consequently they may be saved from destruction.

In Fig. 5 the above-mentioned cooling elements are designed as turbulence chambers 440, which are arranged vertically on the rear of the copper lining 420. Each of these turbulence chambers 440 comprises an outer pipe connection piece 442, an inner pipe connection piece 444, a feed pipe 446 and a return pipe 448 for a cooling liquid. The outer pipe connection piece 442 is secured, e.g. welded, at one open end to the rear of the copper lining 420. A blind hole 441 may enlarge the chamber 443 formed in the outer pipe connection 442 into the copper plate. The inner pipe connection piece 444 is introduced into the chamber 443 through the closed other end of this outer pipe connection piece 442. It forms a central nozzle 450 in the immediate vicinity of the surface of the copper lining 420. The cooling liquid flows through the feed pipe 446 into the inner pipe connection piece 444 and is sprayed by the nozzle on to the surface of the copper lining 420. Consequently strong turbulence is produced in the chamber 443, which intensifies the heat exchange. The turbulence in chamber 443 can, of course, be further increased by inserts. The cooling liquid leaves the chamber 443 via the return pipe 448.

Finally, a further advantage of the ribs 32 will be explained with the aid of the diagram in Fig. 6. This diagram shows the temperature curve in the crosssection of a tapping launder, which is shown under the abscissa axis X. The launder with the molten iron 14 at a temperature of 15000C, the wearing lining 16, the permanent lining 18 and a copper lining 20' can be seen. The temperature curve 50 represented by a solid line shows the temperature curve in the case of a copper lining with ribs 32. The temperature curve 52 represented by a broken line shows the temperature curve for a copper lining without ribs 32 with the same temperature (50 0 C) and same thickness of the base of the copper lining 20'. The 2500C line was plotted in the diagram with a dot-dash line. Above this temperature of 2500C it can in fact be anticipated that the copper loses a large amount of its mechanical strength. As shown in the diagram, the distance between the 2500C isotherm and the surface 54 of the solid copper base is far larger in the case of a copper lining with ribs 32 than for 12 one without ribs 32 (cf. the distances D1 and D2 in the diagram). In other words the ribs 32 ensure additional safety against overheating of the solid copper base, if the thickness of the wearing layer 16 diminishes in the course of time and the 1500 0 C isotherm thus comes closer to the copper lining.

Claims (5)

1. Tapping launder for a molten iron, comprising an outer supporting structure; a refractory lining in the supporting structure, a channel for the molten iron being formed in this refractory lining; a copper lining, which encloses the refractory lining in the supporting structure, and a cooling device for the forced cooling of the copper lining; wherein solid ribs of the copper lining penetrate into the refractory lining.

2. Tapping launder according to claim 1, wherein the refractory lining comprises a wearing lining and a permanent lining, the ribs extending essentially to half the thickness of the permanent lining.

3. Tapping launder according to claim 1 or 2, wherein the refractory lining is poured on to the copper lining at least in the area of the ribs. sl 4. Tapping launder according to claim 1, 2 or 3, wherein the copper lining is formed by solid copper plates. 0 15 5. Tapping launder according to claim 4, wherein a base plate and two side plates are made from copper.

6. Tapping launder according to claim 5, wherein the base plate is covered by graphite

0900.: plates. 7. Tapping launder according to claim 5 or 6, wherein the copper lining has a corner area S 20 between the base plate and side plates, the copper lining being force cooled directly with a liquid coolant as far as this corner area. 8. Tapping launder according to any one of claims 1 to 7, wherein the ratio of height "H" of the ribs to thickness of the copper lining in the grooves between the ribs is between 1:2 and 1:1. 9. Tapping launder according to any one of claims 1 to 8, wherein the ratio of width of the ribs to width of the grooves between the ribs and the ratio height of ribs to width of the ribs is between 1:3 and 3:1 in each case. Tapping launder according to any one of claims 1 to 9, wherein the cooling device comprises cooling ducts in the copper lining, each of the cooling ducts being covered by a rib. 11. Tapping launder according to claim 10, wherein the ribs and cooling ducts run parallel with the longitudinal direction of the tapping launder. 12. Tapping launder according to claim 11, wherein the copper lining is formed by continuously cast copper plates, cooling ducts being formed as through-ducts in the casting Sdirection during continuous casting. [R:\LIBFF]04086.doc:mrr 14 13. Tapping launder according to claim 11 or 12, wherein the ribs are formed by crenellations in a continuous casting mould during continuous casting. 14. Tapping launder according to any one of claims 1 to 9, wherein the cooling device has an external cooling circuit with a liquid coolant, which cools the copper lining from the rear. 15. Tapping launder according to claim 14, wherein the cooling device cools the copper lining from the side of the supporting structure. 16. Tapping launder according to claim 14 or 15, wherein the external cooling circuit has a spraying device, which is opposite the rear of the copper lining. 17. Tapping launder according to claim 16, wherein the rear of the copper lining is enlarged by grooves. 18. Tapping launder according to claim 14 or 15, wherein the cooling circuit comprises 0:0, outer cooling elements, through which a cooling liquid flows, which are mounted thermoconductively on the rear of the copper lining. 19. Tapping launder according to claim 18, wherein the cooling elements comprise solid 00* 15 copper bars with integrated cooling ducts. *:o0 20. Tapping launder according to claim 19, wherein the copper bars are welded or S soldered on to the rear of the copper lining. ~21. Tapping launder according to claim 14 or 15, wherein the cooling elements comprise turbulence chambers for the cooling liquid, which are arranged at right angles to the rear of the copper lining. :too* 22. Tapping launder according to claim 21, wherein each turbulence chamber comprises the following parts: t an outer pipe connection piece, which is secured in a sealed manner at one open end to the rear of the copper lining, a closed inner chamber being formed in the outer pipe connection piece; an inner pipe connection piece, which is introduced in a sealed manner into this inner chamber, where it forms a nozzle in the immediate vicinity of the surface of the copper lining; a feed pipe for a cooling liquid, which terminates in the inner pipe connection piece; and a return pipe for the cooling liquid, which terminates in the outer pipe connection piece. 23. A tapping launder, substantially as hereinbefore described with reference to any one of the accompanying drawings. [R:\LIBFF]04086.doc:mrr 24. A tapping launder according to any one of claims 1 to 23, when used for tapping molten iron. Dated 6 July, 2001 Paul Wirth S.A. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON *too o* 4 0.09 a ***to 0096 *oto.* Beeo o* *o [R:\LIBFF]04086.doc:mnrr