EP0020527A1

EP0020527A1 - Cooling of surfaces adjacent molten metal

Info

Publication number: EP0020527A1
Application number: EP19790901399
Authority: EP
Inventors: Kenneth Copley Sharp
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-11-07
Filing date: 1980-05-20
Publication date: 1981-01-07
Also published as: WO1980001000A1; JPH0141917B2; JPS55500879A

Abstract

Un appareil de refroidissement de la chemise refractaire des fours peut aussi etre utilise pour refroidir des outils, tels que des lances a oxygene qui doivent etre utilisees a proximite du metal en fusion. L'appareil comprend des tubes de chaleur (26, 27) ayant leurs extremites de condensation dans une chambre (15) de fluide de refroidissement. Les extremites d'evaporation des tubes thermiques sont enfermees de preference dans un bloc solide de conduction de chaleur (18). Lorsqu'il est utilise pour refroidir une chemise de four (11) le bloc peut consister en une douve ou une plaque et peut etre relie a une enveloppe (14) qui definit la chambre de refroidissement. L'enveloppe peut comprendre les moyens d'attache de l'appareil au four en etant boulonnee a la coquille du four (10).A furnace cooling jacket can also be used to cool tools, such as oxygen lances that should be used near molten metal. The apparatus includes heat tubes (26, 27) having their ends of condensation in a coolant chamber (15). The evaporation ends of the thermal tubes are preferably enclosed in a solid block of heat conduction (18). When used to cool an oven jacket (11) the block may consist of a stave or a plate and may be connected to an envelope (14) which defines the cooling chamber. The envelope may include the means for attaching the appliance to the oven by being bolted to the shell of the oven (10).

Description

Cooling of Surfaces Adjacent Molten Metal

TECHNICAL FIELD

This invention relates to cooling arrangements for use in vessels or tools intended for operation in the vicinity of molten metal; it also relates to furnaces that have apparatus for cooling their walls or linings.

BACKGROUND ART

When tools or working surfaces are required to be in the vicinity of molten metal a problem arises from the fact that these tools or surfaces may themselves be eroded by the heat to which they are exposed. For example one of the major inconveniences and sources of expense in the operation of a shaft furnace is the need to replace the refractory lining of the furnace at intervals. By cooling the refractory lining it can be made to last longer but the replacement of the cooling means increases the complexity and expense of the relining operation. Methods of cooling the lining of shaft furnaces that have been known for many years include a provision of metal blocks which support water carrying pipes being disposed adjacent the lining of the furnace. In one such system cast iron blocks, known as staves, are fixed to the furnace shell behind the refractory lining and water carrying pipes are disposed at varying distances from the hottest surface of the stave. The disposition of the pipes is such that as one pipe fails as a result of the erosion of the stave other pipes situated further from the hottest surface are still operating and take over as the cooling element of the hottest part of the stave. This cooling system presents several difficulties. Firstly the cooling effect of the water carrying pipes is rather limited and only serves to slightly moderate the erosion of the stave and hence the furnace lining. Secondly it is difficult to cast the pipes in the stave because the pipes tend to become carbonised and hence brittle and may then crack under stress. If, as is usual, the pipes are insulated to avoid becoming carbonised heat transfer between the stave and the water in the pipes is reduced. Each pipe is required to have its own inlet and outlet, and in the case of the most common system where four pipes in each stave are used considerable piping costs are incurred. Thirdly when the stave is eroded back to a pipe and the pipe then ruptures then leakage of water into the furnace occurs. This water ingress is serious and can cause explosions, and accordingly great care has to be taken to ensure that the water supply is shut off when a pipe becomes ruptured. In mid to late campaigns this leakage of water becomes more and more frequent. Another example of the technique of cooling furnace linings by using a block supporting water carrying, pipes is in the system known as plate cooling where flat plates of solid metal having bores in which the pipes are located are disposed horizontally in the furnace walls and are usually built into the furnace walls as the lining is built up. This type of cooling is particularly used in the bosh zone of the furnace although it can be used in the other zones. It is usual for about seven to nine cooling plates to be interconnected by intermediate water inlet and outlets so that a single main water inlet and single main water outlet only need by provided for the series plates. This type of cooling is very efficient whilst it is operating normally since the cooled face of the plate is close to the inner face of the lining of the surface. However the problems of leakage mentioned above is still present as are most of the other disadvantages of the stave cooling system.

Similar problems of erosion occur in other articles that are used close to molten metal and one such is the nozzle of the gas lances that are used in steel production. A typical process is the LD process in which a long tube referred to as a lance is used to conduct high pressure oxygen onto the surface of molten iron in a converter. The lance is typically twenty metres in length and its nozzle is, in operation, situated close to the molten iron and the nozzle is usually made from copper. The oxygen lance nozzle is subject to very high temperatures, in excess of 2000°C, when operated in the converter vessel and its survival is solely due to the cooling arrangement. The cooling means conventionally applied to lance nozzles includes two sleeves around the central oxygen supply bore of the lance, which jackets define annular water conduits for inlet and outlet cooling water. The bore through which oxygen is applied divides into a number, typically four, outlet venturi tubes at-the lance tip which are narrower than the main bore and give maximum penetration and combustion efficiency.

For the cooling water to have an appreciable effect it is necessary that the copper walls between the surface of the lance tip and the cooling water are relatively thin. However in making the walls thin the effect of erosion on the copper walls becomes more serious and the possibility of dangerous water ingress into the converter becomes greater. This danger is compounded by the fact that the cooling water is required to be supplied at high pressure to obtain the necessary transfer of heat. There are in existence well known high conductivity devices known as heat pipes. A heat pipe is a relatively simple structure that transmits thermal energy very efficiently and comprises a sealed enclosure containing a fluid material and a wick. In operation one end of the pipe, referred to as the evaporating end, is situated adjacent a heat source and the other end of the pipe, referred to as the condensing end is situated adjacent the sink. The working fluid in the pipe is chosen so as to be liquid at the sink temperature and in the vapour phase at the heat source temperature. The vapour diffuses from the hot end to the cold end where it condenses and the resultant liquid is transported back to the hot end by the capilliary action of the wick. Heat pipes are most often cylindrical in shape, but can be made in other forms, for example, a laminar shape.

DISCLOSURE OF INVENTION

The present invention in a first aspect provides a cooling arrangement for use in vessels and tools intended for operation in the vicinity of molten metal, the cooling arrangement comprising a block of heat conducting material adjacent, or part of, said vessel or tool and having cooling means therein characterised in that said cooling means comprises at least one heat pipe. In a second aspect the present invention provides a furnace having apparatus for cooling its walls or lining characterised in that the apparatus includes at least one heat pipe one end of which contacts a cooling fluid and the other end of which is thermal contact with the furnace wall or lining. The invention stems from the fact that the inventor has appreciated that heat pipes can be used to cool those surfaces which are adjacent to molten metal more efficiently than existing arrangements and further more has appreciated that other disadvantages of existing systems can be alleviated by the heat pipes, in particular the danger of water ingress into a furnace or other enclosure of molten metal is relieved when heat pipes are used since these are sealed enclosures which can rupture without allowing cooling water to pass into the molten metal enclosure. The present invention also provides a stave or a plate for cooling the walls of a furnace which-comprises a. block in the evaporating ends of the heat pipes are inserted integral with, or connected to the block. Similar advantages accrue from the use of the invention in relation to the nozzle of an oxygen lance in a steel making process and where the increased conductivity allows a more massive nozzle to be used. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is an axial section through a heat

Pipe; Figure 2 is a cross sectional view in a vertical plane through a side region of a shaft furnace illustrating in cross section a stave cooling system in accordance with the present invention;

Figure 3 is a cross sectional view similar to that of Figure 2 but showing an alternative form of stave cooling in accordance with the present invention;

Figure 4 is an enlarged view of part of a stave illustrating one arrangement of heat pipe locatioon;

Figure 5 is a vertical section through part of the wall of a blast furnace which incorporates a plate cooling system in accordance with the present invention;

Figure 6 is a transverse section through a cooling plate utilised in the system illustrated in Figure 5; Figure 7 is a cross sectional view of the plate of Figure 6 through the line X-X;

Figure 8 is a similar view to Figure 7 throug an alternative type of cooling plate;

Figure 9 is a transverse section through the plate shown in Figure 8 taken along the line Y-Y;

Figure 10 is an actual section through the nozzle of an oxygen lance; and

Figure 11 is a transverse section through the line A-A of Figure 10. BEST MODE OF CARRYING OUT INVENTION

Referring to Figure 1 a typical heat pipe used in the embodiment:: to be described below is shown, and comprises a sealed cylindrical structure having an outer wall 1 and concentric inner cylindrical wall 2. The space enclosed by the inner wall 2 is filled with refractory material 3. A wick 4 is provided around the outer surface of the wall 2 and a wick 5 is similarly provided around the inner surface of the outer wall 1. These two wicks act independently to transfer liquid from the condensing end of the pipe to the evaporating end.

The working fluid used in the heat pipe is typically water, but other fluids may be found as, or more, appropriate. Referring now to Figures 2 and 3 of the drawings a shaft furnace is illustrated that is enclosed by a steel shell 10. The interior of the shell 10 is lined by a thick layer of refractory material 11. A number of cast iron blocks (staves) 12 are secured on the inside surface of the shell 10 in the region of the bosh of :the furnace by bolts 13. The stave 12 is connected to a casing 14 either by bolting or welding. This casing defines a reservoir 15 for cooling fluid. The surface 16 of the stave 12 which is towards the interior of the furnace has a chequered pattern of alternate rectangular recesses, e.g., 17 and rectangular projecting portions, e.g., 18.. A number of transverse bores 19 extend into the stave 12 from the reservoir space 15 enclosed by the.casing .14. Each part of the surface 16 of the stave at the base of each recess 17 has a bore, e.-g., 20 extending towards it from the reservoir 15, and similarly each part of the surface 16 at the forward end of a projecting portion 18 has a corresponding b'ore, e.g., 21 extending towards it. All the bores 20 and 21 terminate a few centimetres short of the surface 16, thus giving rise to two sets of bores the longer ones 21 extending towards the projecting parts of the surface 16 and the shorter ones 20 extend ing towards the recess part of the surface 16.

The casing 14 attached to the stave has an outlet pipe 22 extending out through the steel shell 10 of the furnace at the top of the stave, and an inlet pipe 23 and drain cock 24 similarly extending through the shell 10 but at the lower end of the stave. A number of staves are provided in the furnace and these are located in columns with the respective outlet pipes 22 being connected to the respective inlet pipes 23 of the stave immediately above. The casing 14 has a number of baffle plates 25 projecting into the reservoir.15 generally perpendicular to the direction of a fluid flow in the reservoir.

Each of the bores 20 and 21 receives a heat pipe 26 or 27, those 26 which are in the bores 20 being shorter than those 27 in the bores 21. The heat pipes 26 and 27 are inserted in the far end of the respective bores 20 and 21 and are substantially longer than the bores so that their condensing ends 28 project into the reservoir 15. In many applications a ratio of the portion of the heat pipe in the cooling fluid to that in the hot block of 6:1 has been found favourable, althoughit may be found preferable to forego maximum heat transfer in favour of further insertion for strength.

Referring now to Figure 4 a protective arrangement for the heat pipe is shown in which a refractory or ceramic sleeve 29 is inserted to line each of the bores 20 and 21. A bore which receives the ceramic sleeve 29 is made correspondingly wider than those previously described to accommodate the sleeve. At the end of the bore having the sleeve adjacent the cooling reservoir 15 a threaded ring 30 receives the heat pipe 26 or 27 by screw thread engagement and allows it to be screwed into the sleeve 29. These parts can be welded together after insertion. Referring again to Figures 2 and 3 alternate methods of securing the stave 12 and casing 14 to the shell 10 of the furnace are shown respectively in these Figures. In the embodiment shown in Figure 2 the shell 10 in the vicinity of the stave is flat and the casing 14 is bolted to the inside surface of the shell 10. In the embodiment shown in Figure 3 the shell 10 is formed with a recess 31 in the vicinity of the stave, the recess being shaped to receive the casing 14 and has a depth such that only the casing 14 of the joined stave and casing is received in the recess. It will be appreciated that in this embodiment cooling is improved as a result of the reservoir being positioned outside the main volume enclosed by the furnace shell.

When the stave cooling arrangement described above is in operation the stave will eventually be worn back by heat and mechanical erosion to the heat pipes 26, the reservoir cooling liquid will not enter the furnace however even though the heat pipes 27 will have ruptured.When the eventually the heat pipes 26 are destroyed the drain cocks 24 are opened and the cooling liquid is allowed to flow down the outside of the shell 10 to provide a last line of defence against overheating before the furnace needs to be re-lined. Figure 5 shows the application of the invention to a plate cooling system and in Figure 5 part of the furnace shown is the lower bosh zone and the zone around a tuyere 40. The walls of the blast furnace are built up in layers and cooling plates 41 are interposed with these layers at intervals.

The cooling plates 41 are tapered towards their edges 42 which face towards the inside of the furnace. The cooling plates are partially hollow and the interior chambers of the cooling plates receive a flow of cooling water via inlets 43 at their rearwardly facing edges.

Referring to Figures 6 and 7 each plate 41 located in the walls of the furnace is a generally flat structure having a first portion 44 which is solid and made from heat conductive material. The solid portion 44 is that part of the plate which is located closer to the interior of the furnace. A wall 45 extending from the perimeter of the rearwardly. facing surface of the portion 44 defines a chanber 46 for the cooling fluid. A back plate 47 is welded onto the wall 45 to complete the enclosure of the cooling chamber 46. The back plate includes inlet and outlet apertures connecting with the cooling chanbers of other cooling plates. The solid portion 44 of the plate includes a number of bores 48 extending from its rearward surface towards its front edge 42. These bores terminate before the front edge 42 of the solid portion and are so dimensioned to receive cylindrical heat pipes 49, so that when located in the bores 48 the heat pipes 49 extend to a consider and throughable extent out from the solid portion 44 intoλthe cooling chamber 46. Sealing rings 50 are provided at the openings of the bores 48 on the rearward facing surface of the solid portion 44 so that a water tight seal is maintained around the heat pipes 49 when located in the bores. The heat pipes can be moved towards and away from the inner facing edge 42 of the plate by moving them within the bores 48 so that some heat- pipes may be positioned further from the hottest surface so that they may remain operative even when the hot ends of the fully inserted heat pipes have been worn back.

Referring now to Figures 8 and 9, in an alternative arrangement the cooling plate may include a removable back plate 51 connected to a flange 52 extending from the enclosure wall 45. The connection may be made by means of bolts 53 allowing the back plate 51 to be removed so that the heat pipes, may be removed or their positions in the bores altered.

Each plate in the system may be fabricated from copper, or alternatively it may be cast in alloy steel, refractory or a combination of metal and high conductivity refractory. The heat pipes may be curved to suit the contour of the cooling plates and may be partly cast in the solid portion 44 of the cooling plates.

Another embodiment of the invention is shown in Figures 10 and 11 which show a nozzle for an oxygen lance which includes a block of copper 60 formed either as a solid casting or from a solid block. For angled venturi tubes 61 are bored through the box symmetrically around its axis and further closed bores 62 and 63 are bored- to form two circularly spaced arrays around the centre of the block 60 outside the venturi tubes 61. The closed bores 62 and 63 receive heat pipes 64 and 65 respectively. The bores 62 have a depth less than that of the bores 63 as will be discussed below. The heat pipes 64 and 65 are secured in the bores.-62 and 63 by welding or alternatively by screw thread, e.g., 66.

An oxygen supply pipe 67 is fixed to a corresponding flange 68 formed on the block 60 around the exterior of their venturi tubes 61 the pipe 67 being welded into its correct location. A return water sleeve 69 is located around the oxygen pipe 67 and welded to the copper block 60 at its edge adjacent the copper block, the sleeve 69 has a number of openings through which the cooling water flows from an inlet water chamber defined by an outer sleeve 70 welded to a peripheral flange 71 on the copper block 60. In other versions of the invention use may be made of the stream of oxygen itself to act as a cooling fluid for the condensing ends of the heat pipes.

The lance nozzle as described can be fitted to existing lances but requires considerably less water pressure to provide sufficient cooling to the evaporating ends of the heat pipes than that required for conventional water cooling.

To increase the life of a nozzle yet further the inner surface of each of the venturi tubes may be lined with a removable refractory insert 72 which may replaced with wear. It will be appreciated that such inserts are only possible with the increased thickness of the present nozzle over conventional types of lance nozzles. It will also be appreciated that the differing depths of the bores 62 and 63 allows for the possibility of the walls of the nozzle being eroded back to the deepest heat pipe which would then no longer function; whilst a less deeply inserted heat pipe would remain functional. Since heat pipes are closed structures the fact that erosion occurs at one end this does not mean water ingress into the combustion chamber can occur. Various other configurations of the nozzle components may be used which further utilise the advantageous properties of the heat pipes, including allowing for the water flow in the two channels to be reversed and providing additional angled heat pipes extending into the central area of the nozzle tip.

INDUSTRIAL APPICABILITY

It will be appreciated from the foregoing that the present invention has many applications in vessels or tools operated close to molten metal. The hotter ends of the pipes are preferable mounted in heat conducting blocks as described and the pipe casings may be cast in situ. Removable back plates on the reservoirs of staves and plates give access to the pipes and can be utilised to replace defective pipes and to discover if a pipe is functioning by measuring the temperature of its casing.

Claims

1. A cooling arrangement for use in vessels or tools intended for operation in the vicinity of molten metal, the cooling arrangement comprising a block of heat conducting material (12) adjacent, or part of, said vessel or tool and having cooling means therein characterised in that said cooling means comprises at least one heat pipe.

2. A cooling arrangement as claimed in claim 1 characterised in that said cooling means comprises a plurality of heat pipes at least the evaporating ends of which are located within the block such that these ends are spaced at more than a single distance from a surface (16) of the block which, in operation, faces towards the location of the molten metal.

3. A cooling arrangement as claimed in claim 1 or claim 2 characterised in that said block is a stave adapted for attachment to the walls (10) of a furnace to cool the furnace lining (11).

4. A cooling arrangement as claimed in claim 1 or claim 2 characterised in that said block is part of a plate (41 ) adapted for location transversely through the wall of a furnace to cool the furnace lining.

5. A cooling arrangement as claimed in claim 1 or claim 2 characterised in that the cooling arrangement is for the nozzle of a gas lance and said block is the tip of the nozzle (60) of the gas lance.

6. A cooling arrangement as claimed in claim 5 characterised in that one or more heat pipes (64,65) whose evaporating ends are located in said tip, have their respective condensing ends located in a chamber for cooling fluid, extending along the length of the lance.

7. A cooling arrangement as claimed in claim 6 characterised in that two of said chambers are provided (69,70), the chambers communicating at their respective ends closer to the lance nozzle tip to enable cooling fluid to flow towards and away from the lance nozzle tip in respective ones of said chambers.

8. A cooling arrangement as claimed in claim 5 characterised in that at least one heat pipe is so located in the lance nozzle that in operation of the lance its condensing end is cooled by the gas passing down the lance.

9. A cooling arrangement as claimed in any one of claims 5 to 8 in which the nozzle has a plurality of outlet venturi tubes (61) for the gas, characterised in that the venturi tubes haveceramic protective linings (72).

10. A furnace having apparatus for cooling its walls or lining characterised in that the furnace includes at least one heat pipe one end of which is in thermal contact with the furnace lining.

11. A furnace as claimed in claim 10 characterised in that the apparatus includes a plurality of said heat pipes (26,27), at least the evaporating ends of which are enclosed within a block of heat conductingmaterial (12) located within or adjacent the furnace lining.

12. A furnace as claimed in claim 11 characterised in that said block of heat conducting material has connected therewith means (14) defining a chamber (15) for codling fluid, into which chamber the condensing ends of the heat pipes extend.

13. A furnace as claimed in claim 11 characterised in that the evaporating ends of the heat pipes are located in bores (20,21) in said block, the bores being closed at respective first ends, which are those ends nearer to the interior of the furnace.

14. A furnace as claimed in claim 13 characterised in that the surface of the block that faces towards the interior of the furnace has a chequered pattern of recesses (17) and projections (18) which interfit with refractory bricks that form the furnace lining.

15. A furnace as claimed in claim 13 characterised in that said bores, are lined with refractory material (29).

16. A furnace as claimed in claim 13 or 15 characterised in that the open end of each bore has a seal (50) preventing the entry of cooling fluid into the bore.

17. A furnace as claimed in claim 12 in that the furnace is the type having an outer shell (10) and wherein said block is a stave attached to the outer shell.

18. A furnace as claimed in claim 18 characterised in that the furnace shell has an outwardly projecting recess (31 ) which accommodates said means defining the chamber for cooling fluid.

19^. A furnace as claimed in claim 12 characterised in that the furnace has a plate-type cooling system wherein said block is part of a plate (41) disposed transversely in the lining of the furnace.

20. A furnace as claimed in claimed 12 character ised in that the means defining the chamber for cooling fluid has a removable portion (51 ) enabling access to the heat pipes.

21. A furnace as claimed in any one of claims 10 to 20 characterised in that a plurality of said heat pipes are provided, the evaporating ends of at least two of which are located at different distances from the inner surface of the furnace lining.

22. A furnace as claimed in claim 17 or claim 19 characterised in that a plurality of blocks and associated chambers are provided, the chambers for cooling fluid associated with the blocks being connected for a flow of cooling fluid therebetween.