Method of sealing and repairing a refractory tap hole

Abstract

A method of sealing a slag drain in a direct smelting vessel is disclosed. Also disclosed are a method of maintaining a slag drain channel and a direct smelting vessel with a slag drain channel that extends through a sleeve of refractory material installed in the direct smelting vessel. The method for sealing the slag drain includes locating a pre-formed refractory material at an inlet end of the slag drain channel so that it is exposed to a molten bath contained within the direct smelting vessel and sealing the slag drain channel with sealing material downstream of the pre-formed refractory material.

Claims

1. A method of sealing a slag drain in a direct smelting vessel for containing a molten bath of slag and molten metal, the direct smelting vessel comprising at least one solids injection lance extending downwardly and inwardly through a refractory-lined side wall of the vessel for injecting metalliferous material and/or carbonaceous material, the slag drain comprising a slag drain channel extending from an inlet end at an inner surface of the refractory-lined side wall in the direct smelting vessel, the inlet end being exposed to the molten bath, to a location at or near an exterior of the direct smelting vessel, the method comprising locating a pre-formed refractory material at the inlet end of the channel, wherein the pre-formed refractory material is positioned substantially flush with the inner surface of the refractory-lined side wall so that it is exposed to the molten bath and sealing the channel with sealing material downstream of the pre-formed refractory material wherein the pre-formed refractory material has corrosion resistant properties that are similar to a surrounding refractory lining.

2. The method defined in claim 1, wherein the sealing material introduced downstream of the pre-formed refractory material includes an alumina-based plugging material.

3. The method defined in claim 2, wherein the sealing material introduced downstream of the pre-formed refractory material includes tar or phenolic-based plugging mass downstream of the alumina-based plugging material.

4. The method defined in claim 1, wherein the pre-formed refractory material is a solid chrome-based refractory material at the time that it is located within the channel.

5. The method defined in claim 1, wherein the pre-formed refractory material may be a refractory brick.

6. The method defined in claim 1, further comprising maintaining a slag drain channel formed in refractory lining of a direct smelting vessel that contains a molten bath of slag and molten metal and that has a forehearth with an overflow weir for discharging molten metal, wherein the maintaining includes: (a) reducing the slag and metal inventory from the inventory under normal operating conditions; (b) temporarily plugging the slag drain channel for stopping slag flow when a level is deemed low enough for allowing further maintenance activities; (c) opening a tap hole located in the forehearth, below the overflow weir, for tapping further metal; (d) temporarily increasing the gas vessel pressure in the direct smelting vessel to cause molten metal to flow from the direct smelting vessel into the forehearth to further decrease a metal level in the vessel to be below the slag drain and the forehearth tap hole when the gas pressure is reduced to atmospheric pressure; (e) adjusting the pressure in the vessel to be atmospheric pressure and removing a section of refractory lining surrounding the slag drain channel to form an enlarged channel and installing a refractory sleeve in the enlarged channel, the sleeve including a channel for draining slag; and (f) sealing the slag drain channel by locating a pre-formed refractory material at the inlet end of the channel so that it is exposed to the molten bath and sealing the channel by introducing a sealing material downstream of the pre-formed refractory material.

7. The method defined in claim 6, including step (f) as a further step that includes plugging the forehearth tap hole and sealing the slag drain channel by locating a pre-formed refractory material at the inlet end of the channel so that it is exposed to the molten bath.

8. The method defined in claim 6, wherein the pre-formed refractory material is a chrome-based refractory brick.

9. The method defined in claim 6, wherein the method includes maintaining sufficient slag and molten metal in the vessel to enable commencement of a direct smelting process without additional input of molten metal to the vessel from an external supply.

10. The method defined in claim 6, wherein reducing the slag inventory includes tapping slag from a tap hole above the slag drain channel.

11. The method defined in claim 6, wherein reducing the slag inventory includes draining slag via the slag drain channel during the temporary pressure increase, such that, after the temporary pressure increase, the level of the molten bath is below a level of the slag drain channel.

12. The method defined in claim 6, wherein the method includes causing the temporary pressure increase by controlling a flow of vessel off-gas through downstream off-gas processing operations.

13. The method defined in claim 6, wherein the pre-formed refractory material is positioned substantially flush with the inner surface of the refractory-lined side wall.

14. The method defined in claim 6, wherein the pre-formed refractory material has corrosion resistant properties that are similar to the surrounding refractory lining.

15. The method defined in claim 6, wherein the sealing material introduced downstream of the pre-formed refractory material includes an alumina-based plugging material.

16. The method defined in claim 6, wherein the sealing material introduced downstream of the pre-formed refractory material includes tar or phenolic-based plugging mass downstream of an alumina-based plugging material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described further, by way of example only, with reference to the accompanying drawings, of which:

(2) FIG. 1 is a vertical cross-section through a HIsmelt direct smelting vessel;

(3) FIG. 2 is a vertical cross-section through the slag drain and the side wall of a section of the direct smelting vessel in FIG. 1.

(4) FIG. 3 is a schematic horizontal cross-section through the vessel in FIG. 1 in the plane indicated by arrows III-III showing the level of molten metal and slag during a slag drain before maintenance in accordance with an embodiment of the invention.

(5) FIG. 4 is a schematic vertical cross-section through the vessel in FIG. 1 showing the level of molten metal and slag during a slag drain after maintenance in accordance with an embodiment of the invention.

DESCRIPTION OF EMBODIMENT

(6) Although the following description is in the context of a HIsmelt vessel, it will be appreciated that the invention is applicable to other direct smelting vessels that contain a molten bath of slag and molten metal, including HIsarna vessels.

(7) FIG. 1 shows a direct smelting vessel 11 that is suitable particularly for carrying out the HIsmelt process as described by way of example in international patent application PCT/AU96/00197 (WO 1996/031627) in the name of the applicant.

(8) The following description is in the context of smelting iron ore fines to produce molten iron in accordance with the HIsmelt process.

(9) It will be appreciated that the present invention is applicable to smelting any metalliferous material, including ores, partly reduced ores, and metal-containing waste streams via any suitable molten bath-based direct smelting process and is not confined to the HIsmelt process. It will also be appreciated that the ores can be in the form of iron ore fines.

(10) The vessel 11 has a hearth that includes a base 12 and sides 13 formed from refractory bricks, side walls 14, which form a generally cylindrical barrel extending upwardly from the sides 13 of the hearth, and a roof 17. Water-cooled panels (not shown) are provided for transferring heat from the side walls 14 and the roof 17. The vessel 11 is further provided with a forehearth 19, through which molten metal is continuously discharged during smelting, and a tap-hole 21, through which molten slag is periodically discharged during smelting. The roof 17 is provided with an outlet 18 through which process off gases are discharged.

(11) In use of the vessel 11 to smelt iron ore tines to produce molten iron in accordance with the HIsmelt process, the vessel 11 contains a molten bath of iron and slag, which includes a layer 22 of molten metal and a layer 23 of molten slag on the metal layer 22. The position of the nominal quiescent surface of the metal layer 22 is indicated by arrow 24. The position of the nominal quiescent surface of the slag layer 23 is indicated by arrow 25. The term quiescent surface is understood to mean the surface when there is no injection of gas and solids into the vessel 11.

(12) The vessel 11 is provided with solids injection lances 27 that extend downwardly and inwardly through openings (not shown) in the side walls 14 of the vessel and into the slag layer 23. The solids injection lances 27 are described in more detail in relation to FIGS. 3 and 4. Two solids injection lances 27 are shown in FIG. 1. However, it can be appreciated that the vessel 11 may have any suitable number of such lances 27. In use, heated iron ore fines and ambient temperature coal (and fluxes, typically lime) are entrained in a suitable carrier gas (such as a free oxygen-deficient carrier gas, typically nitrogen) and are separately supplied to the lances 27 and co-injected through outlet ends 28 of the lances 27 into the molten bath and preferably into metal layer 22. The following description is in the context that the carrier gas for the iron ore fines and coal is nitrogen.

(13) The outlet ends 28 of the solids injection lances 27 are above the surface of the metal layer 22 during operation of the process. This position of the lances 27 reduces the risk of damage through contact with molten metal and also makes it possible to cool the lances by forced internal water cooling, as described further below, without significant risk of water coming into contact with the molten metal in the vessel 11.

(14) The vessel 11 also has a gas injection lance 26 for delivering a hot air blast into an upper region of the vessel 11. The lance 26 extends downwardly through the roof 17 of the vessel 11 into the upper region of the vessel 11. In use, the lance 26 receives an oxygen-enriched hot air flow through a hot gas delivery duct (not shown), which extends from a hot gas supply station (also not shown).

(15) The vessel 11 further includes a slag drain hole 60 in the side 13 of the base 12 (FIG. 2) which is, under quiescent conditions, at a level of the interface between the metal layer 22 and slag layer 23. Slag is drained by drilling a channel 70 (FIG. 3) through a monolithic refractory block 68 which forms part of the refractory lining 66. The channel 70 enables the slag to flow from the vessel 11, along a launder (not shown) and into a nearby containment pit (not shown).

(16) The vessel 11 further includes an end-tap metal drain hole 62 in the side 13 of the base 12 and adjacent the floor of the vessel 11 (FIG. 2). In the event of the need to fully drain the metal, the slag is first drained and then a channel is drilled through the refractory lining 66 so that molten metal is able to flow from the vessel 11 via the end-tap metal drain hole 62. The metal is drained via a separate launder into a separate containment pit (not shown).

(17) The typical approach to maintaining the slag drain hole 60 involves draining slag and metal from the vessel and allowing the vessel 11 to cool so that maintenance can be carried out on a cold vessel. More specifically, this involves removing refractory brickwork surrounding a monolithic slag drain block 68 (FIGS. 3 and 4) and removing the block 68. The block 68 and the refractory brickwork are then replaced. This is an extensive operation that requires access to the interior of the vessel 11, which, in turn, requires the vessel 11 to be cold. When the slag drain block 68 is replaced, the slag drain channel 70 is sealed with plugging mass or other appropriate material, typically tar or phenolic-based plugging mass, in preparation for restarting the direct smelting process. When the direct smelting process is operating, the slag is drained according to the typical method described above, i.e. by drilling a channel 70 (FIG. 4) through a monolithic refractory block 68 and which channel 70 is resealed by injection of plugging mass into the channel 70.

(18) The applicant has realized that this can be avoided by tapping some slag and metal and retaining some slag and metal in the vessel 11 for the duration of the maintenance work. This is a significant advantage because it avoids the down-time associated with a vessel shut-down. A further significant advantage is that the direct smelting process to be restarted without input of molten metal from an external source. This simplifies plant operation and reduces costs because it avoids the need to prepare a separate charge of molten iron on site and transfer it safely into the vessel 11.

(19) There are two aspects to this method. The first aspect is tapping the molten bath from a full inventory to the extent required for the maintenance work. In this regard, the slag is tapped initially via the tap-hole 21 and then via the slag drain hole 60 until the tip of the lances 27 are above slag level 23. Hydrostatic pressure on the underlying molten metal is reduced so that the level of metal in the forehearth 19 recedes from the level of an overflow weir 16. However, the slag layer 23 will still be above the level of the slag drain hole 60 and the metal level 24 at the slag drain level 60.

(20) The surface 24 is further lowered to a level below the slag drain 60 by sealing the slag drain hole 60, opening the trim tap hole 64, increasing the pressure in the gas space 29 above the molten bath and opening the trim tap hole 64 in the forehearth 19. The elevated pressure in the vessel 11 forces molten metal to flow from the vessel 11, through the forehearth connection 20, into the forehearth 19 and out through the trim tap hole. The pressure is increased by 5 to 40 kPa, and typically around 20 kPa. Sufficient molten metal is tapped via the trim tap hole 64 so that the level of the molten bath, once the pressure in the gas space 29 is reduced to atmospheric pressure, will be sufficiently below the level of the slag drain hole 60 to expose refractory lining surrounding the slag drain hole 60 that is corroded and that needs to be replaced. Additionally, the level of molten metal in the forehearth will also decrease so as to also provide safe access to maintain metal trim tap hole 64.

(21) When sufficient molten metal is tapped and the affected refractory lining is exposed, the pressure in the vessel 11 is brought into equilibrium with the ambient air pressure to enable a volume 76 of the refractory lining 66 to be excavated by core drilling. The excavation opens the vessel 11 to direct access from outside the vessel 11. The volume 76 is selected to encompass the corroded refractory lining 66 along the inner hot wall surface 90 of the refractory lining 66 as shown in FIG. 4. Given that the volume extends to a level below the slag channel it is important for the molten bath to be tapped to a level that is below the level of the lowermost point of the volume 76 in order to contain slag in the vessel 11 during excavation and replacement of the slag drain hole 60 of the refractory lining.

(22) With the volume 76 excavated, a replacement refractory sleeve 88 is installed into the volume (FIG. 4). Replacement refractory tiles 72 are installed behind the refractory sleeve 88. Each tile has a central opening 71 (through which slag can be tapped) which is aligned with the channel 70 in the refractory sleeve 88 to form a continuous channel from the inner wall surface 90 of the refractory lining 66 to the exterior of the vessel. The tiles are held in place by refractory cement 74.

(23) Contrary to the typical method of sealing the slag drain hole slag 60 with plugging mass, the slag channel 70 is sealed by locating a pre-formed refractory material, in the form of core-drilled refractory brick 80 in the end of the channel 70 so it is exposed to the interior of the vessel 11. The brick 80 is formed of a chrome-based refractory material. It is manually located in the end of the channel 70 by pushing it into position with a bar or rod so that the exposed end of the refractory brick 80 is substantially flash with the exposed end surface of the refractory sleeve 88.

(24) High-alumina content ramming 82 is located in the sleeve 70 behind the refractory brick 80 to further seal the sleeve 70 under the high-temperature conditions experienced in the refractory lining 66. It will be appreciated, however, that other forms of material that can withstand high temperatures may alternatively be used instead of the high-alumina content ramming 82. The outer part of the sleeve 70 is sealed with packing 84 in the form of phenolic mud. However, other suitable materials for sealing the rear end of the sleeve 70 may alternatively be used.

(25) In the event the refractory brick 80 projects slightly from or is recessed slightly from the inner wall surface, slag washing will corrode edges or corners that stand proud of the inner wall surface and the sleeve 88. Otherwise, it is expected that the corrosion of the brick 80 and the sleeve 88 will be similar to the corrosion of the refractory lining 66 in the vessel 11.

(26) In order to drain slag via the reconstructed slag drain 60, the brick 80, the ramming 82 and the plugging mass seal 84 are excavated by drilling with a pricker (not shown) or with another suitable drill. Once a slag drain is completed, a new brick is placed at the end of the channel 70 and the channel 70 is sealed in the manner described above. This process can be repeated as required until it becomes necessary to replace the sleeve 88. In which case, the process for replacing the sleeve 88 as described above is utilised. It is expected that the drilling during each slag drain may increase the cross-section of the channel 70. At some point, the brick 80 will not properly seal the channel 70 at a comfortable location into the channel 70. It is at this point that the sleeve will be replaced by the method described above.

(27) The applicant recognises that sealing the sleeve 88 with the refractory brick 80 reduces the corrosive effect of the high-FeO slag during normal production times. Specifically, the refractory brick 80 is similarly resistant to corrosion by the high-FeO slag as the refractory sleeve 88 and the remainder of the refractory lining 66. This means that, during normal production, the sleeve 88 and the channel 70 are less susceptible to corrosion than when the channel 70 is filled with phenolic mud which dissolves away gradually to expose the channel 70. It is expected that this reduced susceptibility to corrosion will result in the slag drain being less likely to form a funnel-shaped corrosion pattern.

(28) It is also expected that reduced corrosion during production times will reduce the frequency of slag drain maintenance. While corrosion of the slag drain will still occur as a result of draining slag, the above described method for replacing the sleeve 88 can be used whenever required.

(29) Whilst a number of specific apparatus and method embodiments have been described, it should be appreciated that the apparatus and method may be embodied in many other forms.

(30) In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.