Method of repair of the refractory lining of the wall of a shaft furnace

Abstract: A method of repair of a defective portion of a refractory lining of a wall of a shaft furnace, e.g. a blast furnace, is described. The lining has water-cooled panels (5) located at the inside of the steel furnace jacket (3) and at least one inside layer (6) of refractory lining material at the inside of the panels (5). The method comprises the steps of removing at least one of the water-cooled panels (5) at the location of the defective lining portion, replacing the removed panel or panels by a further refractory lining layer (11) having a high thermal conductivity e.g. at least 50 W/mK, and providing the steel furnace jacket (3) at the repair region with an external water cooling system (12,13,14).

Description: The invention relates to a method of repair of a defective portion of the refractory lining of the wall of a shaft furnace which has water-cooled panels (also known as stave coolers) inside a steel furnace jacket and at the inside side of the panels at least one inner layer of refractory lining material. The invention is particularly but not exclusively applicable to the repair of the hearth wall of a blast furnace, and will be described below in this connection, but is applicable to other shaft furnaces of the type described above. If the inner layer of the lining becomes too thin the thermal loading of the water-cooled cooling panels becomes too high, resulting in a high risk of a breakout in the hearth wall. The lining can be affected as a result of various causes. Its thinning may be the result of prolonged operation, yet it may also be caused by water leaking from a cooling panel or from a water-cooled tuyere. Also, the above-mentioned causes may have already resulted in an actual breakout in the hearth wall. In all these cases repairs to the hearth wall are necessary. A conventional repair method comprises the operations of complete cooling down of the blast furnace and subsequent removal of the charge from it. Next the hearth wall may be fully restored to its original condition, or a new structure may be selected for it. Cooling down and emptying the blast furnace requires much time and a considerable loss of material. Then again it is frequently also necessary to repair other parts of the furnace structure which have been seriously affected by the cooling. During the whole period of cooling down, emptying, repairing, refilling and gradually blowing-in there is considerable loss in production time. US-A-4465648 describes a method of repair of a blast furnace lining by cutting an opening through the steel shell and the refractory bricks, and inserting an injection nozzle for injecting repair material. The nozzle carries reinforcing studs which are brought into radially projecting positions and become embedded in the injected repair material. This disclosure is not concerned specifically with the problem of wear of a blast furnace lining including water-cooled panels. US-A-4017960 describes repair of a defective lining portion of a furnace or hot air duct, in which the outer shell and defective portion are cut out with a flame jet cutter, a replacement refractory lining block is inserted and welded in place with the same flame jet cutter, and the shell is repaired. This can be done while the lining is hot but is limited to materials which can be welded in this manner. The object of the present invention is at least partly to overcome the disadvantage of known methods mentioned above. The invention provides a method with which it has been found possible to repair the hearth structure described in such a way that the said losses in material, time and production may be substantially reduced. The present invention consists in a method of repair of a defective portion of a refractory lining of a wall of a shaft furnace, which lining has water-cooled panels located at the inside of a steel furnace jacket and at least one inside layer of refractory lining material at the inside of the panels, characterised by the steps of removing at least one of said water-cooled panels at the location of the defective lining portion, replacing the removed panel or panels by a further refractory lining layer having a high thermal conductivity, and providing the steel furnace jacket at the repair region with art external water cooling system. The said further refractory lining layer preferably has a thermal conductivity of at least 50 W/mK and is preferably of graphite blocks, which have e.g. a conductivity of 50-1000 W/mK. The external water cooling system provided for the steel jacket may be a spray cooling system of a type in itself known. In such a spray cooling system, for example, sufficient water is sprayed at this hearth jacket close to its top end that a closed film or curtain of water flows along it downwards. Thus in accordance with this repair method a different system of cooling at the defective region than the original one with water-cooled panels is selected. It should be noted that within the invention situations may be contemplated where the original refractory lining becomes inadequate only locally. In that case the repair method may be carried out also only locally, so that a mixed structure results with cooling panels partially remaining. The method of the invention may easily be performed while the furnace is still hot from operation, even when safety requirements permit while still at the temperature of the molten metal, e.g. iron, in the furnace. Preferably, prior to insertion of said further refractory lining layer, said inside layer of refractory lining material is repaired. It has even been found that the new method lends itself to a situation in which a breakout in the hearth wall has taken place. Yet in this case, prior to the second layer of refractory lining being fitted, the place of the breakout through the original lining must be restored with refractory tamping mass. In the construction of the furnace wall with water-cooled panels it is usual firstly to apply a refractory tamping mass on the panels and then to place carbon blocks against it. However, other structures are also known. In any event in the invention after removing the panels it is desirable to smooth or flatten the remaining layer of refractory lining. The "new" refractory layer may then be built up on that, preferably first from graphite blocks and on the outer side of those a thermally conductive filling of spraying mass. This spraying mass must fill up the gap between the graphite blocks and the steel jacket well, so that it ensures a good thermal contact between the liquid cooled jacket and the refractory lining. If the blast furnace is of the column-supported type and it has sufficient structural support from the tuyeres upwards, then removal of the entire hearth jacket may be considered when carrying out the new method. Such a method is risky, however, certainly if the original lining is in poor condition all round. In accordance with the invention a better and safer method consists in that, before the water-cooled panel or panel is removed, a portion of the steel furnace jacket corresponding in location to the water-cooled panel or panels to be removed is cut out, and after the removal of the panel or panels and the insertion of the further refractory lining layer, the cut-out portion of the furnace jacket is re-inserted or replaced. The part of the jacket removed may correspond to for example 1, 2 or 4 cooling panels. Prior to cutting out a part of the steel jacket, extra safety may be further obtained by reinforcing the jacket by means of welding on reinforcement members, e.g. steel profiles adjacent the part to be cut out. Subsequently, following the repairs, these member may be removed. This ensures adequate support and stiffness of the structure during repairs, and the method is thus less sensitive to the type of structure of the furnace as a whole. The method described is suitable for carrying out very local repairs on the furnace wall. However, it may also be used successfully in the event that a substantial part of the furnace wall or even the entire furnace wall has to be renewed. In that case the method described above may be repeated on successive parts of the wall in the circumferential direction of the furnace. If the entire wall or most of it is indeed being repaired the method may be carried out with a substantial saving of time, if the method described above is commenced at several locations spaced equally around the circumference of the hearth. Embodiments of the invention will now be illustrated by way of example and with reference to the accompanying drawings, in which:- Fig. 1 shows schematically in vertical section one half of a blast furnace hearth to be repaired. Fig. 2 shows the same view as Fig. 1 after the repair. Figs. 3 to 6 show four stages of the method of repair embodying the invention. Fig 7. shows schematically a working sequence in a case of multiple simultaneous application of the method of the invention. In Fig. 1 there are illustrated the concrete foundation 1 and the refractory bottom 2 of the hearth of a blast furnace. The cooling system is not shown for the bottom since it is of no importance for understanding of the present invention. The hearth structure is surrounded by a steel hearth jacket 3 which has an opening at the location of a tap hole 4. The wall of the hearth to which the invention relates is formed by cooling panels 5 through which water flows inside the hearth jacket 3 and an inner refractory lining layer 6. The structure of these cooling panels 5 is generally known, as is the way they are linked to a water system. For this reason details of it are not illustrated. A conventional form of the refractory lining 6 takes the form of carbon blocks, and a tamped layer 9 is also applied between these carbon blocks and the cooling panels 5. The gap between the cooling panels 5 and the hearth jacket 3 is likewise filled with a layer of filling mass 10. The original profile of the lining is indicated by reference numeral 7, which profile may have become worn as a result of various causes, as shown by line 8, for example. Fig. 2 shows the structure following repair. The location of the cooling panels 5 is now occupied by a layer 11 of stacked graphite blocks 11 of approximately the same thickness as the cooling panels replaced. Not shown in the figure is a thin layer of spraying mass which is pressed in between the hearth jacket 3 and the layer 11 of graphite blocks having a high thermal conductivity typically at least 50 W/mK. An external water cooling system is now fitted to the jacket 3. In this, water from a ring main (bustle pipe) 12 is sprayed against the outer side of the hearth jacket 3 and is collected in a gutter 13 beneath the hearth. As it falls the spray water forms a closed cooling film or curtain 14 on the outer wall of the hearth jacket 3. The remaining carbon lining 6 is now intensively cooled via the highly heat conductive graphite layer 11. Thanks to the intensive cooling, this layer 6 may once again accumulate molten slag from the charge. Fig. 3 illustrates a part of the jacket 3 beneath the blast air openings 15. Onto these, while the furnace is still hot, two steel reinforcement profiles or sections 16,17 are first welded for reinforcing the hearth jacket, so that a piece 19 may then be cut out, for example by means of a cutting torch, without any harm to the hearth jacket 3. As shown by the Fig. 4, the dimensions of the hole formed correspond with those of four cooling panels 20 belonging to the system of panels 5 shown in Fig. 1. Depending on the extent of repair needed on the hearth wall and on other considerations determined by local factors, the hole formed may alternatively be made to correspond with 1, 2 or possibly even 8 cooling panels. At the same time Fig 4 illustrates how the cooling panels 20 may be removed through the hole formed. The next stage following this is to flatten well the outer wall of the lining 6 now visible, which may mean removing residues of the original layer of tamping material. If necessary a new layer of refractory mass may be applied at this location before the layer of graphite blocks 22 is built up against the old lining (Fig. 5). As shown in Fig 6 the hole is then closed again by inserting a new piece of hearth jacket 23. Next an adjoining piece is cut out of the old hearth jacket, after reinforcement section 17 has first been removed and welded into a new position 25. Finally, spraying mass is injected under pressure between the new piece of hearth jacket and the wall of graphite blocks 22. The operations described are now repeated at the location of the new hole. In this manner the entire hearth wall may be repaired stage by stage. Finally Fig 7 indicates schematically how this repair method may be carried out simultaneously at a plurality of locations spaced circumferentially around the hearth, so that a substantial saving in time is obtained. Fig. 7 shows a cross-section of the hearth during repairs. In the case illustrated, repairs are being carried out stage by stage in an anti-clockwise direction starting from positions A and B. Reference numerals 20 indicate the cooling panels, 22 the graphite blocks which have taken their place, and 16 and 25 the respective reinforcement sections. It is clear that it is also possible to work around the hearth at three or four places simultaneously. From case to case, different local factors will determine the selection of the best manner of organising the work.

Claims: A method of repair of a defective portion of a refractory lining of a wall of a shaft furnace, which lining has water-cooled panels (5) located at the inside of a steel furnace jacket (3) and at least one inside layer (6) of refractory lining material at the inside of the panels (5), characterised by the steps of removing at least one of said water-cooled panels (5) at the location of the defective lining portion, replacing the removed panel or panels by a further refractory lining layer (11) having a high thermal conductivity, and providing the steel furnace jacket (3) at the repair region with an external water cooling system (12,13,14). A method according to claim 1 wherein said further refractory lining layer (11) has a thermal conductivity of at least 50 W/mK. A method according to claim 1 or claim 2 wherein said external water cooling system has water spraying means (12) providing a curtain (13) of water running down the jacket (3). A method according to any one of claims 1 to 3 wherein said repair is performed while the lining is still hot from operation of the furnace. A method according to any one of claims 1 to 4, wherein prior to insertion of said further refractory lining layer (11), said inside layer (6) of refractory lining material is repaired. A method according to any one of claims 1 to 5 wherein prior to insertion of said further refractory lining layer (11), said inside layer (6) of refractory lining material is made smooth at its outside surface. A method according to any one of claims 1 to 6, wherein said further refractory lining layer (11) is made of graphite blocks and a spraying mass of high thermal conductivity is applied at the outside of the graphite blocks. A method according to claim 7 wherein said spraying mass is injected after replacement of the furnace jacket outside said graphite blocks. A method according to any one of claims 1 to 8 wherein, before the water-cooled panel or panels (5) is removed, a portion (19) of the steel furnace jacket (3) corresponding in location to the water-cooled panel or panels (5) to be removed is cut out, and after the removal of the panel or panels and the insertion of the further refractory lining layer (11), the cut-out portion (19) of the furnace jacket is re-inserted or replaced. A method according to claim 9 wherein, prior to cutting out of said portion (19) of the furnace jacket, reinforcing members (16,17) are welded to the furnace jacket (3) adjacent said portion (19). A method according to claim 9 or claim 10 wherein the repair method is performed repeatedly on circumferentially successive parts of the hearth wall. A method according to any one of claims 9 to 11, wherein the repair method is performed simultaneously at a plurality of circumferentially spaced locations around the hearth wall.

Inventors: VAN LAAR JACOBUS, VAN STEIN CALLENFELS JOHAN EGE, VAN LAAR, JACOBUS, VAN STEIN CALLENFELS, JOHAN EGENOLFF
Applicants: HOOGOVENS GROEP BV, HOOGOVENS GROEP B.V.
Application year: 1992
Main classification: C21B7
IPC codes: F27D9, F27D1, F27B1, C21B7, C21C5