HK1035214B - Device for preheating charging stock, comprising replaceable stack wall sections - Google Patents

Description

Furnace charge preheating furnace with replaceable furnace wall section

Technical Field

The present invention relates to a charge preheating furnace for preheating a charge to be charged into a melting chamber, and more particularly to a charge preheating furnace having a replaceable wall section.

Background

A charge preheating furnace of the above-mentioned type is described, for example, in WO-a 1-95/04910. The advantages of using A furnace preheating of the general type are taught in patent WO-A-90/10086. In this case, the outer furnace cover part of the electric arc furnace can be replaced by a shaft fixed to the holding structure, and the hot furnace gas can pass through the shaft. In heat exchange relationship, they heat the burden placed in the shaft and energy savings can be realized. The cross section of the burden preheating furnace in the form of a shaft can be circular or oval with a single furnace wall. Preferably quadrangular, that is to say polygonal in cross-section, so that a receiving space is defined by the four furnace walls for the charge material to be heated.

The walls of the charge preheating furnace are known to be made of refractory material, such as refractory bricks, refractory spray material or refractory cast material, but may also be made of water-cooled steel wall elements, preferably in the form of tubular plates.

If the furnace walls comprise refractory material on the inside towards the furnace interior space for the charge preheating, the shaft, as it happens when loaded, involves mechanical loads, the inside of which is subject to a greater degree of wear and a greater risk of damage than water-cooled steel wall elements. For this reason, and also for weight reasons, operators have exchanged the furnace walls for liquid-cooled steel walls, in particular tubular forms that can be connected to a cooling circuit.

As already mentioned, the inside of the furnace walls is subjected to high mechanical loads when charging operations involving charge materials, in particular when heavy scrap is used as charge material. If heavy scrap contains, for example, cut and broken sections of rail, when the furnace walls comprise refractory material, the sharp edges of these rail sections break the inside of the furnace walls into relatively large pieces when the material is loaded into the shaft from a basket which is moved to the upper loading port of the shaft. Even in the case of tubular plates with a relatively high mechanical load-bearing capacity, these loads can lead to serious damage occurring, such as leakage.

Although the kinetic energy of the scrap pieces falling from above into the furnace is greater in the lower region of the shaft, and the risk of damage is greater in the lower region substantially inside the furnace wall than in the upper region, it is not very possible to predetermine the locations where damage has to be repaired, and it is not possible to pre-reinforce these locations to avoid local repair of the inside of the furnace wall.

If repairs are required, particularly in the case of refractory walls, there is a significant downtime for the charge preheating furnace due to the necessary cooling time. In addition, in the case of water-cooled walls, eliminating leaks also requires an unacceptably long downtime due to the necessity of stopping the water circulation and the need for welding operations.

If liquid-cooled walls are used, which are able to withstand high mechanical loads, this involves problems of energy loss compared to walls with a refractory coating on the inside. For shaft cooling of medium-sized furnaces, about 700m per hour is required³The cooling water of (2). The average cooling water temperature is between 5 ℃ and 6 ℃, from which it can be deduced that the average energy loss in the cooling water is 3360kwh, i.e. about 45kwh per ton of molten steel, for 75 tons of molten steel produced in 45 minutes. The obstacle to replacing a strong liquid cooled steel wall with a refractory furnace wall in view of reducing the extent of energy loss is to lead to greater susceptibility to repairs and long down times.

US No. 3632094 a discloses a furnace for preheating charge materials, comprising two vertical tubular members of identical construction symmetrically mounted on either side of a central zone having an air permeable partition and rotatable through 180 °. In order to reduce the amount of wear, in the case of a furnace for preheating charge materials according to claim 1, the device ensures that the charge material does not have to pass through the entire shaft from the charging opening in the upper region into the discharge opening in the lower region of the shaft, and that it makes it possible to heat charge materials of different types in two stages in two regions before they are transferred to and charged into the furnace.

In order to operate the known charge preheating furnace, the device must comprise a central zone with gas-permeable partition walls and which can be rotated through 180 °, and a device which is rotated after the furnace charge has been emptied from the component. In view of the high mechanical loads involved during rotation, the known charge preheating furnaces are only suitable for preheating those charges of relatively small quantity.

Disclosure of Invention

The object of the present invention is to provide a furnace for preheating charge materials which reduces the repair and downtime and the costs for repair of local damage to the inside of the shaft, especially to the refractory walls. And the shaft of the burden preheating furnace reduces energy loss compared with the shaft of the preheating furnace with liquid cooling steel walls. The invention also provides a smelting device provided with the furnace charge preheating furnace.

In order to achieve the object of the invention, a furnace for preheating charge material to be charged into a melting chamber is proposed, comprising a shaft fixed in a frame structure, the upper region of which has a closable charging opening and an exhaust opening for charging material, and the lower region of which has a discharge opening and an intake opening for discharging material, the walls of said shaft defining a receiving space for the charge material to be heated, characterized in that at least one of said walls is subdivided into wall segments, said wall segments being individually fixed in the frame structure and individually replaceable.

To achieve the object of the invention, the invention also provides a smelting plant comprising an electric arc furnace comprising a smelting chamber with a furnace cover comprising a first and a second cover part, wherein said first cover part comprises at least one electrode opening for inserting an electrode and said second cover part comprises a shaft secured in a holding device, characterized in that said shaft is constructed according to one of claims 1-13 and that said holding device and said smelting chamber are interchangeable in a horizontal direction with respect to each other.

In the charge material preheating furnace according to the invention, the furnace wall, or the individual furnace walls in the case of a shaft with a polygonal cross section, is subdivided into furnace wall sections which are fixed in a frame structure and are individually replaceable. On the one hand, for the inner side in locations where low mechanical loads are expected, in particular in the upper region, the shaft can be lined with refractory material or made of refractory material plates, while strong steel wall elements are used in locations that are subjected to greater loads. On the other hand, allows a quick replacement of the damaged furnace wall section, irrespective of whether it concerns a refractory section requiring repair or a leaking tubular plate. It is desirable to take into account the storage aspects of the replacement furnace walls, which are sized so as to reduce the number of different sizes required.

Those columns which have proved particularly advantageous are those which, when they are fitted into the frame structure, have bearing surfaces on their outer sides, against which the columns bear against corresponding, cooperating counter-fixing elements on the frame structure. The frame structure is preferably mounted in such a way that it can be raised and lowered in a holding device by means of which the shaft can be pivoted or moved sideways from a position above the smelting chamber. If it is necessary to replace a damaged shaft, the shaft is moved out of the working position above the melting chamber to the side and replaced with a new or repaired one. After the vertical cylinder moves back to the original position, the furnace charge preheating furnace is in a ready-to-work state again.

The shaft containing the liquid cooled steel wall element can be taken out of the cooling circuit separately to speed up the replacement operation.

Drawings

The invention is further illustrated by the following examples with reference to the drawings. The present invention is mounted on a modified electric arc furnace having a melting chamber with a circular lower portion, the space of which is limited due to the arrangement of the shaft beside the electric plate. Thus, the braking member in the column needs to be designed in this way; when the shaft is full, the furnace walls next to the electrodes are subjected to considerable mechanical loads.

In the drawings:

fig. 1 shows a smelting plant comprising an electric arc furnace and a charge preheater arranged side by side beside the electrodes, the furnace lid being closed.

Figure 2 shows the smelting plant with the shaft of figure 1 removed,

FIG. 3 shows a top view of the smelting plant shown in FIG. 2, in which the shaft is sectioned along the line III-III in the figure,

fig. 4 is a cross-sectional view of the section IV-IV shown in fig. 3, wherein the shaft is arranged above the smelting chamber,

figure 5 is an enlarged view of a portion of figure 4,

fig. 6 is an enlarged view of a portion of fig. 5, illustrating the manner in which the furnace wall sections are secured to the frame structure,

figure 7 is a view of a modified furnace wall section corresponding to figure 6,

fig. 8 and 9 are perspective views from above, partly in section, to facilitate understanding of the shaft discharge above the smelting chamber.

Detailed Description

The smelting plant described in fig. 1-5 comprises an electric arc furnace 1 with a smelting chamber 3 mounted on furnace supports 2, and an arched furnace lid 4 covering the upper edge of the smelting chamber. The melting chamber 3 comprises a lower melting chamber portion 5 and an upper melting chamber portion 6, the lower melting chamber portion 5 being formed as a refractory lined hearth containing molten metal and the upper melting chamber portion 6 being typically formed from water cooled elements. As can be seen in particular from fig. 3 to 5, the furnace lid 4 comprises a first lid part 7 and a second lid part 8, the first lid part 7 being shown in fig. 3 in a pivoted-out position, the second lid part 8 being formed essentially by the lower end of a vertical shaft 9 or a frame 10 which carries the vertical shaft 9 (fig. 1 and 2). In fig. 1, both furnace covers are closed, and in fig. 2, the second cover part, which comprises the shaft 9, is already extended.

As shown in detail in fig. 3-5, the parts shown on the right side of the centre of the melting chamber in the figures correspond to a conventional electric arc furnace with a circular melting chamber and electrode 12, the electrode 12 being movable into the melting chamber coaxially with the centre 11 of the furnace (see centre line of the furnace in fig. 3 and 4). Only the left-hand region of the electrode 12 shown in the figure is modified above the lower melting chamber part compared to a typical arc furnace configuration having a circular furnace shape.

The first cover part 7 is of an arched configuration and has a so-called cover core 13, which has an electrode opening 14 (fig. 5) into which three electrodes 12 are inserted, from which the three electrodes 12 enter the melting chamber, arranged in a triangular arrangement as is usual for three-phase electric arc furnaces. The electrode 12 is mounted on an electrode holder arm 15 which can be raised/lowered and pivoted sideways by an electrode lift and pivot means 16. The first lid part 7 can be lifted from the position shown at the edge of the melting chamber in figures 4 and 5 and pivoted to the position shown at the side in figure 3 by means of lid lifting and pivoting means 16 to open the melting chamber for a basket charging operation such as that described above. Suitable lid lifting and pivoting means are described for example in EP-0203339.

In the illustrated embodiment, not only the melting chamber 3, but also the lid lifting and pivoting means 17 and the electrode lifting and pivoting means 16 are fixed to the furnace frame 2 so that the melting chamber and the electrode can be tilted together.

Thus, the electrode assembly need not be changed when changes or modifications are made, and the illustrated construction provides an oval first cover portion defined by a chord 18, which includes the usual electrode configuration. When the first cover is mounted to the melting chamber, the chords must be oriented obliquely, that is to say perpendicular to the plane of the paper in figure 2. In the manner described above, the tilting of the melting chamber can be carried out when the tapping or deslagging operation is carried out with the lid portion 7 closed and without the lid portion 8 being moved, in which case the shaft 9 needs to be lifted only slightly, which reduces the energy losses due to radiation, or the hot furnace gas for the main components entering the shaft being preheated. It is likely that the gap which occurs between the lower edge of the shaft or second lid portion 8 and the edge of the melting chamber (39 in figure 5) when the shaft 9 is lifted can be sealed by means of a cover plate or other means mounted on the shaft or melting chamber edge.

The columns 9 are fixed in a frame structure 20 which encloses the columns in the form of cages, the frame 10 of the second cover part 8 shown in figures 1 and 2 representing a part of the frame structure. The frame structure 20 with the columns 9, which is illustrated in detail in fig. 5-9, is mounted on a holding device 21 in such a way that the frame structure 20 is raised and lowered together with the columns by means of a lifting device 22. For this purpose, the cross member 23 of the frame structure is provided with a connecting detent 24 for positioning the lifting device 22 supported on the holding device 21, so that the cross member 23 and the frame structure 20 with the attached column can be lifted from the lower position shown in fig. 1 to the upper position shown in fig. 2. In that case the guide rod 25 ensures the required guiding action.

The gripping device 21 is movable in the horizontal direction together with the vertical shaft 9. For this purpose, the support structure 26 is provided with guide rails 27, and the gripping device 21 is provided with wheels 28 to enable the gripping device 21 to be moved in the horizontal direction.

The shaft 9 can be closed at the upper end by means of a cover 29 in the embodiment shown in the figures, which can be moved horizontally on rails and which opens an upper loading opening 61 for loading by means of a basket 31 (fig. 4) transported by the crane. In the rear direction in fig. 1, the cover 29 is of a round cap or dome-shaped configuration and has a gas passage opening 32 which is connected to an exhaust gas line 33 when the shaft 9 and its associated frame 10 are in the position shown in fig. 1.

Figures 3, 8 and 9 show that the chimney 9 is of rectangular cross-sectional configuration. When the assembly comprises a braking member for feeding or charging, as described in detail below, the chimney is preferably rectangular in the lower region. Thus, the shaft has a rectangular wall at least in the lower region, and when the cover of the melting chamber is closed (fig. 1, 4 and 5), the front wall 34 is adjacent to the chord 18 of the first cover part, the rear wall 35 is remote from the chord 18, and two lateral walls 36 and 37 are connected to the front and rear walls. In that case, the length of the front furnace wall 34 is substantially equal to the length of the chord 18, that is to say the furnace wall 34 is adjacent to the chord 18, with a narrow cover gap 38, which is shown on an enlarged scale in fig. 5.

It should be noted that in the case of a dome-shaped roof (as shown in fig. 4 and 5), the upper chord is only a straight line in plan view, but follows a line of the dome-shaped contour segment, so that the lower edge of the front furnace wall 34 is likewise shaped.

When the lid is closed, i.e. in the case shown in fig. 1, 4 and 5, the outer contour of the lid is formed by the lower edge of the rear wall 35, the lower edges of two adjacent lateral walls 36 and 37 and the oval portion adjacent to the first lid portion 7. The upper edge 39 of the melting chamber, i.e. the upper edge of the upper melting chamber zone 6, fits into this contour. The profile of the upper edge 39 of the melting chamber corresponds to the oval shape defined by the trapezoidal lines (wall sections 40a, 41 a).

The transition from the edge zone of the melting chamber defined by the double trapezoidal line to the corresponding zone of circular cross-section of the lower melting chamber zone is the converging wall zone 42a of the upper melting chamber zone 6 (see fig. 3).

As already mentioned and shown in fig. 5, a gap 38 extending parallel to the chord 18 separates the first cover part 7 from the second cover part 8 to enable the tilting of the melting chamber in the direction defined by the furnace support, in which direction a tap hole 43 and an operating hole 44 are provided, both of which are visible from the centre 11 of the melting chamber and are not obstructed by the adjacent front wall 34 of the shaft 9. The second cover part 8 and the shaft 9 are fixed to the holding means carried by the support structure 26, that is to say not on the furnace frame, so that part of the cover cannot tilt. However, in order to allow the melting chamber with the shaft and the inserted electrode to be tilted slightly, it is sufficient to lift the upper edge of the shaft slightly away from the upper edge 39 of the melting chamber.

In order to prevent furnace gas from escaping from the gap 38 between the cover parts, means are provided for sealing the gap 38 at least at one of the two mutually adjacent edges 45 and 46 of the respective first and second cover parts.

In the illustrated embodiment, a sealing gas 47 fills the gap 38 to provide a seal. For this purpose, a channel 48 with a slot-like nozzle opening or a row of holes facing the cover gap 38 is provided along the edge 46, i.e. on the front furnace wall 34.

In addition, at the edge 45 of the first cover part, a band-like means 51 is provided, made of a cooling tube, which engages in the groove with a certain clearance when the cover is closed.

The shaft is preferably provided with a burden stop 54 (finger). A detent of the type described in WO-95/04910 is particularly suitable for this purpose. However, those detents need to be made in a specific configuration or layout depending on the respective contours of the upper melting chamber edges 39, 40, 41 and the configuration of the converging wall section 42.

In the illustrated embodiment, the transition from the rectangular cross-section of the shaft to the circular cross-section of the lower smelting chamber zone 5 is formed by a polygonal cross-section, in this case a trapezoidal line. The transition point is from the upper edge 39 of the upper melting chamber zone, in this connection the lower shaft zone below the stopper 54, the configuration of the corners between the furnace walls 35, 36 and 35, 37 converging towards the center of the melting chamber. The converging brickwork sections are indicated by reference numerals 58, 59 (see figure 3). There are planes which transform the rectangular section into the cross-sectional profile of the walls 35, 36 and 37, which are in the shape of a trapezoidal line and are reflected by the rectilinear zones 40a and 41a into the profile of the upper melting chamber edge 39. A further transition is made from the area below the shaft 9 by means of the converging wall zone 42a following the contour of the trapezoidal line of the upper melting chamber edge 39 to the circular cross section of the lower melting chamber zone.

The pivoting fingers 54 are equally spaced apart in parallel arrangement (see fig. 3) and are mounted on a pivoting bracket 56. The swivel mounts are mounted in the frame structure 20 on the rear furnace wall 35. Pivoting fingers 54 are pivotable downwardly from a closed position shown in solid lines in FIG. 5, in which the inner portions of the fingers extend into the interior space of the shaft to prevent the passage of charge material, to a released position shown in phantom lines in FIG. 5, in which the inner portions of the fingers are directed downwardly to allow the passage of charge material through the shaft. Pivoting fingers 54 may also be angled downward at an angle of about 20 from horizontal in the closed position.

The fingers 54 mounted on the furnace wall sections 58 and 59 cannot pivot as far downward as the middle fingers. The solid lines of fig. 3 show the release position of the fingers 54 and the dashed lines show the closed position. It will be seen that the maximum open position of the three corresponding fingers adjacent the furnace walls 36 and 37 is not pivoted as far down as the middle finger. This allows for the prediction of the respective activation of the pivoting of those fingers, while the intermediate fingers can be jointly pivoted.

When pivoting fingers 54 are pivoted together downwardly from the closed position to the open position, charge material is introduced into the center of the furnace, i.e., into the circular lower melting chamber section, so that wall section 42 of the upper melting chamber section is protected from excessive loads.

Figures 5, 6 and 9 show the specific structure and arrangement of the chimney 9.

For further understanding, and in particular figures 8 and 9, which reproduce a simplified illustration of the invention, the columns 9 are shown housed in a frame structure 20 which encloses them in a cage-like configuration. The frame structure 20 includes four vertical tubes 63, 64, 65, 66 at the corners that are welded together by horizontal tubes 67, 68, 69 in the upper, middle and lower planes to form the cage frame structure 20. The furnace walls 34-37 are subdivided into lower and upper furnace wall sections, indicated by/1 and/2, respectively, only one of which is shown in the figure for each furnace wall. For example, fig. 8 shows only 34/1, 35/2, 37/1 and 37/2 of the furnace walls. And the rear furnace wall section 35/2 is further subdivided horizontally into three equal width sections, fig. 8 and 9 only showing a single furnace wall section 35/2 adjacent the furnace wall 37. The lower furnace wall sections 34/1 to 37/1, referred to herein as the first furnace wall sections, are designed as liquid cooled steel wall elements in the form of tubular panels 70. The tubular plate 70 has tubular portions arranged in parallel with each other and associated at the ends, which extend in a vertical direction, i.e. in the direction in which the charge moves when charging and discharging it.

The upper furnace wall sections 34/2 through 37/2 are refractory wall elements. On its inner side facing the space 62 for receiving the charge 60, there is a layer of refractory material 71. The second furnace wall section 34/2 shown in fig. 5 and 6 is formed by liquid-cooled refractory wall elements 71 with cooling boxes 72 on the outside, whereas the second furnace wall section 34/2 shown in fig. 7 is not liquid-cooled. Refractory material is added to the sheet metal element 73, the edge of which is angled to the interior of the shaft.

In order to allow rapid replacement of the furnace wall sections, on the outside, there are angle-shaped bearing surfaces 74 which are mounted on bearing lugs 75 and bear on mating, opposite angle-shaped fixing elements 76 which are welded in place on the respective horizontal tubes 67, 68, 69 on the frame structure 20. Thus, such easily removable fixing members are provided for both the first and second furnace wall sections, which can be quickly and individually replaced.

In the event of damage to the furnace wall sections, the same type of furnace wall sections can be quickly replaced after emptying the shaft charge. It is desirable for the furnace wall elements to be made as standard as possible in terms of their size and removable fasteners in the frame structure so that storage can be minimized. The cooling circuit can be disconnected separately from operation.

In view of reducing energy losses, it has proved advantageous to use cast steel sheets where high mechanical loads are to be experienced, the temperature of which is measured by at least one temperature sensor and which is below the temperature at which the cast steel sheet is deformed under the mechanical load during the charging operation (approximately 800 to 1000 ℃).

Claims (16)

1. A furnace for preheating charge material to be charged into a melting chamber (3), comprising a shaft (9) fixed in a frame structure (20) and having in its upper region a closable charging opening (61) for charging the charge material (60) and an exhaust opening (32) and in its lower region a discharge opening and an intake opening for discharging the charge material (60), the walls of said shaft defining a receiving space (62) for the charge material to be heated,

characterized in that at least one of said furnace walls (34 to 37) is subdivided into furnace wall sections (34/1, 34/2 to 37/1, 37/2) which are individually fixed in the frame structure (20) and individually replaceable.

2. Furnace as in claim 1, characterized in that said single wall (34, 35) is subdivided vertically into at least two wall sections (34/1, 34/2; 35/1, 35/2) side by side.

3. Furnace as in claim 1, characterized in that said single wall (34, 35) comprises at least a first wall segment (34/1, 35/1) in the form of a steel wall element (70) cooled by forced cooling means.

4. The furnace as claimed in claim 3 wherein said steel wall member is in the form of a liquid cooled tubular plate.

5. The furnace as claimed in claim 4, characterized in that said tubular plates are formed by mutually parallel tubular portions parallel to the direction of movement of the charge during charging and discharging.

6. The furnace as claimed in claim 3, wherein said wall elements are in the form of cast steel plates, the temperature of which is controlled by said forced cooling means on the basis of measured values, and the measured values of the temperature are measured by at least one temperature sensor.

7. Furnace as in claim 1, characterized in that said single wall (34, 35) comprises at least a second wall segment (34/2, 35/2) in the form of refractory wall elements formed by a layer of refractory material (71) on the inner side of the containment space (62) facing said charge (60).

8. The furnace as claimed in claim 7, characterized in that said refractory wall elements have a liquid-cooled enclosure (72).

9. Furnace as in claim 7, characterized in that said refractory wall element is formed by a sheet-metal element (73) whose edge is angled with respect to the inside of said shaft and is lined internally with refractory material (71).

10. The furnace as claimed in claim 3, wherein said liquid cooling wall section is connectable to the cooling circuit of said forced cooling means and is capable of being disconnected independently during operation.

11. Furnace as in claim 1, characterized in that said wall sections (34/1, 34/2, 35/1, 35/2) have, on the outside, bearing surfaces (74) bearing on cooperating opposite retaining elements (76) of said frame structure (20).

12. The charge preheating furnace of claim 1, characterized by: the first furnace wall sections (34/1 to 37/1) are provided in the lower region of the shaft (9) and the second furnace wall sections (34/2 to 37/2) are provided in the upper region of the shaft.

13. Furnace as claimed in claim 1, characterized in that said frame structure (20) is in the form of a cage structure (63 to 69) enclosing said furnace walls (34 to 37).

14. The charge preheating furnace of any one of claims 3 to 13, comprising: a shaft (9) provided in its lower region with a braking member for braking the charge to be heated, the braking member being formed by a plurality of equally spaced parallel fingers (54) and being mounted on a rotary support (56) so as to be pivotable downwardly from a closed position, in which inner portions of said fingers project obliquely downwardly into the interior of said shaft to block a passage for the charge therethrough, to a release position, in which inner portions of said fingers (54) are directed downwardly to allow the passage of charge therethrough,

characterized in that the furnace wall (34) facing the inner end comprises one or more first furnace wall sections in the region which is subjected to a particular mechanical load during the charging of the shaft as a result of the resilient springback of the fingers.

15. A smelting apparatus comprising an electric arc furnace (1) including a smelting chamber with a furnace cover (4) comprising first and second cover parts (7, 8), wherein said first cover part includes at least one electrode hole (14) for inserting an electrode (12), said second cover part (8) includes risers (9) secured in a holding means (21),

characterized in that the shaft (9) is constructed according to one of claims 1 to 13 and that the holding device (21) and the melting chamber (3) are interchangeable in the horizontal direction with respect to each other.

16. Smelting plant according to claim 15, characterized in that said frame structure (20) with said shaft (9) is mounted in such a way that it can be raised/lowered in said holding means (21).