Technical field

The present invention generally relates to the field of sinter manufacturing for the ironmaking industry. More particularly, the invention relates to a sinter cooling system for a sinter plant.

Background Art

Sintering machines are commonly used to agglomerate fine particles by a sintering process, in which a normally porous mass is formed from the particles while largely maintaining their chemical properties. The product of the sintering process - generally referred to as the 'sinter' - may be used in a subsequent process. In steel production for example, it is known to produce sinter from iron ore and other particles, which sinter is afterwards used in a blast furnace. After the sintering process, the sinter, initially having a high temperature about 600°C-700°C, is cooled down to a moderate temperature of e.g. 100°C in a sinter cooler. Commonly used sinter cooling systems comprise a ring shaped tank rotating around a vertical axis. Hot sinter is deposited in the upper region of the tank. The sinter moves down in the tank while being cooled down by circulating air, before being discharged by means of a scraper through a lower discharge opening.

In its lower region, the tank comprises an outer peripheral opening through which the sinter is discharged. This requires -in known solutions- an overhanging structure, i.e. the outer wall of the tank is fixed by cross-beams to the inner wall. The tank is thus composed by a heavy mass of structural elements, the conception of which is complex, in particular in consideration of the high temperature environment. Document JP 5138245 B2 for example discloses a sinter cooling system comprising a ring shaped tank where sinter is deposited at the upper region and discharged in the lower region. Also, the system comprises rotary driving means that rotate the tank about a vertical axis and a scraper for the discharge of the sinter. A main drawback of this system is its overhanging structure, as explained above. WO 2016/016106 by the present Applicant discloses an improved solution, in that the tank comprises in its lower region a plurality of compartments with side walls featuring radial vanes for cooling air. Hence the tank comprises alternating compartments and vertical passages. The design proposed in this document permits an improved air circulation, but includes an outer peripheral opening through which the sinter is radially discharged, hence requiring a heavy support structure.

Technical problem It is thus an object of the present invention to provide a sinter cooling system which is of simple and effective construction. This object is solved by a sinter cooling system according to claim 1 .

General Description of the Invention

To achieve this object, the present invention proposes a sinter cooling system comprising a ring shaped tank configured to receive hot sinter from an upper charge opening and to discharge cooled sinter through a lower discharge opening. Rotary drive means are provided for rotating the ring shaped tank about a vertical axis. At least one scraper allows for the discharge of cooled sinter through the lower discharge opening. According to the invention, the ring shaped tank comprises in its lower region a ring shaped casing with an annular bottom wall bridging between facing inner and outer annular walls, the bottom wall including an annular discharge slot forming said lower discharge opening. An annular guiding member is arranged above and spaced from the bottom wall and configured to cover the annular discharge slot and guide descending sinter into the casing. The at least one scraper is arranged in the casing at least partially below the annular guiding member and configured to guide sinter accumulated in the casing towards the annular discharge slot.

The inventive sinter cooling system does no longer require a complex internal structure to support the outer wall in the lower tank region. Indeed, the lower discharge opening is an annular slot provided in a transversal bottom wall extending between outer and inner walls. The discharge opening is thus located below the tank; there is no annular opening in the outer tank wall.

The casing defines a sinter accumulation region between the guiding member and the bottom wall, the latter being divided by the annular discharge slot into an outer annular accumulation surface and an inner annular accumulation surface. The portion of each accumulation surface located below the guiding member is referred to as free accumulation surface. Under normal operation, sinter descends in the tank, is guided towards the inner and outer periphery of the tank by the guiding member, and enters the accumulation region of the casing. Sinter arrives at the free accumulation surface, where it accumulates freely, i.e. without supporting the load of the descending sinter mass since the free accumulation surface is located vertically under the guiding member. Therefore, an annular heap of coal tends to form on the free accumulation surfaces, which has a free surface following the natural angle of repose of the sinter material. This heap of sinter can easily be scraped by the scraper.

There are two immediate benefits:

- since the sinter residing on the free accumulation surfaces is not under the vertical compression of the sinter mass, it is less subject to degradation when collected by the scraper; - the scraper also is relieved from vertical compression by the sinter mass, which reduces wear of the scraper and reduces mechanical stress in the scraper assembly. Less power is required to drive the scraper, hence reducing the demand on motor power.

Preferably, the annular guiding member has a convex-shaped upper profile, in particular with an apex situated at mid-distance of the inner and outer annular walls, in order to guide descending sinter towards respectively towards the inner and outer periphery of the bottom wall. The annular guiding member may presents a slope inclined with an angle above 10° relative to the vertical, preferably between 40° and 60°. In embodiments, the annular guiding member comprises a plurality of air inlet vanes to allow cooling air moving up from the annular discharge slot through the annular guiding member into sinter residing in the tank. It is thus possible to introduce cooling air in the hearth of the tank, continuously over the whole circumference. This provides an improved cooling effect. Preferably inlet vanes are arranged to introduce air radially inward and outward, to promote an equal distribution of cooling air.

Advantageously, the radial extent of the free accumulation surface is designed to be at least equal, and preferably greater, than the corresponding axial extent of the sinter heap that is intended to form on the free accumulation surface, having taken into account of the spacing between the bottom wall and guiding structure and of the natural angle of repose of the sinter. This ensures proper support of the free heap of sinter forming on the free accumulation surface.

In embodiment, one or more scrapers may be used. For example, first scraper extends over at least part of said outer accumulation surface and a second scraper extends over at least part of said inner accumulation surface. In normal use, each scraper extends only its respective free accumulation surface. The scrapers may be fixed to a respective, substantially vertical shaft that is preferably pivotable to adjust the position of the scraper over the inner, respectively outer, accumulation surface.

These and other features of the present invention are recited in the appended dependent claims 2 to 15.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 : is a principle view of the present sinter cooling system;

Fig. 2: is a vertical sectional view of an embodiment of the present sinter cooling system;

Fig. 3: is a horizontal sectional view of the same embodiment of sinter cooling system; and Fig. 4: is a vertical sectional view of the same embodiment of sinter cooling system.

Description of Preferred Embodiments

The invention will first be described with respect to Figure 1 , which is a principle drawing of the present sinter cooling system 10.

The sinter cooling system 10 comprises a ring shaped tank 12 that includes an annular outer wall 12.1 and an annular inner wall 12.2, and is configured to receive hot sinter from an upper charge opening 18 and to discharge cooled sinter through a lower discharge opening 20. The inner and outer walls 12.1 and 12.2 thus define a storage volume for sinter; in the drawings the granular sinter material is designated 1 1 and represented by crosses.

Rotary drive means 14 are provided for rotating the ring shaped tank 10 about a vertical axis A.

At least one scraper 16 is provided for discharging cooled sinter through the lower discharge opening 20. The scrapers are typically installed in a selected portion of the circumference to cooperate with sinter collecting means (comprising e.g. a conveyor belt, designated 34 in Fig .1 , passing below the scraper 16 to collect the sinter falling vertically through the discharge slot 20.

The ring shaped tank 12 comprises in its lower region 21 a ring shaped casing 22 with an annular bottom wall 24 that bridges between facing inner and outer annular walls 26 and 26'. Preferably, the inner and outer annular walls 26 and 26' of the 22 casing correspond to the lower part of the outer and inner walls 12.1 and 12.2 of the tank 12. While the walls 12.1 and 12.2 in Fig.1 are slightly oblique (defining a trapezoidal cross-section), they may also be vertical (parallel) or have other shapes or angle, as may be appropriate.

It shall be appreciated that an annular discharge slot 20 is provided in the bottom wall 24 of the tank in order to form the lower discharge opening.

The ring shaped tank 12 further comprises in its lower region 21 an annular guiding member 32 that is arranged above and spaced from the bottom wall 24. The annular guiding member 32 is configured to cover the annular discharge slot 20 and guide descending sinter towards the casing 22. The annular guiding member 32 is said to cover the annular discharge slot 20 in the sense that its radial extent is greater than the (radial) width of the discharge slot 20 and it is positioned so that there is no vertical line of sight between the interior of the tank, above the casing, discharge slot 20. In other words, the annular guiding member 32 prevents a direct vertical flow of the sinter material into the discharge slot 20.

Also to be noticed, the scraper(s) 16 is (are) arranged in the casing 22 at least partially below the annular guiding member 32 and is configured to guide sinter accumulated in the casing 22 towards the annular discharge slot 20. Since the one or more scraper(s) 16 are located in the casing 22 below the annular guiding member 32, they do not bear the weight of sinter material residing in the tank.

By way of the above design, descending sinter is guided by the annular guiding member 32 in such a way that it flows towards the inner and outer peripheral lower regions of the tank, entering the casing 22 and first accumulating on the bottom wall 24, i.e. on bottom wall portions remote the discharge slot 20. As will be better understood from the following drawings, sinter will also accumulate below the guiding member 32, where it will be discharge by the scraper(s) 16.

While Fig.1 has been provided to illustrate the principles of the invention, Figs. 2 to 4 provide constructional details about a practical embodiment of sinter cooling system 100 according to the present invention. Each of these views is a section view and, for ease of understanding, the corresponding cut planes have been represented on the sketch of Fig.1 . Like elements are designated with same reference signs. Figure 2 is a vertical sectional view (corresponding to line ll-ll in Fig.1 ) of the cooling system 100, at the level of the scraper 16. One will recognize the annular outer and inner walls 12.1 , 12.2 (which are here substantially vertical) and the casing 22, with the facing annular outer and inner walls 26, 26' (corresponding to the lower part of walls 12.1 and 12.2). The annular bottom wall 24 extends between the two walls 26 and 26', and comprises the annular discharge slot 20 through which sinter is discharged by the scraper 16 while the tank 12 is rotated. Although only scraper 16 is shown in Fig.1 , this embodiment preferably includes a pair of scrapers 16 and 16' located in a same region of the circumference of the tank.

Hence, the casing 22 forms the lower end of the tank 12. The bottom wall 24 is tightly peripherally assembled to the annular walls 26 and 26' and closes the lower end of the tank 12, except for the annular slot 20. In other words, in the present system 100 there is no outer peripheral slot for the radial extraction of the sinter. Sinter is scraped from the bottom wall 24 inside the casing 22 and guided towards the annular slot 20, through which it is discharged vertically below the tank 12. Hence, in the present design the bottom wall 24 extends transversally, between outer and inner walls. The bottom wall 24 is preferably substantially horizontal, but may be slightly tilted, e.g. up to 10°; hence the discharge slot is in a substantially horizontal plane or in a similarly tilted plane.

The annular guiding member 32 is arranged above the discharge slot 20 and covers the latter, in the sense that the guiding member 32 is configured to extend over the discharge slot in 20 such a way as to prevent a direct vertical flow of sinter into the discharge slot from the inside of the tank. The radial width W _M of the guide member is therefore greater than the width W _s of the discharge slot. In fact, the guide member 32 is further configured to guide the descending sinter towards the inner and outer peripheral regions of the bottom wall 24. One can also observe in Fig.2 that the scraper 16 is entirely covered by the guiding member 34; this is preferably the normal operating position of the scraper. Also to be noted, the discharge slot 20 and guide member 32 are preferably centrally arranged in the tank 12.

Preferably, the guiding member 32 has a convex-shaped upper side facing the sinter load. Here the guiding member 32 comprises an upper wall 32.1 that forms a hill with an apex 36 that is in the present case at mid-distance from the outer and inner annular walls 26 and 26'. The slope of the hill is determined by angle a (half- angle at the apex), which is generally greater than 10°, preferably between 40° and 60°. Also, the annular guiding element 32 is provided with a plurality of inlet vanes 38 that allow entry of cooling air in the heart of the cooling tank 12, from the annular discharge slot 20. Air can thus move up through the residing mass of sinter, enabling the "counter current" air cooling described in the introductory section. The simple arrows represent the ascending flows of air in the lower region 21 of the tank 12.

The casing 22 defines a sinter accumulation region between the guiding member 32 and the bottom wall 24. It may also be noticed that the bottom wall 24 is divided by the discharge slot 20 into an outer accumulation surface 24.1 and an inner accumulation surface 24.2, both of annular shape.

A further remarkable aspect of the casing is that both accumulation surfaces 24.1 and 24.2 are partly covered by the guiding member 34; the portion of each accumulation surface located below the guiding member is referred to as free accumulation surface 25.1 and 25.2.

As it will be understood, the mass of sinter in the tank 12 descends therein due to gravity, as sinter is progressively evacuated through the discharge slot 20. The guiding member 32 prevents vertical direct fall of the sinter in discharge slot 20. In fact, guiding member 32 guides the descending sinter inside the accumulation region of the casing 22, towards the outer and inner periphery of the accumulation surfaces 24.1 and 24.2, i.e. initially away from the annular slot 20. Seen in the radial direction, before and beyond the guiding member 32 the peripheral portions of the accumulation surfaces 24.1 and 24.2 are in direct vertical sight with the inside of the tank. On these peripheral sections (next to the outer and inner walls), accumulated sinter supports the weight of a full column of sinter in the tank.

But sinter also moves and accumulates below the guiding member 32. The mass of sinter accumulating below the guiding member, i.e. on the free accumulation surfaces 25.1 and 25.2, is not subject to the weight of the sinter mass situated above in the tank. Therefore sinter tends to accumulate by spontaneously forming an annular heap of sinter, noted 33, with an upper surface following the angle of repose (natural dumping angle β) of the granular sinter material, which is indicated by dotted lines 33.1 in Fig.2.

Under the guiding member 32, the heap 33 of sinter is not subject to vertical compression forces and can therefore be more easily collected by the scraper 16. This avoids crushing/destruction of sinter during scraping and early wear of the scraper blade; there is no need for heavy scraper drives since the torque is rather low due to the absence of a sinter column resting on the scraper.

A constructional feature may be noted at this point, with reference to Fig.4. One will recognize the annular heap 33 of sinter depicted by the dash-lined triangle that has formed on the free accumulation surface 25.1 . As it has been explained, sinter heap 33 forms with an angle β (natural angle of repose) on the corresponding free accumulation surface 25.1 . The radial extent of the heap, indicated L1 , depends on the spacing Z between the bottom wall 24 and the lower end of the guiding member 32. The greater the spacing Z, the larger L1 , for a given angle of repose β. Accordingly, the bottom tank region is designed such that, for a given spacing Z and in consideration of a given angle of repose β of the sinter material, the radial extent L2 of the free accumulation surface 25.1 is greater than the corresponding axial extent L1 of the free heap 33 that is intended to form on the free accumulation surface. In Fig.2 the scraper 16 (more precisely scraper blade) extends horizontally inside the casing over the bottom wall and is fixed to a pivotable vertical shaft 40. The shaft 40 is associated with an actuating mechanism (not shown) that allows adjusting the scraper blade to a desired orientation.

In normal operation the scraper 16 extends over the bottom wall 24 but only over the free accumulation surface 25.1 , 25.2. The scraper 16 enters thus only comes into contact with sinter showing a natural damping angle.

This can also be seen in Fig.3 (horizontal sectional view Ill-Ill). The radial extent of guiding member 32 is depicted by dashed lines 42. In normal operation as illustrated here, the first scraper 16 extends over the outer free accumulation surface 25.1 and the second scraper 16' extends over the inner free accumulation surface 25.2. If desired, for example for cleaning purposes, the scrapers 16, 16' can be pivoted to extend over the whole radial extent of the respective accumulation surface.

As shown in Fig.3, the annular heap of sinter 33 formed on each free accumulation surface 25.1 , 25.2 is scraped by the respective scrapers 16, 16', due to the rotation of the tank in the direction of arrow 56, and thus guided towards the central annular slot 20. It may be noticed that in the present embodiment, the inner and outer walls 12.1 , 12.2 as well as the bottom wall 24 consist of assembled metal sheets resting on a support structure. The support structure comprises a plurality of inner and outer support members 50, 52 distributed around the tank. The support members 50, 52 may typically be section-steels, which can have any appropriate shape. In the shown embodiment, the support members 50, 52 are e.g. L-shaped section steels. Referring back to Fig.2, the outer support members 50 comprise a vertical element 50.1 supporting the outer tank wall 12.1 and a horizontal, radially extending element 50.2 supporting the outer accumulation surface 24.1 . The inner support members 52 comprise a vertical element 52.1 supporting the inner tank wall 12.2 and a horizontal, radially extending element 52.2 supporting the inner accumulation surface 24.2. As can be seen in Fig.3, support members 50, 52 are here arranged by pairs and are radially aligned, although this is not required. The guiding member 32 is preferably fixed inside the tank 12 by radially extending horizontal supports 54 fixed to the vertical elements 50.1 and 52.1 . The support members 50, 52 may be manufactured from universal beams. The horizontal supports 54 may also be universal beams. Any other appropriate section steels can be used for the support members.

Still to be noted in Fig.2 is the annular hood 60 that closes the annular charge opening 18 of the tank 12. Conventionally, hood 60 is fixed and comprises one outlet 62 for drawing cooling air out of the tank 12 a, for example by way of a fan system (not shown). At another position of the circumference, the hood has an inlet (not shown), through which hot sinter is introduced in the tank 12. Water seals 64 are conveniently arranged at the top of the tank 12 to provide tight closure between the rotating tank 12 and fixed hood 60.

Figure 4 is a vertical cross sectional view IV-IV of the sinter cooling system 100, at a position remote from the scrapers. Here the rotary drive means 14 are represented in more details. In this embodiment they comprise a first set of wheels 66 distributed along a circle below the outer wall 12.1 to provide a first, outer support and drive path. A second set of wheels 68 distributed along a circle below the inner wall 12.2 to provide a second, inner support and drive path. The wheels 66, 68 are mounted on a fixed support on the ground and can freely rotate about an axis. One or more of the wheels 66, 68 are coupled to a driving motor 70, e.g. an electric motor. The motor 70 provides the driving force for rotating the respective wheel 66 and causing the tank 12, supported on the sets of wheels, to rotate around central axis A (in Fig.1 ). It remains to be noticed in Fig.4 that an annular rail 72 is fixed below each of the outer and inner walls of the tank, more specifically to the lower side of the support members 50, 52. The rails 72 provide continuous sliding surfaces by which the tank 12 can be properly supported on the sets of wheels 66, 68. A plurality of rollers 80 may be distributed circumferentially to be in contact with an annular guide flange 82 affixed to the lower part of the support structure. This avoids radial deviation of the tank 12 during rotation.

Finally, a possible embodiment of the sinter collecting means is shown in Fig.2. A first conveyor belt is indicated 76. It extends in a plane perpendicular to that of Fig.2. Sinter falling through discharge slot 20 thus falls on conveyor 76 and is forwarded to a second conveyor 78 which carries the sinter further away in a direction transversal to that of conveyor 76. This is only one possible embodiment of collecting means and should not be construed as limiting. The collecting means may also employ receiving funnels and/or bins.

LIST OF REFERENCE SIGNS

10 sinter cooling system

1 1 granular sinter material

12 ring shaped tank

12.1 , 12.2 outer wall

14 rotary drive means

12.2 annular inner wall

16, 16' scraper

18 upper charge opening

20 lower discharge opening

21 lower region

22 ring shaped casing

24 annular bottom wall 25.1 , 25.2 free accumulation surface

26, 26' annular wall

32 annular guiding member

33 heap of sinter, noted

33.1 upper surface

34 conveyor belt

40 pivotable vertical shaft

50, 52 support members

42 radial extent of guiding member

50.1 , 52.1 . vertical element

50.2, 52.2 radially extending element

54 horizontal support

56, arrow

62 outlet

66, 68 wheels

70 driving motor

72 annular rail

76 first conveyor belt

78 second conveyor

80 roller

82 guide flange

100 sinter cooling system

Z spacing

L1 , L2 radial extent

β natural dumping angle