EP3325673A1

EP3325673A1 - Tilting converter

Info

Publication number: EP3325673A1
Application number: EP16757075.3A
Authority: EP
Inventors: Alfredo Poloni; Marco Ansoldi; Yuri RAFFAGLIO
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2015-07-17
Filing date: 2016-07-15
Publication date: 2018-05-30
Anticipated expiration: 2036-07-15
Also published as: EP3325673B1; WO2017013554A1; ITUB20152291A1

Description

"TILTING CONVERTER"

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Field of the invention

The present invention relates to an oxygen tilting converter provided with a suspension system for the converter container, connecting said container to a trunnion ring.

Background art

It is the main object of an oxygen converter to convert the cast iron produced in the blast furnace into crude liquid steel, which can then be refined in the secondary steel production department.

The main functions of the oxygen converter, also known as B.O.F. (Basic Oxygen Furnace), are to decarburize and remove phosphorus from the cast iron and optimize the temperature of the steel so that further treatments can be implemented prior to casting with minimum heating and cooling of the steel.

The exothermic oxidation reactions occurring in the converter produce much heat energy, more than is necessary to reach the set temperature of steel. This extra heat is used to melt scrap and/or additions of iron ore. The B.O.F. container, being substantially a furnace, is also subject to strong thermal expansion.

The converter consists of a container, defining the reactor and having generally a central cylindrical body, hemispherical bottom or substantially truncated cone bottom and a substantially truncated cone upper zone provided with a loading mouth.

The container or vessel is supported by an annular support structure (trunnion ring), which coaxially surrounds it and is suitably spaced apart therefrom. The trunnion ring has two diametrically opposite supporting pins (trunnion pins), which define a rotation axis of the entire system to allow both the loading of the material to be melted (or of the already molten cast iron coming from upstream processes) and the tapping of the molten material and all the other activities related to steel production. The whole system is supported by two supports anchored to the ground. The rotation control of the container is keyed on one of the two trunnion pins.

Suspension elements are suitably provided for the container of the converter, connecting the container to the trunnion ring.

The following are in particular used among the various vertical suspension elements:

- elastic bars in the form of tie-rods constrained, at an upper end thereof, to the upper surface of the trunnion ring and at a lower end thereof to a cantilever shelf integral to the container in a zone below the trunnion ring;

- or lamellae or lamellae packs constrained, at an upper end thereof, to the lower surface of the trunnion ring and at a lower end thereof to a cantilever shelf integral to the container in a zone below the trunnion ring.

The solution with tie-rods provides for the tie-rods being arranged in a distributed manner along the trunnion ring and the axis of the tie-rods being preferably parallel to the longitudinal axis of the container, orthogonal to the ground, and therefore vertically when the container is arranged with the loading mouth facing upwards. However, the tie-rods could also be arranged with a certain angle with respect to the ground, other than 90 °.

The solution with lamellae provides for the single lamellae or the lamellae packs being arranged in a distributed manner below the trunnion ring, considering the converter in its straight position with the loading mouth facing upwards. In this configuration, the single lamellae or the lamellae packs are generally arranged tilted by an angle of about 20-25 ° with respect to a respective vertical plane containing the longitudinal axis defined by the converter. In an alternative configuration, the single lamellae or the lamellae packs are instead arranged parallel to a respective vertical plane containing the longitudinal axis of the converter.

The following are for example used among the various horizontal suspension devices:

- suspension devices having a first structure welded to the container and a second T-shaped structure bolted to the trunnion ring. A shim may be provided at the interface between the container and the T-shaped structure attached to the ring which allows to adjust the two structures in the assembly step;

- or suspension devices having a first anchor attached to the container and a second anchor directly attached to the trunnion ring. A wedge-shaped shim is provided at the interface between the two anchors in turn attached by screws in the assembly step of the converter, allowing an adjustment of the suspension device both during assembly and during maintenance of the converter.

Currently, many of the working parameters of the B.O.F. are calculated indirectly in the preceding steps and in the subsequent steps of the smelting step. For example, how much material is loaded, how much molten material is poured and how much slag is discarded for each casting is calculated.

However, there is no very accurate manner to determine the amount of liquid material, i.e. molten material, which is kept in the container at the end of each smelting; the wear of the refractory; whether the container is subjected to overheating, but also to mechanical overloads due to the undesired accumulation of material.

Therefore, the need to implement an oxygen converter which allows to overcome the above drawbacks is felt.

Summary of the invention

It is the primary object of the present invention to implement an oxygen converter provided with a continuous monitoring system of the deformations of the suspension elements, so as to monitor the integrity of the suspension system while directly deriving, even during the operating steps, a variety of information about the process which is currently available only indirectly by cross-checking data of preceding steps and subsequent steps of the various processes taking place in the BOF.

The present invention therefore aims to achieve the objects outlined above by implementing a tilting converter which, according to claim 1 , comprises:

a container, defining a first longitudinal axis X, having a bottom;

a trunnion ring (support ring), coaxial to the container and spaced apart from said container, provided with two diametrically opposite trunnion pins (supporting pins), defining a second axis Y orthogonal to the first axis X, adapted to allow a rotation of the converter about said second axis Y;

a suspension system, connecting said container to said trunnion ring, comprising suspension elements or groups of suspension elements, said suspension elements or said groups of suspension elements being arranged along a cylindrical or truncated cone side surface, coaxial to the first axis X, wherein there are provided deformation detecting means adapted to detect in real time the deformations to which the suspension elements are subjected,

and wherein said deformation detecting means comprise deformation measuring instruments applied in at least one zone of each of said suspension elements 7. The monitoring system of the deformation of suspension elements according to the present invention aims at quantifying the deformation of the vertical suspension elements of a BOF, whether they are tie-rods or lamellae, preferably through the use of measuring instruments of the deformations to which the surface of the suspension element to which they are applied is subjected.

A preferred solution of the invention contemplates the use of strain gauges or similar devices applied to the tie-rods or to the lamellae.

Strain gauges are measuring instruments used to detect dimensional deformations of a body subjected to stress. Strain gauges have the property of varying their internal resistance depending on the deformation to which the surface to which they are applied is subjected. They consist of a circuit made of a sensitive element, usually a very fine wire of metal or semiconductor material, which varies its resistance according to the deformation it receives from the body to which it is applied. Measuring the above resistance variations by means of a Wheatstone bridge or other similar devices, it is possible to derive the extent of the deformation which caused them.

Strain gauges, suitable for temperatures up to 250 °C, can for example be glued onto the tie-rods or on the lamellae which connect the trunnion ring to the vessel walls.

The dependent claims describe preferred embodiments of the invention.

Brief description of the drawings

Further features and advantages of the invention will become more apparent from the detailed description of preferred, but not exclusive, embodiments of a tilting converter, shown by way of a non-limiting example with the aid of the accompanying drawings, in which:

Figure 1 shows a partial sectional view of a converter according to the invention; Fig. 2 is a top view of a first example of converter with suspension elements in the shape of tie-rods;

Fig. 3 is a partially sectional view of the converter in Figure 2;

Figure 4 is a top view of a second example of converter with suspension elements in the shape of lamellae;

Figure 5 is a sectional view along plane B-B of the converter in Figure 4.

The same reference numerals in the figures identify the same elements or components.

Detailed description of preferred embodiments of the invention

With reference to the Figures, preferred embodiments of a tilting converter, globally indicated with reference numeral 1 , are shown.

Such a converter 1 comprises:

- a container 2, defining an axis X provided with a loading mouth 4 of scrap and liquid cast iron and provided with a side discharge hole 5 (only shown in Figure 3) of the liquid steel obtained at the end of the conversion process;

- a trunnion ring 3 (support ring) for supporting container 2, said ring 3 being arranged coaxially to container 2 and suitably spaced apart therefrom;

- two supporting pins 6, or trunnion pins, of said trunnion ring 3, diametrically opposite to each other and defining an axis Y, orthogonal to axis X, with at least one of said trunnion pins 6 connected to a tilting mechanism (not shown);

- a suspension system which connects container 2 to the trunnion ring 3 and which also carries out a centering function between container and ring.

By defining a further axis Z as the axis orthogonal to the plane X-Y and passing by the point of intersection of axes X and Y, a plane Y-Z is defined which can be considered an "equatorial" plane of the converter, and a plane X-Z, both orthogonal to plane X-Y.

With particular reference to Figures 3 and 5, container 2 comprises a central cylindrical zone 20 and two truncated cone zones 21 , 22, each truncated cone zone being arranged laterally to said central cylindrical zone. A first truncated cone zone 21 is welded at one end to said central cylindrical zone 20 while at the other end it comprises the loading mouth 4 of the container. Generally, the side discharge hole is provided in said first truncated cone zone 21 . A second truncated cone zone 22 is welded at one end to said central cylindrical zone 20, on the side opposite to the first truncated cone zone 21 , while at the other end it comprises bottom 2' of container 2.

Alternatively, for example as shown in Figure 1 , the second zone 22 comprises a truncated cone section closed by a hemispherical bottom. A further alternative (not shown) contemplates that the second area 22 is totally hemispherical.

The trunnion ring 3, arranged at the central zone 20 of container 2, is hollow and preferably has a rectangular cross section. Ring 3 has a surface 10 facing towards the part of the container comprising the loading mouth 4; a surface 11 , opposite to surface 10, facing towards the part of container 2 comprising its bottom 2'; an inner surface facing towards the central part of the container; an outer surface opposite to the inner surface.

With reference to the examples of converters shown in Figures 2-3 and 4-5, which show the converter of the invention in its straight position with the loading mouth 4 facing upwards, such a converter includes:

- at least one pair of horizontal suspension elements 8, each arranged at a respective trunnion pin 6 and transversally with respect to plane X-Y,

- and vertical suspension elements 7 or groups 12 of vertical suspension elements 7, said elements 7 or groups 12 of elements 7 being arranged substantially mutually equidistant along a cylindrical or truncated cone side surface coaxial to axis X, in a position between the trunnion ring 3 and bottom 2'.

In both examples in Figures 2-3 and 4-5 there are provided four groups 12 of vertical suspension elements 7 and each horizontal suspension element 8 is arranged, in the zone in the vicinity of the trunnion pin, between two respective groups 12 of suspension elements 7, each group 12 being made up of four suspension elements 7. In other examples, each group 12 may consist of two or three or more than four suspension elements 7. In a preferred variant, the four groups 12 of suspension elements 7 may be arranged at a same angular distance between one group and the next one (90 °) so as to obtain a balanced distribution of loads for each group 12 of suspension elements 7. Groups 12 of suspension elements 7 are arranged symmetrically with respect to plane X-Z and plane X-Y. In an alternative variant, the four groups 12 of suspension elements 7 can be arranged still symmetrically but closer to the trunnion pins. Therefore, the groups are no longer spaced apart from one another by 90 °.

In a further alternative variant, three groups of vertical suspension elements may be provided, arranged at a same angular distance between one group and the next one (120 °).

In the variant in Figures 2-3, the vertical suspension elements 7 for the vertical suspension of the converter are longitudinal bars interlocked at a first end to container 2, preferably at a cantilever shelf of said container, and interlocked at a second end to the trunnion ring 3, preferably to the upper zone or surface 10 of said trunnion ring. The longitudinal bars 7 are locked at the ends to prevent the presence of parts with relative motion, and since there are no parts subject to wear, maintenance works are eliminated or at least greatly reduced. Bars 7, acting as tie-rods or struts, can be adjusted to compensate for any unevenness in the length of the bars, thus ensuring a correct positioning thereof during assembly. Bars 7 are suitably sized to operate as elastic support means to absorb expansions. Said bars 7 preferably have a circular section. However, other section shapes may be contemplated according to the design longitudinal extension of the bars.

With reference to Figures 2-3, an advantageous configuration of the converter includes:

- four groups of elastic bars 7 arranged parallel to axis X and at a same angular distance between one group and the next one (90 °);

- a pair of suspension devices 8, said suspension devices 8 being arranged, each at a respective trunnion pin 6, symmetrically with respect to plane X-Z on a respective plane parallel to plane Y-Z.

Each suspension device 8 is provided in the space between two groups of elastic bars 7 and arranged in the vicinity of the first surface 10 of ring 3 (Figure 2). Alternatively, each suspension device 8 may be arranged in the vicinity of the second surface 11 of the ring.

The four groups of elastic bars 7 are arranged so that two pairs of groups of bars 7 are arranged mutually symmetrically with respect to plane X-Y.

Another advantageous configuration (not shown) of the converter includes two pairs of suspension devices 8, a first pair of suspension devices 8 being arranged at a first side of plane Y-Z and a second pair of suspension devices 8 being arranged at a second side of plane Y-Z. The suspension devices 8 are further arranged symmetrically with respect to plane X-Z. Considering the converter in vertical position, bars 7 are in vertical position while the suspension devices 8 are in horizontal position. Bars 7 orthogonally cross plane Y-Z. The suspension devices 8 are instead parallel to plane Y-Z and cross plane X-Y. In particular, a pair of suspension devices 8 is arranged at a first side of plane Y-Z, i.e. above plane Y- Z and of the trunnion ring 3 when the converter is in vertical or straight position; while another pair of suspension devices 8 (not shown) is arranged at a second side of plane Y-Z, i.e. below plane Y-Z and the trunnion ring 3 when the converter is in vertical or straight position.

All suspension devices 7, 8 are arranged, in plan, substantially along a circumference. Therefore, they are arranged substantially along the side surface of a cylinder.

The elastic bars 7 of groups 12 are constrained at one end to container 2 by blocking them on the fixing supports 14. They are instead constrained at the other end by blocking them directly on the first surface 10 of the trunnion ring 3. The constraint is an interlocking (interlocked beam). Both the fixing supports 14, welded or bolted to container 2, and the first surface 10 of ring 3 have through holes in which the elastic bars 7 are inserted; the ends of such bars are threaded and the blocking thereof on supports 14 and on the first surface 10 of the ring is by means of a self-aligning locking system and nuts. The elastic bars 7 cross, at least with an end thereof, the cavity of ring 3, optionally within a respective sleeve having the function of delimiting the passage channel of the respective bar 7. Advantageously, a single fixing support 14 may be provided for each group 12 of elastic bars 7.

With reference to Figure 3 (converter in vertical position), the elastic bars 7 are attached to container 2 in a position below the trunnion ring 3, i.e. below plane Y-Z; while they are attached to ring 3 directly on the first surface 10 of the latter, i.e. above plane Y-Z.

The suspension devices 8 may be, for example, of the type (half) shown in Figure 3, comprising a central structure 8' attached to a container 2; a first side structure 29 arranged at a side of said central structure 8' and attached to surface 10 of the trunnion ring 3 of the container; a second side structure (not shown) arranged at a second side of said central structure 8', opposite the first side and attached on said surface 10 of the trunnion ring 3; wherein two wedge-shaped elements 15 are provided, each wedge-shaped element 15 being arranged between the central structure 8' and a respective side structure and configured so as to slide on two sliding surfaces of the central structure 8' and of the respective side structure, respectively; wherein each wedge-shaped element 15 is crossed by at least one tie-rod 16 connected thereto; and wherein the elastic means associated to the at least one tie-rod 16 or said at least one tie-rod with its intrinsic elasticity are configured to produce a constant wedging of the wedge-shaped element 15 so that an automatic adjustment of the suspension device 8 is carried out upon the variation of the expansions occurring between central structure 8' and side structures during the operation of the converter.

In the variant in Figures 4-5, the suspension elements 7 are lamellae arranged tilted with respect to axis X. The tilting with respect to axis X is by an angle preferably comprised between 10 ° and 20 °. Alternatively, the suspension means 7 are lamellae arranged parallel with respect to axis X.

Each suspension element 7 is constrained at a first end to container 2 and at a second end to the trunnion ring 3 by blocking it on respective fixing supports 13, 14, such as brackets, by fixing means such as through screws, shear pin bushes, keys, tabs or other equivalent means. Advantageously, a single fixing support 13 and a single fixing support 14 may be provided for fixing the ends of the suspension elements 7 of each group 12. In particular, the fixing support 13 is integral to surface 11 of the trunnion ring 3 facing towards bottom 2' of the container; while the fixing support 14 is integral to the truncated cone zone 22 or integral to both said truncated cone zone 22 and to bottom 2' of container 2.

As regards the horizontal suspension means 8, they are arranged parallel to plane Y-Z, orthogonal to the first axis X and symmetrically with respect to plane X-Z. The suspension means 8 cross plane X-Y and are arranged in the vicinity of surface 10 and/or surface 11 of the trunnion ring 3. The horizontal suspension means 8 which can be used may be of various types, such as those described above with reference to Figure 3, or other types already known in the art.

In all the variants, the two trunnion pins 6, actuated by at least one tilting mechanism, allow the rotation of the converter about axis Y.

The converter usually switches from a first position, in which it is in its vertical position with the loading mouth 4 facing upwards (Figures 3 and 5) to a second position tilted by an angle of about 45 ° from the vertical, through a rotation of the trunnion pins 6 in a rotation direction. In this second position, the liquid cast iron and the scrap is loaded through mouth 4. After loading, the converter returns to the first position shown in Figures 3 and 5. One or more nozzles, introduced into the container through mouth 4, blow oxygen for a predetermined period of time in order to drastically lower the carbon content and reduce the concentration of impurities such as sulfur and phosphorus. After the conversion into liquid crude steel, the converter switches from first position shown in Figures 3 and 5 to a third position tilted by an angle of about 90 ° from the vertical, through a rotation of the trunnion pins 6 in a direction opposite to said previous rotation direction. In this third position, the liquid steel is discharged through the discharge hole provided in the container of the converter. In all possible variants of the converter, the load, determined by the sum of the weights of container 2, of the liquid cast iron and of the scrap, is discharged to the ground through the trunnion ring 3, the vertical suspension elements 7, the horizontal suspension devices or elements, the trunnion pins 6 and the relative supports.

In particular, the configuration of the suspension elements 7 and of the suspension elements 8 allows to absorb the weight for any inclination of container 2.

The suspension means 7 mainly act as tie-rods for a tilting angle of the converter from the vertical equal to 0 °, while they mainly act as struts for a tilting angle equal to 180 °, and gradually both as tie-rods and as struts for angles other than 0 ° and 180 °. The position with tilting angle equal to 180 °, with loading mouth 4 facing downwards, is used for cleaning the container, when emptied.

The suspension means 8 ensure optimal support, stability and rigidity of the container. Said suspension elements 8 mainly serve for supporting the load component orthogonal to axis X of the converter.

In general, therefore, the load on the suspension means 7 gradually switches from a maximum value with converter in vertical position to a minimum value with converter in horizontal position, while the load on the suspension elements 8 switches gradually from a substantially zero value to a maximum value when the converter switches from the vertical position to the horizontal position. The moments which are generated with the rotation of the converter about axis X are perfectly absorbed by the configurations of the suspension elements 7 and of the suspension elements 8.

Advantageously, the suspension system of the converter according to the present invention is provided with deformation detecting means adapted to detect in real time the deformations to which the suspension means 7 are subjected during all the steps described above, including the smelting step.

Said deformation detecting means comprise deformation measuring instruments 30 applied in at least one zone of each of the suspension elements 7, whether in the form of tie-rods (Figures 2 and 3) or lamellae (Figures 4 and 5).

Said deformation measuring instruments 30 are applied at least in an upper zone and/or a lower zone of each of said suspension elements 7, considering the container 2 with the loading mouth 4 facing upwards (Figure 1 ).

The measuring instruments 30 may also be applied in a central zone of each of the suspension elements 7.

In a preferred variant, the deformation measuring instruments 30 are strain gauges, preferably glued in said zones of the suspension elements 7.

Advantageously, there are provided an acquisition device 31 adapted to acquire data on the deformations suffered by the suspension elements 7 and at least one calculation unit 32 for processing said data. At least one storage device 33 of said data is also provided.

In an exemplary but non-limiting solution, the circumference of container 2, seen from above, is divided into four quadrants (see for example Figure 4). Each quadrant contains a group consisting of "n" vertical suspension elements 7, suitably provided with measuring instruments 30, preferably strain gauges, applied thereto and preferably insulated in a known manner. Preferably, but not necessarily, the strain gauges 30 are applied in a number of four on each of the two/three zones of the suspension elements 7. For example, four strain gauges 30 are applied in the upper zone, in the middle and in the lower zone of the suspension elements 7, respectively.

The deformations suffered by the strain gauges 30 are detected through the acquisition device 31 and they allow to calculate the magnitude of the load acting on the tie-rods or lamellae.

The next step relates to data management: through at least one calculation unit 32, which may be on board the converter or communicating therewith, such as via Wi-Fi, a "map" can be built which shows the deformations of the suspension elements 7 and therefore the differential deformations between vessel 2 and trunnion ring 3. This data set provides real time indication of the situation of the stresses on the suspension system, allowing direct control over the conditions of the suspension system and the converter. Through data storage, using the storage device 33 it is possible to define how the converter behaves by monitoring the suspension system over time.

Moreover, these data detected continuously allow to understand the situation of the load contained into container 2 during the various process steps. In fact, it is possible to estimate the amount of material loaded, discharged, slagged and kept as liquid (molten) material. Moreover, by measuring the initial load-less weight and the process-end weight, it is possible to understand how much refractory was consumed in the various castings. Abnormal overload situations can be also detected.

Claims

1 . A tilting converter comprising:

a container (2), defining a first longitudinal axis X, having a bottom (2');

a trunnion ring (3), coaxial to the container (2) and spaced apart from said container, provided with two diametrically opposite trunnion pins (6), defining a second axis Y orthogonal to the first axis X, adapted to allow a rotation of the converter about said second axis Y;

a suspension system, connecting said container (2) to said trunnion ring (3), comprising suspension elements (7) or groups of suspension elements (7), said suspension elements (7) or said groups of suspension elements (7) being arranged along a cylindrical or truncated cone side surface, coaxial to the first axis X,

wherein there are provided deformation detecting means adapted to detect in real time the deformations to which the suspension elements are subjected,

and wherein said deformation detecting means comprise deformation measuring instruments applied in at least one zone of each of said suspension elements (7).

2. A converter according to claim 1 , wherein said deformation measuring instruments are applied in an upper zone and a lower zone of each of said suspension elements (7).

3. A converter according to claim 2, wherein said deformation measuring instruments are also applied in a central zone of each of said suspension elements (7).

4. A converter according to any one of the preceding claims, wherein said deformation measuring instruments are strain gauges.

5. A converter according to claim 4, wherein said strain gauges are glued to said suspension elements (7).

6. A converter according to any one of the preceding claims, wherein there is provided an acquisition device adapted to acquire data on the deformations suffered by said suspension elements (7).

7. A converter according to claim 6, wherein there is provided at least one calculation unit for processing said data.

8. A converter according to claim 6 or 7, wherein there is provided at least one storage device for storing said data.

9. A converter according to any one of the preceding claims, wherein said suspension elements (7) or said groups of suspension elements (7) are in a position between the trunnion ring (3) and the bottom (2').

10. A converter according to any one of the preceding claims, wherein said suspension elements (7) are tie-rods or lamellae.

11 . A converter according to claim 10, wherein said tie-rods are constrained at a first end thereof to the container (2) by blocking them on fixing supports (14) protruding from the container (2), and are constrained at a second end thereof by blocking them directly on a upper surface (10) of the trunnion ring (3).

12. A converter according to claim 10, wherein said lamellae are constrained at a first end thereof to the container (2) and at a second end thereof to the trunnion ring (3) by blocking them on respective fixing supports (13, 14).