FI3903057T3

FI3903057T3 - Walking beam furnace for continuously discharging and shredding scale

Info

Publication number: FI3903057T3
Application number: FIEP19845707.9T
Authority: FI
Inventors: Michel Maternova
Priority date: 2018-12-24
Filing date: 2019-12-17
Publication date: 2023-01-13
Also published as: EP3903057A1; WO2020136321A1; PL3903057T3; FR3090836B1; CA3122609A1; ES2935359T3; MX2021007697A; EP3903057B1; US20220074665A1; FR3090836A1; BR112021011695A2

Description

EP3 903 057

WALKING BEAM FURNACE FOR CONTINUOUSLY DISCHARGING AND

SHREDDING SCALE

Technical field

The invention relates to reheating walking-beam furnaces intended to heat steel products, for example made of carbon steel or stainless steel, in particular slabs, blooms, blanks or billets, at a suitable temperature for their hot rolling.

Prior art

The furnace makes it possible to bring the products to high temperatures, about 1.150 °C for a carbon steel. The heating of the furnace is commonly carried out by burners operating with slight excess air, which results in the presence of oxygen in the furnace. A significant oxidation of the products in the furnace results from the combination of a high temperature and the presence of oxygen.

Steelwork reheating furnaces operate continuously and have significant production capacities, ranging for example from 120 t/h to 650 t/h. The weight loss of the products resulting from oxidation is commonly of the order of 0,6 %.

When it is detached from the products, scale falls to the hearth of the furnace on which it accumulates.

By the term scale, the present description designates not only the scale itself resulting from the oxidation of the products, but more generally any solid polluting residue.

The scale can be removed during periodic shutdowns of the furnace. This solution is not satisfactory, since it leads to a significant loss of production due to the time required for cooling the furnace, the manual removal of the scale, then the rise in temperature of the furnace. The furnace can be equipped with de- slagging doors from which an operator will rinse, that is to say, scrape and remove the scale using a tool, of a rake type. This solution is not satisfactory, because access to scale located at the center of the furnace is not easy.

Furthermore, the opening of these de-slagging doors causes air to enter the furnace, which has the effect of increasing the oxidation of the products present inside. Examples of this type of apparatus are described in document GB813362.

” EP3 903 057

The walking beam furnace equipped with fixed beams and walking beams is known.

The beams have cooled andirons and keels. The walking beams allow the transport of products inside the furnace by following a rectangular cycle having a first raising phase which makes it possible to lift the products from the fixed beams. It is followed by a second phase of horizontal transport then by a third phase of depositing the products on the fixed beams. The products are thus moved by one step on the fixed beams before the fourth phase for returning the walking beams back to their initial position. The total duration of a rectangular cycle is approximately 55 seconds.

To limit the black marks caused by the shadow of the andirons on the products, the beams can be offset transversely toward the outlet of the furnace, also called the unloading zone.

At the location of the offsetting of the andirons, at the inlet of the furnace in the area for depositing the products and towards the outlet of the furnace where the temperature of the products is greater, more scale is formed, which must be discharged periodically.

The applicant has improved the operation of a furnace as presented and has filed patent application EP2516950 for a heating furnace with walking beams which ensures, simply and effectively, the automatic discharge of some of the scale, or other polluting residue, while avoiding the aforementioned disadvantages. For this purpose, it has been proposed that, in the zones of the furnace where the scale, or other polluting residue, in particular toward the inlet and the outlet of the furnace is mainly produced, the hearth is thicker than in the rest of the furnace, that inclined surfaces are installed in this thicker zone of the hearth, with a slope of walls sufficient to avoid material roll-back, in such a way as to collect the scale and the residues and lead them to discharge pipes which open into water tanks, and that the water tanks are fixed to the translation frame allowing a part of the scale from the discharge pipes to be continuously discharged, while maintaining the impermeability of the furnace. Indeed, increasing the thickness of the hearth makes it possible to install hoppers formed by the inclined surfaces having a significant slope while having a wide opening flush with the hearth in order to cover as much surface as possible. This feature contributes to the discharge of the scale or other residue.

EP3 903 057

The applicant has continued to work on the possibilities of improvements in such walking beam furnaces.

Indeed, the solution according to the prior art is not entirely satisfactory, since the scale falls predominantly on the hearth between the passages for a movable keel outside the hoppers described above, and this scale is not discharged.

Also, the removal of this majority of the scale can be carried out only during periodic stoppages of the furnace, at a period of between six and twelve months.

Disclosure of the invention

One aim of the invention is in particular to remedy all or some of the aforementioned drawbacks.

According to a first aspect of the invention, a refractory beam furnace is proposed comprising walking beams having movable andirons supported by movable keels, and fixed beams comprising fixed andirons supported by fixed keels, and drive means arranged to move a lifting frame and a translation frame according to a rectangular movement cycle having two vertical positions, respectively upper and lower, and an intermediate vertical position according to which the movable andirons are at the same height as the fixed andirons, the movable andirons protruding above the fixed andirons in the upper position, the movable andirons being located at a lower level than the fixed andirons in the lower position.

According to the invention, the furnace further has: - a plurality of fixed refractory beams extending longitudinally, - a plurality of walking refractory beams extending longitudinally.

The walking refractory beams are arranged transversely between the fixed refractory beams and separated on each side of the fixed refractory beams by a space, the movable keels are fixed to the walking refractory beams, and the walking refractory beams are fixed to the translation frame and arranged substantially at the same height as the fixed refractory beams in the intermediate position.

EP3 903 057

The furnace further comprises a plurality of longitudinal water tanks arranged in line with the separation spaces and fixed to the fixed refractory beams delimiting a separation space, and a plurality of skirts fixed to the walking refractory beams delimiting said separation space and submerged in the water tanks.

The fixed refractory beams and the walking refractory beams can extend over all or part of the length of the furnace.

Advantageously, the fixed refractory beams and the walking refractory beams have an inclined and rounded profile on the upper part, the inclined profile being able to have a slope forming, with the horizontal, an angle greater than the angle of repose of the scale.

According to one possibility, the fixed refractory beams and the walking refractory beams are made of concrete with a low cement content, based on tabular alumina and spinel.

The furnace may also have scrapers fixed to the plurality of skirts. The profile of the scrapers can be adapted to promote the crushing and discharging of the scale. The scrapers may for example have a spade-shaped profile.

The water tank can be eguipped with flushes arranged to flush the water, and the scale, from the furnace exit to the furnace entrance.

According to one embodiment, the furnace may comprise refractory beams over only a part of the length of the furnace.

At least one water tank can have a rectangular shape, at least one transverse section of the water tank providing a connection between two longitudinal sections of the water tank arranged on either side of a refractory beam.

According to one embodiment, the furnace has water tanks equipped with two water flushes at their end located on the furnace entrance end, allowing the discharge of the scale, and a part of the water, into a transverse tank in the direction of a central discharge.

” EP3 903 057

According to a second aspect of the invention, a method is proposed for continuously grinding and discharging the scale in a refractory beam furnace comprising walking beams comprising movable andirons supported by movable keels, and fixed beams comprising fixed andirons supported by fixed keels, and drive means arranged to move a lifting frame and a translation frame according to a rectangular movement cycle having two vertical positions, respectively upper and lower, and an intermediate vertical position according to which the movable andirons are at the same height as the fixed andirons, the movable andirons protruding above the fixed andirons in the upper position, the movable andirons being located at a lower level than the fixed andirons in the lower position.

The furnace implemented in the method for continuously grinding and discharging the scale has a plurality of fixed refractory beams extending longitudinally, a plurality of walking refractory beams extending longitudinally, the walking refractory beams being arranged transversely between the fixed refractory beams and separated on each side of the fixed refractory beams by a separation space, the movable keels being fixed to the walking refractory beams, and the walking refractory beams being fixed to the translation frame and arranged substantially at the same height as the fixed refractory beams in the intermediate position, the furnace further having a plurality of water tanks arranged in line with the separation spaces and fixed to one oftherefractory beams, and a plurality of skirts, fixed to the other refractory beam delimiting said separation space, submerged in the water tanks, the scale being ground by the beams when it passes through the separation spaces and being discharged continuously by the plurality of water tanks.

Description of the figures

Other advantages and particularities of the invention will become apparent on reading the detailed description of implementations and embodiments that are in no way limiting, with reference to the appended drawings, in which: - [Fig. 1] is a schematic view in longitudinal section of a reheating walking beam furnace according to the prior art, with a cutaway in the central part, - [Fig. 2] is a schematic top view of the inside of the furnace shown in Figure 1,

EP3 903 057 - [Fig. 3] is a schematic view in longitudinal section of a reheating furnace according to a first embodiment of the invention, with a cutaway in the central part, - [Fig. 4] is a top view of the inside of the furnace shown in Figure 3, - [Fig. 5] shows, on its left part, a half-section along the section B-B of

Figures 3 and 4, and has, on its right part, a half-section along the section A-A of

Figures 1 and 2, - [Fig. 6] shows three vertical positions of a walking refractory beam relative to fixed refractory beams according to the invention of the furnace shown in Figure 3, - [Fig. 7] is a schematic view in longitudinal section of a reheating furnace according to a second embodiment of the invention, with a cutaway in the central part, - [Fig. 8] is a top view of the interior of the furnace shown in Fig. 7, - [Fig. 9] is a detail view on a larger scale of the furnace shown in Figure 7, with the right lateral part cut away, - [Fig. 10] is a top view of the inside of a furnace according to a third embodiment of the invention, - [Fig. 11] is a detail view of a water tank shown in top view on the left part of the drawing and in transverse section on the right part of the drawing, according to a first embodiment of the invention, - [Fig. 12] is a detail view of a water tank shown in top view on the left part of the drawing and in transverse section on the right part of the drawing, according to a second embodiment of the invention.

Description of embodiments

The embodiments described below not being in any way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of features described hereinafter, isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention with respect to the prior art. This selection

EP3 903 057 comprises at least one characteristic, preferably functional, without structural details, or with only a portion of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

In the figures, an element appearing in multiple figures retains the same reference.

Description of the prior art

Fig. 1 schematically shows a side view of a reheating furnace F with walking beams 10 according to the prior art. The two ends of the furnace, on the entrance side and on the exit side are shown, the central part being cut away. As shown by the arrow in Figure 1, which illustrates the direction of travel of the products, the entrance side is located on the right of the figure and the exit side on the left. This is the same for all the figures that show a furnace in a side view.

A translation frame 3 rests on upper translation rollers 33 of a lifting frame 2 which itself rests on ramps 1 having an inclined plane, via lower rollers 22.

A drive means (not shown) according to a horizontal alternating movement, parallel to the longitudinal direction of the furnace, is provided for the translation frame 3; another similar drive means (not shown) is provided for the lifting frame 2.

These drive means are for example hydraulic cylinders. The combination of the back-and-forth movements, and the vertical upward and downward movement due to the ramps 1, makes it possible to obtain a rectangular movement cycle.

The walking beams 10 have movable keels 100 and movable andirons 10C, the andirons being supported by the movable keels which are fixed below the translation frame 3.

The movable keels 100 pass through the fixed hearth 6.

Fixed beams 11 (Figure 2), having fixed keels 110 mounted on the hearth 6, and fixed andirons 11C, the fixed andirons being carried by the fixed keels, are inserted between the walking beams 10.

The fixed hearth 6 has, on the laboratory side of the furnace, a part covered with refractory materials forming a fixed refractory hearth 6R.

” EP3 903 057 when the movable keels 10Q pass through the hearth, the impermeability between the hearth 6 and the mechanical workings under hearth is obtained by longitudinal water tanks 4 (Figure 1) secured to the translation frame 3, traversed by the movable keels 10Q, and skirts 7 integral with the hearth 6 and submerged in the water of the water tanks 4.

Oblong openings OB (FIG. 2), also called buttonholes, are provided in the hearth 6 for the passage and the longitudinal relative movement of the movable keels 10 Q.

When it is detached from the products, a small amount of scale falls into the oblong openings OB existing in the hearth 6 in line with the passage of the movable keels 100 and in the bottom of the water tanks 4.

A plurality of scrapers 5 (Fig. 5) is fixed to the base of the skirts 7, over the length thereof, and is thus submerged in the water tanks 4. The scrapers 5 allow the scale to be routed to recovery hoppers (not shown), placed at the end of the water tanks 4, by the relative movement between the water tanks 4 and the scrapers 5, obtained by the association of the fixed position of the scrapers 5 and the rectangular movement of the water tanks 4.

More specifically, in the high position, at each advance of the water tanks 4 fixed to the movable translation frame 3, the scrapers 5 fixed to the fixed skirts which open into the water tanks 4 push the amount of scale located in the bottom of the water tanks 4 by one translation step from the outlet of the furnace to the inlet of the furnace, that is, from the exit to the entrance, all the way to the ends of the water tanks 4.

The discharge of the scale recovered under the installation is ensured via discharge pipes. The discharge pipes open into, or are connected to, discharge circuits provided with diaphragm valves 20 (Figure 1), acting as a flush 20, allowing each opening to discharge an amount of scale and water, which falls, via a transverse chute 21, into a wagon on wheels 23.

Description of the invention

EP3 903 057

Figure 3 schematically shows a first embodiment of a furnace FF according to the invention. The two ends of the furnace, on the entrance side and on the exit side are shown, the central part being cut away.

As in the prior art, the furnace FF has the translation frame 3 which rests on upper translation rollers 33 of the lifting frame 2 which itself rests on ramps 1 having an inclined plane, via lower rollers 22.

The means for driving the lifting and translation frames (not shown) are as in the prior art.

The walking beams 10 are likewise formed of movable keels 12Q and movable andirons 10C. The movable keels 120 according to the invention are shorter than the movable keels 100 according to the prior art. They are supported by a new type of walking refractory beam LRM.

The walking refractory beam LRM is placed, and fixed, on the translation frame 3 over the entire length of the furnace. According to another possibility, the walking refractory beam LRM is placed on the translation frame over only one or several parts of the length of the furnace.

The movable keels 120 pass through, and are fixed to, the walking refractory beam LRM having refractory materials that rest on a metal structure.

At each end of the oven, a clearance J (Figure 4) is provided at each walking beam, such that the longitudinal travel of the walking beam is possible.

Fixed refractory beams LRF of a new type are proposed.

The fixed refractory beams LRF have fixed keels 130 and fixed andirons 11C, the fixed andirons 11C being carried by the fixed keels 130. The fixed refractory beams LRF are inserted between the walking refractory beams LRM.

Therefractory materials of which the walking refractory beams LRM and the fixed refractory beams LRF are made are refractory concretes for high temperature of use, and are highly resistant to abrasion and impacts. They may

EP3 903 057 for example be concretes with a low cement content, based on tabular alumina and spinel. For example, concrete may contain 92 % A1203 and 5 % MgO.

The refractory materials may be of heavy concrete which has a particularly high density. After drying, this density is for example 3.000 kg/m3 (even up to 6.000 km/m3)in contrast to 2.000 to 2.300 km/m° for traditional concrete (for comparison, the density of light concrete is between 300 and 2.000 kg/m3).

More specifically, the fixed LRF and walking LRM refractory beams comprise a lower metal portion, on the side opposite the laboratory of the furnace, on which the refractory material rests. This lower metal part is connected to the translation frame for the walking refractory beams and to the fixed hearth for the fixed refractory beams. The fixed and movable keels pass through the refractory material and are fixed to the lower metal parts.

As shown in Figure 5 in its left part, the transverse juxtaposition of the walking refractory beams LRM and of the fixed refractory beams LRF according to the invention forms a functional equivalent of the refractory hearth 6R of the furnace according to the prior art shown on the right part of Figure 5.

A space E is left between the walking refractory beams LRM and the fixed refractory beams LRF, over the entire refractory height. The function of this space E is, in a first upper part of conical shape, to guide the scale toward a discharge passage located in its lower part. We thus have a space for discharging scale on either side of the fixed refractory beams LRF and the walking refractory beams LRM, all along the furnace, or over the length equipped with refractory beams LRM and LRF according to the invention.

The upward and downward movements and translation movements of the walking refractory beams relative to the fixed refractory beams allow the grinding of the scale and facilitate the passage of the scale without blocking an amalgam, or even pieces, of refractory lining.

The distance between the beams in the lower part of the space E is sufficient for the scale to pass through after being ground up. In its lower part, it is for example between 50 and 100 mm.

EP3 903 057

It is understood that the scale that previously remained on the fixed refractory hearth 6R can now fall through the discharge passages E.

In addition, the fixed LRF and walking LRM refractory beams according to the invention transversely have an inclined and rounded profile on the upper part on which the keels are positioned. The inclined profile is determined with an angle greater than the angle of repose, facilitating the grinding and discharging of the scale in the passage E provided for this purpose between the fixed refractory beams and the walking refractory beams LRM. The angle of the inclined profile is for example greater than 45°.

The impermeability between the hearth, formed by the fixed and walking refractory beams, and the mechanical workings under the furnace consisting of the lifting frame and the translation frame, is obtained by longitudinal water tanks 40 (Fig. 3 and 5) integral with the fixed refractory beams and metal skirts 70 integral with the walking refractory beams and submerged in the water tanks 40.

The water tanks 40 are fixed on each side of the fixed refractory beams LRF.

The skirts 70 are fixed on each side of the walking refractory beams LRM.

Furthermore, the profile of the skirts /0 makes it possible to avoid direct radiation of the environment of the furnace laboratory onto the surface of the water contained in the water tanks 40, in order to minimize heat losses through the openings and water consumption.

The water tanks 40 are no longer passed through by the movable keels 100.

The length of the movable keels is shorter compared to the prior art, by about one meter and fifty centimeters.

As can be seen in Figure 6, the walking refractory beams may have three vertical positions relative to the fixed refractory beams, respectively low (on the left of the figure), intermediate (in the center of the figure), and high (on the right of the figure).

In addition, the keel passage according to the prior art was surrounded by fibrous materials which when torn off led to oxidation. This is no longer the case with the

EP3 903 057 solution according to the invention in which the keel 12Q is embedded in the refractory of the walking refractory beam LRM. Solutions to cover the bottom of the keel had been sought, for example by means of stainless steel sheets, but these sheets would heat and deform and would not hold.

According to the example shown in this embodiment, the movable skirts 70 are eguipped with a plurality of scrapers 50 fixed to the metal skirts 70. The scrapers 50 submerge into the water tanks 40 and allow the scale to be routed to recovery hoppers (not shown), placed at the end of the tanks, by the relative movement between the water tanks and the scrapers obtained by the association of the rectangular movement of the scrapers 50 and the fixed position of the water tanks 40.

More specifically, the translation frame 3 being in the high position, at each advance of the walking beams LRM, the metal scrapers 50 push the amount of scale located in the bottom of the water tanks 40 between two scrapers by one translation step towards the end of the water tanks 40.

The scrapers contribute to crushing the scale, which facilitates its discharge into the water tank 40. The scrapers thus have a profile suitable for promoting the crushing and the discharge of the scale, for example in the shape of a spade.

The end of the water tank 40 is equipped with a diaphragm valve 20 (Figure 3), acting as a flush 20, which discharges the scale through the chutes 21 into the wagons on wheels 23, the discharge taking place in the direction of the outlet of the furnace toward the inlet of the furnace.

According to a first variant of this first embodiment, only described for its differences with the first embodiment, the skirts 70 are not equipped with scrapers.

The scale can be driven from the water tanks 40 onto which it falls by a device external to the furnace, for example by hoses akin to fire hoses.

According to a second variant of this first embodiment, the water tanks 40 may be provided with water spray nozzles (80) (Figure 3), arranged at the exit side, which push the scale toward the end of the water tank 40 located on the entrance side.

EP3 903 057

The water tanks 40 may be provided with water injection 80, for example spray nozzles, which, under pressure, flush the scale to the flushes 20.

According to this variant, it is possible to not equip the skirts 70 with scrapers.

Of course, the skirts 70 may also be equipped with scrapers for improving the crushing of the scale.

According to a third variant of this first embodiment, only described for its differences with the first embodiment and optionally combinable with the first variant, it is possible to provide two or three intermediate scale discharge points.

To this end, it is proposed to arrange, at each of these discharge points, a transverse tank provided with pipes receiving the scale from the water tanks 40.

On either side of the transverse tank, the tank is equipped with flushes which push the scale toward the center of the transverse tank, provided with other pipes equipped with diaphragm valves.

Each of the transverse tanks can advantageously be placed between two wheels 33.

This second variant is particularly advantageous in the context of a very long furnace.

The water tanks can also be fixed to the walking refractory beams LRM. In this case, it is necessary to take into account the wave effect at the end of the water tank generated by the movement of the beams.

Figures 7 to 9 schematically show a second embodiment of a furnace FFF according to the invention.

The furnace FFF is described only for its differences with the first embodiment, and could replicate the features of one or more of the variants of the first embodiment.

As shown in Figure 7, on the entrance side, the furnace has a longitudinal part

P2 similar to that described according to the prior art, from the entrance to a longitudinal position from which a part P1 begins that is similar to what was described with reference to the first embodiment of the invention.

EP3 903 057

It will be noted that, in order to limit the black marks caused by the shadow of the andirons on the products, the refractory beams can also be offset transversely toward the outlet of the furnace, as can be seen in Fig. 8.

In this embodiment, the furnace comprising refractory beams LRF, LRM over only part of its length, at least one water tank 40 has a rectangular or U-shaped form, at least one transverse section 41 of the water tank providing a connection between two longitudinal sections 42 of the water tank arranged on either side of a fixed refractory beam.

Figure 11 shows an example embodiment of a water tank 40 according to the invention, in the case shown in Figures 3 and 4 where the water tank is the entire length of the furnace, with a top view of the water tank on the left part of the figure and a transverse cross-section thereof on the right part of the figure. The rectangular- shaped water tank comprises two longitudinal parts 42 arranged on either side of a fixed refractory beam, not shown, and two transverse links 41 between these longitudinal parts arranged on either side of the refractory beam, at each end of the longitudinal parts. To ensure the sealing of the furnace, skirts 70, not shown, submerge into the water tank along the longitudinal parts 42 and the transverse connections 41, thus ensuring continuity of the hydraulic seal. It is also noted that the water tank is eguipped with two flushes 20, installed on the transverse link 41 located onthe entrance side of the furnace, one for each longitudinal part of the water tank, and water spray nozzles 80 represented by arrows.

Figure 12 shows another example embodiment of a water tank 40 according to the invention, in the case shown in Figures / and 8 where the refractory beams according to the invention are only on part of the furnace, in this case the entrance, with a top view of the water tank on the left part of the figure and a transverse cross-section thereof on the right part of the figure. The rectangular- shaped water tank also comprises two longitudinal parts 42 arranged on either side of a fixed refractory beam, not shown, and two transverse links 41 between these longitudinal parts arranged on either side of the refractory beam, at each end of the longitudinal parts. It will be noted that in this embodiment, the water tank is eguipped with a flush 20 arranged on each longitudinal part of the water tank, and water spray nozzles 80 shown by arrows.

EP3 903 057

Figure 10 shows a variant of the embodiment shown in Figure 8 in which the transverse offset of the beams in order to limit the black marks caused by the shadow of the andirons on the products is carried out on the part P1 of the furnace, in this example at approximately mid-length thereof.

Of course, the invention is not limited to the examples just described, and many adjustments can be made to these examples without going beyond the scope of the invention. Furthermore, the various features, forms, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible with or exclusive of each other. [Tables 1] invention

PB joessa =.

Ps [fkedmetarheata

SR |bedwfeoyhesn 0 11C fixed andiron

EP3 903 057 falling within this zone. [80 [water spray nozzle mawatertank