EP0336864B1 - Construction process of an open chambers furnace to avoid deformations - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method of constructing ovens with open chambers, also called "rotary fire ovens" or "fire advancement ovens" mainly intended for cooking carbon anodes for the production of aluminum by electrolysis according to the Hall process. -Héroult.

STATE OF THE ART

This type of furnace generally comprises two parallel spans, the total length of which can reach nearly two hundred meters. Each span comprises a succession of chambers, separated by transverse walls and open at their upper part to allow the loading of raw anodes (or other carbonaceous blocks) and the unloading of cooled cooked anodes. Each chamber comprises, arranged parallel to the major axis of the oven, a set of hollow partitions, with relatively thin walls in which the hot gases ensuring the cooking will circulate, these partitions alternating with cells in which the baking anodes which are embedded are stacked. in carbonaceous dust (coke, anthracite, or any other powdery packing material). There are, for example from 16 to 74 rooms and per room 7 heating partitions separating 6 cells. During cooking, the maximum temperature reached is around 1200 ° C.

The chambers of a span are contained in a concrete casing formed by a horizontal raft and two vertical sails. The concrete is protected from temperature, inside, by thermal insulation. The entire oven is housed in a building supporting the rolling tracks of handling equipment.

• ― poussée horizontale sur les voiles par le réfractaire qui constitue les chambres, de l'intérieur vers l'extérieur. Ces contraintes peuvent atteindre à la base des voiles un niveau de 400 kN par mètre linéaire.
• ― poussée du terrain, du fait du remblaiement, en sens inverse de cette première poussée.
• ― effet "bilame" (dilatation différentielle) du radier enterré ou semi-enterré et des voiles dû au gradient de température dans leur épaisseur.

Generally, when the level of the water table does not oppose it, the ovens are buried or semi-buried, which simplifies operation, handling and reduces investment costs. Concrete casing walls are subjected to three types of force:

• - horizontal thrust on the sails by the refractory which constitutes the chambers, from the inside to the outside. These constraints can reach at the base of the sails a level of 400 kN per linear meter.
• - pushing of the ground, due to backfilling, in the opposite direction to this first push.
• - "bimetal" effect (differential expansion) of the buried or semi-buried raft and sails due to the temperature gradient in their thickness.

• ― dans les fours enterrés, il y a fléchissement des voiles vers l'intérieur du four, ce qui gêne les manutentions d'anodes dans les alvéoles en déformant le réfractaire par compression; dans ce cas, la poussée du terrain est prépondérante.
• ― dans les fours semi-enterrés la poussée du réfractaire l'emporte et les voiles fléchissent vers l'extérieur; il en résulte une désorganisation du briquetage qui "s'épanouit" dans l'espace agrandi et l'application d'une force plus ou moins grande sur le bâtiment lorsque les voiles arrivent à son contact, notamment au niveau des poteaux supportant la charpente métallique.

Backfilling means that deformations escape direct observation and manifest themselves in different ways depending on the level and type of backfill:

• - In buried ovens, there is a deflection of the webs towards the interior of the oven, which hinders the handling of anodes in the cells by deforming the refractory by compression; in this case, the thrust of the terrain is preponderant.
• - in semi-buried ovens the push of the refractory material prevails and the sails flex outwards; this results in a disorganization of the brickwork which "flourishes" in the enlarged space and the application of a greater or lesser force on the building when the sails come into contact with it, in particular at the posts supporting the metal frame .

The present invention proposes to remedy this state of affairs.

OBJECT OF THE INVENTION

The object of the invention is therefore a method of constructing the concrete casing of a chamber furnace which very greatly reduces the deformations due to the differential thermal expansion between the various elements of the furnace and to the thrusts of all kinds which are exerted on the walls.

More specifically, the invention consists of a method of constructing an oven with open chambers intended for cooking carbonaceous blocks, this oven consisting of a plurality of chambers arranged in series on one or two parallel spans, each chamber being contained in an independent concrete casing formed by a raft and concrete side sails, characterized in that there is on the external face of each sail a plurality of vertical buttresses which are put under prestressing in the vertical direction.

The prestressing is applied by means of at least one fixed steel cable, at the two ends on a metal plate coming to bear at the base and at the top of each buttress.

In addition, the upper part of the transverse walls which separate the different chambers of the oven is held in place with a tie rod on which an adjustable tension is applied between 0 and 200 kN.

DESCRIPTION OF THE INVENTION

• · La figure 1 rappelle pour la bonne compréhension de l'invention, la structure des chambres, des alvéoles et des murs transversaux.
• · La figure 2 schématise la direction de la poussée principale selon que le four est enterré (à droite de la figure) ou semi-enterré (à gauche de la figure).
• · La figure 3 schématise en vue de dessus, complétée par une élévation 3A, et la figure 4 en coupe transversale, la structure d'un cuvelage de four selon l'invention.
• · La figure 5 représente le renforcement, par mise sous précontrainte, des contreforts des voiles.
• · La figure 6 représente la mise sous tension par un tirant de la partie supérieure des murs transversaux.

Figures 1 to 6 illustrate the invention.

• · Figure 1 recalls for the proper understanding of the invention, the structure of the chambers, cells and transverse walls.
• · Figure 2 shows schematically the direction of the main thrust according to whether the oven is buried (on the right of the figure) or semi-buried (on the left of the figure).
• · Figure 3 shows schematically in top view, supplemented by an elevation 3A, and Figure 4 in cross section, the structure of an oven casing according to the invention.
• · Figure 5 shows the reinforcement, by prestressing, the buttresses of the sails.
• · Figure 6 shows the tensioning by a tie of the upper part of the transverse walls.

In FIG. 1, we see the partitions 1 connected at their upper part, by nozzles 2, to the pipe 3 itself connected to the general manifold 4. The suction and blowing pipes are connected to the ports of the chambers according to our FR 2535834. In the cells 5 are arranged the baking anodes 6, visible on the cutaway of the left side of Figure 1.

The baffles 7 of the heating partitions are intended to lengthen the path of the hot gases and to homogenize the temperature in the partition. At the upper part of the chambers, the openers 8 allow the installation, in correlation with the advancement of the fire, of the blowing, suction and burner pipes. The successive chambers are separated by transverse walls 9. The successive partitions of the various chambers are brought into communication by openings 10, located at the upper part of the transverse wall. The main axis of the furnace is indicated by the line XX ′.

In Figure 2 which is a very simplified cross section, we has shown, in thickened lines, the concrete webs 11 which constitute the framework of the furnace, which is supported by a raft 12 resting on piles 13, the depth of which depends on the nature of the terrain T.

In FIGS. 3, 3A and 4, the sails 11 have, according to the invention, been provided with external buttresses 14, put under prestressing.

As indicated in FIG. 5, the prestressing is carried out by inserting, over the entire height of the buttress, prestressing cables 15, coated with a protective sheath 16, injected after tensioning the cables, and bolted at their two ends on plates 17, which are supported on the upper and lower ends of each buttress 14.

In addition to this reinforcement of the sails, it is possible to intervene on the transverse walls 9. Indeed, in the conventional design of the walls, these are provided at their upper part with openings 10A intended for the passage of the registers which make it possible to establish or to interrupt the circulation of combustion gases in the heating partitions 1 according to the heating cycle.

If we use a sealing device placed inside the partition such as for example the deployable shutter which is the subject of our French patent application 87-08564 (FR-A-2616525), filed on June 9, 1987, it is then possible to remove the transverse wall outlet 10 A and to achieve communication between the rooms through an opening 10A, which no longer constitutes a weak point of the wall, and which can be closed thanks to the deployable shutter introduced by the shutter 8A closest to the corresponding partition.

Under these conditions, as illustrated in FIG. 6, it becomes possible to energize the upper part of the wall 9, by means of at least one tie rod 21 arranged horizontally, and anchored on two steel plates 22 placed in abutment on the two ends of the wall 9.

The tension is adjustable between 0 and 200 kN by spring and / or "Belleville" washer, or any other equivalent means.

EXAMPLE OF IMPLEMENTATION

The invention was implemented during the reconstruction of an oven with rooms with two parallel spans, with a total width of 25 meters.

The side sails 11 have a height of 5 meters, a length of 10 meters and are reinforced by 5 buttresses put under prestressing as shown in FIG. 5 by means of two steel cables surrounded by a metal protective sheath.

The prestressing force applied was fixed at 600 kN by cable. The upper part of the transverse walls has been tensioned by means of a metal tie 21 adjusted so that the maximum force exerted during the passage of the fire is equal to 140 kN. After one year of uninterrupted operation, it was found that the maximum range of movement of the veil in the upper part during the passage of the light did not exceed 25 mm.

Claims (4)

1. A process for constructing a furnace with open chambers, which is intended for baking carbonaceous blocks and which comprise a plurality of chambers disposed in series in one or two parallel bank, each chamber being contained in an independent concrete casing structure formed by a floor (12) and lateral wall portions (11) of concrete, characterised in that disposed on the external face of each wall portion (11) is a plurality of vertical buttresses (14) which are prestressed in the vertical direction.

2. A process according to claim 1 characterised in that the prestressing is applied by means of at least one steel cable (15) fixed at the two ends to a metal plate (17) which bears against the base and the top of each buttress (14).

3. A process according to claim 1 or claim 2 characterised by using a closure device which is inserted within the partition, the openings (10) of which have been omitted, and by applying to the upper part of the walls (9) an adjustable force of between 0 and 200 kN.

4. A process according to claim 3 characterised in that the upper parts of the transverse walls are put under tension by means of at least one metal the member (21) which is disposed horizontally and which is subjected to an adjustable tension.

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