EP0149575B1 - Improved shells for hot blast stoves or identical apparatus - Google Patents

Description

The present invention relates, in particular, to blast furnace cowpers, that is to say reversing devices in which the air sent to the blast furnace nozzles is heated.

Such an apparatus comprises a side wall consisting of welded sheet plates, surmounted by a dome also made of welded sheet. The enclosure formed by the side wall and the dome houses a combustion chamber and a ruching chamber.

The conditions prevailing in cowpers and in particular the temperature conditions (the latter possibly exceeding 1300 ° in certain areas) frequently cause incidents at the level of their metal walls. In fact, after a few years of operation, there are the appearance of cracks, in particular at the level of the dome and of the combustion shaft. These cracks develop from the internal face of the metal wall, mainly near the welds, parallel or transverse to the latter. They are due to the corrosive action of the nitrates produced by the nitrogen oxides formed at high temperature, in areas where the tensile stresses undergone by the metallic envelope are significant. It is therefore a phenomenon of cracking corrosion under tension.

Such incidents can take on significant proportions and require the complete replacement of these devices, which, on the one hand, represents an extremely high cost and, on the other hand, entails immobilization which can result in complete shutdown - oven they serve.

To remedy such incidents, it has been proposed in patent FR-2,526,810 to produce a second envelope around the wall of the cowper and to fill the space thus delimited by the two envelopes with a carbide-based filling material. silicon and graphite.

The purpose of the present invention is to provide a lining of the double jacket more specially adapted to the thermal stresses to be transmitted, while being easy to implement.

To this end, the subject of the invention is an envelope for a cowper or similar air heating device comprising a first wall made of welded sheet metal and comprising a second wall of welded sheet metal, external and parallel to the first, these two walls delimiting a space filled with a filling material, characterized in that the filling material is based on shot of a metal or a light alloy, embedded in a binder based on thermosetting resin.

The invention also relates to a method of manufacturing such an envelope: in which an inner sheet metal wall is doubled by a second outer sheet metal wall, parallel to the first, this second wall delimiting with the first wall a space, characterized in that this space is filled with a filling material comprising shot of a metal or a light alloy and a binder based on thermosetting resin.

• - les particules métalliques ont des dimensions comprises entre 0,2 et 2 mm environ et, de préférence, entre 0,5 et 1,5 mm;
• - on utilise de l'aluminium ou un alliage à base d'aluminium.

According to other characteristics:

• - The metallic particles have dimensions of between 0.2 and 2 mm approximately and, preferably, between 0.5 and 1.5 mm;
• - using aluminum or an aluminum-based alloy.

• - la Fig. 1 est une vue en coupe de l'enveloppe d'un cowper, réalisée suivant l'invention;
• - la Fig. 2 est également une vue en coupe montrant un exemple de réalisation dans le cas d'épaisseurs variables des parois.

The invention will be described in more detail with reference to the appended drawing, given solely by way of example and in which:

• - Fig. 1 is a sectional view of the envelope of a cowper, produced according to the invention;
• - Fig. 2 is also a sectional view showing an exemplary embodiment in the case of variable wall thicknesses.

We see in Fig. 1 a part of a cowper envelope or similar device comprising a metallic inner wall 1 made of welded sheet, the thickness of which may be comprised, for example between 15 and 30 mm. On the face of this wall facing the interior of the device is a refractory lining 2.

On the external face of this sheet metal are supported sheet metal strips 3 arranged horizontally and vertically and which are welded to a second series of sheets constituting an external wall 4.

Between the two walls and the spacers 3 are delimited cells 5 filled with a filling material 6.

The outer wall is preferably made in the same grade of steel as the inner wall and has a roughly comparable thickness.

In this regard, in the embodiment of FIG. 2 we can see an area of the envelope in which the interior and exterior walls have variable thicknesses. The inner wall comprises for example a lower part 1a having a thickness of 24 mm and an upper part 1 having a thickness of 17mm. The thickness of the outer wall 4a, ^4b may vary accordingly, as shown in the drawing. Similarly, the thickness of the interval 5a, ^5b of limit between the two walls can vary between for example 3 and 30 mm, a thickness of the order of 10 mm being however preferred.

The filling material of the gap between the walls is, according to the invention, constituted by aluminum shot or an aluminum alloy whose particles preferably have the dimensions between 0.2 and 2 mm, for example, a dimension of the order of 0.5 or 1.5 mm being particularly favorable. In fact, the average size of the metal granules is chosen so as to obtain optimal filling of the cells and is, in any event, less than the minimum width of the gap between the two walls.

Regarding the composition of this metallic shot, aluminum will be used or preferably an aluminum-based alloy or another metal or light alloy with high thermal conductivity.

The interstices between the metal granules are filled with a binder based on resin or a mixture of thermosetting resin resistant to a temperature equal to or greater than 110 ^° C. This resin can for example be a powdered phenolic polyurethane resin or in the form of a liquid gel, containing the adjuvants necessary for its hardening and possibly a filler as is conventional in the techniques of molding or casting of such resins.

According to one embodiment, the filling of the cells can be carried out as follows: first of all, in a mixer, the metal particles are coated, using the resin in powder or in the form of liquid gel.

Then, the mixture thus prepared is put into place, by injection or by pouring, optionally under neutral gas such as nitrogen, through orifices 7 into which tubes such as 8 are introduced, for example by screwing. vent holes are provided, if necessary in this same wall 4. This positioning of the mixture can be carried out cold. During this filling operation or immediately after, a vibration operation is carried out so as to obtain an excellent filling of the cells. This can be done using a high frequency unidirectional vibrator.

The curing of the resin takes place between 20 minutes and one hour approximately after the introduction of the mixture, this duration naturally depending on the proportions of hardener contained in the mixture.

This hardening can possibly be accelerated by a slight increase in temperature.

The orifices such as 7 are then closed, for example by means of screwed or welded plugs, so as to restore the continuity of the outer wall 4.

• - sa bonne conductivité thermique permet d'éviter la formation d'un gradient de température élevé entre les deux parois et par conséquent de limiter les contraintes dûes à une dilatation différentielle;
• - les alvéoles entre les parois étant entièrement remplis en particulier du fait de la présence d'une résine qui comble les interstices entre les granules métalliques, on empêche la mise en pression de l'espace entre les parois et le passage de tout agent gazeux ou liquide agressif venant de l'enceinte du cowper vers la nouvelle enveloppe ;
• - le produit de remplissage utilisé n'est pas attaqué par les nitrates de sorte que la paroi extérieure se trouve isolée de ces derniers, même après fissuration de la paroi intérieure ;
• - le mélange introduit entre les parois a une faible densité, par exemple comprise entre 1,2 et 1,5, ce qui limite les charges et les efforts de traction exercés sur les tôles, ne nécessitant pas une augmentation de l'épaisseur des parois pour résister aux pressions et température régnant dans l'enceinte du cowper;
• - le procédé de mise en place est particulièrement simple puisque il n'est pas nécessaire de chauffer les parois ou si un tel chauffage est réalisé, il n'est effectué qu'à une température relativement faible de quelques dizaines de °C au-dessus de zéro.

This type of filling is particularly interesting. Indeed :

• - Its good thermal conductivity makes it possible to avoid the formation of a high temperature gradient between the two walls and consequently to limit the stresses due to differential expansion;
• - the cells between the walls being completely filled in particular due to the presence of a resin which fills the interstices between the metal granules, the pressurization of the space between the walls and the passage of any gaseous agent is prevented or aggressive liquid from the cowper enclosure to the new envelope;
• - the filling product used is not attacked by nitrates so that the outer wall is isolated from them, even after cracking of the inner wall;
• - The mixture introduced between the walls has a low density, for example between 1.2 and 1.5, which limits the loads and the tensile forces exerted on the sheets, not requiring an increase in the thickness of the walls to withstand the pressures and temperature prevailing in the enclosure of the cowper;
• - the installation process is particularly simple since it is not necessary to heat the walls or if such heating is carried out, it is only carried out at a relatively low temperature of a few tens of ° C. above from zero.

Alternatively, the spacers 3 can be omitted, the method however being implemented under the same conditions.

Claims (8)

1. Shell for a Cowper stove or similar air heating apparatus comprising a first wall (1) made of welded sheet metal and having a second wall (4) made of welded sheet metal, arranged outside and parallel to the first one, these two walls defining a space (5) filled with a filling material (6), characterized in that the filling material is based on light-metal or light-alloy shot embedded in a binder based on a thermosetting resin.

2. Shell as claimed in claim 1, characterized in that the filling material consists mainly of aluminum or aluminum-based alloy shot.

3. Shell as claimed in either one of claims 1 and 2, characterized in that the metal particles have dimensions of between approximately 0.2 and 2 mm and preferably of between 0.5 and 1.5 mm.

4. Method for constructing a shell as claimed in any one of claims 1-3, comprising lining an internal sheet-metal wall (1) with a second external sheet-metal wall (4), arranged parallel to the first one, this second wall defining a space (5) together with the first wall, and charaterized by the step of filling this space with a filling material (6) comprising light-metal or light-alloy shot and a binder based on a thermosetting resin.

5. Method as claimed in claim 4, characterized by the preliminary step of mixing the metal shot and the resin-based binder.

6. Method as claimed in any one of claims 4 and 5, characterized in that the filling material is filled in at ambient temperature or at a temperature slightly above ambient temperature.

7. Method as claimed in any one of claims 4 to 6, characterized in that the shell is vibrated after the said space (5) has been filled.

8. Cowper stove or similar air-heating apparatus, comprising a shell as claimed in any one of claims 1 to 3.

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