EP0451052B1 - Improved construction for the burner or tuyere openings in furnaces and vertical reactors - Google Patents

Description

The present invention relates to improvements in the production of burner openings or surrounding nozzles of furnaces and vertical reactors.

• les contraintes mécaniques statiques résultant du poids de la maçonnerie et des efforts de confinement exercés par l'enveloppe métallique extérieure du four ou réacteur ;
• les contraintes mécaniques dynamiques résultant de l'abrasion exercée par la charge solide qui descend dans le four ou réacteur, et de l'érosion provoquée par le ruissellement de verres, laitiers et/ou métaux fondus le long des pièces ou par les gaz chauds qui remontent dans le four ou réacteur ;
• les contraintes thermomécaniques dues aux températures élevées qui règnent dans le four ou réacteur, aux gradients thermiques qui existent en marche stabilisée ou au choc thermique survenant lors des arrêts et redémarrages des brûleurs ou de l'injection de gaz chauds par les tuyères ;
• la corrosion qui peut se produire soit sur la surface des pièces au contact de la charge du four ou réacteur, soit dans l'épaisseur des pièces par infiltration ou diffusion d'éléments agressifs émis par la charge du four ou réacteur.

Vertical furnaces and reactors operating at high temperatures, such as, for example, blast furnaces and cupola furnaces, are usually heated by a set of burners or hot gas injection nozzles arranged in a belt relative to the inside the furnace or reactor. The metal burners or nozzles, generally removable, are housed in openings or enclosures made of pieces of refractory material. These refractory parts are subjected to mechanical and thermal stresses and to significant corrosion. We can distinguish, in particular:

• the static mechanical stresses resulting from the weight of the masonry and from the confinement forces exerted by the external metal envelope of the furnace or reactor;
• the dynamic mechanical stresses resulting from the abrasion exerted by the solid charge which descends into the furnace or reactor, and from the erosion caused by the runoff of glasses, slag and / or molten metals along the parts or by the hot gases which go back into the furnace or reactor;
• thermomechanical constraints due to the high temperatures prevailing in the furnace or reactor, the thermal gradients which exist in stabilized operation or the thermal shock occurring during burner shutdowns and restartings or the injection of hot gases by the nozzles;
• corrosion which can occur either on the surface of the parts in contact with the charge of the furnace or reactor, or in the thickness of the parts by infiltration or diffusion of aggressive elements emitted by the charge of the furnace or reactor.

These stresses and the corrosion undergone are the causes of a process of destruction of the parts.

Thus, for example, in the case of blast furnace nozzle surrounds, the constituent parts of the surrounds are subject to cracking by thermal shock, to impregnation with potassium vapors which condense in the form of K₂O or K₂CO₃ and attack the refractory material in depth making it brittle, and wear by abrasion and erosion caused by the downward load on the material weakened by the previous attacks.

It is therefore imperative that the burner openings and the nozzles surrounding furnaces or vertical reactors have good resistance to thermal shock and good mechanical resistance, which is maintained even in the event of deep chemical attack.

The burner openings or the nozzles surrounds are traditionally constituted by the assembly of a large number of refractory, ceramized keys, for example made of silicon carbide with a silicon nitride binder or based on corundum grains with a mullite or sialon binder , of different and relatively complex shapes.

This technology, if it is satisfactory, is however very expensive because it implies, for the manufacturer, the production of a large number of molds and the use of non-automated shaping techniques, such as manual tamping, and, for the 'user, the need for a skilled workforce. In addition, the assembly time on site is very long, typically around seven days for a nozzle belt of a blast furnace.

In order to save time during assembly on site, it has been proposed to deliver sets of keyboards in pre-assembled form, that is to say secured in factory by known means, for example using a cement. However, this technique offers no other advantage compared to traditional practice.

It has also been proposed to produce each workpiece or entourage, no longer by assembling a large number of elementary keyboards, but by assembling a small number (for example four) of suitably shaped elements obtained by molding a concrete refractory. This way of working makes it possible to minimize the costs of molds and labor, and to save time during the assembly on the site: one can thus, for example, reduce the assembly time to 4-5 days, instead 7 days in the case of an assembly of keys.

However, experience has shown that, even using the best high-compact refractory concretes available, such as those described in French patent 2,390,400, or the corresponding German patent 27,599,809, the resulting openings or entourages had, at the use, a resistance to abrasion and to hot erosion very much lower than that of ceramic keyboards at high temperature, in particular to those of keyboards based on corundum grains and / or silicon carbide with nitride binder or sialon, in particular in the case where corrosion occurs simultaneously in the mass by infiltration or diffusion of aggressive elements, such as K₂O or K₂CO₃.

Another variant which has been tested consists in making the openings or surrounds by assembling 4 carbon blocks machined to the shape. This solution is not satisfactory, however, because it leads to significant heat losses and the carbon blocks wear out quickly by oxidation.

The present invention aims to solve the above-mentioned problems by providing burner ports and improved nozzle surrounds for ovens or vertical reactors.

More specifically, the invention relates to a burner flue or a nozzle surround of a vertical furnace or reactor constituted by the assembly of at most four prefabricated elements of molded refractory concrete, characterized in that each element further comprises , a coating bonded to concrete and consisting of ceramic refractory keys of identical shape and dimensions, forming a unitary composite assembly with said element and disposed between the part of the element of refractory molded concrete and the opening intended to receive the burner or the nozzle.

The ceramic keyboards constituting the covering, all being of the same shape and dimensions, can be easily produced by an automatic shaping process, for example by uniaxial pressing. As constituent materials of these ceramic keyboards, use will preferably be made of a material based on corundum grains and / or silicon carbide bonded by a nitride or sialon binder, such as the CORANIT ^{(R) product} comprising approximately 75% of alumina and 25% of a nitrided binder of the sialon type and silicon oxynitride; the product SICANIT ^(R) 20 which comprises approximately 76% of silicon carbide and 25% of a nitrided binder or the product SICANIT ^(R) AL comprising approximately 9.5% of alumina, 67% of silicon carbide and 23 , 5% of a nitrided binder of the sialon type, which are sold by the applicant.

The coating of keyboards can be put in place either at the time of the molding of the concrete part of the elements, by placing the keyboards in the mold used for molding the concrete during the casting of the latter, or after demolding of the concrete part. elements, by jointing by means of a refractory cement, so that the concrete-keystone association forms a unitary composite assembly.

As refractory concretes, use may be made of those described in French patent 2,390,400 or the corresponding German patent 27 59809, the teachings of which are incorporated here by reference, with the exception of concrete containing carbon whose presence is to be avoided. In short, these concretes are formed, by weight, by (A) 70-90% of a refractory aggregate and by (B) 10-30% of a cement consisting of (i) 10-30% of a substance alkaline earth mineral, (ii) 14-54% of ultra-fine particles with a particle size of 100 nm to 0.1 µm and (iii) 14-54% of fine particles with a particle size of 1 to 10 µm. Among this family of concretes, it is preferable to use in particular vibrated concretes comprising an aggregate formed of alumina with a hydraulic binder such as CRISTARAM ^(R) concrete with 93% of alumina, the aggregate of which is white corundum quine requires only 3% of 'water and which has a density of 3250 kg / m³ and a resistance to cold crushing greater than 140 MPa; or CORAL ^(R) concrete with 89% alumina, the aggregate of which is corundum brown, which requires only about 2.5% water and which has a density of 3350 kg / m³ and resistance to cold crushing greater than 50 MPa, both of which are sold by the plaintiff. Such concretes also have the advantage of being thermally insulating, having a thermal conductivity at 800 ° C of approximately 4W / mK. By way of comparison, materials based on carbon or silicon carbide have a thermal conductivity. more than 15W / mK

Advantageously, the molded refractory concrete elements are reinforced by incorporating reinforcing elements, such as stainless steel fibers, into the concrete used. As an indication, one can incorporate approximately 1 to 3% of reinforcing elements. An example of commercially available reinforcing stainless steel fibers are the ZP 30/40 SS 304 fibers sold by the company DRAMIX. The addition of steel reinforcing fibers improves resistance to fragmentation by thermal shock, thus avoiding the fragmentation of parts. Surprisingly, tests have shown that resistance to corrosion by carbon monoxide is not affected by the incorporation of steel fibers, as might have been feared.

The description which follows, made with reference to the drawing, will make the invention clear.

• Les figures 1 et 2 sont des vues schématiques en coupe et de face, respectivement, d'un entourage de tuyère de haut-fourneau traditionnel.
• Les figures 3 et 4 sont des vues schématiques en coupe et de face, respectivement, d'un entourage de tuyère de haut-fourneau selon l'invention.

On the drawing :

• Figures 1 and 2 are schematic sectional and front views, respectively, of a traditional blast furnace nozzle surround.
• Figures 3 and 4 are schematic sectional and front views, respectively, of a blast furnace nozzle surround according to the invention.

Figures 1 and 2 show a conventional surround 1 of the nozzle 2 of a blast furnace 3 (shown partially). This entourage, which is shown hatched in Figure 1, is formed by the assembly of a large number of ceramic refractory keys 4 of different shapes, the resulting assembly defining an opening or passage 5 adapted to the housing of the frustoconical nozzle 2, the axis of which is slightly inclined downwards.

Figures 3 and 4 show an entourage according to the invention 11. This entourage is formed by the assembly of four prefabricated elements 12. Each element 12 is formed of an outer part 13 of refractory molded concrete (shown in thin shading on the Figure 3), integral with an inner coating 14 defining the opening or passage 5 intended to receive the nozzle 2 of the blast furnace 3 and constituted by the assembly of ceramic refractory keys 15 of identical shape and size, which have a shape corner in their vertical and longitudinal directions. Advantageously, these pins only extend over part of the total thickness of the elements 12, this part including the face of the elements facing the interior of the furnace or reactor. This is interesting from an economic point of view because it makes it possible to reduce the quantity of the material constituting these pins which is an expensive material. Once the four elements 12 have been assembled, the coverings 14 constitute together an inner crown of frustoconical shape whose axis is slightly inclined downward and which is embedded in the parts 13 of refractory concrete of the elements, the front face 16 of this crown being located on the side of the interior 17 of the top- furnace.

The elements 13 are composite concrete-ceramic key elements which exhibit excellent behavior in service. The internal crown in ceramic refractory keys (for example in corundum and / or silicon carbide with nitride or sialon binder) simultaneously exhibits excellent resistance to thermal shock, low thermal conductivity, very high mechanical resistance making it possible to withstand static mechanical stresses acting on the entire surrounding, as well as excellent resistance to abrasion and erosion which makes it possible to slow down the wear of the refractory concrete parts which surround it.

The molded concrete parts can, for their part, be considered as playing the role of a cradle for holding the keyboards and of a filling material.

It should be noted that the assembly of the elements 12 can be done by simple juxtaposition of the said elements, with or without jointing using a refractory cement or mortar.

It goes without saying that the embodiment described is only an example and it could be modified, in particular by substitution of technical equivalents, without departing from the scope of the invention.

Claims (6)

1. Tuyere opening assembly of a vertical furnace or reactor, formed by assembling at most four prefabricated elements (12) made of moulded refractory concrete, characterized in that each element comprises, furthermore, a lining (14) consisting of ceramised refractory keystones (15) of identical shape and size forming a unitary composite assembly with said element and arranged between the part (13) of the element made of moulded refractory concrete and the orifice (5) intended for receiving the burner or tuyere.
2. Tuyere opening assembly according to claim 1, characterized in that the refractory concrete comprises alumina granulates and a hydraulic binder.
3. Tuyere opening assembly according to claim 1 or 2, characterized in that the ceramised refractory keystone is comprised of grains of corundum and/or silicon carbide bonded by a nitride or sialon binder.
4. Tuyere opening assembly according to claim 1, characterized in that the keystones extend only over part of the total thickness of the elements, this part including the face of the elements turned towards the interior of the furnace or reactor.
5. Process for producing a tuyere opening assembly as defined in any of claims 1 to 4, characterized in that the ceramised keystones are positioned in the mould of the prefabricated concrete element during the moulding of the latter.
6. Process for producing a tuyere opening assembly as defined in any of claims 1 to 4, characterized in that the concrete part of the element is first produced by moulding, then the keystone-made lining is fixed to said part after the latter has been removed from the mould.

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