NL9201170A - METHOD AND MIXTURE FOR FORMING A COHERENT FIRE-RESISTANT MASS ON A SURFACE. - Google Patents

Description

Method and mixture for forming a cohesive refractory mass on a surface

The present invention relates to a method for forming a cohesive refractory mass on a surface, simultaneously projecting on this surface oxygen, a mixture of refractory particles and combustible particles which react exothermically with projected oxygen to generate sufficient heat to melt the surface of at least the refractory particles and thus form the refractory mass under the action of the combustion heat. The invention also relates to a mixture of particles intended for a method of forming a cohesive refractory mass on a surface by projecting a mixture and oxygen against this surface, which comprises refractory particles and flammable particles capable of exothermic react with oxygen to release sufficient heat to melt at least the surfaces of the refractory particles to form, under the heat of combustion, said refractory mass.

If one wishes to form a refractory mass in situ on a surface, one can choose from two known important methods.

According to the first of these methods, sometimes referred to as "ceramic welding" and described in GB patent 1,330,894 (Glaverbel) and GB patent 2,170,191 (Glaverbel), a cohesive refractory mass is formed on a surface by a mixture thereon of refractory and flammable particles in the presence of oxygen The flammable particles are particles whose composition and grain size are such that they exothermically react with oxygen to form a refractory oxide and release the heat necessary to form the projected Melt refractory particles, at least superficially Aluminum and silicon are examples of such flammable materials It is known that, strictly speaking, silicon should be classified as semi-metal, but because silicon behaves like certain metals (it is capable of to undergo highly exothermic oxidation to form a refractory oxide), it is qualified for reasons of n convenience, these flammable elements as metal flammable substances. It is generally recommended to perform the projection of the particles in the presence of a high oxygen concentration, for example, to use commercial grade oxygen as the carrier gas. Thus, a cohesive refractory mass is formed which adheres to the surface on which the particles are projected. Due to the greatly elevated temperatures that the ceramic welding reaction can reach, it can penetrate the slag which may be present on the surface of a refractory being treated and soften or melt the surface to form a good bond. reached between the surface to be treated and the newly formed refractory mass.

These known methods of ceramic welding can be used to form a refractory element, for example a block with a special shape, but they are much more often used to form coatings or repair blocks or walls and are particularly useful for repairing or reinforcing existing refractory structures, for example for repairing walls or coatings of refractory equipment such as the walls of glass furnaces or coke ovens.

This operation is generally performed when the refractory base is hot. Thus, eroded refractory surfaces can be repaired while the equipment remains essentially at its operating temperature, and, in some cases, even while in operation.

The second known method, for forming a refractory mass on a surface, is called "flame spraying method". It consists of directing a flame where a refractory mass is to be formed and spreading the refractory powder through this flame. The flame is fed with a gaseous or liquid fuel or even with coke powder. It is clear that the efficient use of this flame-spraying technique requires complete combustion of the fuel to create the hottest flame possible and achieve maximum efficiency. In general, the temperature of the flame obtained in a flame spraying process is not as high as that which can be obtained with a ceramic welding technique, and as a result, the coherence of the refractory mass formed is not so great, and because the connection between the new refractory mass and the surface of the refractory base is formed at much lower temperature, this connection will not be as strong either. In addition, such a flame is less suitable than a ceramic welding reaction to penetrate the slag which may be present on a refractory surface being treated.

The composition of the mixture used in a ceramic welding process is generally chosen to form a repair mass which has a chemical composition similar or near that of the refractory base. This contributes to ensuring the compatibility and adhesion between the new material and the base material on which it is formed.

We have found, however, that problems arise when one wants to repair certain types of refractory structures, and that even when a refractory mass is formed with a chemical composition similar to that of the refractory base mass.

For example, the repair of surfaces with silicon carbide refractory structures using a mixture containing mainly silicon carbide particles as well as metallic flammable particles, such as aluminum and silicon particles, provides a refractory mass which does not always exhibit sufficient adhesion to the refractory base.

Refractories based on silicon carbide are used in certain metallurgy equipment, particularly in iron blast furnaces or zinc distillation columns. During operation of this equipment, certain parts of the refractory structures may have a rather low minimum operating temperature, for example, of the order of 700eC, and may also be subject to significant ambient temperature variations. It has been observed that the refractory masses produced by known techniques on these parts of refractory structures do not always exhibit sufficient adhesion to the base refractory mass and, in certain cases, especially when the repair is carried out on a block or refractory wall whose temperature is low, the new refractory mass is completely separated from the base refractory mass and detaches itself during equipment operation.

Similar problems arise when one wishes to repair refractory structures with a high density silica base (so to distinguish them from traditional silica refractories whose density is lower) used in certain coke ovens; even though one can form a refractory similar in chemical composition to the refractory base mass, the new mass does not always adhere sufficiently and may even quickly detach from the refractory base mass when the oven is in operation.

A method is known from international patent application WO 90/03848 (Willmet / Willard) for the repair of, for example, furnace coatings, in which an inert carrier gas and particles of refractory oxide and flammable, oxidizable material are fed to a flame atomizing device, in which oxygen is pressurized under high pressure the carrier gas / particle mixture aspirates and accelerates. Willard uses this method in the repair of refractory blocks / bricks in the blow nozzle of a copper melt converter as well as in the repair of silicon carbide tray columns. For example, a mixture containing 79% silicon carbide, 16.25% silicon, 4% aluminum and 0.75% magnesium is projected through a dual venturi air-oxygen system but a silicon carbide tray column.

However, the use of magnesium metal powder in this method is disadvantageous, at least in the sense that since magnesium metal is relatively volatile, there is a degree of uncertainty about the composition of the refractory coating formed.

One of the objects of the present invention is to solve these problems.

The present invention relates to a method for forming a cohesive refractory mass on a surface based on a silicon compound, projecting simultaneously with oxygen, a mixture containing refractory particles and flammable particles exothermic with the projected react oxygen by releasing sufficient heat to form the refractory mass under the action of the heat of combustion, projecting characterized in that the mixture: (i) flammable silicon particles; (ii) as a major part by weight of the mixture, refractory particles of one or a large number of substances, and (iiia) additive particles of another substance which, during formation of the refractory mass, causes silica entrapment formed by the combustion of the silicon part - particles, in a crystalline grid and / or (iiib) additive particles of a non-metal compound which, during the formation of the refractory mass, induce the said other substance which incorporates the silica formed by the combustion of silicon particles, in a crystalline lattice.

The present invention also relates to a mixture of particles intended for a method of forming a cohesive refractory mass on a surface based on a silicon compound by projecting the mixture and oxygen onto said surface, the mixture refractory particles and flammable particles capable of reacting exothermically with oxygen to release sufficient heat to form, under the action of the combustion heat, said refractory mass, characterized in that the mixture comprises: (i) flammable silicon particles? (ii) as an important weight percentage of the mixture, refractory particles of one or a large number of substances; and (iiia) additive particles of another substance which, during formation of the refractory mass, causes silica entrapment, formed by the combustion of the silicon particles, in a crystalline grid and / or (iiib) additive particles of a nonmetal compound, which are the formation of the refractory mass, said other substance which triggers the incorporation of silica formed by the combustion of silicon particles in a crystalline grid.

Such a mixture and method are useful for forming high quality refractory masses for the repair of surfaces based on a silicon compound, such as, for example, furnace refractory structures as well as for welding together parts. It is possible to obtain a refractory mass which exhibits excellent adhesion to the refractory base when the repaired surface undergoes repeated variations of thermal conditions during equipment operation and / or when the repair is performed on a surface whose temperature is relatively low, such as between 600 ° C and 1000 ° C (for example, 700 ° C), although the invention is applicable to surfaces with temperatures outside this range.

The refractory masses prepared according to the invention exhibit thermal expansion properties at the interface between the surface and the refractory mass formed which are different from those which would be obtained if the starting mixture did not contain any substance which contained in a crystalline silica grid formed by burning silicon causes. We believe that the advantages obtained with the invention result, at least in part, from this difference at the interface than that the resulting refractory masses show thermal expansion properties at the interface that are well adapted to those of the refractory structures in matter.

The flammable silicon particles (i) can be used as the sole flammable material or they can be mixed with particles of a further flammable material, such as aluminum. Thus, the mixture preferably further comprises flammable aluminum particles. Aluminum particles can be quickly oxidized with a significant release of heat and themselves form refractory oxides. The modification of this property therefore favors the formation of high quality refractory masses.

The mixtures according to the invention preferably do not contain more than 15% silicon. This is important to limit the amount of unreacted silicon that can remain in the refractory mass formed. We have found that the presence of unreacted silicon in the refractory mass formed can decrease its qualities.

The refractory particles (ii) may be present in an amount of at least 70% by weight, most preferably at least 75% by weight, to obtain a homogeneous mass.

The additive particles (iiia) and / or (iiib) preferably form the remainder of the mixture and may comprise up to 25% by weight of the mixture, preferably 5-15% by weight.

The flammable particles (i) used in the mixture preferably have an average particle size of less than 50 µm.

The refractory particles (ii) preferably substantially do not include particles larger than 4 mm in size, most preferably no larger than 2.5 mm in order to facilitate the formation of a regular jet or powder. The additive (iiia) and / or (iiib) used in the mixture preferably has a particle size of less than or equal to 500 µm. if particles that are too large are used, there is a risk that they will not play an effective role. Preferably, these particles are at least 10 µm in size. When particles that are too small are used, there is a risk that they volatilize during the reaction.

Numerous compounds are suitable for inducing, during the formation of the refractory mass, the uptake of silica formed during the combustion of slicium, in a crystalline grid.

The aforementioned additive (iiia) which triggers the incorporation of silica formed by the combustion of silicon into a crystalline grid is preferably introduced into the mixture in the form of magnesium oxide particles.

The presence of this compound in the mixture to be projected onto the refractory surface to be repaired helps to ensure proper heat-resistant properties of the refractory mass formed.

In addition, the introduction of magnesium oxide into the mixture allows for the formation of a refractory mass in which at least part of the silica formed by the combustion of silicon is contained in a crystalline grate of the forsterite type. This also helps to ensure proper heat resistant properties of the refractory mass formed.

If the mixture contains both aluminum and magnesium oxide, a refractory mass may be formed, with at least part of the silica formed by the combustion of silicon being contained in a crystalline grid with the forsterite structure and / or in a crystalline grid with the spinel structure and / or in a crystalline grid with the corietrite structure.

The presence of a crystalline lattice of the cordierite structure in the refractory mass formed helps to ensure excellent thermal shock resistance of this mass. The presence of a crystalline lattice of the forsterite structure and / or spinel structure on the other hand favorably influences the heat resistance of the refractory mass formed.

Other oxides such as calcium oxide or iron oxide (II) can also be used as the additive (iiia) which causes the incorporation of silica formed by the combustion of silicon into a crystalline grid.

A mixture of particles may be used which additionally or alternatively comprises an additive substance or substances (iiib) the composition of which is such that when the refractory mass is formed they produce a substance which incorporates silica formed by the combustion of silicon in a crystalline lattice. For example, peroxides such as calcium peroxide, nitrides, carbides can be used.

An oxide, for example calcium oxide, can be introduced in the form of a compound, for example in the case of calcium oxide, in the form of wollastonite (CaO SiO2).

The present invention is particularly useful for repairing silicon carbide-based refractories or high-density silica refractories. Accordingly, it is preferred that ceramic welding be carried out with a mixture, the major weight of which comprises silicon carbide or silicon, respectively.

It goes without saying that the invention may also be useful for repairing other types of refractories based on a silicon compound than the aforementioned, such as normal silica bricks and silica-alumina bricks.

The substance or substances that form the main part by weight of the mixture may correspond to the composition of the refractory one wishes to repair, or may be of another material. In the latter case, a refractory mass is formed which may have deviating properties from, and ideally improve from, that of the refractory to be repaired, for example, improved abrasion resistance or improved refractoriness.

The present invention will now be further illustrated by the following examples:

EXAMPLE I

A refractory mass was formed on a wall of the zinc distillation column. This wall included bricks on a silicon carbide basis. A mixture of refractory particles, flammable particles that are exothermally oxidizable by forming a refractory oxide / and magnesium oxide particles was projected onto these bricks. The temperature of the wall was 800 ° C. The mixture was projected in a flow of pure oxygen at a rate of 60 kg / h. The mixture had the following composition:

SiC 79 wt%

Si 8 wt%

Already 5 wt%

MgO 8 wt%

The silicon particles had a size below 45 µm and a specific surface area between 2500 and 8000 cm2 / g. The aluminum particles had a size below 45 µm and a specific surface area between 3500 and 6000 cm2 / g. The size of the silicon carbide particles was less than 1.47 mm with 60 wt% from 1 to 1.47 mm, 20 wt% from 0.5 to 1 mm, and 20 wt% below 0.125 mm. The MgO particles had an average size of about 300 µm. "Average Size" designates a dimension such that 50% by weight of the particles have a smaller size than this average.

The wall repaired in this way was subjected to significant ambient temperature variations and the new refractory mass was observed to adhere to the support durably.

The structure of the formed mass was examined under the microscope. Excellent continuity was observed between the new refractory mass and the refractory mass of the base. It was also observed that the silica formed by the combustion of silicon was contained in the crystalline grids of forsterite, cordierite and aluminum-containing spinel.

For comparison, a mixture containing no magnesium oxide was projected under the same conditions. The composition of this mixture was as follows:

SiC 87 wt%

Si 12 wt%

Already 1 wt%

The refractory mass formed was observed to quickly detach from the wall and detach itself into solid blocks if the zinc distillation column remained in operation.

In a modification of this example, this mixture was used to repair the bottom of a coke oven made of normal silica bricks and silica-alumina bricks. A repair compound with good abrasion resistance was obtained which adhered well to the wall, even when subjected to significant thermal changes.

EXAMPLE II

As a variation of Example I, a mixture of the following composition was used:

SiC 82 wt%

Si 8 wt%

Already 5 wt%

MgO 5 wt%

The wall that was repaired contained bricks based on silicon carbide and had a temperature of 700 ° C.

The refractory mass obtained also adheres permanently to the wall.

EXAMPLE III

The goal was to form a refractory mass on a coke oven wall containing high-density silica bricks. While the apparent density of traditional bricks is on the order of 1.80, the apparent density of high-density bricks is about 1.89. Such bricks have recently appeared on the durable material market, exhibiting favorable properties compared to traditional silica bricks, particularly with regard to the properties of gas permeability and thermal conductivity.

The repair was carried out on a wall whose temperature was about 750 ° C using the following mixture:

SiO2 80.5 wt%

Si 11.1 wt%

Already 1 wt%

MgO 7.4 wt%

The size of the SiO 2 particles was less than 2 mm, with a maximum of 30 wt% from 1 to 2 mm and less than 15 wt% below 100 rpm.

The formed mass adhered permanently to the wall.

In contrast, projecting a similar mixture containing no magnesium oxide under the same operating conditions yielded a refractory mass that easily detached itself from the wall when the latter was subjected to different thermal conditions present when the oven is in operation.

EXAMPLE IV

The aim was to form a refractory mass on a wall of a refractory coke oven made of a silicon compound refractory subject to significant ambient temperature variations and the temperature of which did not exceed 900 ° C. The repair was performed on a wall whose temperature was about 750 ° C using the following mixture:

SiO2 80 wt%

CaO Si02 (wollastonite) 8 wt%

Si 8 wt%

Already 4 wt%

The average size of the wollastonite particles was about 300 µm. The metal particle size was as given in Example 1 and the silica particle size was as given in Example 3.

Claims (18)

A method for forming a cohesive refractory mass on a surface based on a silicon compound, simultaneously projecting with the oxygen a mixture against the surface comprising refractory particles and combustible particles which react exothermically with the projected oxygen by releasing sufficient heat to form the refractory mass under the action of the heat of combustion, characterized in that the mixture comprises: (i) flammable silicon particles; (ii) as an important weight percentage of the mixture, refractory particles of one or a large number of substances; and (iiia) additive particles of another substance which, during the formation of the refractory mass, causes entrapment of silica formed by the combustion of the silicon particles, in a crystalline grid and / or (iiib) additive particles of a non-metal compound which, during the formation of the refractory mass, produces the said other substance which causes the incorporation of silica formed by the combustion of silicon particles into a crystalline grid. A refractory mass forming method according to claim 1, characterized in that said substance (iiia) which causes inclusion of silica formed by the combustion of the silicon particles in a crystalline grid is introduced into the mixture in the mixture. form of magnesium oxide particles. Refractory molding process according to claim 2, characterized in that at least part of the silica formed by the combustion of silicon is enclosed in a crystalline grid with the forsterite structure. A refractory mass forming method according to any one of claims 1 to 3, characterized in that said flammable particles (i) further comprise aluminum particles. Refractory molding process according to claims 2 and 4, characterized in that at least part of the silica formed by the combustion of silicon is enclosed in a crystalline grid with the forsterite structure and / or in a crystalline grid with the spinel structure and / or in a crystalline grid with the cordierite structure. Refractory molding process according to any one of the preceding claims, characterized in that said non-metallic compound (iiib) is introduced into the mixture in the form of particles of a peroxide or a silicate. A refractory mass forming method according to any one of claims 1 to 6, characterized in that said refractory particles (ii) constituting the major weight part of the mixture are silicon carbide particles. A refractory mass forming method according to any one of claims 1 to 6, characterized in that said refractory particles (ii) constituting the major weight part of the mixture are silica particles. Method according to any of the preceding claims, characterized in that the temperature of the surface is less than 1000 ° C. A mixture of particles intended for a method of forming a cohesive refractory mass on a surface based on a silicon compound by projecting the mixture and oxygen onto said surface, the mixture comprising refractory particles and flammable particles capable of exothermically reacting with oxygen to release sufficient heat to form said refractory mass under the action of combustion heat, characterized in that the mixture comprises: (i) flammable silicon particles; (ii) as an important weight percentage of the mixture, refractory particles of one or a large number of substances; and (iiia) additive particles of another substance which, during formation of the refractory mass, causes entrapment of silica formed by the combustion of the silicon particles, in a crystalline grid and / or (iiib) additive particles of a nonmetal compound which, during the formation of the refractory mass, produces said other substance which triggers the incorporation of silica formed by the combustion of silicon particles in a crystalline grid. A method according to claim 10, characterized in that said mixture contains magnesium oxide particles as said particles of another substance (iiia). Mixture according to claim 10 or 11, characterized in that said mixture contains particles of a peroxide or a silicate as said non-metallic compound (iiib). Mixture according to any one of claims 10 to 12, characterized in that said flammable particles (i) further comprise aluminum particles. Mixture according to any one of claims 10 to 13, characterized in that said refractory particles (ii), which constitute the major part by weight of the mixture, are silicon carbide particles. Mixture according to any one of claims 10 to 13, characterized in that said refractory particles (ii), which make up the major part by weight of the mixture, are silica particles. Mixture according to any one of claims 10 to 15, characterized in that said additive particles (iiia) or (iiib) have a particle size less than or equal to 500 µm. Mixture according to any one of claims 10 to 16, characterized in that the additive particles (iiia) or (iiib) have a particle size of at least 10 pin. Mixture according to any one of claims 10 to 17, characterized in that the silicon content therein is not more than 15% by weight.