EP2340408A1 - Ofen zur verbrennung von kohlenstoffblöcken - Google Patents

Ofen zur verbrennung von kohlenstoffblöcken

Info

Publication number
EP2340408A1
EP2340408A1 EP09744483A EP09744483A EP2340408A1 EP 2340408 A1 EP2340408 A1 EP 2340408A1 EP 09744483 A EP09744483 A EP 09744483A EP 09744483 A EP09744483 A EP 09744483A EP 2340408 A1 EP2340408 A1 EP 2340408A1
Authority
EP
European Patent Office
Prior art keywords
less
equal
oven according
matrix
nitrogen
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09744483A
Other languages
English (en)
French (fr)
Inventor
Frédéric ROULET
Eric Jorge
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Original Assignee
Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Saint Gobain Centre de Recherche et dEtudes Europeen SAS filed Critical Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Publication of EP2340408A1 publication Critical patent/EP2340408A1/de
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B13/00—Furnaces with both stationary charge and progression of heating, e.g. of ring type, of type in which segmental kiln moves over stationary charge
    • F27B13/06—Details, accessories, or equipment peculiar to furnaces of this type
    • F27B13/08—Casings
    • F27B13/10—Arrangements of linings
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
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    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
    • C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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    • C04B2235/9684—Oxidation resistance

Definitions

  • the invention relates to an oven for firing carbonaceous blocks, and in particular anode blocks for electrolysis, for example aluminum, according to the Hall-Héroult process.
  • an anode block baking oven 10 has two longitudinal walls 14 and 16 parallel, generally more than 100 meters long and several meters high. Transverse walls partition the space between the longitudinal walls 14 and 16 into a plurality of substantially identical chambers.
  • transverse walls 18 and 20 thus define a chamber 22.
  • the chamber 22 is itself longitudinally partitioned by hollow heating partitions 24.
  • the transverse walls 18 and 20 and the heating partitions 24 ("flue walls" in English) thus define a succession of cells 26, the upper part of which can be opened in order to allow the loading and unloading of the anode blocks.
  • a heating partition 24 conventionally comprises two parallel and vertical side walls 28 and 30, spaced apart from each other so as to define an internal volume of circulation of the gases. Baffles, preferably in contact with each of the two side walls 28 and 30, are conventionally provided for improving the heat exchange between the gases flowing in the internal volume and the side walls 28 and 30.
  • the heating partition 24 may be constituted by a assembly of bricks 36 or by a panel assembly, as described for example in US 5,078,595.
  • the green anode blocks In an alveolus, the green anode blocks, conventionally based on carbon grains and carbon binder, are stacked, embedded in a coke coating in order to maintain a reducing atmosphere during cooking.
  • Burner ramps generally mobile, not shown, are positioned on openings 38 located at the top of the heating partitions 24 delimiting the cells 26. The burners can thus inject hot gases into the heating partitions, the flow of gases being impeded by the baffles of the heating partitions.
  • the heating partitions can thus bake the anode blocks, typically for a period of the order of ten to thirty days, at a maximum cooking temperature of about 1000 0 C to 1100 0 C.
  • the heating partitions are therefore subjected to several stresses:
  • An object of the invention is to respond, at least partially, to this need.
  • the invention proposes an oven for firing carbonaceous blocks, in particular for firing anode blocks for the electrolytic production of aluminum, said furnace comprising at least one region, in particular in the form of a block or a partition, made of a sintered refractory material constituted by a matrix-bound granulate, said material comprising a SiAION phase of formula Si ⁇ Al y O u N v constituting at least a part of the matrix and such that:
  • - x is greater than or equal to 0.01 and less than or equal to 1;
  • y is greater than or equal to 0 and less than or equal to 1;
  • u is greater than or equal to 0 and less than or equal to 1;
  • v is greater than 0 and less than or equal to 1, x, y, u and v being mass proportions.
  • nitrogen matrix material exhibits an excellent behavior under the conditions of a carbonaceous block baking oven.
  • said nitrogen matrix material comprises a total content of residual metals, in particular residual silicon and / or residual aluminum, of less than 1.8%, as a percentage by weight on the basis of the material.
  • said nitrogenous matrix material has an air permeability at 20 0 C of less than 15 mDarcy, or even less than 10 mDarcy, or even less than 5 mDarcy.
  • An oven according to the invention preferably comprises a heating partition, in particular of the type defined in the preamble of the description, comprising, or even constituted by, a nitrogen matrix material, in particular in the form of a brick or a panel.
  • the invention also relates to a heating partition suitable for use in a carbonaceous block cooking furnace, or a portion of such a heating partition, said heating partition comprising, or even consisting of, a nitrogen matrix material.
  • a heating partition may in particular comprise one or more baffles facilitating the distribution of gases in the interior volume of the heating partition.
  • region of an oven is meant a part of this oven, for example one or more blocks of this oven.
  • a furnace liner can also be considered as a region of this furnace. It is the same with a monolithic partition.
  • shaped material is a structured material, that is to say, that retains its shape when it is handled, such as a demolded preform or a sintered product.
  • the term "sintering” is understood to mean a heat treatment for consolidating a preform by which a microstructure consisting of a granulate whose grains are joined together by means of a matrix is formed by a partial melting of the constituents.
  • a preform is a shaped product, unlike a molten liquid material.
  • the SiAION of the nitrogen matrix material may be obtained by sintering in a non-oxidizing atmosphere if nitrogen is supplied by at least one of the constituents of the feedstock or by sintering under a nitrogen atmosphere, preferably at a temperature between 1300 and 1600 0 C.
  • “Sintering under nitrogen” means sintering in a gaseous environment comprising more than 90%, preferably more than 95% or, more preferably, substantially 100% nitrogen, as a percentage by volume. Sintering under nitrogen is the technique conventionally used to form nitrogen matrices.
  • Silicon or "residual" aluminum is silicon or aluminum, respectively, in metallic form present in the matrix of the sintered material.
  • aggregate refers to all the refractory grains bonded by the matrix and which, during sintering, have substantially retained the shape and the chemical nature they had in the feedstock.
  • the grains of the granulate are, at best, only superficially melted during sintering.
  • granulate all of these grains as they appeared in the starting charge.
  • the nature of the granulate is not limiting, the granulate being characterized by its structural stability and its chemical stability during sintering.
  • matrix is meant a crystallized phase or not, ensuring a continuous structure between the grains of the granulate and obtained, during sintering, from the constituents of the feedstock and possibly constituents of the gaseous environment of this feedstock. starting during sintering.
  • the “matrix” refers to the binder phase resulting from the sintering and must therefore be distinguished from the binder phase that may be present before sintering, for example because of the activation of a hydraulic binder. Sintering SiAION granulate does not lead to SiAION "matrix".
  • the methods of manufacture described in EP 0 242 849, JP 07126072 or JP 07069744 do not lead to an SiAION matrix.
  • the chemical compositions of the granulate and the matrix can be obtained by chemical analysis of the material in the general case where the granulate is in a material different from the matrix. Otherwise, if the aggregate is made of a material identical to some of the constituents of the matrix, it is necessary to separately analyze the granulate and the matrix, the granules of the aggregate being conventionally much larger than the constituents of the matrix.
  • nitrogenous crystalline part is meant all the nitrogenous phases of a material, whether in the granulate or in the matrix.
  • the crystallized nitrogen portion can be measured by an overall analysis of the material.
  • impurities is meant unwanted constituents of the material. Impurities can be introduced with the raw materials or result from reactions during the manufacturing process. Impurities are not necessary constituents, but only tolerated. Residual metals are considered impurities.
  • “Silica in micron form” means a silica powder whose particles, partially amorphous, have a median size of between 0.01 and 4 microns. "Silica in colloidal form” has a median particle size that may be smaller, generally of the order of a few nanometers.
  • thermosetting resin is meant a polymer transformable by heat treatment (heat, radiation) or physicochemical (catalysis, hardener) infusible and insoluble material.
  • Thermosetting resins include, in particular, phenolic resins, silicone-based resins or epoxides.
  • the “median size” of a set of particles or grains generally denoted D 50 , the size dividing the grains or particles of this set into first and second populations equal in mass, these first and second populations comprising only grains or particles having a size greater or smaller respectively than the median size.
  • reaction refers to any method of shaping, in particular by pressing, extrusion, casting, vibration, shelling or by a technology combining these different techniques.
  • An “overall” dimension is a distance measured, in a determined direction, between the two points of the outer surface of a block that are the most distant from each other.
  • the overall dimension is particularly useful for evaluating the size of "U" shaped blocks, or blocks having open and / or closed hollow portions, especially blocks used for anode block baking oven walls. intended for the electrolysis of aluminum.
  • the overall "transverse” dimension corresponds to a dimension measured in a transverse plane, that is to say on a section perpendicular to the release axis of the block.
  • the overall transverse length and width are appropriate transverse dimensions, for example, to measure the spacing between the two side faces of the "U” branches which are parallel and outwardly oriented towards the "U” (this is that is, not oriented towards the soul of the "U”).
  • FIG. 1 represents a perspective view of an example of anode block baking oven
  • An oven according to the invention can be chosen from all the types of carbonaceous block baking furnaces used to date, in particular for baking anode blocks intended for the electrolytic production of aluminum, provided that it comprises a material nitrogen matrix and, preferably, a heating partition of which at least one region, preferably at least one region of a side wall, preferably always a whole side wall, is made of a nitrogen matrix material.
  • An oven according to the invention may in particular be an oven of the type described in FR 2 535 834, incorporated by reference.
  • a nitrogen matrix material comprises a matrix resulting from the sintering operation and binding a granulate.
  • SiAION-based matrix materials are in particular known from US 4,533,646, US 3,991,166, or US 4,243,621.
  • the matrix preferably represents at least 5%, at least 10%, at least 13%, or even at least 15% of the weight of the nitrogen matrix material and / or less than 60%, less than 40%, less than 30% or less than 25% of the mass of the nitrogen matrix material.
  • the 100% complement is constituted by the granulate.
  • the nitrogen matrix material comprises a SiAION phase of formula Si ⁇ Al y O u N v , constituting at least a part of the matrix.
  • the SiAION content in the nitrogen matrix material is greater than 12%, greater than 14%, or even greater than or equal to 15%, by weight percent based on the nitrogen matrix material.
  • this content is measured by X-ray diffraction.
  • x is greater than or equal to 0.1, or even greater than or equal to 0.2.
  • y is greater than or equal to 0.01, greater than or equal to 0.05 or greater than or equal to 0.14.
  • u is greater than or equal to 0.01, greater than or equal to 0.05, or even greater than or equal to 0.14.
  • v is greater than 0.01, greater than 0.1, or even greater than 0.3.
  • the phase SiAION is a phase Si 3 N 4 , that is to say such that y and u are equal to zero, x is equal to 0.6 and v is equal to 0.4 .
  • Binder matrix materials of the Si 3 N 4 type with addition based on phosphorus for example from US 3,468,992, are known.
  • the SiAION phase comprises less than 50%, less than 30%, less than 20%, less than 10%, of Si 3 N 4 phase, in percentage by weight on the basis of the matrix, or substantially not of phase Si 3 N 4 . In one embodiment, y and / or u are strictly greater than 0.
  • the SiAlON phase is a phase of the formula Si6- z Al z 0 z N 8 - z, where 0 ⁇ z ⁇ 4.2, phase called " ⁇ 'SiAION" z can in particular be greater than 1 or even greater than 3 and / or less than 4, or even less than 3.5.
  • the granulate comprises less than 10%, or even less than 5% or less than 1%, as a weight percentage, of the SiAION of the nitrogen matrix material, or substantially no SiAION. In other words, SiAION is predominantly, if not all, in the matrix.
  • the SiAION phase and in particular the ⁇ 'SiAION phase, preferably represents more than 60%, or more than 70%, or even more than 75% of the mass of the nitrogenous crystalline part.
  • the SiAION phase can even represent more than 90%, more than 95%, or even substantially 100% of the crystallized nitrogen portion.
  • the nitrogen-containing crystalline part may in particular also comprise a phase AIN15R, the AIN15R phase preferably representing more than 5% or even more than 10%, more than 20%, of the mass of the nitrogen-containing crystalline part.
  • the nitrogenous crystalline portion consists, for more than 80% by weight, of SiAION phase, and in particular of the ⁇ 'SiAION phase and, where appropriate, of the AIN15R phase, in percentage by mass on the base of the matrix.
  • the SiAION phase, in particular the ⁇ 'SiAION phase, and the eventual AIN15R phase can together represent more than 85%, or even more than 90% or even more than 95%, or more than 99%, or even substantially 100% of the mass. of the crystallized part.
  • the nitrogenous crystalline part may also comprise other nitrogen phases, in particular BN, TiN, Si 3 N 4 , ZrN, Si 2 ON 2 , O'SiAION of formula Si 2 -x Al x 0 x + iN 2-x with 2>x> 0 or X SiALON, as described in US 5,521,129.
  • the total nitrogen content, in crystalline or non-crystalline form, is preferably greater than 3.1%, greater than 3.5%, or even greater than or equal to 4%, as a weight percentage on the basis of the nitrogen matrix material.
  • At least 90%, or even at least 95%, or even at least 99%, or even 100% by weight of the nitrogenous crystalline part is part of the matrix.
  • the crystallized nitrogenous portion may represent at least 50%, or at least 80%, or even at least 90%, or even at least 95%, or even substantially 100% of the mass of the matrix.
  • said matrix comprises more than 60%, or more than 70%, or even more than 75%, by mass percentage, of SiAION phase as already defined above.
  • the portion of the matrix complementary to the nitrogenous crystalline portion may comprise, or even consist of, a hydraulic binder, a resin, in particular a thermosetting resin as defined above, or a mixture of these constituents. It may also include alkaline earth oxides, metal oxides, phosphorus and impurities. Preferably, all these constituents and the crystalline nitrogenous portion represent 100% of the mass of the matrix.
  • the blocks obtained have high residual metal core contents, typically greater than 2%. They may also have hygroscopic and / or non-refractory crystalline phases. These blocks may also have phases whose oxidation is harmful and porosity heterogeneities or internal gradients of unacceptable properties, including color gradients and / or appearance. These internal gradients can indeed cause high thermal gradients within the block in use, and therefore mechanical stresses that lead in particular to cracks in the block and its premature wear.
  • the matrix of the nitrogen matrix material has a phosphorus content of greater than 0.2%, as a percentage by weight based on said matrix. The inventors have indeed found that this phosphorus content makes it possible, in a surprising manner, to obtain a mechanical resistance, especially to crushing and cold bending, an oxidation resistance and an abrasion resistance. high, even for large blocks.
  • the matrix of the nitrogen matrix material may comprise more than 0.3%, preferably more than 0.4%, phosphorus, as a percentage by weight based on the matrix.
  • the matrix comprises less than 2.5%, or less than 2%, or even less than 1, 5%, or even less than 1%, of phosphorus, in percentage by weight based on the matrix.
  • the impurity content is less than 10%, preferably less than 5%, or even less than 2%, by mass percentage based on the nitrogen matrix material.
  • the impurities present in the matrix may comprise in particular traces of alumina, or even silica, residual metals, and alkali metal oxides.
  • the total content of residual metals, in particular of silicon is less than 1, 7%, or even less than 1, 5%, or even less than 1%, in weight percentage on the basis of the nitrogen matrix material.
  • the nitrogenous matrix material preferably has a total content of alkali metal oxides, in particular Na 2 ⁇ and K 2 O, less than 1, 2% or even less than 0.7%, in mass percentage based on the product. Preferably, however, this content is however less than 1%. This preferred characteristic makes it possible to increase the refractivity and the creep resistance of the material.
  • the presence of alkaline earth oxide is desired and results from the addition of a hydraulic binder.
  • the alkaline earth oxide content is then greater than 0.2 percent percent based on the nitrogen matrix material.
  • the alkaline earth oxides are preferably part of the impurities.
  • the nitrogen matrix material has a total content of alkaline earth oxides, in particular CaO, of less than 2%, preferably less than 1.5% or even less than 0.8% in weight percentages on the base of the nitrogen matrix material.
  • the material then has improved refraction and creep resistance.
  • metal oxides for example iron oxides, may have been introduced into the feedstock to facilitate nitridation or to remove impurities.
  • the nitrogen matrix material comprises a matrix of silicon nitride (Si 3 N 4 ).
  • the material may comprise, in percentages by weight, a total content of calcium and boron, preferably a boron content, of between 0.03% and 3%, preferably between 0.05% and 1.5%, of preferably about 1.2%.
  • the nitrogen matrix material comprises at least 0.05%, preferably at least 0.3%, more preferably at least 0.5% boron and / or between 0.05% and 1.2% of boron. calcium.
  • boron and / or calcium, preferably boron provides a significant improvement of the properties in the intended application, in particular with regard to the resistance to oxidation, the Thermal transfer properties and dimensional stability under oxidation conditions.
  • the nitrogen matrix material preferably further comprises, in percentage by weight, less than 3% boron.
  • the silicon nitride (Si 3 N 4 ) in beta form represents, in percentages by weight, at least 40%, preferably at least 60%, more preferably at least 80%, of all the nitride of silicon (Si 3 N 4 ) in beta form and in alpha form.
  • the Si 2 ON 2 content as a percentage by weight is preferably less than 5%, preferably less than 2%. More preferably, the boron is not in TiB 2 form.
  • the nature of the granulate is not limiting.
  • the granulate may in particular be composed for more than 70%, or even more than 80% or even more than 90%, or even substantially 100%, by weight, of grains made of a material chosen from alumina, and in particular corundum, white or black, or tabular alumina, mullite, mullite precursors, chromium oxide, zirconia, zircon, nitrides, especially silicon nitride Si 3 N 4 , carbides, and in particular carbide silicon SiC, amorphous carbon or in at least partially crystallized form, and mixtures of these materials, and / or is composed of a mixture of grains mentioned above.
  • the granulate comprises grains of silicon carbide SiC, or even consists of such grains.
  • the material to be nitrogen matrix comprises more than 5%, preferably more than 30%, more than 50%, more than 60%, more than 70% or even more than 90% of SiC, in weight percent based on the nitrogen matrix material .
  • the granulate is neither nitrogen nor phosphorus.
  • At least 90% by weight of the grains of the granulate have a size of between 150 ⁇ m and 15 mm.
  • granules of aggregate have a size greater than 0.2 mm and / or at least 15 %, or even at least 20%, or even at least 25% of the grains have a size greater than 2 mm, or even greater than 3 mm or greater than 5 mm, and / or at least 90%, or even at least 95% by weight granules of granules have a size less than 20 mm, or even less than 15 mm, or even less than 10 mm or less than 5 mm.
  • the median size D 50 of the granules of the aggregate is greater than 3 mm, or even greater than 4 mm and / or less than 15 mm, less than 10 mm, or less than 6 mm. mm.
  • the median size D 50 of the grains of the granulate is greater than 5 ⁇ m, or even greater than 10 ⁇ m, greater than 30 ⁇ m or greater than 50 ⁇ m and / or less than 3 mm, less than 2 mm, less than 1 mm, less than 500 ⁇ m, or even less than 100 ⁇ m.
  • the granulate base material i.e. the bulk constituent in the granulate, the nitrogenous crystalline portion, the phosphorus and the impurities represent 100% of the weight of the nitrogen matrix material.
  • the nitrogen matrix material may be all or part of a block.
  • the block may in particular have a mass of more than 20 kg, more than 50 kg, more than 150 kg, more than 300 kg, and even more than 900 kg and / or less than 2 tonnes. In particular, it can have a mass of about 1 ton.
  • the shape of the block is not limiting.
  • the block may have at least one dimension (thickness, length, or width) of at least 120 mm, preferably at least 150 mm, or even at least 200 mm, or even at least 300 mm, or even at least 400 mm, even at least 600 mm or even at least 800 mm, or even at least 1000 mm.
  • the thickness, the length and the width of the block are at least 120 mm, even at least 150 mm, or even at least 300 mm, or even at least 400 mm, at least 600 mm or even at least 800 mm, or even at least 1000 mm.
  • At least one overall dimension of the block is greater than 150 mm, 300 mm, 600 mm, or even 900 mm.
  • the block may have an outer surface of generally convex shape, for example a parallelepiped shape, or an outer surface of general shape having concavities.
  • the outer surface of the block may include concavities changing its general shape.
  • the block may be of cross-section in the form of "U", "+", or "X".
  • the block may also have, locally, one or more holes, through or not through, for example in the form of cell or tubular hole, rectilinear or not, for example provided to facilitate the possible passage of a fluid (liquid or gas ) or increase the heat exchange surfaces.
  • the block 10 has recesses 14 or passage channels 16 for gases.
  • Blocks 10 in the form of "X”, “U”, cylinder, or "+” are shown in Figures 3 to 6, respectively.
  • the blocks may locally have reliefs, holes or cells, open or closed.
  • Their outer surface 13 may be smooth ( Figures 4 to 7) or carry corrugations 17 (Figure 3), in particular to increase the heat exchange surface.
  • the block is part of or constitutes a furnace wall.
  • the block has the shape of a panel of a heating partition, and in particular a side panel of a heating partition.
  • this panel comprises at least one protuberance intended, possibly in cooperation with another panel, to form a baffle for a flow of gas flowing in the heating partition.
  • the panel may in particular be in accordance with the panels described in US 5,078,595, incorporated by reference.
  • the block can also have the shape of a brick.
  • the nitrogen matrix material may also be used in the form of a thin product, i.e. having a thickness "e" of from 3 to 120 mm as shown in FIG.
  • a sintered thin product may have a thickness "e" of less than 100 mm, less than 50 mm, and even less than 25 mm. It may in particular be in the form of a coating, and in particular a coating of a heating partition.
  • It may in particular be in the form of a plate or a thin wall, for example a wall of a tube, or in the form of a tile.
  • At least one anti-dust agent selected from calcium and boron may be present in a surface layer of the sintered refractory material, the mass ratio of all of said anti-dust agents in said surface layer being greater than that measured under said layer .
  • under the surface layer is meant a region of the material extending immediately below the surface layer. Preferably this region extends at most up to 5 cm, preferably at most up to 500 ⁇ m below the surface layer.
  • the average levels of anti-dust agents are compared in the surface layer and in a layer of a thickness. at most 5 cm, preferably at most 500 ⁇ m extending immediately below the surface layer.
  • the level of anti-dust agent of the surface layer is greater than that measured at any point of the product located under this superficial layer, that is to say that the region "under the superficial layer” includes all the product except the superficial layer.
  • the boundary between the "superficial layer” of a product and the region "under the surface layer” is determined by the depth from which, by penetrating from the surface to the center of the material, the level of anti-agent (s) -dust remains substantially constant depending on the depth, this rate to be kept constant for at least 500 microns after the border.
  • the level of anti-dust agent (s) then stabilizes at a value lower than that measured, on average, in the superficial layer.
  • the surface layer corresponds to the region extending from the surface of the product to the end of the possible diffusion zone of the deposited anti-dust agents.
  • brushing the sintered product is no longer necessary, especially to ensure good adhesion of the jointing cement to the assembly of the blocks to form the walls of the oven.
  • the surface layer preferably extends over the entire surface of the product, but may also extend to only a portion of it.
  • the surface layer has a mass content of anti-dust agents (boron + calcium) greater than or equal to 0.25%.
  • the surface layer has a level of calcium or boron greater than the level of calcium or boron, respectively, of the material under this surface layer.
  • Calcium and / or boron may be present in the form of at least one calcium compound and / or at least one boron compound, respectively, these compounds being preferably non-oxide compounds, that is to say without oxygen.
  • the calcium compound is preferably selected from the group consisting of oxides, carbides, nitrides, fluorides, metal alloys, organometallic compounds containing calcium and, more preferably, from CaB 6 , CaSiO 3 and CaCO 3.
  • the boron compound is preferably selected from the group consisting of oxides, carbides, nitrides, fluorides, metal alloys, organometallic compounds containing boron, in particular B 4 C, CaB 6 , BN, TiB 2 or H 3 BO 3 , preferably in the group formed by B 4 C and CaB 6 , more preferably the boron compound is B 4 C.
  • Said surface layer preferably has a thickness of less than 1000 ⁇ m, preferably less than 500 ⁇ m.
  • the level of boron is greater than 0.05% and / or the level of calcium is greater than 0.2% and, under said layer, the level of boron is less than 0.05% and or the calcium level is less than 0.2%, respectively, in percentages by weight.
  • the mass ratio of the anti-dust agent (s) in the surface layer is preferably, on average, at least 10%, preferably at least 20% higher than that measured under the surface layer, on the base of the rate measured in the superficial layer.
  • the material may have, on the surface, a reduction in its porosity, for example due to a grinding or oxidation treatment.
  • the reduction of the porosity can extend to a depth greater than 500 ⁇ m, or even greater than 1 mm, and generally less than 10 mm.
  • the invention also relates to a carbonaceous block baking oven as described above, wherein said region is a reactively sintered refractory material.
  • a nitrogen matrix sintered material when in the form of a block, may be manufactured by a process comprising the following steps: a) preparing a feedstock comprising refractory granulate, SiAION precursors; b) pouring said starting charge into a mold; c) forming the starting charge inside the mold, by compaction, so as to form a preform; d) demolding said preform; e) drying the preform, preferably so that the residual moisture is between 0 and 0.5%; f) sintering the preform under a non-oxidizing atmosphere if nitrogen is supplied by the feedstock or under a reducing atmosphere of nitrogen, preferably at a temperature of between 1300 and 1600 ° C.
  • step a the particulates are conventionally mixed until a homogeneous mixture is obtained.
  • step f The nature and quantities of raw materials are determined so that the block of refractory material obtained at the end of step f) is a "nitrogen matrix material" as described above.
  • the manner of determining the proportions of the constituents of the feedstock is well known to those skilled in the art. For example, one skilled in the art knows that the silicon carbide present in the feedstock is found in the sintered material. He also knows which constituents will be transformed to form the matrix.
  • Some oxides can be provided by the additives conventionally used to produce products, for example sintering agents, nitriding agents, for example iron oxide, dispersants such as alkali metal polyphosphates or methacrylate derivatives.
  • the composition of the feedstock may therefore vary, in particular as a function of the quantities and nature of the additives present, as well as the degree of purity of the raw materials used.
  • the granulate may consist of grains based on refractory oxides or non-oxide refractories, or grains based on carbon, in particular anthracite or graphite, or based on carbides such as silicon carbide.
  • the granulate may in particular consist of grains whose composition comprises the elements aluminum (Al) and / or silicon (Si).
  • the granulate does not comprise aluminum or silicon in metallic form.
  • the aggregate is composed for more than 70%, or even more than 80% or even more than 90%, or even substantially 100% by weight, of alumina grains, and in particular corundum, white or black , or tubular alumina, and / or mullite or mullite precursors, and / or chromium oxide, and / or zirconia, and / or zircon and / or nitrides, and in particular silicon nitride Si ⁇ lsU, and / or carbides, and in particular silicon carbide SiC. It can also be formed by grains consisting of a mixture of the preceding constituents. Finally, it may be formed of a mixture of the grains mentioned above.
  • the granulate comprises grains of silicon carbide SiC, or even consists of such grains.
  • the material may then comprise more than 5% SiC, as a percentage by weight based on the product.
  • the material can then have excellent thermal conductivity.
  • the feedstock must include a source of silicon, and an oxygen source, or even a source of nitrogen, and optionally a source of aluminum and / or a source of phosphorus, in proportions and under a Suitable shapes for forming SiAION by reactive sintering under nitrogen, or by sintering under a non-oxidizing atmosphere if nitrogen is present in sufficient quantity in the feedstock.
  • the silicon element for producing the SiAION of the matrix is provided by silica, in particular in the form of micronic silica (for example in the form of silica fume or micronized silica) or of colloidal silica, in particular for making blocks.
  • silica in particular in the form of micronic silica (for example in the form of silica fume or micronized silica) or of colloidal silica, in particular for making blocks.
  • the feedstock comprises more than 1%, more than 5%, or even more than 8%, and / or less than 15%, or even less than 10% of silica, as a percentage by weight on the basis of the material dry of the starting charge.
  • the SiAION silicon of the matrix may also be provided, at least in part, by a silicon metal powder.
  • the feedstock comprises more than 0.5% and / or less than 5% or even less than 2% of silicon metal, in percentages by weight on the basis of the dry matter of the feedstock, the median size silicon metal being preferably less than 200 microns, or even less than 60 microns.
  • the source of aluminum for making the SiAION of the matrix may include a powder comprising aluminum metal.
  • the use of aluminum metal makes it possible, after sintering, to obtain a stable matrix and well surrounding the grains of the granulate.
  • the feedstock comprises more than 1%, even more than 2% or even more than 5%, and / or less than 15% or even less than 10% of aluminum metal, in percentages by mass based on the dry matter of the feedstock, the median size of the aluminum metal being preferably less than 200 microns, or even less than 60 microns.
  • the aluminum sources for the SiAION of the matrix also include powders of alumina, in particular calcined alumina.
  • the feedstock comprises more than 0.5%, more than 1%, and / or less than 10%, less than 8%, or even less than 5% calcined alumina, in percentages by weight based on the dry matter of the feedstock, the median size of the calcined alumina being preferably less than 10 microns, or even less than 5 microns.
  • the silicon source is powdered silica and / or the aluminum source is aluminum powder and / or an aluminum alloy;
  • the feedstock in step a) can comprise a compound, liquid or solid, containing phosphorus.
  • the weight ratio R of the phosphorus on the aluminum metal contained in the particulate mixture is then preferably greater than 5.10 " and / or less than 5.10 " 2 .
  • Phosphorus can be provided, for example in liquid form or in the form of a solid in the form of a powder. It may in particular be provided in the form of a phosphorus-containing compound chosen from phosphates, and especially hydrogen phosphates, polyphosphates, and especially aluminophosphate or alkali metal polyphosphates, for example sodium hexametaphosphate, organophosphorus compounds, organophosphorus polymers, and mixtures of these compounds.
  • aluminophosphate powder which makes it possible to simultaneously bring the phosphor element and in part the aluminum element, is preferred.
  • the feedstock comprises between 0.1% and 2%, preferably less than 0.5% of a dispersant, in percentages by weight relative to the mass of the dry feedstock.
  • the dispersant may for example be chosen from alkali metal polyphosphates or methacrylate derivatives. All the known dispersants are conceivable, pure ionic, pure steric, for example of the sodium polymethacrylate type, or both ionic and steric. The addition of a dispersant makes it possible to better distribute the fine particles, of size less than 150 microns, and thus promotes the mechanical strength of the matrix.
  • a phosphate dispersant must be taken into account to determine the amount of phosphorus remaining to be optionally added to the feedstock.
  • a binder can still be added to the feedstock.
  • the function of the binder is to allow the particulate mixture of the feedstock to retain its shape until sintering.
  • the choice of binder is dependent on the desired shape.
  • a lime cement type hydraulic binder may be advantageous for curing the preform and imparting good mechanical strength to the sintered material.
  • the total content of alkaline earth oxides, and in particular CaO, in the feedstock may be greater than 0.2%, as a percentage by weight relative to the mineral mass of the dry feedstock.
  • the total content of alkaline earth oxides in the feedstock is less than 2%, preferably less than 1, 5%, or even less than 1%, in percent by weight relative to the mineral mass of the dry feedstock.
  • These oxides are indeed detrimental to refracting and deformation under load. In addition, these oxides can harm the nitru ration.
  • the dry starting batch is dry blended sufficiently to obtain a homogeneous mixture.
  • water is conventionally added to the feedstock.
  • at least 2%, preferably at least 2.5%, and / or less than 10%, or less than 8%, or even less than 5%, of water, are added in percentages. mass relative to the mineral mass of the dry feedstock.
  • the water is gradually added to the mixer in operation until a substantially homogeneous wet mixture is obtained.
  • step b) the wet mixture is cast in a mold shaped for the production of a block of the desired dimensions, for example 1.0 ⁇ 0.8 ⁇ 0.25 m 3 .
  • at least one of the dimensions of the block, or all the dimensions of the block is greater than 0.15 m, or greater than 0.25 m, or even greater than 0.4 m.
  • the content of the mold may for example undergo a vibration step and / or tamping and / or pounding and / or pressing.
  • a vibration step and / or tamping and / or pounding and / or pressing are examples of a vibration step and / or tamping and / or pounding and / or pressing.
  • a conventional vibrating needle such as those used in civil engineering.
  • the vibration of the needle within the wet mixture is preferably maintained for a period of between 3 and 20 minutes, depending on the size of the block.
  • the mold is preferably covered with a tarpaulin to reduce surface drying.
  • the mold is preferably immediately placed in an oven, at the end of the compaction, at a temperature preferably greater than 40 ° C. and preferably less than 60 ° C., and for a variable duration depending on dimensions of the block, usually from a few hours to 24 hours.
  • the preform is then demolded (step d)) and then dried (step e)). Drying can be carried out at a moderately high temperature. Preferably, it is carried out at a temperature of between 1 and 200 ° C, preferably under air or humidity controlled atmosphere. It typically lasts between 10 hours and one week depending on the format of the preform, preferably until the residual moisture of the preform is less than 0.5%.
  • the demolded preform advantageously has sufficient mechanical strength to be handled, transported and possibly assembled.
  • the dried preform is then cooked (step f)).
  • the duration of the cooking generally between 3 and 15 days of cold cold, varies depending on the materials but also the size and shape of the block.
  • the cooking is preferably carried out under nitrogen. Baking in a neutral atmosphere, for example under argon, is also possible if the nitrogen is supplied by the raw materials.
  • the firing cycle is preferably carried out under a nitrogen pressure close to 1 bar, but a higher pressure could also be suitable, and at a temperature preferably between 1300 0 C and 1600 0 C.
  • the nitrogen reacts ("reactive sintering") with some of the constituents of the preform, in particular with the calcined alumina and the silica in micron form and the metal powders, to form the matrix and thus bind the grains of the aggregate.
  • the matrix comprises a crystallized phase of SiAION. It is obtained exclusively from the constituents of the feedstock and, where appropriate, constituents of the gaseous environment of this feedstock during sintering.
  • the matrix substantially surrounds the grains of the granulate, that is to say the coats.
  • a matrix obtained by reactive sintering has particularities. Especially during the reactive sintering, nitriding of the metals occurs.
  • the resulting increase in volume typically from 1 to 20%, advantageously makes it possible to fill the pores of the matrix and / or to compensate for the shrinkage caused by the sintering of the grains.
  • the reactive sintering thus makes it possible to improve the mechanical strength of the product.
  • the reactively sintered products thus have an open and / or closed porosity that is significantly lower than that of the other products sintered under conditions of similar temperature and pressure. During cooking, the sintered products reactively have substantially no shrinkage.
  • Weight gain is an indicator of cooking quality for a particular cooking process.
  • a sintered block is obtained.
  • the The preform can be put in place in its operating position without having been sintered, the sintering being carried out in situ.
  • a sintered block having a reduced open porosity and outstanding cold crushing and bending strengths is obtained. More specifically, the product has a cold crushing strength greater than or equal to 50 MPa, or even greater than 100 MPa.
  • the homogeneity of the nitriding is illustrated by the low content of residual metals, in particular silicon. This content is in fact less than 1, 8%, less than 1, 5%, or even less than 1%, as a percentage by weight on the basis of the product, even in the heart of the blocks.
  • phase AIN15R which is a well-known phase of the type [4 (AIN)] (SiO 2 ), typically represents more than 5% or even more than 10% of the nitrogen-containing crystalline phases of the matrix, in percentages by weight.
  • the manufactured block can then be assembled to form a part of an oven according to the invention.
  • it may constitute a part of a heating partition of this furnace, in particular a part in contact with the internal volume of a heating partition through which the heating gases circulate.
  • a feedstock was made by dry blending the various constituents added as powders. The water was then gradually added to the mixer in operation to obtain a mixture of a consistency suitable for pouring into the mold.
  • the mold was consistent with the manufacture of blocks of dimensions 300mm x 300mm x 75mm for examples 1 and 3, and dimensions 300mm x 300mm x 250mm for examples 2 and 4.
  • a vibration step was performed by means of a vibrating needle of the civil engineering type for a period of between 1 and 5 minutes.
  • the mold was then covered with a tarpaulin in order to limit the surface drying, then immediately placed in an oven at a temperature of about 40 to 60 ° C., for a duration of about 10 hours in order to facilitate the hardening of the product.
  • the block was then demolded and then subjected to drying at 110 ° C. under air so that the residual humidity is less than 0.5%. Finally, the dried block was fired under nitrogen at 1500 0 C for at least 10 hours.
  • SiC silicon carbide powder having substantially the following particle size distribution, in percentages by weight:
  • silica fume of the 983 U type marketed by the Elkem Company
  • calcined alumina powder AC 44B4 having a median size of approximately 4 microns, marketed by the Alcan Company
  • HMPNa sodium hexametaphosphate powder, sold by the Rhodia Company, lime aluminate cement CA 270, sold by the Alcoa Company.
  • Open porosity and bulk density were measured according to ISO 5017. Measurements of mechanical resistance to cold crushing were carried out on cylindrical specimens of 50 mm in diameter and 50 mm in height cut at the heart of the blocks, according to standard NFB 40322.
  • Nitrogen (N) contents in the products were measured using LECO analyzers (LECO TC 436DR, LECO CS 300). Values are provided in percentages by mass.
  • the phosphorus contents were conventionally measured by X-ray fluorescence.
  • the crystallized phases were measured by X-ray diffraction. The phases are expressed as a percentage by weight of the crystallized phases present in the product.
  • the thermal conductivity was measured by the laser flash method according to recommendation EN821-2.
  • the CO resistance was measured according to ASTM C288.
  • the letter A corresponds to an absence of visible degradation after
  • test pieces of 150 * 25 * 25 mm 3 are placed in a mixture of potassium carbonate and coke. The mixture is heated to 925 ° C and maintained at this temperature for 6 hours.
  • L 0 denotes the initial length of the specimen (150 mm)
  • the relative decrease in length during the test (LL o ) / L o is an indication of the corrosion resistance.
  • Table 1 provides the values (LL o ) / L o .
  • the creep resistance was evaluated by the loss of height, in percentage, during a treatment under air, at 1350 ° C., under a pressure of 2 bars for 20 hours, according to the ISO3187 standard. The greater the loss of height of the tested specimens, the lower the creep resistance.
  • the resistance to sagging under load was carried out according to the ISO1893 standard, under air, under a pressure of 2 bar.
  • the table specifies the temperature, in 0 C, corresponding to a decrease in height of the tested test piece by 0.5%. The higher this temperature, the better the product resists sagging.
  • Examples 1 to 4 show a high resistance to creep and a very high resistance to sagging under load.
  • Examples 1 to 4 exhibit a high cold crush resistance that allows them to withstand mechanical attack during the loading of carbonaceous blocks, and in particular to abrasion.
  • Examples 1 to 4 have a very low permeability, which advantageously contributes to reinforcing the sealing of the heating walls with respect to the hot gases.
  • Examples 1 to 4 have an improved thermal conductivity, that is to say, increased by about three times that of the reference example, or even more than 10 if the granulate is SiC. This higher thermal conductivity is conducive to better heat transfer of the heating walls. It also contributes, in combination with the high mechanical strength and the moderate coefficient of thermal expansion, to improve the resistance to thermal gradients, and therefore to thermal cycling.
  • the invention is not limited to the embodiments described, provided by way of illustration and not limitation.
  • the region of a furnace according to the invention consisting of a sintered refractory material formed by a matrix-bound granulate is not limited to a partition of this furnace.

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EP09744483A 2008-10-29 2009-10-26 Ofen zur verbrennung von kohlenstoffblöcken Withdrawn EP2340408A1 (de)

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FR0857369A FR2937637B1 (fr) 2008-10-29 2008-10-29 Four de cuisson de blocs carbones
PCT/IB2009/054730 WO2010049878A1 (fr) 2008-10-29 2009-10-26 Four de cuisson de blocs carbones

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FR2953512B1 (fr) * 2009-12-09 2017-03-31 Saint Gobain Centre De Rech Et D'etudes Europeen Produit refractaire a matrice de siaion dope bore
CN101936659A (zh) * 2010-10-14 2011-01-05 四川省眉山市金石耐火材料有限公司 敞开式阳极焙烧炉模块式火道墙

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EP0482984A1 (de) * 1990-10-24 1992-04-29 Savoie Refractaires Feuerfest Erzeugnisse durch eine Sialon-Matrix gebunden und Verfahren zu ihrer Herstellung

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DE242849T1 (de) * 1986-04-21 1989-01-05 Vesuvius Crucible Co., Pittsburgh, Pa. Mit kohlenstoff gebundene feuerfeste koerper.
US5078595A (en) * 1989-07-14 1992-01-07 Roenigk Howard L Carbon flue wall and method of making
JPH0769744A (ja) * 1993-06-28 1995-03-14 Hitachi Metals Ltd 耐火性被覆材およびアルミニウム溶湯用部材
JPH07126072A (ja) * 1993-10-28 1995-05-16 Hitachi Metals Ltd 窒化物系耐火物、その製造方法およびそれを用いたアルミニウム溶解・鋳造用部品

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