TECHNICAL FIELD TO WHICH THE INVENTION The present invention relates to the production of calcium aluminate.

It concerns more particularly a method for continuously calcium aluminates implementing an industrial melting furnace.

BACKGROUND

Calcium aluminates, through their hydraulic and binding properties, used to manufacture cement or concrete with many qualities. Aluminous cements indeed resist to aggressive agents and high temperatures. They are the source of many technical products such as special mortars, refractory concrete, etc. They can also be used as reactive mineral associated with other components. They are thus used in various industries, such as the refractory industry, chemical construction, metallurgical flux (trapping molten metal impurities) or in the pipe industry and sanitation.

Calcium aluminates may have various mineralogical phases such as 3CaO.AI 2 O 3 (C3A in cement notation) CaO.AI 2 O 3 (CA), CaO.2AI 2 O 3 (CA2), CaO.6AI 2 O 3 (CA6) or 12CaO.7AI 2 O 3 (C12A7). These mineralogical phases, which reflect both the structure at the atomic scale that the chemical composition of calcium aluminate, influence the final properties, such reactivity, said calcium aluminate.

In addition, final, and in particular reactive properties, the calcium aluminate-based products based in part on the amount of alumina (Al 2 O 3 ) and / or aluminum (Al) and calcium oxide (lime or CaO) and / or calcium (Ca) contained in calcium aluminate. Is often called a calcium aluminate by its mass ratio Al / Ca, ie the ratio between the total mass of aluminum and the total mass of calcium contained in calcium aluminate.

Currently, calcium aluminates are produced mainly by means of two high-temperature processes, namely according to a method by sintering or by a melt process in cement kilns, such as sintering furnaces, rotary furnaces flames, vertical melting furnaces or electric melting furnaces.

For example from document discloses FR2291 162 a process for producing the sintering calcium aluminates which comprises calcining, that is to say heating in the solid state raw material sources of calcium, for example lime CaO , and raw materials sources of aluminum, for example, alumina Al 2 O 3 , in a rotary kiln flame at a temperature between 1400 ° C and 1600 ° C.

In general, a rotary kiln consists of a tube, slightly inclined, coated on its inside with refractory bricks, a flame being disposed at the lowermost end of the tube. Sources of calcium and aluminum are then introduced into the furnace through the uppermost end. They are then usually heated to a temperature between 1400 and 1600 degrees Celsius (° C) for a period of envircn 30 minutes before being discharged into the lower part, close to the flame.

Such sintering process consists of a surface reaction between the powdery raw materials which react together without a generalized liquid state.

According to the method described in this document FR2291 162, the raw materials used should have a particle size less than 208 microns to permit their calcination. The resulting clinker has over 80% of mineralogical phase CA.

It is therefore necessary to finely grind the raw materials, which is costly and burdensome.

Are also known the document FR1013973, a process for producing calcium aluminates by fusion which comprises heating up the liquid raw material sources of calcium and aluminum in a flame rotary furnace at temperatures 1430 ° C to 1450 ° C.

Calcium sources raw materials (limestone CaCO 3 ) and aluminum (ferruginous bauxite, a mineral rich rock alumina and containing iron, silica and other compounds in varying amounts) used in such a process are first ground very finely in order to pass through a sieve No. 4900, then mixed and compacted to been in the form of briquettes. The briquettes generally have an average size between 15 millimeters (mm) to 20 centimeters (cm).

According to the method described in this document FR1012973, the procedure is discontinuous and sequential manner: first loads the raw material briquettes, then heating the raw material briquettes by slowly rotating the furnace until a mass uniform melt, and is finally evacuated by pouring tube the melt. In practice, it retrieves the melt immediately after reaching the melting temperatures of the raw materials.

Is known on the other hand the document DE21 16 495, a method for producing fusion calcium sulfo-aluminates in an electric furnace.

The raw materials used in this process are a source of alumina whose average particle size (that is to say the maximum value of the particle size distribution) is less than 5 mm and a calcium oxide source such as the lime whose average particle size is one to ten times greater than that of alumina.

The method described in this document DE21 16 495 is a block method, a sequence corresponding to the load of the raw materials, melting them, and a partial discharge of the melt.

Thus, these processes are known fusion implemented in furnaces in which it is necessary to operate in a sequenced manner and discontinuous.

In addition, the known melting furnaces have several modes of operation (e.g., a charge operation and a discharge mode of operation) and their operation requires many passages from one mode of operation to another.

Finally, we know that a vertical melting furnace can be used to make fusion processes.

This vertical melting furnace has a vertical portion whose height can reach about ten meters and a generally horizontal portion from which is recovered the liquid mass of calcium aluminates obtained.

More particularly, load through an opening in an upper region of the furnace blocks of limestone and bauxite in the vertical part of the melting furnace and heated by a flame disposed in a lower region of the furnace. The flame heats the blocks at a temperature of 1500 ° C to melt and form a liquid mass which is directly recovered by a tap hole.

During the process, the flue gases are formed and take a path against the current of one of the blocks. They are discharged through a chimney located in the upper area of ​​the oven, in its vertical part. These combustion gases having a temperature greater than 1500 ° C, flowing between the blocks and preheat.

Before being brought into contact with the flame, the blocks of raw materials thus undergo a drying and dehydration and decarbonation by the combustion gas flowing up the vertical part of the melting furnace.

Such a process requires the use of raw materials into blocks excluding fine particles which would cause blockages and damage to the vertical part of the melting furnace.

Thus, the methods for producing calcium aluminates by fusion or sintering are known binding in terms of particle size of raw materials used (fine grinding of raw materials, milling and compaction in the form of briquettes; specific particle size ratio between the lime and alumina; or use of bauxite blocks).

In particular, in the case of the melt process in a vertical melting furnace, bauxite blocks are less commercially available. In addition, during extraction, the production yield of bauxite blocks is low. Indeed, for 100 tons of ore, only obtained 10 tons of raw bauxite comprising themselves 8 tons of fine non-usable particles in the melt process in the shaft furnace, and 2 tons of bauxite usable blocks, together with 90 tonnes of waste can not be used by industries.

OBJECT OF THE INVENTION

To remedy the aforementioned drawbacks of the prior art, the present invention provides a calcium aluminate manufacturing process fusion few restrictions regarding the size of the raw material, which does not require the use of blocks bauxite and which recovers fine particles of extracted raw materials that are available on the market. In addition, the present invention provides a process wherein the oven operating mode changes are limited.

More particularly, the invention provides a method

calcium aluminate in an industrial furnace, wherein:

a) is introduced continuously into a tank made of refractory material containing a molten bath heated continuously, fine particles of a first alumina source material (Al 2 0 3 ) and / or aluminum (Al) and a first source of calcium oxide material (CaO) and / or calcium (Ca) having a median diameter d50 less than or equal to 6000 μιτι to melt said fine particles of raw material, and

b) is recovered continuously, tank outlet a mass of liquid calcium aluminates.

The median diameter d50 of any set of particles is a magnitude representative of the statistical distribution of sizes of these particles, ie the size of this set of particles.

The median diameter d50 is a reference diameter defined as the diameter below which is 50% of the fine particles used, by weight based on the total weight of all of said fine particles.

In other words, for a set of fine particles having a median diameter d50 given, 50% by weight of such fine particles has a diameter less than said median diameter d50 given, and 50% by weight of such fine particles has a diameter greater than that median diameter d50 given.

Here, the term "diameter" the largest dimension of the particle, whatever its form.

The median diameter d50 of an assembly of fine particles is obtained from a particle size distribution curve representing the statistical distribution of the size of each of fine particles of the set.

In practice, the median diameter d50 of a set of fine particles can be determined by various techniques, such as sedimentation method (detection by absorption RX) or the laser diffraction method (ISO 13320).

In the context of the present invention, the size of fine particles is measured according to ISO 13320 standard by the laser diffraction method with, for example, a particle size analyzer Mastersizer 2000 laser or 3000 type sold by the company Malvern.

Advantageously, the method according to the invention makes it possible to use both very fine particles as fine particles of raw materials.

In other words, thanks to the process according to the invention, the particle size constraints on the raw materials used are greatly reduced.

In particular, thanks to the process according to the invention, it is not necessary to use particles in the form of blocks, or to compact already fine particles, or to reduce the form of very fine particulate powder.

In addition, thanks to the process according to the invention, the introduction of raw materials and recovery of the body of liquid calcium aluminates are performed continuously, throughout the operation of the furnace. The furnace thus operates substantially in accordance with a stable mode of operation, without transitions from one mode of operation to load a mode of discharge operation. In this stable mode of operation of the furnace according to the method of the invention, the usual operating parameters of the oven, such as heating temperature, the particle size of the feed particles, the chemical composition of raw materials introduced can be adjusted.

Advantageously, the manufacturing method of the invention uses fine particles of raw material, not emphasized in the current technology, from the mining and ore processing to produce by melting the calcium aluminates.

Thus, the method according to the invention allows the use of raw materials usable in the melt process in the current vertical melting furnaces.

In addition, here, these fine particles are directly immersed in a calcium aluminate bath heated to a temperature that allows their fusion. thus recovered output tank calcium aluminate homogeneous liquid mass, that is to say without unmelted.

The term "unmelted" raw material particles still in solid form, which have not reacted during the process.

Moreover, the process according to the invention, and in contrast to existing prior art processes, it is possible to prevent the achievement of preliminary stages of dehydration and decarbonization of raw materials, the dehydration and the intervening decarbonization directly into the melt.

Moreover, the process according to the invention, the bubbles generated by the calcining of the raw materials when they melt in the melt naturally involved in mixing this melt. This natural shear mixing the fine solid particles in the liquid material in the melt, thereby promoting the fusion of said fine particles. Therefore, this natural brewing helps to improve the homogeneity of the liquid mass of calcium aluminate obtained. The method according to the invention thus stabilizes the quality of finished products.

Advantageously, in step a) of the manufacturing method according to the invention, the melt is placed under a reducing atmosphere comprising carbon monoxide (CO).

In particular, said reducing atmosphere comprises an average of nearly 0.1% to 100% carbon monoxide (CO).

Advantageously, the reducing atmosphere in which is placed the melt makes it possible to control, at least partly, the mineral phases calcium aluminates obtained, for a given proportion of lime and alumina contained in said calcium aluminate.

The "mineralogical phases" describe both the structure at the atomic scale and the chemical composition of calcium aluminate. For example, these mineral phases are: C3A phase (3CaO.AI 2 O 3 ), the AC phase (CaO.AI 2 O 3 ), CA2 phase (CaO.2AI 2 O 3 ), the CA6 phase (CaO. 6Al 2 O 3 ) or the C12A7 phase (12CaO.7AI 2 O 3 ).

calcium aluminate used as the hydraulic binder, that is to say, as a material capable of reacting with water to form a paste which hardens in cold agglomerating aggregates them, generally contain an amount CA important mineralogical phase, which allows the development of high mechanical strength after the hydraulic jack.

The term "hydraulic jack" hardening of the hydraulic binder.

It turns out further that the mineralogical phase C12A7 influenced the reactivity of the calcium aluminate used as hydraulic binder.

Specifically, the C12A7 mineralogical phase is an accelerator for calcium aluminate outlet whose main phase is the mineralogical phase CA. In other words, calcium aluminate harden more quickly in contact with the water they contain a large proportion of C12A7 mineralogical phase, compared to other mineralogical phases may be contained in said calcium aluminate.

Thus, the mineralogical phase C12A7 has a strong impact on the workability of the hydraulic binder, and its short-term cure. In particular, a variation of the proportion by mass of the C12A7 phase calcium aluminate of a few percent, or less than 1 percent, can have a measurable impact on the workability and curing of the hydraulic binder.

The calcium aluminate can be used for various applications, based on which a user will prefer a quick hydraulic jack or slow, it is particularly interesting to be able to control the proportion of C12A7 mineralogical phase contained in the calcium aluminate. The target proportion of C12A7 mineralogical phase contained in the calcium aluminate for a given application is determined for example with an accuracy of between 0.1% and 0.5%, for example equal to 0.1%; 0.2%; 0.3%; 0.4%; 0.5%.

Advantageously, the method according to the invention allows such control. Other non-limiting and advantageous features of the method according to the invention, individually or in all technically possible combinations, are:

- the temperature of the calcium aluminate of the melt is between 1300 ° C and 1700 ° C;

- the temperature of the calcium aluminate of the melt is between 1400 ° C and 1600 ° C;

- the residence time of said fine particulate raw material in said molten bath of calcium aluminates is less than 24 hours;

- the residence time of said fine particulate raw material in said molten bath of calcium aluminates is between 30 minutes and 9 hours;

- in step a), the raw material source of alumina and / or aluminum introduced into the vessel is selected from: bauxite, corundum grinding wheels, catalyst supports, refractory bricks, hydroxides, metallurgical aluminas, calcined aluminas and melted, by-products of the aluminum industry and not conform to manufacturing high alumina or a mixture thereof, and the first source of calcium oxide material and / or calcium introduced in the vessel is selected from: limestone, lime and byproducts from consuming processes limestone and lime as

dairy or slag or steel electrometallurgy, or a mixture thereof;

- the fine raw material particles have a median diameter d50 of between 100 and 1000 μιτι μιτι;

- the fine raw material particles have a median diameter d50 of between 150 and 500 μιτι μιτι;

- after step b), cooling the mass of liquid calcium aluminates recovered tank outlet;

- cooling occurs naturally;

- the cooling is carried out in a controlled manner;

- milled mass calcium aluminate cooled to form a calcium aluminate cement;

- said fine particles of the first alumina source material (Al 2 0 3 ) and / or aluminum (Al) and raw material source of calcium oxide (CaO) and / or calcium (Ca) are introduced into the tank in the form of a loose powder.

DETAILED DESCRIPTION OF AN EMBODIMENT The following description in the accompanying drawings, given by way of non-limiting example, explains in what the invention is and how it can be achieved.

In the accompanying drawings:

- Figure 1 is a size distribution curve of a first set of bauxite particles suitable for the process according to the present invention;

- Figure 2 is a bar graph representing the distribution of the diameters of a second set of bauxite particles suitable for the invention;

- Figure 3 is a bar graph representing the distribution of diameters of a third set of bauxite particles suitable for the invention;

- Figure 4 is a bar graph representing the distribution of diameters of a fourth set of bauxite particles suitable for the invention; and

- Figure 5 is a schematic cross-sectional view of a furnace for the implementation of the calcium aluminates manufacturing process according to the invention.

In the following description, and unless otherwise specified, the indication of a range of values ​​"X to Y" or "between X and Y" is understood to include the X values Y.

Device

In Figure 5, partially and schematically shows an example of furnace 1 suitable for implementation of the calcium aluminate manufacturing method according to the present invention.

Overall, oven 1 comprises a horizontal vessel 15 - a sort of pool - covered by a roof 5, and an exhaust opening of the fumes (not shown).

This vessel 15 is adapted to contain a molten bath 1 1 obtained and maintained in the liquid state by a heating system 10 of the furnace 1.

The tank 15 is also adapted to receive through an inlet opening 9 of the solid raw materials 7 and discharging through an outlet opening 12 of the melt, ie a mass of 16 liquid calcium aluminates.

For this purpose, the furnace 1 comprises a charging system 2 of the raw materials 7 connected to the inlet opening 9 of the tank 15, and an exhaust system 3 of the melt connected to the outlet opening 12 the tank 15.

As explained in detail below, this arrangement creates a flow of material between the inlet 9 of the tank 15 and junction 12 of the tank 15.

In this furnace 1, there is therefore a real flow of material supplied by the raw material 7 fed continuously through the inlet opening 9, which are processed in the melt 1 1 liquid calcium aluminates, themselves discharged through the outlet opening 12.

We shall speak hereinafter of "dwell time" to indicate the time that elapses between the introduction of a raw material particle in the melt 1 1 of the tank 15 of the furnace 1 and its evacuation by the outlet opening 12.

Specifically, as shown in Figure 5, the tank 15 defines a generally rectangular volume here.

The walls of the tank 15 comprise in particular a sole 4 forming the bottom of the tank 15 and a peripheral wall 14 which rises vertically from the hearth 4.

The sole 4 has here a rectangular shape so that the peripheral wall 14 comprises four panels arranged in pairs at right angles.

Of course according to other embodiments of the oven, the tank may have a different shape. In particular, the sole and the peripheral wall may have different shapes and form between them at different angles to maximize the flow between the inlet and the outlet of the tank but also the distribution of the raw material in the bath melting and evacuation of the molten material.

One of these four panels of the peripheral wall 14, called the input panel includes the inlet opening 9 of the container 15 enabling the charging system 2 of the raw materials 7 to access the vessel 15.

The panel opposite the input panel, called output panel, comprises the exit opening 12 of the tank 15, also called taphole, for connecting the vessel 15 to the exhaust system 3 of the melt.

The portion of material flow is thus in the longitudinal direction of the furnace 1 from the inlet opening 9 to the outlet opening 12 of the tank 15.

The raw material stays more or less time in the tank 15 depending on the size of the tank 15.

The surface of the laboratory vessel 15, that is to say the internal surface of the vessel 15 intended to be in contact with the bath of Fusion 1 1 is between 20 m 2 and 200 m 2 , preferably it is equal to about 100 m 2 .

The walls of the vessel 15 and the arch 5 are coated internally with an inert refractory material chemically with the calcium aluminates.

The refractory material of the tank 15 and / or the arch 5 is selected from the agglomerated refractory materials or electrocast refractory materials and / or mixtures thereof.

Specifically, the nature of refractory materials can be used according to their location in the oven (vault tank) and associated stresses. Thus, it is possible to use agglomerated or fused-cast refractory material for the arch 5 and electrocast refractory materials for the tank 15.

These two families of electrocast agglomerated refractory materials and are differentiated primarily by their forming methods: casting a cast type for the electrocast refractory materials and sintering in the case of agglomerated refractory materials.

Thus, the agglomerates are sintered refractory ceramic materials, large or small grains obtained by unidirectional or isostatic pressing, or by vibrocasting by slip casting. They are characterized by an open porosity of up to 20% reduced in the case of isostatically pressed materials. In this category, there are several chemical compositions of refractory products. The most common chemistries agglomerated refractory materials are summarized in Table 1 below.

These chemical compositions are given in weight percent. The weight percentage of compounds (MgO, Cr0 3 , Al 2 0 3 , Zr0 2 , Si0 2 , CaO, Fe0 3 ) is sometimes given as A / B, which means that the agglomerate in question refractory material comprises, by weight relative to the total weight of said refractory consolidated material, A% to B% of compound.

Table 1

Electrocast refractory materials have a lower porosity than the agglomerated refractory materials. They also have an organization of the crystalline structure to dramatically increase their resistance to corrosion.

There are four main families of electrocast refractory materials: alumina - zirconia - silica (AZS), the Alumina - Zirconia - Silica -Chrome (CBAHWs), Very High Content Zirconia (THTZ) and High Alumina content (HA) .

Table 2 below summarizes the chemical compositions of some fused-cast refractory materials. These chemical compositions are

data by percentage weight. As in Table 1, the weight percentage of compounds is sometimes given as A '/ B', which means that the electro-cast refractory material in question comprises, by weight based on the total weight of said electro-cast refractory material, A ' % to B '% compound.

Table 2

The tank 15 thus formed is adapted to contain the melt January 1. This merger is January 1 bath here is bath of molten calcium aluminate.

The heating system 10 is adapted to heat permanently bath Fusion 1 1 contained in the tank 15.

Here, the heating system 10 equips the inside of the arch 5.

It is preferably a 10 per combustion heating system which comprises flame burners, such as oil burners or gas.

For example, there is an air combustion heater system wherein the oxidant is the oxygen (0 2 ) from the air.

Provision could also be an oxy-fuel heating system wherein the oxidant is dioxygen (O 2 ) from a source of pure oxygen.

In addition, the furnace 1 may optionally comprise a regenerative heat system not shown here.

The regenerator system is made of refractory materials such as those used for the roof 5 or the vessel 15.

Advantageously, this heat regenerator system is generally associated with the heating system 10 for recycling the combustion energy. It increases the thermal efficiency of the furnace. This is for example refractory brick stacks crossed by many channels which circulate alternately the gases of combustion and air or pure oxygen for combustion: gases yield their energy to restore the bricks during the passage of air or pure oxygen.

In an alternative not shown oven, one could predict that the

heating system or electric melting bath.

This heating system may include, for example dipping electrodes or electrodes arranged in the vessel bottom.

These electrodes may be electrodes made of molybdenum.

Furthermore, from an overall point of view, the container 15 surmounted by a roof 5 form a closed chamber containing the partially melt January 1.

It is possible to choose the composition of gases in the chamber above the tank 15.

Advantageously, here the chamber in close part is adapted to receive a gas mixture containing carbon monoxide (CO) which forms a reducing atmosphere above the tank 15.

More specifically, said reducing atmosphere comprises gases in contact with the bath surface of Fusion 1 1 contained in the tank 15.

With the heating system 10 by the combustion furnace 1 described above, namely the air combustion heating system or the oxyfuel combustion heating system, the atmosphere in the chamber naturally contains carbon monoxide (CO) from combustion.

In particular, it is possible to control the carbon monoxide content (CO) gas contained in the enclosure by precisely controlling the combustion reaction, and in particular the stoichiometry of the oxidising reactants (O 2 ) and fuel (oil, gas) .

Advantageously, it may also be provided to add a feed of the enclosure system carbon monoxide (CO) (not shown).

In the furnace 1 with the heating system 10 by combustion, the carbon monoxide content (CO) is not uniform throughout the enclosure, that is to say, it is not identical in all points of the enclosure. In general, for the reasons set out above stoichiometry, it is generally stronger near the flame burners.

We then speak of "average" content of carbon monoxide (CO). This content "average" carbon monoxide (CO) is evaluated in the gas discharged from the enclosure through the opening of smoke outlet (not shown) of the furnace 1. It is for example measured by a sensor disposed in a smoke exhaust duct into which said exhaust opening of the fumes.

In the case of the variant comprising the electrical heating system, the oven will necessarily be provided with an artificial addition of carbon monoxide system (CO).

The electric furnace may also comprise control means of the carbon monoxide (CO) content of the atmosphere contained in the enclosure.

This means of controlling the carbon monoxide content (CO) allows to precisely adjust the carbon monoxide content (CO) in the enclosure.

Carbon monoxide (CO) is, for example pure injected into the chamber where it mixes with the ambient air. It can also be introduced directly mixed with air.

It can also be injected pure so that the enclosure comprises only carbon monoxide (CO).

On the other hand, as best seen in Figure 5, the charging system 2 of the furnace 1 is connected to the inlet opening 9 of the tank 15.

This charging system comprises a silo 2 6 funnel for storing or homogenizing raw material 7, and a ramp 8 for the introduction of these raw materials 7 in the tank 15 via the inlet opening 9 of the tank 15.

The ramp 8 is a conduit having one end connected to the outlet of the silo 6 and whose other end opens into the inlet opening 9 of the tank 15.

Raw materials 7 may be moved by gravity from the silo 6 to the inlet of the vessel 15 via the ramp 8. A pusher system (not shown) may be provided to force the circulation.

In practice, here said raw materials 7 include a first alumina source material (Al 2 O 3 ) and / or aluminum (Al), and a first source of calcium oxide material (CaO) and / or calcium (It).

Said first alumina source material (Al 2 O 3 ) and / or aluminum (Al) means any chemical compound comprising an atom of group AI 2 O 3 and / or an aluminum atom.

Similarly, said first source material of calcium oxide (CaO) and / or calcium (Ca) means any chemical compound comprising a group

of CaO atom and / or a calcium atom.

Thus, alternatively, the silo 6 can optionally include two separate compartments (not shown) adapted to receive respectively said first alumina source material (Al 2 0 3 ) and / or aluminum (Al), and said first source material calcium oxide (CaO) and / or calcium (Ca). One could for example envisage that these separate compartments open downstream into a common part of the silo 6 located upstream of the output of said silo 6. In this joint portion, said first source of alumina material (Al 2 O 3 ) and / or aluminum (Al) and said first source of calcium oxide material (CaO) and / or calcium (Ca) are then mixed to form the raw material 7.

Regardless of the variant envisaged the charging system 2, this charging system 2 used for supplying the melt 1 1 raw material 7, and it continuously.

In addition, as shown clearly in Figure 5, the exhaust system 3 of the furnace 1 is connected to the outlet opening 12 of the tank 15.

The exhaust system 3 of the body of liquid 16 calcium aluminate comprises an exhaust duct 13 connected on one side to the outlet opening 12 of the tank 15, and which opens on the other side, a cooling zone (not shown) of the calcium aluminates.

The outlet opening 12 of the vessel 15 is a so-called outlet "overflow" to the extent that the molten material, namely molten calcium aluminate, is discharged from the tank 15 by overflowing thereof into the conduit discharge 13.

Advantageously, this outlet opening 12 to overflow is compatible with the very high temperatures of Fusion 1 1 bath.

Process

In the following description, we will detail more specifically the process of calcium aluminate production implemented by an operator in industrial furnace 1 described above.

Remarkably, according to this method:

a) is introduced continuously into the vessel 15 made of refractory material containing the bath of Fusion 1 1 Heat continuously, fine particles of said first alumina source material (Al 2 O 3 ) and / or aluminum ( al) and said first source of calcium oxide material (CaO) and / or calcium (Ca)

having a median diameter d50 less than or equal to 6000 μιτι to melt said fine particles of raw material, and

b) recovering, in continuous and vessel outlet 15, a mass 16 of liquid calcium aluminates.

In a step prior to step a), the operator prepares the melt January 1.

For this, the commissioning of the furnace 1, the tank 15 is initially charged in a preliminary mixing calcium aluminate.

This premix is ​​heated by the heater 10 so as to obtain a liquid mass without unmelted, of molten calcium aluminate. This liquid mass then form the initial melt in the vessel 15 at the beginning of the implementation of the manufacturing process according to the invention.

The Fusion 1 1 bath is formed by the initial melt, to which is added said first alumina source material (Al 2 0 3 ) and / or aluminum (Al), and said raw material oxide source calcium (CaO) and / or calcium (Ca), which will melt in their turn.

Thus, in the following description, the Fusion 1 1 designates a bath liquid mass without unmelted, of molten calcium aluminate.

The volume of the initial melt is such that it is flush with the outlet opening 12 to the overflow tank 15.

The weight ratio Al / Ca premix calcium aluminate initially charged into the tank 15, namely the ratio between the total mass of aluminum (Al) and the total mass of calcium (Ca) contained in this preliminary mixture, is close to that of calcium aluminate that the operator wishes to get the tank outlet 15, but not necessarily identical to this one.

Indeed, the weight ratio Al / Ca of the calcium aluminate content in the chamber 15 - that is to say forming the melt 1 1 - evolves during the process, by the introduction to the step a), raw materials 7. Thus, it should be understood that the weight ratio Al / Ca of the calcium aluminate recovered tank outlet 15 may be different from that of the initially charged calcium aluminate in the vessel 15.

The mass ratio Al / Ca calcium aluminate recovered tank outlet 15 tends to become equal to the mass ratio Al / Ca commodities

introduced.

Thus, there is a transient state in which the mass ratio Al / Ca calcium aluminate recovered tank outlet is different from the mass ratio Al / Ca of introduced raw materials.

At the end of the transitional regime, the mass ratio Al / Ca calcium aluminate recovered tank outlet becomes equal to weight ratio Al / Ca raw material introduced entrance tank.

Conventionally, it is estimated that the duration of the transitional regime is at most equal to 5 times the residence time of the particles in the vessel 15.

For example, for a residence time of about 1 hour, it is estimated that the transitional regime ended after 5 hours.

In step a), the operator loads the charging system 2 material 7 containing a first alumina source material (Al 2 0 3 ) and / or aluminum (Al), and a first source material calcium oxide (CaO) and / or calcium (Ca).

At this stage a), the operator enters into the furnace 1, via the inlet opening 9 of the tank 15 in the form of fine solid particles, said first source of alumina material (Al 2 0 3 ) and / or aluminum (Al), and said first source of calcium oxide material (CaO) and / or calcium (Ca).

Here, the term "fine particles" a loose powder having a median diameter d50 less than or equal to 6000 μιτι.

The loose powder is considered a split state of the solid matter which is then in the form of very small pieces.

Advantageously, a free powder having a median diameter d50 such has a large specific surface favorable to its melting in the melt 1 January.

The sets of fine particles having a median diameter d50 less than or equal to 6000 μιτι are for example those having the following d50 median diameter: 6 mm; 5 mm; 4 mm; 3 mm; 2 mm; 1 mm; 500 μιτι; 250 μιτι; 150 μιτι; 100 μιτι; 50 μιτι; 25 μιτι, and lower.

Preferably, the median diameter d50 of fine particles suitable for the process according to the invention is greater than or equal to 25 μιτι and less than or equal to 6 mm.

Indeed, fine particles having a median diameter d50

less than 25 μιη could cause fouling of the furnace 1. Fine particles having a median diameter d 50 greater than 6 mm may for their part lessen the production and / or quality of the calcium aluminates generating unmelted in the melt Bathrooms 1 1, then the tank outlet.

More preferably, the fine particles have a median diameter d50 of between 100 and 1000 μιτι μιτι.

Still more preferably, they have a median diameter d50 of between 150 and 500 μιτι μιτι.

Ideally, the median diameter d50 of the fine particles is 250 μιτι. In addition, the maximum diameter of the fine particles is another feature size to choose the fine particles most suitable for carrying out the invention.

The maximum diameter is a reference diameter defined as the diameter below which is 100% of the fine particles used.

In other words, all the fine particles of all the considered particles have a diameter smaller than the maximum diameter.

Preferably, the fine particles have a maximum diameter less than or equal to 20 000 μιτι, that is to say less than or equal to 2 cm.

Thus, sets of fine particles having the following maximum diameters may be suitable for carrying out the invention: 20 000 μιτι; 19 000 μηπ; 18 000 μιτι; 17 000 μιτι; 16 000 μιτι; 15 000 μιτι; 14 000 μιτι; 13 000 μηπ; 12 000 μηπ; 1 1000 μιτι; 10 000 μιτι; 9000 μιτι; 8000 μιτι; 7000 μιτι; 6000 μιτι; 5000 μιτι; 4000 μιτι; 3000 μιτι; 2000 μιτι; and lower.

Generally, the maximum diameter of the fine particles is chosen so as to ensure complete melting of all the fine particles during the residence time of the fine particles in the furnace vessel. The maximum diameter depends on the size of the furnace vessel.

Plus the maximum diameter of the fine particles, the greater the residence time for the complete melting of these fine particles increases, the size of the furnace should be large.

Very advantageously, the method according to the invention can be adapted quickly and easily to many particle sizes.

The maximum diameter of the fine particles used is determined by the cost of purchase and / or production of these fine particles and the size

the furnace 1.

To date, the particles are the more expensive they are small because they generally require a grinding stage. It is economically advantageous to use the largest possible particles, which require neither specific nor specific grinding compaction. But a great length of vessel needed to melt the larger particles, requires a large furnace size, so a higher cost for the construction and maintenance of this oven.

If the cost of purchase and / or production of the smaller particles would decrease, it would probably be advantageous to use these particles rather than coarse particles and the maximum diameter of the particles could be lowered.

For example, there is shown in Figure 1 the particle size distribution curve of a first set of fine bauxite particles that can be used in the process according to the invention.

In this figure 1, the ordinate axis gives the amount of particulate expressed in mass percentage relative to the total mass of the total amount of particles and the abscissa axis gives the particle diameter in micrometers (μιτι) on a scale logarithmic.

The granulometric curve shown here is a so-called curve

"Cumulative", that is to say that each point of this particle size curve represents the percentage of particles having a diameter less than or equal to that corresponding to the point of the curve studied.

For example, this particle size distribution curve indicating that 70% of the particles of the first set of particles have a diameter less than or equal to 100 μιτι.

Similarly, in this first set of particles, the median diameter d50 is equal to 60 μιτι, that is to say that 50% of the first set particles have a diameter less than or equal to 60 μιτι.

The maximum particle diameter is 300 μιτι here, which means that

100% of the particles of the first set of particles have a diameter less than or equal to 300 μιτι.

There is shown in Figures 2-4 the granulometric diagrams of second, third and fourth sets of fine particles can be used in the process according to the invention.

The bar charts of Figures 2, 3 and 4, give the weight percentage of particles having a diameter less than or equal to that indicated below each bar.

For example, the diagram in Figure 2 bar indicates that the median diameter d50 of the second set of particles suitable for the invention is between 0.5 millimeter (mm) to 1 mm. It is estimated that said median diameter d50 is in this case about 0.9 mm.

In this figure 2, it is seen that the maximum particle diameter of this second set is 2 mm.

Similarly, the bar charts of Figures 3 and 4 respectively indicate that the median diameter d50 of the third set of fine particles suitable for the invention is between 1 mm and 2 mm, and that the median diameter d50 of the fourth set of fine particles suitable for the invention is between 2 mm and 3.15 mm.

It is estimated that said median diameter d50 is about 1, 4 mm for the third set of particles corresponding to the diagram shown in Figure 3, and about 3 mm for the fourth set of particles corresponding to the diagram shown in Figure 4.

The maximum particle diameter of the third set corresponding to the diagram shown in Figure 3 is 4 mm. It is 20 mm for the fourth set of particles corresponding to the diagram shown in Figure 4.

Generally, the median diameter d50 of fine particles may vary depending on the type of raw materials 7 used in the implementation of the method according to the invention.

In particular, the median diameter d50 of fine particles of raw material source of alumina and / or aluminum may be different from the source fine particles of calcium oxide and / or calcium.

Advantageously, provision may be made according to the invention to make particle size of the raw material source of alumina (Al 2 O 3 ) and / or aluminum (Al) and a source of calcium oxide (CaO) and / or calcium (Ca) using a grinder before being introduced into the melt 1 January.

In other words, provision can be made to reduce the diameter of the raw material particles so as to obtain a set of fine particles whose median diameter d50 is as desired.

Furthermore, preferably, the first alumina source material (Al 2 0 3 ) and / or aluminum (Al) comprises, by weight based on the total weight of said first alumina source material (Al 2 0 3 ) and / or aluminum (Al), at least 30% or at least 40% or 50%, alumina (Al 2 0 3 ) and / or aluminum (Al).

Preferably, the first source material of calcium oxide (CaO) and / or calcium (Ca) comprises, by weight based on the total weight of said raw material source of calcium oxide (CaO) and / or calcium (Ca), at least 50% or at least 70% or 90% of calcium oxide (CaO) and / or calcium (Ca).

In the manufacturing process according to the invention, the first alumina source material (Al 2 O 3 ) and / or aluminum (Al) is preferably selected from: bauxite as the monohydrate bauxite and / or trihydrate bauxite, white bauxite, red bauxite, grinders corundum, catalyst supports, refractory bricks, hydroxides, metallurgical aluminas, calcined aluminas and melted, by-products of the aluminum industry and not conform high alumina content manufacture or a mixture thereof.

Preferably, when carrying out the process according to the invention in the variant of the oven having the electrical heating means, the first alumina source material (Al 2 O 3 ) and / or aluminum (Al) contains little iron (Fe).

Also preferably, the first source material of calcium oxide (CaO) and / or calcium (Ca) is chosen from: limestone, lime and byproducts from consuming processes limestone and / or lime as dairy or slag or steel electrometallurgy, or a mixture thereof.

Raw materials source of alumina (Al 2 O 3 ) and / or aluminum (Al), and a source of calcium oxide (CaO) and / or calcium (Ca) can also contain iron (Fe) and silica (SiO 2 ) in varying amounts. For example, the trihydrate bauxite may comprise by weight, from 46% to 50% of alumina (AI 2 O 3 ), from 14% to 20% of iron oxide in different oxidation states and 7% at 12 % silica (SiO 2 ).

In addition, raw material source of alumina (Al 2 O 3 ) and / or aluminum (Al), and a source of calcium oxide (CaO) and / or calcium (Ca)

introduced in step a) of the process according to the invention are preferably metered so that the weight ratio Al / Ca in the final product, that is to say, in the calcium aluminate recovered tank outlet 15, is between 0.5 and 1, 7, and preferably between 0.9 and 1, 5.

Even more preferably, the mass ratio of aluminum (Al) on calcium (Ca) in the calcium aluminate recovered tank outlet 15 is between 1 and 1, 1.

In order to respect this mass ratio, the first alumina source material (Al 2 0 3 ) and / or aluminum (Al) and the raw material source of calcium oxide (CaO) and / or calcium (Ca) are dosed either when in the form of fine particles having the median diameter d50 desired, either before they are reduced to present said median diameter d50 desired.

Then, they are mixed in a mixer to form the raw materials 7 which are introduced into the tank 15 of the furnace 1. This mixture is carried out on the raw materials reduced to the state of fine particles with a median diameter d50 desired.

7 Raw materials preferably comprise, by weight based on the total weight of said raw material 7, at least 70% of the group consisting of calcium oxide (CaO), alumina (Al 2 O 3 ), an iron oxide (e.g. Fe 2 O 3 ) and silica (SiO 2 ).

In other words, calcium oxide (CaO), alumina (Al 2 O 3 ), iron oxide (e.g. Fe 2 O 3 ) and silica (SiO 2 ) represent at least 70% of raw material 7, by weight based on the total weight of said raw materials 7.

By at least 70% is meant that the raw material 7 may comprise 70%, 75%, 80%, 85% or 90% of the group consisting of calcium oxide (CaO), alumina (AI 2 O 3 ), iron oxide (e.g. Fe 2 O 3 ) and silica (SiO 2 ) by weight based on the total weight of said raw materials 7.

Raw material or fuel may contain other minor phases and / or impurities, such as sulfates SO 3 . For example, a SO sulphate content 3 less than 4% by mass relative to the total mass of raw material 7, in particular less than 3%, less than 2%, especially less than 1%, is compatible with the present invention.

Commodities 7 do not include raw material

would specifically source of calcium sulfate CaS0 4 or specific source of fluorine compounds.

In other words, no calcium sulfate CaS0 4 or fluorine compounds are specifically added to the raw materials 7. Nevertheless, said raw materials 7 include impurities and may therefore contain traces of fluorine compounds or calcium sulfate.

Raw materials 7 can for example have the compositions described in Tables 3 and 4.

Table 3 - First example of raw materials used 7

The operator can perform the assay and the mixture of raw materials source of alumina and / or aluminum (Al) and a source of calcium oxide (CaO) and / or calcium (Ca) before said raw material source alumina (Al 2 0 3 ) and / or aluminum (Al) and a source of calcium oxide (CaO) and / or calcium (Ca) are transported to the charging system 2 of the furnace 1 and in particular to the silo 6 storage. This transport can take place via a pump or other transfer means.

Alternatively, the dosage and mixing said raw material source of alumina (Al 2 O 3 ) and / or aluminum (Al) and a source of calcium oxide (CaO) and / or calcium (Ca) s can perform directly in the silo 6 of the charging system 2 of the furnace 1 when the latter is provided with two separate compartments opening into the common part of the silo 6.

Advantageously, according to the manufacturing method according to the invention, in step a) of the melt temperature for 1 1 is between 1300 ° C and 1700 ° C.

Preferably this temperature is between 1400 ° C and 1600 ° C.

In addition, a particularly advantageous manner, the present invention proposes to control the partial pressures of gases contained within the enclosure formed by the arch 5 and the tank 15 of the furnace 1, so as to obtain calcium aluminates having a controlled mineralogy.

Thus, advantageously, also in step a), the Fusion 1 1 bath is under a reducing atmosphere.

In chemistry, a very general way, a gearbox is a chemical species capable of donating one or more electrons to another chemical, called oxidant, in a redox reaction. Conversely, an oxidizing is a chemical species able to capture one or more electrons in a redox reaction.

Here, the term "reducing atmosphere" in an atmosphere with the oxidation capacity was reduced by decreasing the proportion of oxidant therein.

In particular, here, the reducing atmosphere contains a reduced level compared to air, dioxygen O 2 , which is an oxidizing compound.

In addition, here, the reducing atmosphere comprises a proportion of gases that are reducing the air in general, and the oxygen O 2 in particular.

Here, said reducing atmosphere under which is placed the bath Fusion 1 1 comprises carbon monoxide (CO).

In particular, the method according to the invention proposes to control the carbon monoxide content (CO) contained in the atmosphere situated above the Fusion 1 1 bath.

Said average content of carbon monoxide (CO) of the reducing atmosphere is here between about 0.1% and 100%.

CLAIMS

1. A method of manufacturing calcium aluminate in an oven (1) Industrial, wherein:

a) is introduced continuously into a tank (15) of refractory material containing a molten bath (1 1) heated continuously, fine particles of a first alumina source material (Al 2 O 3 ) and / or aluminum (Al) and a first source of calcium oxide material (CaO) and / or calcium (Ca) having a median diameter d50 less than or equal to 6000 μιτι to melt said particulate material first, and

b) recovering, in continuous and tank outlet (15) a mass of calcium aluminate (16) liquid.

2. The manufacturing method according to claim 1, wherein, in step a), the melt (1 1) is placed in a reducing atmosphere comprising carbon monoxide (CO).

3. Manufacturing process according to one of claims 1 and 2, wherein, in step a), said reducing atmosphere comprises from 0.1% to 100% carbon monoxide (CO).

4. Manufacturing process according to one of claims 1 to 3, wherein the melt temperature (1 1) of calcium aluminates is between 1300 ° C and 1700 ° C.

5. The manufacturing method according to claim 4, wherein the melt temperature (1 1) of calcium aluminates is between 1400 ° C and 1600 ° C.

6. Manufacturing process according to one of claims 1 to 5, wherein the residence time of said fine raw material particles in said melt (1 1) of the calcium aluminate is less than 24 hours.

7. The manufacturing method according to claim 6, wherein the residence time of said fine raw material particles in said melt (1 1) of calcium aluminates is between 30 minutes and 9 hours.

8. Manufacturing process according to one of claims 1 to 7, wherein, in step a), the first alumina source material (Al 2 O 3 ) and / or aluminum (Al) introduced into the tank (15) is selected from: bauxite, wheels corundum, catalyst supports, refractory bricks, hydroxides, metallurgical aluminas, calcined aluminas and melted, by-products of the aluminum industry and not conform manufacturing a high content of alumina or a mixture thereof, and the first source material of calcium oxide (CaO) and / or calcium (Ca) placed in the vessel (15) is selected from: limestone, lime and by-products from consuming processes limestone and lime as dairy or slag or steel electrometallurgy, or a mixture thereof.

9. Manufacturing process according to one of claims 1 to 8, wherein the fine raw material particles have a median diameter d50 of between 100 and 1000 μιτι μιτι.

10. A method of manufacture according to claim 9, wherein the fine raw material particles have a median diameter d50 of between 150 and 500 μιτι μιτι.

January 1. Production method according to one of claims 1 to 10, wherein, after step b), the mass is cooled calcium aluminate (16) recovered liquid tank outlet (15).

12. The manufacturing method according to claim 1 1, wherein the cooling occurs naturally or controlled manner.

13. Production method according to one of claims 1 1 and 12, wherein the mass is ground calcium aluminate (16) cooled to form a calcium aluminate cement.

14. Production method according to one of the preceding claims, wherein said fine particles of the first alumina source material (Al 2 O 3 ) and / or aluminum (Al) and raw material source of calcium oxide (CaO) and / or calcium (Ca) are introduced into the vessel (15) in the form of a loose powder.