Method for reducing iron iii oxides contained in calcined clay

Abstract

The invention relates to a method and a facility for reducing iron III oxides contained in calcined clay, the method comprising: a step of introducing a calcined clay containing iron III oxides into a reduction reactor (100), a step of reducing the calcined clay in the reduction reactor (100), said step comprising an operation O1) of bringing the calcined clay into contact with a reducing gas containing hydrogen atoms to obtain reduced clay particles containing iron II oxides and / or triiron tetroxide, and a reducing gas stream to be treated, and a step of cooling the reduced clay particles in a cooling loop.

Description

PROCESS FOR REDUCING IRON III OXIDES CONTAINED IN CALCINED CLAY

[0001] The invention relates to a method for reducing iron III oxides contained in a calcined clay. In particular, the invention relates to a method for reducing iron III oxides contained in a calcined clay for the production of a binder having desired color characteristics. Technical background

[0002] In the following, we are particularly interested in the reduction of iron III oxides contained in a calcined clay intended for use in the manufacture of cement, although the calcined clay can be used for other manufacturing purposes.

[0003] Cement manufacturing uses for the most part a fired material, clinker, which is produced from minerals whose essential constituent is calcium carbonate.

[0004] Clinker is obtained from a raw material composed of a mixture of minerals, including clay, a source of aluminosilicates, and limestone, a source of calcium carbonate. These minerals are successively mixed, dried, ground, preheated, decarbonated, then fired and partially melted in a rotary kiln to a temperature of approximately 1500°C, then the clinker thus formed is cooled.

[0005] Cement is obtained by finely grinding a mixture composed mainly of clinker.

[0006] In the clinker manufacturing process, in addition to the CO2 emissions from the combustion of the fuels used, calcium carbonate, which comes mainly from limestone, is decarbonated to obtain lime capable of recombining with silicon, aluminum, and iron oxides in the rotary kiln to form clinker. This decarbonation step releases a significant amount of carbon dioxide into the atmosphere.

[0007] National legislation on carbon dioxide emissions is becoming stricter and requires stakeholders to reduce the quantities released.

[0008] In addition to clinker, cement contains gypsum, which helps regulate the setting time of mortars and concretes. Cement also increasingly contains, and in ever-increasing proportions, materials commonly called "cement additives," which replace clinker in order to reduce the environmental impact and cost of cement manufacturing.

[0009] For example, the most commonly used clinker substitutes currently include limestone, blast furnace slag, fly ash from coal-fired power stations and natural pozzolan.

[0010] Apart from limestone, which simply acts as a "filler", an anglicism commonly used to designate fillers, these clinker substitute materials have a pozzolanic reactivity allowing them to participate in the hydraulic setting reaction. This pozzolanic reactivity contributes to maintaining the desired mechanical properties of mortars and concretes when the clinker content decreases.

[0011] Clays, especially those containing kaolinite, acquire pozzolanic reactivity when calcined and then become excellent substitutes for clinker in cement manufacturing. They are also called "artificial pozzolans."

[0012] Unlike clinker production, calcined clay production emits little CO2.

[0013] By judiciously decreasing the proportion of clinker while increasing the proportion of calcined clay, it becomes possible to produce a cement with desired properties.

[0014] Due to the iron III oxides, Fe2O3, it contains, clay has a reddish tint. If left untreated, adding calcined clay to cement will result in a cement with a pinkish tint.

[0015] Cement producers and end users want a gray colored cement.

[0016] Several processes have been implemented to modify the natural color of the calcined clay and make it gray.

[0017] Among these techniques, we can cite a process that consists of chemically reacting iron III oxide molecules Fe2O3 to obtain triiron tetroxides Fe3O4. This is an oxidation-reduction reaction. After an initial calcination step of the clay, the clay is sent to a reduction zone where a liquid reducing agent is injected directly onto the clay, in particular diesel. The diesel creates the conditions that allow a reduction of iron III oxides to obtain triiron tetroxides and iron oxides FeO.

[0018] Although this process produces a grey clay, it has two major drawbacks:

[0019] - a significant quantity of diesel for the reduction of iron III oxides is injected, impacting the cost of clay on the one hand and the environment on the other,

[0020] - the reduction reaction must be carried out at high temperature, impacting the energy efficiency of this process.

[0021] The invention aims in particular to remedy these drawbacks.

[0022] For this purpose, a process for reducing iron III oxides contained in a calcined clay is firstly proposed, the process comprising the following steps:

[0023] a) introduction of a calcined clay containing iron III oxides into a reduction reactor,

[0024] b) reduction of the calcined clay in the reduction reactor comprising an operation O1) of bringing the calcined clay into contact with a reduction gas containing hydrogen atoms to obtain particles of reduced clay containing iron II oxides and / or triiron tetroxides, and a reduction gas stream to be treated,

[0025] (c) suspending, in a cooling reactor, reduced clay particles in a cooling gas flow to cool the reduced clay particles,

[0026] d) mixing the reduced clay particles with at least part of the reduction gas flow to be treated to obtain, at the end of steps c) and d), a mixture containing:cooled reduced clay particles,said at least part of the reduction gas flow to be treated, andthe cooling gas flow,e) separating the mixture to obtain a gas flow separate from the cooled reduced clay particles, and from the cooled reduced clay particles,

[0027] (f) cooling at least a portion of the gas stream separated from the cooled particles of reduced clay to obtain a cooling gas, and

[0028] i) introducing the cooling gas into the cooling reactor so that the cooling gas flow is at least partly made up of the cooling gas obtained in step f), the implementation of step i) leading to the creation of a cooling loop.

[0029] This process advantageously makes it possible to obtain a gray-colored clay using a small amount of reducing agent, significantly lower than the amount used with liquid reducing agents. Furthermore, this process makes it possible to improve the reduction of iron III oxides because the contact of the calcined clay with the reducing gas is maintained for a prolonged period during each of the process stages.

[0030] Various additional features may be provided alone or in combination:the reducing gas comprises dihydrogen and / or carbon monoxide;the reducing gas contains an amount of between 0.1 and 2, preferably between 0.3 and 0.7 moles of reactants per mole of iron III oxide contained in the calcined clay introduced;the method further comprising a step g) of cooling at least part of the cooled particles of reduced clay resulting from the separation step e), the cooling step g) comprising an operation O2) of bringing the cooled particles of reduced clay into contact with the cooling gas resulting from the cooling step f) to obtain a gaseous suspension of cooled particles of reduced clay;the method further comprising, after the cooling step f), an operation O3) of extracting a portion of the cooling gas from the cooling loop to maintain a depression in the cooling loop; the method further comprising, after the extraction operation O3), an operation O4) of sending the extracted portion of the cooling gas to a calciner; the method further comprising an operation O5) of supplying thermal energy and / or fuel into the cooling loop to consume oxygen contained in the gas flow circulating in the cooling loop, the operation O5) being carried out before the cooling step f);the method further comprising a step h) of separating the gaseous suspension of cooled particles of reduced clay to obtain:a cooling gas separated from the cooled particles of reduced clay, the cooling gas containing hydrogen atoms, andcooled particles of reduced clay, the cooling gas introduced into the cooling reactor during step i) consisting of the cooling gas separated from the cooled particles of reduced clay resulting from the separation step h);

[0031] Secondly, a use of a reduction process as described above is proposed to produce calcined clay having desired color characteristics.

[0032] Thirdly, there is proposed an installation for reducing iron III oxides contained in a calcined clay, the system being configured to implement a method as described above and comprising:

[0033] - a reduction reactor configured to bring a calcined clay into contact with a reduction gas containing hydrogen atoms, the reduction reactor comprising an outlet of reduced clay particles containing iron II oxides and / or triiron tetroxides and an outlet of a reduction gas stream to be treated,

[0034] - a cooling reactor in which reduced clay particles are suspended in a cooling gas flow and, optionally, into which the reduction gas flow to be treated is injected, the cooling reactor comprising an outlet through which a mixture containing:

[0035] - cooled particles of reduced clay,

[0036] - the cooling gas flow, and

[0037] - possibly at least one part of the reduction gas flow to be treated,

[0038] - a first gas / particle separation device configured to separate cooled particles of reduced clay from the mixture extracted from the cooling reactor, the first gas / particle separation device comprising:an inlet configured to receive said mixture,a gas outlet of a gas stream separated from the cooled particles of reduced clay, anda particle outlet of the cooled particles of reduced clay,- a cooling means configured to cool at least part of the gas stream separated from the cooled particles of reduced clay, the cooling means comprising an outlet of a cooling gas,

[0039] - a means for introducing the cooling gas into the cooling reactor so that the cooling gas flow is at least partly made up of the cooling gas leaving the cooling means, this leading to the creation of a cooling loop.

[0040] Various additional features may be provided alone or in combination: the installation further comprising a cooling gas ventilation device arranged between the cooling means and the cooling reactor to ensure the circulation of the gas flows in the cooling loop; the installation further comprising a means for supplying thermal energy and / or fuel into the cooling loop to consume oxygen contained in the gas flow circulating in the cooling loop, the supply means being arranged between the first gas / particle separation device and the cooling means;the installation further comprising a second cooling means configured to further cool at least a portion of the cooled particles of reduced clay exiting the first gas / particle separation device, the second cooling means comprising:a gas inlet of at least a portion of the cooling gas, the gas inlet of the second cooling means being connected to the outlet of the first cooling means,a material inlet of said at least portion of the cooled particles of reduced clay exiting the first gas / particle separation device, andan outlet of a gaseous suspension of cooled particles of reduced clay;the installation further comprising a second gas / particle separation device configured to separate at least a portion of the cooled particles from the gaseous suspension of cooled particles of reduced clay, the second gas / particle separation device comprising:a gas outlet of a cooling gas separated from the cooled particles of reduced clay, anda particle outlet of cooled particles of reduced clay, the gas outlet of the second gas / particle separation device being connected to the means for introducing the cooling gas into the cooling reactor.;

[0041] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which:

[0042] This is a schematic representation of an installation according to one embodiment of the invention, and

[0043] This is a schematic representation of an installation according to one embodiment of the invention.

[0044] The drawings and description below contain, for the most part, elements of a certain character. They may therefore not only serve to better understand this disclosure, but also contribute to its definition, if necessary.

[0045] More specifically, in the following, in a non-limiting manner for the invention, it is considered that each of two installations shown in Figures 1 and 2, installations for reducing iron III oxides contained in a calcined clay according to two different embodiments, is part of a general process for manufacturing a binder, for example cement. In particular, it is considered that the reduced calcined clay is intended to be used in the manufacture of a cement as a substitute for part of the clinker or as a reactive filler material incorporated directly into the concrete or as a component of a geopolymer cement.

[0046] Calcined clay is produced by implementing a step a0) of calcination, in a calciner (not shown in the figure), of a raw clay containing iron III oxides.

[0047] For the purposes of the present invention, raw clay means any type of clay mineral, including schists.

[0048] Preferably, the raw clay contains kaolinite.

[0049] Preferably, before implementing the calcination step a0), the raw clay is ground and dried, then preheated in a preheater, and then sent to the calciner. Generally, the calciner comprises a combustion chamber in which hot gases are generated and a calcination reactor in which the clay from the preheater is brought into contact with the hot gases for calcination. The calcination reaction is preferably carried out in an oxidizing atmosphere, with an excess of oxidant. The flue gas outlet from the calciner may be connected to the preheater and possibly to other devices conventionally used in general binder manufacturing processes, such as a raw clay grinding and drying workshop, one or more flue gas decontamination and filtration devices.

[0050] In order to activate the pozzolanic power of the calcined clay and make it usable in the manufacture of cement, step a0) of calcination of the raw clay is carried out at a temperature below 950°C. Step a0) of calcination is carried out under stoichiometric or oxidizing conditions.

[0051] Next, a step a) of introducing the calcined clay into a reduction reactor 100, in particular through a material inlet 1002 of the reduction reactor 100 is carried out. It should be noted that the calcined clay introduced in step a) is at a temperature between 600°C and 950°C, or preferably at a temperature between 750°C and 850°C. The calcined clay is then directed from the calciner to the material inlet 1002 of the reduction reactor 100. The reduction reactor 100 is preferably a reactor of the static reactor, fluidized bed reactor or even rotary reactor type. Reduced clay particles containing iron II oxides and / or triiron tetroxides exit the reduction reactor 100 through the material outlet 1006 and a reduction gas stream to be treated exits through the gas outlet 1008.

[0052] By reduction gas flow to be treated, we mean a gas flow leaving the reduction reactor and sent into the cooling loop to pass into the elements constituting it.

[0053] The calcined clay is preferably maintained in the reduction reactor 100 for a residence time greater than 10 seconds and up to 10 minutes, preferably up to 5 minutes, or even up to 2 minutes, under optimal reduction conditions. The reduction reactor 100 comprises in particular a reduction gas inlet 1004 through which reduction gas is injected. Thus, during a following step, a step b) of reducing the calcined clay, in the reduction reactor 100, is carried out. This reduction step b) comprises in particular an operation O1) of bringing the calcined clay into contact with the reduction gas injected into the reduction reactor 100, the reduction gas containing hydrogen atoms. This makes it possible to reduce at least a portion of the iron III oxides of the calcined clay to Fe3O4 (triiron tetroxides) and / or FeO (iron II oxides).

[0054] The reducing gas containing hydrogen atoms allows the reduction of iron III oxides according to the following formulas to obtain mainly triiron tetroxides and possibly iron II oxides FeO:

[0055]

[0056]

[0057] and according to the following formulas, carbon monoxide, when present, reacts with iron III oxides:

[0058]

[0059]

[0060] Using reducing gas containing hydrogen atoms rather than diesel or any other liquid fuel as a reducing agent significantly reduces the amount of reducing agent used in reduction step b). Grey calcined clay is therefore produced at a significantly lower cost. In addition, the environmental impact of producing grey calcined clay is reduced.

[0061] Advantageously, the reducing gas comprises dihydrogen and / or carbon monoxide.

[0062] Even more advantageously, the reducing gas contains:

[0063] - a mixture containing dihydrogen H2 and carbon monoxide CO, or

[0064] - dihydrogen H2.

[0065] For example, dihydrogen H2 and carbon monoxide CO may come directly from a storage means or result from a dissociation reaction of a hydrocarbon in a reactor dedicated to the generation of the reduction gas. The dedicated reactor may be an endogas or exogas generator from which the reduction gas injected into the reduction reactor 100 is derived.

[0066] It should be noted that the above-mentioned reducing gases may be mixed with other gases, mainly nitrogen and / or carbon dioxide and / or gaseous hydrocarbons of generic formula CnHm which have not been dissociated into dihydrogen H2 and carbon monoxide CO.

[0067] Advantageously, the quantity of reducing gas injected into the reduction reactor 100 and with which the calcined clay is brought into contact corresponds to a quantity substantially between 0.1 and 2 moles of reactants per mole of iron III oxide contained in the calcined clay introduced. By respecting this dosage, a calcined clay with desired gray tones is obtained while minimizing the gas input, which makes it possible to reduce the production costs of the clay and its impact on the environment. Preferably, the quantity of reducing gas injected into the reduction reactor 100 and with which the calcined clay is brought into contact corresponds to a quantity substantially between 0.3 and 0.7 moles of reactants per mole of iron III oxide contained in the calcined clay introduced. Such a range allows an efficient reduction reaction while optimizing the energy consumption necessary for the production of the reducing gas.

[0068] At the end of reduction step b), reduced clay particles containing iron II oxides and / or triiron tetroxides are obtained, and a reduction gas stream to be treated is obtained. The reduced clay particles exit the reduction reactor via the material outlet 1006 and the reduction gas stream to be treated exits via the gas outlet 1008.

[0069] For the purposes of the present application, reduced clay particles are understood to mean calcined clay particles which have undergone the reduction reaction in the reduction reactor and have reached a desired color.

[0070] The reduced clay particles are then sent, and conveyed via a fluid conduit, to a material inlet 1106 of a cooling reactor 110. During a suspension step c), the reduced clay particles are suspended in a cooling gas flow which passes through the cooling reactor 110. In particular, the cooling gas flow passes through the cooling reactor 110 from a gas inlet 1102 to an outlet 1104. This makes it possible to cool the reduced clay particles leaving the reduction reactor 100 and introduced into the cooling reactor 110. A mixture is thus obtained containing cooled reduced clay particles and the cooling gas flow.

[0071] Preferably, at least part of the reduction gas flow to be treated leaving the reduction reactor 100 is also introduced into the cooling reactor 110 via the inlet 1108. A mixing step d) is then carried out, this being then carried out in the cooling reactor 110. Thus, the aforementioned mixture also contains at least part of the reduction gas flow to be treated introduced into the cooling reactor 110. In the exemplary embodiments illustrated in FIGS. 1 and 2, the entire reduction gas flow to be treated is introduced into the cooling reactor 110. However, only part of the reduction gas flow to be treated can be introduced therein.

[0072] In an alternative embodiment not illustrated in the figures, the reduction gas flow to be treated is mixed with the clay particles leaving the reduction reactor 100 before they are introduced into the cooling reactor 110. In this case, the reduced clay particles are introduced into the cooling reactor 110 in the form of a mixture comprising the reduced clay particles and the reduction gas flow to be treated.

[0073] In another alternative embodiment not illustrated in the figures, the reduction gas flow to be treated is mixed with the clay particles leaving the reduction reactor 100 after constitution of the mixture containing the cooled particles of reduced clay and the cooling gas flow, that is to say after the mixture containing the cooled particles of reduced clay and the cooling gas flow leaves the cooling reactor 110.

[0074] In the embodiments illustrated in Figures 1 and 2, the cooling gas is introduced into the cooling reactor 110 through the inlet 1102 and the mixture containing cooled particles of reduced clay, the cooling gas stream, and the reduction gas stream to be treated exits the cooling reactor 110 through the outlet 1104.

[0075] The mixture is then sent, and conveyed via a fluid conduit, to a material inlet 1202 of a first gas / particle separation device 120 configured to, during a separation step e), separate the cooled particles of reduced clay from the gas flow.

[0076] At the end of this separation step e), we then obtain: a gas flow separated from the cooled particles of reduced clay which leaves a gas outlet 1204 of the first gas / particle separation device 120, and cooled particles of reduced clay which leave via a material outlet 1206 of the first gas / particle separation device 120.

[0077] Preferably, the first gas / particle separation device 120 is of the cyclone type.

[0078] After separation step e), the gas flow separated from the cooled particles of reduced clay emerging from the first gas / particle separation device 110, for example via its upper outlet, is transported, directly or indirectly, to a first cooling means 140 to which it is fluidically connected by a pipe.

[0079] Thus, a step f) of cooling, via the first cooling means 140, the gas flow separated from the cooled particles of reduced clay is implemented.

[0080] The first cooling means 140 comprises, on the one hand, an inlet 1402 fluidly connected, directly or indirectly, to the upper outlet, or gas outlet 1204, of the first gas / particle separation device 120 and, on the other hand, an outlet 1404 through which a cooling gas exits. The first cooling means 140 is then configured to obtain a cooling gas. For example, the first cooling means 140 may be a recovery boiler or an air cooler.

[0081] Advantageously, during step f) of cooling the gas flow separated from the cooled particles of reduced clay, the temperature of the reducing gas flow is lowered below a threshold temperature of between 200°C and 450°C. This is referred to as indirect cooling since the gas flow separated from the cooled particles of reduced clay is not in direct contact with the cooling fluid. It is thus possible to connect, to the outlet 1404 of the first cooling means 140, a ventilation device 150 without the latter being damaged by excessively hot gas flows. The ventilation device 150 promotes the circulation of the gas flow in the aforementioned elements of the installation and also in those which will be described below.Furthermore, since the gas flow has been cooled during the cooling step f), the opportunity is left to use a wide range of ventilation devices 150 which would then be suitable for such gas flow temperatures.

[0082] According to the embodiment illustrated in, a step i) of introducing the cooling gas into the cooling reactor 110 is carried out. This allows the cooling gas flow which enters the cooling reactor 110 via the inlet 1102 to be at least partly, or entirely (), constituted by the cooling gas obtained in step f). It should be noted that the implementation of step i) induces the creation of a cooling loop. The cooled particles of reduced clay obtained in the separation step e) which then exit via the material outlet 1206 of the first gas / particle separation device 120, are, in this embodiment, recovered and possibly stored in a suitable storage means. Advantageously, the recovered cooled particles of reduced clay are at a temperature of between 200°C and 600°C, preferably between 350°C and 500°C.

[0083] However, to optimize the cooling of the reduced clay particles, in particular to improve the energy efficiency of the cooling of the reduced clay particles, it is appropriate to carry out multi-stage cooling, for example in two stages using two separate cooling means 140 and 170. Carrying out multi-stage cooling allows for energy optimization of the entire reduction process.

[0084] This is why, according to the embodiment illustrated in, before implementing step i) of introducing the cooling gas into the cooling reactor 110, the cooling gas leaving the first cooling means 140 is used to cool the cooled particles of reduced clay which leave through the material outlet 1206 of the first gas / particle separation device 120. Advantageously, a step g) of cooling the cooled particles of reduced clay which leave through the material outlet 1206 of the first gas / particle separation device 120 is then carried out.

[0085] This step g) is implemented using a second cooling means 170 configured to further cool the cooled particles of reduced clay that have been cooled in the cooling reactor 110. This step g) of cooling the cooled particles of reduced clay comprises an operation O2) of bringing the cooled particles of reduced clay into contact with the cooling gas exiting the first cooling means 140. This further makes it possible to further reduce, in an economical and ecological manner, the temperature of the cooled particles of reduced clay in order to avoid the reoxidation of the iron II oxides and / or the triiron tetroxides of the particles of reduced clay that exit the reduction reactor 100 through its outlet 1006.

[0086] As can be seen in the, the second cooling means 170 comprises a gas inlet 1702 through which the cooling gas is introduced, this gas inlet 1702 being indirectly connected to the outlet 1404 of the first cooling means 140, via the ventilation device 150, and a material inlet 1704, connected to the lower outlet, or material outlet 1206, of the first gas / particle separation device 120, through which the cooled particles of reduced clay from the separation step e) are introduced. The second cooling means 170 further comprises an outlet 1706 through which a gaseous suspension of cooled particles of reduced clay exits. It should be noted that during this cooling step g), the cooling gas heats up in contact with the cooled particles of reduced clay which are hotter than the cooling gas.

[0087] Advantageously, the O2 operation is carried out using direct contact of the cooling gas with the cooled particles of reduced clay to the extent that the cooling gas contains less than 2% oxygen by volume.

[0088] Advantageously, during step g) of cooling the cooled particles of reduced clay, the temperature of the cooled particles of reduced clay is lowered below a threshold temperature of between 200°C and 600°C, and preferably between 350°C and 500°C, this making it possible to guarantee non-reoxidation of the iron II oxides and / or triiron tetroxides in subsequent steps during which the reduced calcined clay is brought into contact with air, for example during final air cooling and handling and storage.

[0089] Advantageously, a step h) of separating the gaseous suspension of cooled particles of reduced clay is carried out after step g) of cooling the cooled particles of reduced clay. This step h) of separating the gaseous suspension of cooled particles of reduced clay is implemented using a second gas / particle separation device 180 configured to separate cooled particles from the gaseous suspension of cooled particles of reduced clay.

[0090] The gaseous suspension of cooled particles is then introduced into the second gas / particle separation device 180 via an inlet 1802 connected to the outlet 1706 of the second cooling means 170. The second gas / particle separation device 180 further comprises, on the one hand, a gas outlet 1806 for a cooling gas containing hydrogen atoms separated from the cooled particles of reduced clay and, on the other hand, a particle outlet 1804 for cooled particles of reduced clay. This second gas / particle separation device 180 may, for example, be of the same type as the first gas / particle separation device 120.The cooled particles of reduced clay exiting through the particle outlet 1804 of the second gas / particle separation device 180 may be cooled during a final cooling step, for example in air, to obtain cooled particles of reduced clay at a temperature between 100°C and 150°C. At this temperature, the particles are easily stored and conditioned. Then, these can be, for example, mixed with clinker intended for the production of cement. Such use makes it possible to produce a gray-colored cement, by reducing the proportion of clinker in the cement by replacing it with calcined clay.

[0091] Advantageously, step i) of introducing, into the cooling reactor 110, the cooling gas separated from the cooled particles of reduced clay leaving the second gas / particle separation device 180 is now carried out. Thus, the cooling gas brought into contact with the calcined clay during operation O1) is at least partly made up of the gaseous suspension of cooled particles of reduced clay.

[0092] It should be noted that introducing into the cooling reactor 110, via the gas inlet 1102, the cooling gas separated from the cooled particles of reduced clay induces the creation of the cooling loop.

[0093] In the presence of such a cooling loop, according to one or other of the embodiments illustrated in Figures 1 or 2, it is advantageous to guarantee a thermal equilibrium and a pressure equilibrium so that the cooling loop is sustainable. In particular, the reduction loop is preferably maintained in a reducing atmosphere and the flow rate of the gas flows circulating in it is greater than the gas injection flow rate of at least part of the reduction gas flow to be treated in the cooling reactor 110.

[0094] Thus, it is advantageous, after step f) of cooling at least part of the gas flow separated from the cooled particles of reduced clay, to implement an operation O3) of extracting from the cooling loop part of the cooling gas to maintain the pressure in the cooling loop at a value lower than the ambient pressure, i.e. to maintain a depression in the cooling loop.The implementation of such an extraction operation O3) also makes it possible to compensate for the volume of gas introduced into the cooling loop, in particular into the reduction reactor 100, during the injection of the reduction gas via the reduction gas inlet 1004 of the reduction reactor 100, during the implementation of step a) of introducing the calcined clay into the reduction reactor 100 via the material inlet 1002, and during the introduction into the cooling loop of false air which is introduced through possible sealing defects in the pipes or equipment.

[0095] The extraction rate from the cooling loop of a portion of the cooling gas during the O2 operation is regulated via the use of a valve-type member 160, so as to maintain a constant depression in the loop.

[0096] Preferably, this valve-type member 160 is configured to extract cooling gas at the outlet of the ventilation device 150, in the direction of circulation of the gas flows.

[0097] Then, an operation O4) of sending the part of the extracted cooling gas into the calciner used to obtain the calcined clay before its introduction into the reduction reactor 100, is possibly carried out. Thus, the extracted cooling gas is incinerated and the energy released during the combustion of gases such as dihydrogen, carbon monoxide or even gaseous hydrocarbons contained in the cooling gas is recovered.

[0098] It is also advantageous to implement an operation O5) of supplying thermal energy and / or fuel into the cooling loop. This supply is a localized supply in the cooling loop and carried out punctually. By doing so, an increase in oxygen in the gas flows circulating in the cooling loop is avoided, and at the same time a change in color, from gray to red, of the reduced calcined clay is prevented.

[0099] Furthermore, such an O5) supply operation makes it possible to consume oxygen contained in the gas flow circulating in the cooling loop and mainly supplied by the false air. Advantageously, as can be seen in Figures 1 and 2, the installation then comprises a means 130 for supplying thermal energy and / or fuel into the cooling loop arranged between the first gas / particle separation device 120 and the cooling means 140. Preferably, the outlet 1204 of the first gas / particle separation device 120 is then connected to the inlet 1302 of the supply means 130 and the outlet 1304 of the supply means 130 is connected to the inlet 1402 of the first cooling means 140. It should be noted that the quantity of fuel introduced into the supply means 130 is higher according to the embodiment illustrated in the figure 1 than in that illustrated in the figure 1.For example, through a specific inlet 1306 of the supply means 130, a thermal supply in the form of a flame or an electric heater, or possibly an additional supply of fuel, is introduced into the supply means 130 so as to raise the temperature of the cooling gas, with a view to consuming the oxygen present in the gaseous flows by reaction with the carbon monoxide (CO) and the dihydrogen (H2) present in this cooling gas. Thus, the oxygen present in the gaseous flows circulating in the cooling loop is consumed. This ensures that the volume concentration of dioxygen in the cooling gas is maintained at a value of less than 2%, and preferably substantially equal to 0% to obtain a neutral atmosphere in the cooling loop.

[0100] Preferably, the installation further comprises sensors configured to continuously or discontinuously measure the temperature of the gas flows circulating in the cooling loop, and the oxygen, hydrogen and carbon monoxide contents. The use of such sensors makes it possible in particular to monitor the oxygen content in the cooling loop and thus to secure the cooling loop by minimizing the risk of explosion caused by the simultaneous presence of oxygen and reducing gas.

[0101] The installation and method described above advantageously make it possible to obtain a gray-colored clay using a small quantity of reducing gas because part of this reducing gas is recycled. Furthermore, this installation and this method make it possible to improve the reduction of iron III oxides because the contact of the calcined clay with the reducing gas is maintained for a prolonged period during certain stages of the process implemented in the installation described above.

Claims

A method for reducing iron III oxides contained in a calcined clay, the method comprising the following steps:a) introducing a calcined clay containing iron III oxides into a reduction reactor (100),b) reducing the calcined clay in the reduction reactor (100) comprising an operation O1) of bringing the calcined clay into contact with a reducing gas containing hydrogen atoms to obtain particles of reduced clay containing iron II oxides and / or triiron tetroxides, and a reducing gas stream to be treated,c) suspending, in a cooling reactor (110), particles of reduced clay in a cooling gas stream to cool the particles of reduced clay,d) mixing the particles of reduced clay with at least part of the reducing gas stream to be treated to obtain, at the end of steps c) and d), a mixture containing:cooled particles of reduced clay,said at least a portion of the reduction gas flow to be treated, andthe cooling gas flow,e) separation of the mixture to obtain a gas flow separated from the cooled particles of reduced clay, and from the cooled particles of reduced clay,f) cooling at least a portion of the gas flow separated from the cooled particles of reduced clay to obtain a cooling gas, andi) introduction of the cooling gas into the cooling reactor (110) so that the cooling gas flow is at least partly made up of the cooling gas obtained in step f), the implementation of step i) inducing the creation of a cooling loop., The method of claim 1, wherein the reducing gas comprises dihydrogen and / or carbon monoxide. Process according to one of claims 1 or 2, in which the reducing gas contains an amount of between 0.1 and 2, preferably between 0.3 and 0.7 moles of reactants per mole of iron III oxide contained in the calcined clay introduced. Method according to one of claims 1 to 3, further comprising a step g) of cooling at least part of the cooled particles of reduced clay resulting from the separation step e), the cooling step g) comprising an operation O2) of bringing the cooled particles of reduced clay into contact with the cooling gas resulting from the cooling step f) to obtain a gaseous suspension of cooled particles of reduced clay. Method according to one of claims 1 to 4, further comprising, after step f) of cooling, an operation O3) of extracting from the cooling loop a portion of the cooling gas to maintain a depression in the cooling loop. Method according to claim 5, further comprising, after the extraction operation O3), an operation O4) of sending the extracted part of the cooling gas to a calciner. Method according to one of claims 1 to 6, further comprising an operation O5) of supplying thermal energy and / or fuel into the cooling loop to consume oxygen contained in the gas flow circulating in the cooling loop, operation O5) being implemented before the cooling step f). The method of claim 7, further comprising a step h) of separating the gaseous suspension of cooled particles of reduced clay to obtain:a cooling gas separated from the cooled particles of reduced clay, the cooling gas containing hydrogen atoms, andcooled particles of reduced clay, the cooling gas introduced into the cooling reactor (110) during step i) consisting of the cooling gas separated from the cooled particles of reduced clay resulting from the separation step h). Use of a reduction process according to one of claims 1 to 8 for producing calcined clay having desired color characteristics. Installation for reducing iron III oxides contained in a calcined clay, the system being configured to implement a method according to one of claims 1 to 8 and comprising:- a reduction reactor (100) configured to bring a calcined clay into contact with a reduction gas containing hydrogen atoms, the reduction reactor (100) comprising an outlet (1006) for reduced clay particles containing iron II oxides and / or triiron tetroxides and an outlet (1008) for a reduction gas flow to be treated,- a cooling reactor (110) in which reduced clay particles are suspended in a cooling gas flow and, optionally, into which the reduction gas flow to be treated is injected, the cooling reactor (110) comprising an outlet (1104) through which a mixture containing:- cooled reduced clay particles,- the cooling gas flow,and- optionally said at least one part of the reduction gas flow to be treated,- a first gas / particle separation device (120) configured to separate cooled particles of reduced clay from the mixture extracted from the cooling reactor (110), the first gas / particle separation device (120) comprising:an inlet (1202) configured to receive said mixture,a gas outlet (1204) of a gas flow separated from the cooled particles of reduced clay, anda particle outlet (1206) of the cooled particles of reduced clay,- a cooling means (140) configured to cool at least one part of the gas flow separated from the cooled particles of reduced clay, the cooling means comprising an outlet (1404) of a cooling gas,- a means for introducing the cooling gas into the cooling reactor (110) so that the cooling gas flow is at least partly made up of the cooling gas leaving the cooling means (140), this leading to the creation of a cooling loop., Installation according to claim 10, further comprising a ventilation device (150) for the cooling gas arranged between the cooling means (140) and the cooling reactor (110) to ensure the circulation of the gas flows in the cooling loop. Installation according to one of claims 10 or 11, further comprising a means (130) for supplying thermal energy and / or fuel into the cooling loop to consume oxygen contained in the gas flow circulating in the cooling loop, the supply means (130) being arranged between the first gas / particle separation device (120) and the cooling means (140). Installation according to one of claims 10 to 12, further comprising a second cooling means (170) configured to further cool at least a portion of the cooled particles of reduced clay exiting the first gas / particle separation device (120), the second cooling means (170) comprising:a gas inlet (1702) of at least a portion of the cooling gas, the gas inlet (1702) of the second cooling means (170) being connected to the outlet (1404) of the first cooling means (140),a material inlet (1704) of said at least portion of the cooled particles of reduced clay exiting the first gas / particle separation device (120), andan outlet (1706) of a gaseous suspension of cooled particles of reduced clay. The installation of claim 13, further comprising a second gas / particle separation device (180) configured to separate at least a portion of the cooled particles from the gaseous suspension of cooled particles of reduced clay, the second gas / particle separation device (170) comprising:- a gas outlet (1806) of a cooling gas separated from the cooled particles of reduced clay, and- a particle outlet (1804) of cooled particles of reduced clay, the gas outlet (1806) of the second gas / particle separation device (180) being connected to the means for introducing the cooling gas into the cooling reactor (110).

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