FR2977660A1 - Regenerator, useful in heat installations, comprises a packed bed of energy storage elements made of a material comprising ferric oxide, alumina, calcium oxide, titania, silica, sodium oxide and other compounds - Google Patents

Abstract

Regenerator comprises a packed bed of energy storage elements made of a material comprising 25-90 wt.% of ferric oxide, 5-30 wt.% of alumina, less than 20 wt.% of calcium oxide, less than 25 wt.% of titania, 3-50 wt.% of silica, less than 10 wt.% of sodium oxide and balance of other compounds, where the sum of ferric oxide, alumina, calcium oxide, titania, silica and sodium oxide is greater than 80 wt.%. An independent claim is included for a heat installation comprising a unit producing heat-generating energy (12) and the regenerator (14, 14'), a heat-transfer fluid ensuring a heat exchange between the unit and the regenerator.

Description

Regenerator Technical field The invention relates to a thermal storage regenerator, as well as to a thermal installation comprising such a regenerator. Technological background The storage of energy, for example heat, makes it possible to shift the production and consumption of this energy over time. The storage of heat energy is also useful for promoting soft energies, such as solar energy, which are renewable but whose production is intermittent. Energy storage can also be useful to take advantage of the differences in electricity prices between the so-called “off-peak” hours during which electricity prices are the lowest, and the so-called “peak” hours during which the rates are the highest. For example, in the case of energy storage by air compression, generating heat energy which is stored in a thermal regenerator, the compression phases consuming electricity are advantageously carried out at a lower cost during off-peak hours. , while the relaxation phases producing electricity are carried out during peak hours, in order to provide electricity which can be injected into the electrical network, according to demand, at an advantageous rate. The heat energy is conventionally stored in a bed (“packed bed” in English) of energy storage elements (“media” in English) of a regenerator, for example in a bed of pebbles. The storage operation, by heat exchange between a stream of calorific fluid and the regenerator, is conventionally called “the load”, the calorific fluid entering the regenerator during the load being called “load calorific fluid”. The transfer of heat energy can lead to an increase in the temperature of these energy storage elements (“sensible” heat storage) and / or to a change of state of these elements (“latent” heat storage). .

The stored heat energy can then be restored, by heat exchange between a flow of heat transfer fluid and the energy storage elements. This operation is conventionally called "the discharge", the heat transfer fluid entering the regenerator during the discharge being called "discharge heat fluid". “A review on packed bed solar energy storage systems”, Renewable and Sustainable Energy Reviews, 14 (2010), p 1059-1069, describes the state of the art in the field of regenerators. During the operation of a regenerator, and in particular when the coolant is humid air, the condensates of the humidity in the air corrode the materials of the regenerator. Moreover, at high pressures, the water present in the air can condense and mix with other condensates or pollutants present. The latter can thus make the water acidic and therefore corrosive. This results in a considerable reduction in the lifespan of the regenerator, which should be greater than 20 years, or even greater than 30 years in industrial installations, and therefore an increase in the overall cost. There is therefore a need to increase the lifespan of regenerators, in particular with regard to corrosive acid attacks, in particular at operating temperatures above 350 ° C, or even above 500 ° C, and in particular for regenerators loaded with humid air. An object of the invention is to satisfy, at least partially, this need Summary of the invention This object is achieved by means of a regenerator, in particular a sensible heat regenerator, comprising a bed of storage elements. energy in a material exhibiting the following chemical analysis, in percentages by mass: - 25% <Fe2O3 <70%, and - 5% <AI2O3 <30%, and - CaO <20%, and - TiO2 <25%, and - 3% <SiO2 <50%, and - Na2O <10%, and - Fe2O3 + AI2O3 + CaO + TiO2 + SiO2 + Na2O> 80%, and - Other compounds: complement to 100%. The inventors have observed that a regenerator according to the invention exhibits remarkable efficiency.

Surprisingly, the inventors have also found that the energy storage elements are particularly resistant to acidic water, which makes them well suited to the applications, according to the invention, in which they come into contact with acidic liquids.

A regenerator according to the invention may also have one or more of the following optional characteristics: Said material has an Fe2O3 content, preferably greater than 300/0, preferably greater than 350/0, preferably greater than 400/0, or even greater than 450/0, or even greater than 500/0, and / or preferably less than 650/0, or even less than 60%; Said material has an Al2O3 content preferably less than 250/0, preferably less than 200/0; Said material has a CaO content preferably greater than 30/0, or even greater than 50/0, or even greater than 100/0; Said material has a TiO2 content preferably greater than 50/0, or even greater than 100/0, and / or preferably less than 200/0, preferably less than 15%; Said material has an SiO2 content preferably greater than 50/0, or even greater than 80/0, and / or less than 400/0, preferably less than 300/0, preferably less than 200/0, preferably less at 150/0; Said material has an Na2O content preferably less than 5 ° / U; Said material has Fe2O3 + Al2O3 + CaO + TiO2 + SiO2 + Na2O, preferably greater than 850/0, or even greater than 900/0; Said material has a sum of the mass contents of Fe2O3, Al2O3 and SiO2, Fe2O3 + Al2O3 + SiO2, preferably greater than 500/0, preferably greater than 600/0, or even greater than 700/0, or even greater than 750/0. ; Said material has a sum of the mass contents of Fe2O3 and Al2O3, Fe2O3 + Al2O3, preferably greater than 400/0, preferably greater than 500/0, or even greater than 600/0, or even greater than 700/0; Said material has an Fe2O3 content, based on the sum of the mass contents of Fe2O3, Al2O3 and SiO2, Fe2O3 + Al2O3 + SiO2, preferably greater than 450/0, preferably greater than 500/0, or even greater than 600 / 0; Preferably, the “other compounds” consist for more than 900/0, preferably for more than 950/0, of oxides; Preferably, MgO, K2O, P2O5, and their mixtures represent more than 90%, more than 95%, or even substantially 100% of the other compounds; Said material has an open porosity greater than 5%, and / or less than 30%, preferably less than 25%, or even less than 20%, or even less than 15%, or even less than 10%, or even less than 6%; Energy storage elements are sintered products. Preferably, said material incorporates residues from the production of alumina, in particular according to the Bayer process, this process being described in particular in “The techniques of engineers”, article “extractive metallurgy of aluminum”, reference M2340, editions. Ti, publication date January 10, 1992 (in particular Chapter 6 starting on page M2340-13 and Figure 7 on page M2340-15). Preferably, the energy storage elements are obtained by sintering a preform resulting from the shaping of a starting charge phase comprising more than 10%, preferably more than 30%, preferably more than 50 %, preferably more than 60%, preferably more than 70%, preferably more than 80% of red sludge, in percentage of dry matter, resulting from the implementation of a Bayer process, in percentage by mass on the basis of the starting charge. Said red sludge can optionally be transformed before use, for example during washing and / or drying steps. The invention also relates to a thermal installation comprising: - a unit producing heat energy, for example an oven, a solar tower, a compressor, and - a regenerator according to the invention, and - a circulation device ensuring, during a charging phase, the circulation of a charge coolant from the unit producing heat energy to the regenerator, then through said regenerator. In one embodiment, the energy storage elements are in contact, permanent or temporary, with an acidic liquid with a pH of less than 6, or even less than 5.5, or even less than 5, or even less than 4.5, see less than 4, especially aqueous. The invention is in fact particularly advantageous under these conditions.

The temperature of the heat transfer fluid entering the regenerator during charging is preferably less than 1000 ° C, or even less than 800 ° C and / or preferably greater than 350 ° C, or even greater than 500 ° C. The thermal installation may in particular be a unit producing more than 50 kW, or more than 100 kW, or even more than 300 kW, or even more than 1 MW, or even more than 5 MW of heat energy. Preferably, the regenerator is heat-sensible, i.e. the material of the energy storage elements and the charge and discharge temperatures are determined so that the energy storage elements remain solid for the operation of the thermal installation. It is in fact in a sensible heat regenerator that the probabilities of condensation of the heat transfer fluid are greatest. Preferably, a thermal installation according to the invention comprises a consumer of heat energy, said circulation device ensuring, during a discharge phase, a circulation of a discharge coolant through said regenerator, then from said regenerator to to the consumer of heat energy. In one embodiment, the unit producing heat energy comprises, or even consists of a compressor powered mechanically or electrically by an incineration plant or an electricity production plant, in particular a thermal power plant, powered by energy. solar, wind, hydro, or tidal power. The unit producing heat energy and / or the consumer of heat energy may include a heat exchanger suitable for ensuring heat exchange, direct or indirect, with the regenerator. In one embodiment, the circulation device ensures, during a charging phase, the circulation of a charge coolant from the unit producing heat energy to the regenerator, then through said regenerator, said coolant fluid. charge entering said regenerator at a charging temperature Tc, and during a discharge phase, circulation of a discharge coolant through said regenerator; the discharge coolant fluid entering said regenerator at a discharge temperature Td, and the energy storage elements are made of a material having a melting temperature greater than Tc + 50 ° C and less than 2000 ° C, the concentration of all the elements leached from said material in response to the test described in the standard EN 30 12457-2 of December 2002, being less than or equal to 0.5 g / I, and said material of the energy storage elements having a characteristic ratio A greater than 0.3, with: A = (Cp (Tc) - Cp (Td)) / Cp (Td) where - Cp (Tc) is the heat capacity of said material at the load temperature, and - Cp (Td) is the heat capacity of said material at the discharge temperature. Preferably, the characteristic ratio is greater than 0.35, preferably greater than 0.40, preferably greater than 0.45, and / or is less than 0.60.

Preferably, the material has a higher melting point of more than 100 ° C, more than 150 ° C, or even more than 200 ° C at the charging temperature. Preferably, the material has a melting point of less than 1950 ° C, less than 1900 ° C, or even less than 1800 ° C, and / or a concentration of all the elements leached from said material, measured according to the EN standard. 12457-2 less than or equal to 0.1 g / l, preferably less than or equal to 0.05 g / l. Brief description of the figures Other objects, aspects, properties and advantages of the present invention will become apparent in the light of the description and the examples which follow and on examination of the appended drawing in which: FIG. 1 represents curves of the change in the temperature of the charge coolant along its path in a regenerator, depending on the length of the regenerator. These curves are considered to be substantially identical to the temperature of the storage elements along said length of the regenerator. Curve C; is the curve obtained at the start of charging and the curve Cf is the curve obtained at the end of charging. The length of the regenerator, in meters, is shown on the x-axis and the temperature of the charge coolant, in this case air, is on the y-axis, in Kelvin; - Figure 2 shows curves of the evolution of the temperature of the discharge coolant along its path in a regenerator, according to the length of the regenerator. These curves are considered to be substantially identical to the temperature of the storage elements along said length of the regenerator. Curve D; is the curve obtained at the start of the discharge and the curve Df is the curve obtained at the end of the discharge. The length of the regenerator, in meters, is shown on the x-axis and the temperature of the discharge coolant, in this case air, is on the y-axis, in Kelvin; - Figures 3a and 3b, 4a and 4b, 5a and 5b schematically represent thermal installations according to the invention; - Figure 6 schematically shows a regenerator; - Figures 7a and 7b show the evolution of the temperature of the storage elements made of a material according to Example 1 and according to Example 2, respectively, arranged on the axis of the cylinder of the regenerator, in a stabilized state, as a function of of the position on said axis ("axial position"). The axial position, in meters, is shown on the abscissa and the temperature of the charging and discharging coolant, in this case air, is on the ordinate, in Kelvin. For Figures 1 and 2, the calculations were carried out for a regenerator having a length of 30 m and a diameter of 5 m, the charging phase and the discharging phase lasting 10,800 seconds.

Figures 3a, 4a and 5a correspond to charging phases. Figures 3b, 4b and 5b correspond to discharge phases. The pipes traversed by a fluid are represented with a thicker line. The valves necessary to modify the circulation in the various circuits have not been shown. In the various figures, identical references are used to designate identical or similar members. Definitions By "unit producing heat energy", we consider not only units which are specifically intended to generate heat energy, such as a solar tower, but also units which, by their operation, generate energy. calorific, for example a compressor. The term “thermal installation” is also to be understood in the broad sense, as meaning any installation comprising a unit producing heat energy. The term “heat energy consumer” designates an element capable of receiving heat energy. This may in particular result in an increase in the temperature of the consumer (for example in the case of heating a building) and / or a transformation into mechanical energy (for example in a gas turbine). In the present description, for the sake of clarity, the term “charge coolant” and “discharge coolant” refers to the coolant circulating in the regenerator during charging and during discharge, respectively. The charge coolant is said to be “cooled” when it leaves the regenerator. The discharge coolant is said to be "reheated" when it leaves the regenerator. The term “bed” of energy storage elements is understood to mean a set of such elements at least in part superimposed on one another. The term “preform” is conventionally understood to mean a set of particles bound by means of a binder, generally temporary, and whose microstructure will change during sintering. The term “sintering” is used to describe heat treatment by which particles of a preform are transformed to form a matrix binding together other particles of said preform. For the sake of clarity, the term “red sludge” is used to refer to the liquid or pasty by-product resulting from an alumina manufacturing process and the corresponding dried product. The oxide contents relate to the overall contents for each of the corresponding chemical elements, expressed in the form of the most stable oxide, according to the usual industry convention. Unless otherwise indicated, all percentages are percentages by weight. By “containing a”, “comprising a” or “comprising a” is meant “comprising at least one”, unless otherwise indicated. Detailed description A thermal installation according to the invention comprises a unit producing heat energy, a regenerator, a circulation device. It can also include a calorific energy consumer and / or a cavity. Heat Energy Generating Unit The heat energy generating unit can be designed to produce heat energy, for example be a furnace or a solar tower. In one embodiment, the heat energy generating unit includes a compressor. The compression of a gaseous fluid, preferably adiabatic, results in the storage of energy therein by increasing its pressure and its temperature. The energy resulting from the increase in pressure can be stored by keeping the fluid under pressure. The restitution of this energy can result from an expansion, for example in a turbine.

According to the invention, the energy resulting from the increase in temperature is stored in a regenerator. The restitution of this energy then results from a heat exchange with the regenerator. Heat energy can be a production by-product, that is to say not be sought after as such. Preferably, the unit producing heat energy produces more than 50 kW, or even more than 100 kW of heat energy, or even more than 300 kW, or even more than 1 MW, or even more than 5 MW. The invention is in fact particularly intended for high-power industrial installations.

Calorific energy consumer The calorific energy consumer can be a building or a set of buildings, a reservoir, a basin, a turbine coupled to an alternator in order to generate electricity, an industrial installation consuming steam from water, for example a pulp production plant.

Regenerator The regenerator is formed, in a conventional manner, by a bed of energy storage elements. A regenerator according to the invention can be manufactured according to a process according to the invention comprising the following steps: a) production of a starting charge, optionally comprising a red sludge; b) shaping of said starting charge in order to obtain a preform, c) optionally, drying of said preform, d) sintering of the preform - at a temperature between 1000 ° C and 1500 ° C, preferably for a period of holding time at this temperature greater than 0.5 hour and preferably less than 12 hours, and - preferably in an oxidizing atmosphere, preferably in air, except if step a) comprises an operation of calcining the red mud , the atmosphere then being preferably reducing, so as to obtain an energy storage element, e) after manufacture of a plurality of energy storage elements according to steps a) to d), grouping of said elements energy storage so as to constitute a bed of a regenerator.

If the starting charge comprises a red mud, step a) can comprise the following operations: a1) optionally, drying of said red mud, a2) optionally, grinding of said dried red mud, in particular to break up any agglomerates formed during drying, a3) optionally, adding a raw material containing iron oxide to the red mud, a4) optionally, calcining at a temperature between 900 ° C and 1300 ° C, in a reducing atmosphere, and, grinding.

All the conventional sintering processes can be implemented, provided that the starting charge is suitable for the manufacture of energy storage elements suitable for a regenerator according to the invention. In step a), a starting charge is prepared. Preferably, the starting charge comprises a red sludge, preferably prepared according to a process comprising the operations a1) to a4). In operation a1), optional, said red sludge is dried at a temperature preferably between 100 ° C and 500 ° C, preferably between 200 ° C and 350 ° C. The holding time at this temperature is preferably between 3 hours and 100 hours. In operation a2), optional, the red sludge dried in operation a1)) is crushed in order to break up the agglomerates which could have formed during the drying operation a1). The grinding can be carried out in a crusher, or in a lump breaker. In operation a3), optional, an iron oxide powder can be added to the red slurry, in order to increase the amount of iron oxide in the mixture. In operation a4), optional, the mixture obtained at the end of operation a2) or a3) undergoes calcination, at a temperature between 900 ° C and 1300 ° C, for a time held at this temperature greater than 0 , 5 hour, preferably greater than 1 hour and preferably less than 10 hours, or even less than 5 hours, in a reducing atmosphere. The calcined mixture can be ground to break up any agglomerates that may have formed. The grinding can be carried out, for example, in a ball mill or in a roller mill. Preferably the starting charge comprises more than 100/0, preferably more than 300/0, preferably more than 500/0, preferably more than 600/0, preferably more than 700/0, preferably more 80%, in percentage by mass on the basis of the dry matter, of red sludge resulting from the manufacture of alumina by the Bayer process, in percentage by mass on the basis of the dry matter. Preferably, the dry matter of the red mud is in the form of a powder of particles of which more than 70%, preferably more than 80%, preferably more than 90% by mass of said particles have a size less than 200 pm. More preferably, more than 50%, or even more than 60% by mass of the particles have a size of less than 10 μm. Preferably, the dry matter of the red mud has the following chemical analysis: - 25% <Fe2O3 <70%, preferably Fe2O3 <65%, or even Fe2O3 <60% and / or preferably Fe2O3> 30%, preferably Fe2O3> 35%, preferably Fe2O3> 40%, or even Fe2O3> 45%, or even Fe2O3> 50%, and - 5% <AI2O3 <30%, preferably <20%, and - CaO <20%, and - TiO2 <25%, preferably <20%, preferably <15%, and - 3% <SiO2 <50%, preferably <40%, preferably <30%, preferably <20%, preferably <15%, and - Na2O <10%, or even less than 5%, and - Fe2O3 + AI2O3 + CaO + TiO2 + SiO2 + Na2O> 80%, preferably> 85%, or even> 90%, or even> 95% and - Other compounds: 100% complement. Preferably, the dry matter of the starting charge consists for more than 90%, preferably for more than 95%, preferably for more than 99% of oxides. In one embodiment, the starting charge contains a powder containing more than 90% by mass of silica, preferably a powder of silica fume. The amount of silica powder, in% by mass on the basis of the dry starting charge, without the additives, is preferably greater than 2%, preferably greater than 3%, or even greater than 5% and less than 10%. In another embodiment, the starting charge contains an alumina silicate powder, in particular a clay and / or a kaolin and / or a sillimanite, preferably containing an alumina content by weight of between 30% and 65%, preferably a clay powder. The amount of alumina silicate powder, in particular clay powder, in% by mass on the basis of the dry starting charge, is preferably greater than 5%, preferably greater than 10%, or even greater than 15%. % and less than 40%, or even less than 30%. Advantageously, the clay can also serve as a shaping additive.

The Andreasen or Fuller-Bolomey compaction models can be used to match the particle size distribution to the bulk density of the energy storage element being manufactured. Such compaction models are described in particular in the work entitled “Treaty of ceramics and mineral materials”, C.A. Jouenne, Editions Septima. Paris (1984), pages 403 to 405. The starting charge can still contain more than 0.1% by mass of a shaping additive. The additive can in particular be chosen from the group consisting of: - clays; - plasticizers, such as polyethylene glycols (or “PEG”) or polyvinyl alcohol (or “PVA”); - binders including temporary organic binders such as resins, lignosulfonates, carboxymethylcellulose or dextrin; - deflocculants, such as alkali metal polyphosphates, alkali metal polyacrylates, polycarboxylates; and - mixtures of these products. Preferably, the shaping additive is chosen from the group consisting of clays, lignosulfonates, PVA, PEGs, and mixtures thereof.

Preferably, the content of shaping additive is less than 6%, as a percentage by mass on the basis of the starting charge, except as regards clay. The amount of water depends on the following steps. It is generally between 0 and 20%, as a percentage by mass on the basis of the starting charge without the additives. In step b), the shaping can be carried out by various techniques, among which there may be mentioned cold pressing, slip casting, plastic paste pressing, granulation and extrusion. In the case of forming by cold pressing, an addition of an amount of water between 1.5% and 4%, as a percentage by mass on the basis of the starting charge without the additives, is preferred. , in particular if the red mud was dried during an operation a1) and / or calcined during an operation a4). In the case of a shaping involving an extrusion, an addition of a quantity of water of between 10% and 20%, as a percentage by mass on the basis of the starting charge without the additives, is preferred, in particularly if the red mud was dried during an operation a1) and / or calcined during an operation a4). In one embodiment, the quantity of water contained in the red mud used in step a) is sufficient to allow shaping, for example by extrusion, without having to add an additional quantity of water.

Drying can be carried out during an optional step c). Preferably, the drying is carried out at a temperature between 100 ° C and 600 ° C, preferably between 200 ° C and 350 ° C. The holding time at this temperature is preferably between 3 hours and 100 hours. In step d), the preform is sintered. The sintering conditions, and in particular the sintering temperature, depend on the composition of the starting charge. Usually, a sintering temperature of between 1000 ° C and 1500 ° C, preferably between 1100 ° C and 1300 ° C is well suited. Preferably, the sintering is carried out in a reducing atmosphere if the process comprises a step a4). If said process does not include an optional step a4), the sintering is preferably carried out in an oxidizing atmosphere, preferably in air. At the end of step d), an energy storage element is obtained. The energy storage element can undergo a finishing operation during an optional step, in particular chosen from among grinding, sawing, surfacing, drilling, machining, in order to adapt it to the geometry of the regenerator. These operations can be carried out according to all the techniques known to those skilled in the art. The method described above is not limiting. The shapes and dimensions of the energy storage elements are not limiting. Preferably however, the smallest dimension of an energy storage element is greater than 0.5 mm, or even greater than 1 mm, or even greater than 5 mm, or even greater than 1 cm and / or preferably less than 50 cm, preferably less than 25 cm, preferably less than 20 cm, preferably less than 15 cm. Preferably the largest dimension of a storage element is less than 10 meters, preferably less than 5 meters, preferably less than 1 meter. The energy storage elements can in particular take the form of balls and / or granules and / or solid bricks and / or perforated bricks, and / or cruciform elements and / or double cruciform elements and / or solid elements and / or perforated elements such as those described in US 6,889,963 and / or described in US 6,699,562.

In step e), said energy storage elements are grouped together so as to constitute a bed. The bed can be organized, for example by equipment of energy storage elements, or be disorganized (“bulk”). For example, the bed can be in the form of a mass of crushed pieces (without any particular shape, like a mass of pebbles). The height of the bed is preferably greater than 5 m, preferably greater than 15 m, preferably greater than 25 m, or even greater than 35 m, or even greater than 50 m. The mass of the bed is preferably greater than 700 T, preferably greater than 2000 T, preferably greater than 4000 T, preferably greater than 5000 T, preferably greater than 7000 T. Preferably, the energy storage elements are grouped together in an enclosure comprising first and second openings intended for the introduction and extraction of a heat transfer fluid in said enclosure, respectively.

In one embodiment, the opening of the regenerator through which charge coolant enters the regenerator during a charging phase is that through which heated discharge coolant fluid leaves the regenerator during a discharge phase. Conversely, the opening of the regenerator through which the discharge coolant to be heated enters the regenerator during a discharge phase is that through which the cooled charge coolant leaves the regenerator during a charge phase. Preferably, the opening of the regenerator through which the heated discharge coolant intended for a furnace leaves the regenerator is in the upper part of the regenerator.

Preferably, the opening of the regenerator through which the discharge coolant to be heated enters the regenerator is in the lower part of the regenerator. Circulation device The circulation device conventionally comprises a set of pipes, valves and pumps / fans / extractors controlled in such a way as to be able to selectively put the regenerator in communication - with the unit producing heat energy in such a way that it can receive a heat transfer fluid leaving said unit, during the charging phases, and - with the calorific energy consumer so that the heated discharge coolant leaving the regenerator can heat said consumer, or more generally transfer water heat energy to said consumer, during the discharge phases, and so as to be able to force the circulation of the charge coolant and / or the discharge coolant through the regenerator. Heat transfer fluids The charge and discharge heat transfer fluids may or may not be of the same type. The coolant used for charging and / or discharging the regenerator can be a gas, for example air, water vapor, or a coolant gas, or be a liquid, for example water. water or thermal oil. Cavity Preferably, in particular when the charge and discharge heat transfer fluid fluids are of the same nature and when the heat transfer fluid has undergone an increase in pressure, such as compressed air for example at 50 bar, or even 100 bar, or even 150 bar, the thermal installation may include an enclosure, called a “cavity”, for temporary storage of the coolant charge, cooled leaving the regenerator. The volume of the cavity is typically greater than 20,000 m3, or even greater than 100,000 m3. The cavity is preferably weakly permeable, or even impermeable to the heat transfer fluid.

Preferably, the thermal installation is configured to be able to operate according to at least one part, preferably all of the rules described below. Operation During charging, the charge coolant enters the regenerator at a temperature Tc, preferably substantially constant, generally via the upper part of the regenerator. Conventionally, under stabilized conditions, the difference between the temperature of the heat transfer fluid Tc and the temperature of the energy storage elements with which it then comes into contact (T,) is 15% to 20% of Tc (i.e. approximately 90 ° C to 120 ° C), and the heat transfer fluid cools rapidly to this latter temperature. Preferably, the temperature Tc at which the charge coolant enters the regenerator during its charge is less than 1000 ° C, or even less than 800 ° C and / or preferably greater than 350 ° C, or even greater than 500 ° C. .

The charge coolant then continues to travel through the regenerator, heating the energy storage elements with which it is in contact. Its temperature therefore drops gradually, as shown on curve C; of FIG. 1, up to the temperature Tc; '.

Preferably the temperature Tc; ' at which the charge coolant leaves the regenerator, at the start of charging, is close to the discharge temperature of the previous cycle. The curve of the evolution of the temperature of the charge coolant along its path in the regenerator depends in particular on the material of the energy storage elements and on the geometry of the regenerator. It changes over time during the charging phase, due to heating of the energy storage elements (displacement of curve C; towards curve Cf). Under steady state conditions, the curves C; and Cf are substantially identical from one charging phase to the next.

When the charge coolant is a gas, its cooling can lead to condensation on the surface of the energy storage elements, in particular in sensible heat regenerators. At high temperatures, such as those considered above in particular, the condensates can be very corrosive. As shown by the examples below, the energy storage elements of a regenerator according to the invention advantageously resist corrosion by these condensates very well. During the discharge, the discharge coolant enters the regenerator at a temperature Td which is preferably substantially constant, generally via the lower part of the regenerator. Conventionally, under stabilized conditions, the temperature Td is close to the temperature of the energy storage elements with which it then comes into contact (T2) and the heat transfer fluid heats up quickly to this latter temperature. The heat transfer fluid then continues its path in the regenerator, cooling the energy storage elements with which it is in contact. Its temperature therefore increases gradually, as shown on curve D; of FIG. 2, up to the temperature Td; '. The curve of the evolution of the temperature of the discharge coolant along its path in the regenerator also depends in particular on the material of the energy storage elements and on the geometry of the regenerator. It changes over time, due to the cooling of the energy storage elements (displacement of curve D; towards curve Df). Under steady state conditions, the curves D; and Df are substantially identical from one discharge phase to the next. The regenerator therefore undergoes a succession of “cycles”, each cycle comprising a charging phase, possibly a waiting phase, then a discharging phase. The cycle can be regular or irregular. Preferably it is regular, the duration of the first phases being identical to that of the second phases.

The duration of a regular cycle is generally greater than 0.5 hour, or even greater than two hours and / or less than 48 hours, or even less than 24 hours. Particular embodiments Figures 3a and 3b, 4a and 4b, 5a and 5b represent various advantageous embodiments. In all these embodiments, a thermal installation 10 according to the invention comprises a unit producing heat energy 12, a regenerator 14, a consumer of heat energy 16 and a circulation device 18. It may also include a cavity. 20, natural or artificial. The circulation device 18 has a charge circuit 22 and a discharge circuit 24 through which circulate a charge coolant and a discharge coolant, respectively. These charging 22 and discharging 24 circuits make it possible to put in a heat exchange relationship the unit producing heat energy 12 and the regenerator 14 during the charging phase, and the regenerator 14 and the heat energy consumer 16. during the discharge phase, respectively. Figures 3a and 3b show a first particular embodiment in which the heat energy consumer 16 comprises a heat exchanger 26 adapted to ensure heat exchange between the discharge coolant from the regenerator 14 (Figure 3b) and a heat transfer fluid secondary circulating in a secondary circuit 28. The secondary circuit 28 is configured to allow a heat exchange relationship of the heat exchanger 26 with, for example, a building 30.

The thermal installation 10 also comprises a direct heating circuit 32 allowing a direct heat exchange connection of the unit producing heat energy 12, for example a solar tower, and of the heat energy consumer 16 during the charging phase (figure 3a).

In this embodiment, the regenerator 14 is preferably close to the unit producing heat energy, for example less than 500 meters, or even less than 250 meters from this unit.

FIGS. 4a and 4b represent a second particular embodiment in which the unit producing heat energy 12 comprises a compressor 34 driven by energy, for example mechanical or electrical, produced by a group 36. The heat transfer fluid of charge, conventionally air, is therefore compressed and is heated by its passage through the compressor 34 before reaching, through the charge circuit 22, the regenerator 14. The regenerator may not be near the installation. which generates the electricity necessary for the compression of the air or of the compressor 34. At the outlet of the regenerator, the compressed cooled charge coolant fluid is stored in the cavity 20.

During discharge, the compressed discharge coolant (i.e. the charge coolant that was stored in the cavity) exits cavity 20, heats up through the regenerator and then passes through a gas turbine 38. The gas turbine 38 can drive an alternator (not shown) for the purpose of generating electricity, for example sent to the domestic network.

Heating allows the discharge coolant to accumulate heat energy in it. This energy, restored during expansion, improves the efficiency of the turbine 38. The turbine 38 therefore serves simultaneously as a consumer of heat energy (reduction in temperature) and as a consumer of mechanical energy (reduction in pressure).

The embodiment of FIGS. 4a and 4b is particularly well suited to installations which are not designed to generate heat energy, such as a wind power plant or an electric power station of the hydroelectric or tidal type. Such an installation is conventionally called an “adiabatic compression energy storage installation”. FR 2 947 015 describes an installation of this type. FIGS. 5a and 5b represent a variant of the second particular embodiment. The thermal installation 10 comprises, in addition to the elements of the second embodiment, a second regenerator 14 'and, in a second charging circuit 22' of the second regenerator 14 ', upstream of the second regenerator 14' (considering the direction of flow of the charge coolant), a second compressor 34 'and, in a second discharge circuit 24', downstream of the second regenerator 14 '(considering the direction of flow of the discharge coolant), a second gas turbine 38 '. The second regenerator 14 ', second charge circuit 22', second charge circuit 24 ', second compressor 34' and second gas turbine 38 'function as regenerator 14, charge circuit 22, charge circuit 24, compressor 34 and gas turbine 38. Together with regenerator 14, acting as a unit producing heat energy, they constitute a thermal installation according to the invention. Preferably, the compressor 34 is a medium pressure compressor and the compressor 34 'is a high pressure compressor. Several thermal installations according to the invention can thus be arranged in series.

FIG. 6 shows an example of a regenerator 14. This regenerator comprises a bed of energy storage elements 40, an upper opening 42 and a lower opening 44 through which the coolant charge and discharge fluids, respectively, enter the tank. regenerator. The charge and discharge heat transfer fluids exit regenerator 14 through lower 42 and upper 44 openings, respectively. Examples The following examples are provided for illustrative and non-limiting purposes.

The shape of the energy storage elements is similar for Examples 1 and 2. The energy storage elements according to Example 2 were produced as follows. In step a), the starting charge consists entirely of a red sludge, exhibiting the following chemical analysis, on the basis of the dry matter of said red sludge: Fe2O3 = 55%, AI2O3 = 16%, CaO = 5%, TiO2 = 11%, SiO2 = 8%, Na2O = 4%, others = 1%, and of which more than 60% by mass of the particles have a size less than 10 μm. Said starting charge contains no additive.

The shaping of said starting charge, in order to obtain preforms of length equal to 11 mm and of diameter equal to 16 mm, is carried out by uniaxial pressing at a pressure of 125 MPa. The preforms are then dried for 12 hours at 120 ° C.

The preforms are then sintered in air, in the following cycle: - rise to 1200 ° C at a speed of 100 ° C / h, - level for 3 hours at 1200 ° C, - fall at a speed of 100 ° C / h . The apparent density and the open porosity were measured according to the ISO5017 standard, after sintering for example 2. The chemical analyzes were carried out by X-ray fluorescence. The resistance to acid water was measured by the following method: product to be tested is ground, and the fraction between 0.3 mm and 1 mm is kept for analysis. 3 grams of this particle size fraction are introduced into a Teflon receptacle with a capacity equal to 180 ml containing 100 ml of deionized water, the resistance of which is greater than 16 Mohms, acidified to pH 3 with sulfuric acid. The container is hermetically sealed with screw lids and is placed in a heating block regulated in temperature at 110 ° C for 24 hours. The container is then removed from the heating block and cooled in ambient air.

The aqueous solution is collected, separated through a cellulose acetate membrane filter having pores of diameter equal to 0.1 μm. The silicon element content of this solution, expressed in mg / I, is analyzed by plasma torch spectrometry, or ICP for “Inductively Coupled Plasma” in English. Since silica is one of the major elements contributing to the cohesion of the products, the concentration of silicon in the acidic aqueous solution is assimilated by the inventors to the fact that the product is more or less attacked by acidic water at a pH equal to 3. Thus, for the inventors, the lower the quantity of silicon found in the acid solution, the more the tested product exhibits significant resistance to acidic water. The following assumptions were used to calculate the calorific energy returned by the regenerator as well as the air temperature at the end of discharge at the regenerator outlet: - regenerator of cylindrical shape, of constant section, of diameter equal to 5 m and length L equal to 20 m, - heat transfer fluid: dry air, constant volume of storage elements, no radial heat losses, charge temperature 800 ° C, i.e. 1073 K, discharge temperature 400 ° C, i.e. 673 K. The following formula gives the quantity of heat energy released by the regenerator: L Tf pSCp (T) .dT.dx 0 Ti In this formula: Ti: temperature at the start of charging in the section of width dx, located at the axial position x x, in Kelvin, Tf: temperature at the end of discharge in the section of width dx, located at the axial position x, in Kelvin, p: apparent density of the bed, in kg / m3, S: circular section of the regenerator in m2 15 L: length of the regenerator r in m, Cp (T): heat capacity of the storage material at temperature T. The analyzes carried out on the storage elements and the results of the calculations carried out appear in the following table 1: Example 1: elements of Example 2: elements granite storage (excluding storage in a product according to the invention) the invention Chemical analysis of the storage elements of the regenerator% iron oxide expressed in the form 4 55 Fe2O3% AI2O3 8 16% CaO 5 5 TiO2 - 11 SiO2 70 8% Na2O 2 4% other compounds 11 1 Other characteristics of the regenerator storage elements Apparent density of the material 2.6 3.3 of the storage elements (gr / cm3) Open porosity (%) 2 21 Cp at 25 ° C (J kg- 'K- »800 700 Results Heat energy restored by the regenerator 379 380 (GJ) Air temperature at the end of discharge, in 459 504 regenerator outlet (° C) Resistance to acid water at 110 ° C for 490 260 24 hours: silicon concentration (mg / I) 20 Table 1 As shown in The results shown in Table 1, after contact at 110 ° C for 24 hours with acidic water at a pH equal to 3, the quantity of silicon measured in said acidic water is less important for the energy storage elements of Example 2 according to the invention. The resistance to acidic water of the energy storage elements of Example 2 according to the invention is greater than that of the energy storage elements of Example 1 outside the invention. The lifespan of a regenerator containing energy storage elements of Example 2 according to the invention will therefore be improved in an acidic environment.

Furthermore, the efficiency of a regenerator depends closely on its geometry and on the material of the energy storage elements used to accumulate and restore heat energy. The inventors have observed that a regenerator according to the invention makes it possible to obtain a temperature of the coolant at the outlet of the regenerator during the discharge, for the same volume of energy storage elements, greater than that which can be obtained with a regenerator outside the invention. Table 1 shows in fact that the regenerator containing energy storage elements of Example 2 according to the invention has a temperature at the end of discharge equal to 504 ° C., higher than the temperature at the end of discharge of the regenerator containing storage elements of Example 1 outside the invention (459 ° C). The performance of a turbine supplied with air at the outlet of the regenerator containing storage elements of Example 2 according to the invention are therefore superior to those of a regenerator containing storage elements of Example 1. This This advantage is all the more obvious given that environmental regulations and the desire to control expenditure encourage industries to seek ever more energy savings. Of course, the present invention is not limited to the embodiments described and shown, provided by way of examples. In particular, combinations of the various embodiments described or shown also come within the scope of the invention. The invention is also not limited by the shape or dimensions of the regenerator. Finally, the energy storage elements can be in contact with a neutral or basic environment.

Claims (30)

CLAIMS 1. Regenerator comprising a bed of energy storage elements made of a material exhibiting the following chemical analysis, in percentages by mass: - 25% <Fe2O3 <70%, and - 5% <AI2O3 <30%, and - CaO <20 %, and - TiO2 <25%, and - 3% <SiO2 <50%, and - Na2O <10%, and - Fe2O3 + AI2O3 + CaO + TiO2 + SiO2 + Na2O> 80%, and - Other compounds: complement to 100%. 2. Regenerator according to the preceding claim, wherein said material has an iron oxide content expressed in the Fe2O3 form greater than 30%, in percentage by mass. 3. Regenerator according to the preceding claim, wherein said material has an iron oxide content expressed in the Fe2O3 form greater than 40%, in percentage by mass. 4. Regenerator according to any one of the preceding claims, in which said material has an iron oxide content expressed in the Fe2O3 form of less than 65%, in percentage by mass. 5. Regenerator according to any one of the preceding claims, in which said material has an Al2O3 content of less than 250/0, in percentage by mass. 6. Regenerator according to the preceding claim, wherein said material has an Al2O3 content of less than 20%, in percentage by mass. 7. Regenerator according to any one of the preceding claims, in which said material has a CaO content of greater than 3%, in percentage by mass. 8. Regenerator according to the preceding claim, wherein said material has a CaO content greater than 10%, in percentage by mass. 9. Regenerator according to any one of the preceding claims, in which said material has a TiO2 content of less than 20%, in percentage by mass. 10. Regenerator according to the preceding claim, wherein said material has a TiO2 content of less than 15%, in percentage by mass. 11. Regenerator according to any one of the preceding claims, in which said material has an SiO2 content of less than 40%, in percentage by mass. 12. Regenerator according to the preceding claim, wherein said material has an SiO2 content of less than 20%, in percentage by mass. 13. Regenerator according to any one of the preceding claims, in which said material has an Na2O content of less than 5%, in percentage by mass. 14. Regenerator according to any one of the preceding claims, wherein said material has, in percentages by mass, an Fe2O3 + Al2O3 + CaO + TiO2 + SiO2 + Na2O content> 85%. 15. Regenerator according to any one of the preceding claims, in which said material has, in percentage by mass, an Fe2O3 + Al2O3 + SiO2 content> 50%. 16. Regenerator according to any one of the preceding claims, in which said material has, in percentage by mass, an Fe2O3 + Al2O3 content> 40%. 17. Regenerator according to any one of the preceding claims, wherein said material has, as a mass percentage, an Fe2O3 content> 45%, based on the sum of Fe2O3 + Al2O3 + SiO2. 18. Regenerator according to any one of the preceding claims, in which the “other compounds” of said material consist for more than 90% of oxides. 19. A regenerator according to any preceding claim, wherein said material is a sintered material. 20. Regenerator according to any one of the preceding claims, in which the energy storage elements are obtained by sintering a preform resulting from the shaping of a starting charge comprising more than 10% of red sludge obtained. of the production of alumina by the Bayer process, as a percentage by mass based on the dry matter of the feedstock. 21. Regenerator according to the preceding claim, wherein said starting charge comprises more than 50% red sludge, in percentage by mass based on the dry matter of the starting charge. 22. Regenerator according to the preceding claim, wherein said starting charge comprises more than 80% red sludge, in percentage by mass based on the dry matter of the starting charge. 23. Regenerator according to any one of the preceding claims, in which the mass of the bed is greater than 700 tonnes. 24. Thermal installation comprising a unit for producing heat energy (12) and a regenerator (14; 14 ') according to any one of the preceding claims, a heat transfer fluid ensuring heat exchange between said unit and said regenerator. 25. Thermal installation according to the preceding claim, wherein the heat transfer fluid from said unit producing heat energy (12) condenses in said regenerator (14; 14 ') in the form of an acidic liquid. 26. Thermal installation according to any one of the two immediately preceding claims, in which the temperature of the heat transfer fluid coming from said unit and entering the regenerator is less than 1000 ° C and greater than 350 ° C. 27. Thermal installation according to the preceding claim, wherein said temperature is less than 800 ° C and greater than 500 ° C. 28. Thermal installation according to any one of claims 24 to 27, wherein the unit for producing heat energy comprises a compressor (34; 34 '). 29. Thermal installation according to any one of claims 24 to 28, comprising - a calorific energy consumer (16), and - a circulation device (18) ensuring - during a charging phase, the circulation of a fluid. charge coolant from the unit producing heat energy to the regenerator, then through said regenerator, and - during a discharge phase, circulation of a discharge coolant through said regenerator and then from said regenerator to 'to the consumer of heat energy. 30. Thermal installation according to the preceding claim, wherein the heat energy consumer comprises a turbine (38; 38 ').