FR3065794A1 - HEAT STORAGE TANK OPTIMIZED FROM GLASS PARTICLES - Google Patents

Abstract

The present invention relates to a thermal storage tank 1 capable of containing at least one heat transfer fluid 6 and comprising at least one chemically inert solid thermal storage material 7 comprising at least glass particles. The invention also relates to a solar power plant comprising at least one storage tank 1 as defined above as well as the use of at least one chemically inert solid thermal storage material 7 as defined above to limit the rate of degradation. a heat transfer fluid 6 in a thermal storage tank 1.

Description

© Publication number: 3,065,794 (to be used only for reproduction orders) (© National registration number: 17 53761 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY

COURBEVOIE © Int Cl ⁸ : F28 D 20/00 (2017.01), F24 J2 / 34

A1 PATENT APPLICATION

©) Date of filing: 28.04.17. © Applicant (s): BABCOCK WANSON — RR and (© Priority: AFIKEMA FRANCE Public limited company - FR. @ Inventor (s): DEYDIER ALEXANDRE, BLANC JEROME and LARNICOL PIERRE. (43) Date of public availability of the request: 02.11.18 Bulletin 18/44. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): BABCOCK WANSON, ARKEMA related: FRANCE Public limited company. ©) Extension request (s): (© Agent (s): CASALONGA.

P4 / OPTIMIZED HEAT STORAGE TANK FROM GLASS PARTICLES.

FR 3 065 794 - A1 _ The present invention relates to a thermal storage tank 1 capable of containing at least one heat transfer fluid 6 and comprising at least one chemically inert solid thermal storage material 7 comprising at least glass particles.

The invention also relates to a solar power station comprising at least one storage tank 1 as defined above as well as the use of at least one chemically inert solid thermal storage material 7 as defined above to limit the rate of degradation. of a heat transfer fluid 6 in a thermal storage tank 1.

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Optimized heat storage tank from glass particles

The present invention relates to a thermal storage tank comprising at least one chemically inert solid thermal storage material containing at least glass particles.

The invention also relates to the use of at least one chemically inert solid thermal storage material comprising at least glass particles to limit the rate of degradation of a heat transfer fluid capable of circulating in a thermal storage tank.

The invention also relates to a solar power plant comprising at least one thermal storage tank containing at least one heat transfer liquid and at least one chemically inert solid thermal storage material comprising at least glass particles.

The energy transition is one of the great challenges of our century because it designates the passage of the current energy system using non-renewable resources, such as oil, natural gas, coal, and radioactive materials such as uranium and plutonium, to a system based mainly on renewable resources, such as biomass, and renewable energy sources such as hydro, wind, solar or geothermal energy.

Among these renewable energies, some have an irregular and intermittent production. Energy storage is therefore in this case a technology allowing to increase their use and constitutes a central element of the energy transition due to its flexibility and efficiency. It not only makes it possible to better value energy but also to better size our future equipment, production as well as consumption.

The so-called conventional energy storage technologies (pumping, batteries, hydrogen, compressed air) generally have in common the often very high cost of the initial investment of the storage installation. In addition, the geographic impact of projects involving a pumped storage system (also called STEP: pumped energy transfer stations), linked to hydraulic energy, or compressed air storage in cavities (still called CAES: Compressed Air Energy Storage in English) is important, because of the size of the installations implemented, and the number of possible sites of establishment can prove to be limited.

Heat is a form of energy that can be stored very easily at low cost, especially at low temperatures, and its storage mainly allows the heating of buildings, which represents a significant part of energy consumption in Europe. In addition, heat storage can also improve the functioning and the lifespan of solar power plants, in particular thermodynamic concentrated solar power plants (called CSP: Concentrated Solar Power).

Heat sources come primarily from solar energy which, by its nature, is intermittent (for example, difference between day and evening or between summer and winter), diluted and random ( especially because of unpredictable cloudy periods) which makes its production offset from daily or seasonal energy demand. The purpose of heat storage is therefore to compensate for the intermittent and random nature of solar energy by reducing the time lag and decoupling between the most productive periods and the periods of greatest demand. In particular, the heat, produced excessively during periods of strong sunshine, can advantageously be stored in order to be subsequently used at the end of the day.

In addition, the heat can come from industrial processes implemented in many fields. In this case, it is possible to store the heat produced by certain industries in addition to their main activity.

Heat storage is usually done from a solid, liquid material or a combination of both, called storage material, having the ability to release or store heat through heat transfer. Such a transfer can be effected by sensible heat, i.e. by changing the temperature of the material (in other words, the heat is stored in the material), or by latent heat, i.e. -display by isothermal phase change at constant pressure of the material (in particular a solid / liquid change of a material for which the volume variation is small).

Heat storage can also be done thermochemically by using reversible chemical reactions generally carried out at a temperature varying from 300 to 1000 ° C. These reactions consume or release heat by dissociation or combination of reactants. By way of example, mention may be made of the reversible reaction of dehydration of calcium hydroxide and of hydration of calcium oxide.

As a result, there are currently three main methods of heat storage.

The methods, aimed at transforming solar energy into heat and then converting the thermal energy obtained into electrical and mechanical energy, are generally implemented from a solar collection system, a thermal energy storage system and a thermodynamic conversion system. These conventional processes are typically used in concentrated thermodynamic solar power plants.

The purpose of the solar collection system is to collect solar radiation and to concentrate it on a receiver in which a heat-transfer fluid flows. During this stage, the solar radiation is converted into thermal energy. Such a system makes it possible to concentrate the sun's rays. In particular, the solar collection system can use cylindro-parabolic reflectors, linear Fresnel reflectors, heliostats (concentrated solar rays at the top of a fixed tower) or parabolic mirrors.

The storage system makes it possible to store and restore the excess thermal energy in order in particular to decorrelate the production of electrical and / or mechanical energy from the solar resource, thus overcoming the drawbacks linked to the intermittent and random nature of solar energy.

The process of storing heat of thermal energy generally takes place in three stages. A charging step, during which the thermal energy from the solar collection system is stored, a heat storage step, having a more or less long duration depending on the process used, and a discharging step ( or destocking) corresponding to the phase of restitution of thermal energy to the thermodynamic conversion system.

The purpose of the thermodynamic conversion system is to convert thermal energy into mechanical and electrical energy, in particular by implementing a thermodynamic cycle, for example a steam turbine, transforming the thermal energy of the heat transfer fluid into mechanical energy. . When the thermodynamic cycle is coupled to an electric generator then the mechanical energy is also transformed into electrical energy.

The heat transfer fluid circulating in the solar collection system can be identical or different from the fluid supplying the thermodynamic cycle. In the case where the heat transfer fluid is different from the fluid supplying the thermodynamic cycle, the latter then corresponds to a working fluid. The heat exchange between the heat transfer fluid and the working fluid is carried out using a heat exchanger. The working fluid therefore stores thermal energy.

During these processes, the heat storage system makes it possible in particular to contribute to the continuous production of electrical energy, to manage production peaks and to adapt production to demand. The role of the heat storage system is therefore to improve the efficiency of this type of process as well as the lifetime of the solar installations implementing them. In other words, the storage system improves the profitability and lifespan of concentrated thermodynamic solar power plants. It also reduces the cost of the electric kWh. In addition, the storage of thermal energy has the advantage of being less expensive than the storage of electrical energy.

In the case of a sensible heat storage system, the thermal energy is stored by raising the temperature of a storage material which may be in liquid, solid or a combination of the two. In other words, the sensible heat storage system is to use the heat properties of the storage material with a simple change in temperature. The heat exchanges taking place between the heat transfer fluid, possibly the working fluid, and the storage material can be carried out using a heat exchanger. The storage material can also correspond to the heat transfer fluid.

Different technologies have been developed on an industrial scale in order to implement sensible heat storage systems.

By way of example, a storage system may consist of two separate tanks filled with a storage fluid having two different temperatures, namely a so-called “hot” tank, that is to say having a constant high temperature, located at the outlet of the solar collection system, and a so-called "cold" tank, that is to say having a constant cold temperature, located at the outlet of the thermodynamic cycle. In particular, the hot tank makes it possible to store the fluid at the outlet of the solar collection system in order to feed the thermodynamic cycle during the period of non-sunshine. Out of it, the cooled fluid is sent to the cold tank before being redirected to the solar collection system. Thus, during the storage phase, the cold fluid is pumped from the cold tank to the solar collection system or the exchanger to be heated and then stored in the hot fluid reserve. While, during the destocking phase, the hot fluid is directed to the thermodynamic conversion system in order to restore the stored thermal energy.

Alternatively, there are also storage systems having a single tank filled with a single fluid having two distinct temperatures, namely a hot temperature (corresponding to the hot fluid) and a cold temperature (corresponding to the cold fluid). Thus the hot fluid and the cold fluid are present in the same tank with a thermal gradient between the two, called thermocline. In other words, in the reservoir, the hot fluid (or the hot zone of the fluid) occupies the upper part, the cold fluid (or the cold zone of the fluid) occupies the lower part; these two parts being spaced from each other by a transition region, called a thermocline, corresponding to the thermal gradient. Such a single tank heat storage system corresponds to thermocline type storage. In this type of system, the fluid corresponds to the heat transfer fluid and possibly to the working fluid. In other words, preferably, the same heat transfer fluid circulates between the solar collection system, the thermocline type storage system and the thermodynamic conversion system.

The use of a single tank has the advantage of reducing the number of components as well as the sizing of heat storage systems. The single-tank thermocline system also has simplified operation compared to a two-tank system. This type of system is therefore financially competitive.

Preferably, the storage material used in a thermocline type storage system corresponds to a mixture of a heat transfer fluid and a solid storage material having a low cost price. In particular, the use of inexpensive solid storage material, available in large quantities and likely to come from various origins, makes it possible to replace a large part of the heat transfer fluid which may be more expensive. Thus the cost of the thermocline type storage system as a whole is lowered. In other words, the use of inexpensive solid storage material increases the competitive edge of a single-tank thermocline system from an economic point of view.

In addition, the solid material acts as a porous flow distributor and avoids flow phenomena, occurring in thermocline storage systems with a single reservoir comprising only the heat transfer fluid, and which can result in the mixture of hot and cold zones. fluid. In other words, the presence of the solid storage material in the single tank leads to an improvement in the segregation between the hot and cold zones of the heat transfer fluid.

During the charging and discharging phases in this type of system, the so-called "thermocline" zone moves axially within the tank, that is to say down and up respectively.

During the charging phase in this type of system, the hot fluid, coming from the solar collection system, is introduced into the upper part of the tank, flows down through the solid storage material. As it flows through the solid storage material, the fluid is cooled and the solid storage material changes from a cold temperature (ie a low temperature, TF) to a hot temperature (ie a higher temperature , TC). The cold fluid is evacuated, through the lower part of the tank, to the solar collection system to store thermal energy. The so-called "thermocline" zone therefore moves axially downwards. Thus the thermal front moves down from the tank.

During the storage step, the hot zone of the heat transfer fluid is located in the upper part of the tank, the cold zone of the fluid occupies the lower part; these two zones being separated by the region or zone called "thermocline".

During the discharge (or destocking) phase in this type of system, the direction of circulation of the heat transfer fluid is reversed. The cold fluid, coming from the thermodynamic conversion system, is introduced into the tank through the lower part and circulates upwards through the solid storage material. As it flows through the solid storage material, the fluid is heated and the solid storage material changes from a hot temperature (ie a high temperature, TC) to a cold temperature (ie a lower temperature , TF). The hot fluid is then evacuated from the tank, through its upper part, to the thermodynamic conversion system to restore thermal energy. The so-called “thermocline” zone therefore moves axially upwards. The thermal front therefore moves to the top of the tank.

In the charging and discharging phases, the solid storage material absorbs or transfers the heat from the heat transfer fluid. This material is therefore capable of storing and restoring the thermal energy of the fluid. In other words, the heat transfer fluid makes it possible to charge and discharge the thermal energy into the solid storage material.

During the system destocking phase, when the hot heat transfer fluid, discharged through the upper part of the tank, returns to the thermodynamic conversion system a temperature identical to that of the initial solid storage material, i.e. the temperature of the solid storage material during the charging phase (temperature TC), then this system behaves like an ideal thermal storage system. Thus the temperature of the heat transfer fluid will be a function of the conditions of heat exchange with the solid storage material.

In addition, the conversion of thermal energy into electrical energy involves a first temperature at the inlet of the thermodynamic conversion system, therefore a hot temperature (temperature TC), and a second temperature at the outlet of the system, therefore a cold temperature (TF temperature). As a result, the limits of the thermodynamic cycle involve two temperature levels. Maintaining these two types of temperature at constant temperatures is actively sought in order to obtain optimized operation of the thermodynamic cycle. In other words, it is important that the thermocline type system leads to a destocking of the heat at a constant temperature for a substantial period of time.

Conversely, it is also important to maintain a constant temperature during the charging phase of the storage system.

Depending on the concentrated solar power plants, the temperature levels mentioned above (TF and TC), provided by the thermal storage systems, are different and can vary in a range from 100 ° C to 650 ° C.

In order to meet the requirements mentioned above, this type of system, based on a heat transfer fluid and a solid storage material, involves fairly low fluid circulation speeds. This improves heat transfer between the fluid and the solid material and minimizes energy loss during heat exchange.

Furthermore, it is also important to control the distribution of the heat transfer fluid within the tank, that is to say to improve the segregation between the hot and cold zones of the fluid, so as to minimize the phenomena of inhomogeneity of temperature, at the outlet or at the inlet of the tank, which could impact on the efficiency of the thermodynamic conversion system and at the same time degrade the quality of the heat transfer fluid.

In other words, one of the challenges of these storage systems is to control and optimize the heat exchange conditions between the heat transfer fluid and the solid storage material in order not only to improve the conversion efficiency. in electrical energy but also to extend the service life of thermocline type storage systems. Indeed, the deterioration in the quality of the heat transfer fluid within the single tank can ultimately lead to a reduction in the life of the storage system, which impacts on the operation of the thermodynamic conversion system.

In addition, operating temperatures can also degrade the quality of the heat transfer fluid.

Thermocline type storage systems have already been proposed with optimized operation.

By way of example, the document WO 2013/167538 describes a heat storage system with a single tank comprising a solid storage material and a heat transfer fluid which are distributed over several stages in fluid communication. In this system, the layers of solid material, distributed over at least two consecutive stages, are separated by a layer of heat transfer fluid. According to the proposed system, the solid storage material consists of rocks, in particular alluvial rocks, and / or sand and, more particularly, this material is arranged in the form of a bed of blocks of rocks and filling sand. the spaces between the rocks.

The purpose of this type of system is to ensure homogenization of the temperature in both the heat transfer fluid layers and the layers of solid material in order to lead to a constant temperature during the charging and discharging phases.

However, there is still a real need to improve the quality of the heat-transfer fluid within a heat storage system with a single tank, ie of the thermocline type, in order to control and optimize its operation so as to prolong its duration. of life and, consequently, the efficiency of conversion into electrical energy of the thermodynamic conversion system.

In particular, there is a need to limit the degradation of the heat transfer fluid, in particular when the latter is subjected to high temperatures, in order to reduce the operational costs associated with the operation of this type of storage system.

One of the objectives of the present invention is therefore to propose a heat storage system with a single tank, i.e. of the thermocline type, having improved performance, in particular during the heat storage and destocking processes.

The subject of the present invention is therefore in particular a thermal storage tank comprising at least one chemically inert solid thermal storage material containing at least glass particles.

The storage material present in the thermal storage tank makes it possible to limit the degradation of the heat-transfer fluid, in particular its rate of degradation when the latter is subjected to high temperatures.

Thus the presence of a storage material based on glass particles in the storage tank according to the invention makes it possible to maintain the quality of the heat transfer fluid over time and ultimately reduce the operational costs associated with the operation of this type. of storage.

In particular, the use of a storage material based on glass particles in the storage tank according to the invention makes it possible in particular to improve the quality of the heat transfer fluid compared to a solid material constituted by rocks and / or sand under the same operating conditions, for example for a period of 500 hours at a temperature of 340 ° C.

This means that the heat transfer fluid can be partially replaced by a storage material based on glass particles without adversely affecting its quality.

The thermal storage tank according to the invention therefore has improved performance, in particular during the heat storage and destocking processes, which induces an optimization of the conversion of thermal energy into electrical energy during thermodynamic conversion using of a turbine.

More particularly, the storage material based on glass particles in the storage tank according to the invention prolongs the life of single tank thermal storage systems.

Furthermore, the thermal storage tank according to the invention retains its attractive appearance from an economic point of view.

Indeed, the storage tank according to the invention induces, on the one hand, lower operational costs than those of a tank filled only with a heat transfer fluid and, on the other hand, has a longer service life. a storage tank containing a heat transfer fluid and a solid storage material consisting of rocks and / or sand.

The invention also relates to the use of at least one solid thermal storage material, chemically inert, containing at least glass particles to limit the rate of degradation of a heat transfer fluid able to circulate in a storage tank. thermal.

In particular, the solid thermal storage material based on glass particles improves the thermal stability of the heat transfer fluid.

Preferably, the solid thermal storage material thus used makes it possible to limit the rate of degradation of a heat transfer fluid in a thermal storage tank in a temperature range from 100 to 500 ° C.

Thus the solid thermal storage material based on glass particles makes it possible to improve the thermal stability of the heat transfer fluid at temperatures which can vary from 100 to 500 ° C.

In this way, the storage material makes it possible to extend the operation of the storage system at temperatures varying from 100 to 500 ° C. and to optimize the operation of the thermodynamic conversion system at such a temperature.

Furthermore, another object of the present invention is a solar power station comprising at least one thermal storage tank containing at least one heat transfer fluid and at least one solid, chemically inert thermal storage material, containing at least glass particles.

Other characteristics and advantages of the invention will appear more clearly on reading the description and the examples which follow.

In what follows, and unless otherwise indicated, the limits of a range of values are included in this range.

The expression "at least one" is equivalent to the expression "one or more".

Thermal storage tank

As indicated above, the thermal storage tank comprises at least one solid, chemically inert thermal storage material based on glass particles.

Within the meaning of the present invention, by thermal storage material is meant a material capable of storing thermal energy by varying its temperature. The amount of energy stored can generally depend on the specific heat of the material, the temperature difference that the material undergoes and the amount of material present in the tank.

For example, if the material temperature rises from a temperature Tl to T2 for a material of mass m, said material stores an energy given by a variation in enthalpy.

For the purposes of the present invention, by "chemically internal material" is meant a material which is not chemically active. In particular, the solid thermal storage material does not react with the heat transfer fluid during the charging and discharging or storage phases. In addition, the elements that make up the thermal storage material do not react with each other.

The chemically inert solid thermal storage material may include glass particles and one or more solid elements.

The solid element (s) can be chosen according to their characteristics linked to the thermal storage capacity and to their thermal behavior, for example their density, thermal mass capacity and thermal conductivity, and to their compatibility. with the heat transfer fluid.

By way of examples, the solid element or elements is or are chosen from alumina, calcium carbonate and steel in its different shades (stainless steel, etc.).

Preferably, the chemically inert solid thermal storage material consists of glass particles. In other words, the storage material only contains glass particles.

According to this preferred embodiment, the solid thermal storage material is glass which is in the form of particles and does not contain additional solid elements.

The glass particles according to the invention may have the shape of spheres, of flakes and / or have totally random shapes.

Preferably, the glass particles have a sphere or ball shape.

In other words, the solid thermal storage material is preferably in the form of glass beads.

Advantageously, the solid thermal storage material consists of glass beads.

For the purposes of the present invention, the term "particle size" means the maximum dimension that it is possible to measure between two diametrically opposite points of the particle. The size of the glass particles is determined by measuring their specific surface and a criterion on the number of biot less than 0.1 allowing to satisfy the hypothesis of a thermally thin body.

Preferably, the glass particles have a size distribution having a diameter dso ranging from 500 to 20,000 microns, in particular from 1,000 to 10,000 microns.

Within the meaning of the present invention, the diameter dso corresponds to the value for which 50% by volume of the glass particles have, in a distribution of particles, a size less than or equal to this diameter. The diameter is also defined as the median of the particle distribution.

Preferably, the glass particles advantageously have at least two different particle sizes, thus ensuring satisfactory filling of the reservoir and reducing the free spaces for the heat transfer fluid.

In this way, the porosity and the quantity of heat transfer fluid capable of circulating in the tank are minimized.

Each particle size thus has a diameter dso of glass particles.

Preferably, in a particle distribution, the volume distribution is as follows: approximately 75% of the glass particles having a diameter ranging from 10,000 to 30,000 microns and 25% of the glass particles having a diameter ranging from 1,000 to 3,000 microns.

Such a particle size distribution contributes to the development of a greater heat exchange surface between the heat transfer fluid and the solid material.

The glass in the form of particles preferably has a composition by weight comprising from 70 to 80% by weight of silica (S1O2) relative to the total weight of the composition, the rest being preferably supplemented by other compounds chosen from Na2O, CaO , MgO, AI2O3 and / or B2O3 in variable proportions.

Advantageously, the glass is borosilicate so that the storage material has a low thermal expansion when the temperature rises as well as an increased impact resistance.

Preferably, the glass has the following composition by weight: from 70 to 80% by weight of silica (S1O2), from 7 to 13% by weight of boron oxide (B2O3), the rest of the composition preferably being supplemented with Na2O3 and / or AI2O3.

More preferably, the glass has the following composition by weight: from 70 to 80% by weight of silica (S1O2), from 7 to 13% by weight of boron oxide (B2O3), from 1 to 11% by weight of carbonate sodium (Na2O3) and from 1 to 12% by weight of alumina (AI2O3), preferably from 2 to 12% by weight of alumina (AI2O3).

The solid thermal storage material can be arranged in the tank according to the invention in the form of a bed comprising at least the glass particles.

In this case, the solid thermal storage material is placed on a support and arranged in the form of beds. The support is suitable for mechanically supporting the bed of solid storage material and allowing the heat transfer fluid to circulate.

As a variant, the solid thermal storage material is distributed randomly throughout the tank without any particular arrangement but so as to minimize the free spaces for the heat transfer fluid.

The solid storage material is arranged in such a way as to maximize the heat exchanges with the heat transfer fluid capable of circulating in the tank.

Preferably, the thermal storage tank also contains at least one heat transfer fluid. In particular, the thermal storage tank contains a heat transfer fluid.

The heat transfer fluid can be liquid at room temperature or in the form of vapor, for example water vapor.

Preferably, the heat transfer fluid is liquid at room temperature.

More preferably, the heat transfer fluid is chosen from molten salts and oils.

The molten salts can be nitrate salts, carbonate salts or a mixture of these salts.

The molten salts can in particular be a mixture of nitrate salts, for example a mixture of sodium nitrate (NaNCL) and potassium nitrate (KNO3), in particular a mixture composed of 60% by weight of sodium nitrate and 40% by weight of potassium nitrate.

The oils are especially chosen from synthetic oils, mineral oils, vegetable oils, in particular rapeseed oil, or a mixture of these.

Preferably, the oils are chosen from synthetic oils and vegetable oils, more preferably synthetic oils.

In particular, synthetic oils can be chosen from:

an oil corresponding to a mixture of Terphenyls, in particular sold under the trade name Therminol 66®, and

- an oil, corresponding to a mixture of dibenzyletoluene isomers, in particular sold under the trade name Jarytherm DBT®.

According to one embodiment, the thermal storage tank is capable of containing a heat transfer fluid chosen from oils and comprising at least one chemically inert solid thermal storage material constituted by particles of glass, in particular glass beads.

According to this embodiment, the glass in the form of particles, in particular beads, is advantageously borosilicate.

In particular, the thermal storage tank according to the invention comprises the heat transfer fluid as defined above.

Preferably, the thermal storage tank comprises an envelope filled with a heat-transfer fluid and with a solid chemically inert thermal storage material comprising at least glass particles, a first longitudinal end, situated at its upper part, and a second longitudinal end located at its lower part; the heat transfer fluid being able to circulate between the first longitudinal end and the second longitudinal end.

Preferably, the first longitudinal end is provided with means for collecting and supplying the heat transfer fluid at a first temperature.

Preferably, the second longitudinal end is provided with means for collecting and supplying the heat transfer fluid at a second temperature.

In accordance with the preferred modes described above, the first temperature is higher than the second temperature.

According to another embodiment, the thermal storage tank according to the invention may have a structure as described in patent application FR 2990502.

Use of storage material

As indicated above, the present invention also relates to the use of at least one solid thermal storage material, chemically inert, containing at least glass particles to limit the rate of degradation of a heat transfer fluid capable of circulate in a thermal storage tank as defined above.

In particular, the solid thermal storage material makes it possible to limit the rate of degradation of a heat transfer fluid in a thermal storage tank as defined above, that is to say filling and / or circulating in said tank.

The solid thermal storage material is as defined above.

Preferably, the solid thermal storage material consists of glass particles, in particular glass beads, that is to say that it does not comprise additional solid elements other than the glass particles.

The heat transfer fluid is as defined above. Preferably, the fluid is liquid at room temperature and is chosen from oils.

More preferably, the heat transfer fluid is a synthetic oil as defined above.

Preferably, the solid thermal storage material thus used makes it possible to limit the rate of degradation of the heat transfer fluid in a temperature range from 100 to 500 ° C.

Solar power plant

Likewise, the present invention relates to a solar power station comprising at least one thermal storage tank containing at least one heat transfer fluid and at least one solid, chemically inert thermal storage material, containing at least glass particles.

The solar power plant contains a storage tank as defined above. Preferably, the storage tank contains a heat transfer fluid as defined above.

Preferably, the solar power plant is a concentrated thermodynamic power plant.

The solar power plant also includes a solar collection system and a thermodynamic cycle, in particular a steam turbine.

Preferably, the first longitudinal end, provided with means for collecting and supplying the heat transfer fluid, and the second longitudinal end, provided with means for collecting and supplying the heat transfer fluid, are connected to the thermodynamic cycle, in particular a turbine. steamed.

Other characteristics and advantages of the invention will appear on detailed examination of an embodiment taken by way of nonlimiting example of a thermal storage tank according to the invention and illustrated by the accompanying drawings, in which :

FIG. 1 represents a view in longitudinal section of a thermal storage tank according to the invention comprising a tank filled with a heat transfer fluid and a solid thermal storage material,

FIG. 2 schematically shows the thermal storage tank according to the invention during a charging phase,

- Figure 3 schematically illustrates the thermal storage tank according to the invention during a discharge phase (destocking step).

Figure 1 shows a thermal storage tank 1 according to the invention produced in accordance with one embodiment.

The tank 1 comprises a tank 2 having a parallelepiped shape having a longitudinal axis A-A oriented vertically. Alternatively, the tank 2 may have an oblong shape, in particular a cylindrical shape, having a longitudinal axis A-A oriented vertically.

Still another variant, the tank 2 corresponds to a ferrule having two rounded ends.

According to Figure 1, the tank 2 is preferably thermally insulated by an envelope 3 made using an insulating material.

Preferably, the casing 3 is in contact with the tank 2 so as to cover both the side walls and the upper and lower parts of the tank 2. The casing 3 has in particular the same shape as the tank 2.

The tank 2 has a first upper longitudinal end 2a provided with an orifice 4, acting as an inlet or outlet for a fluid as a function of the charging and discharging phases of the system, and a second lower longitudinal end 2b provided with an orifice 5, acting as an inlet or outlet for a fluid as a function of the charging and discharging phases of the system.

The orifices 4 and 5 therefore have a function of supplying and / or collecting the heat transfer fluid capable of filling the tank.

2. The orifices 4 and 5 can be provided with means for supplying and collecting the fluid.

The insulating jacket 3 is also open at the holes 4 and 5.

The tank 2 is filled with a heat transfer liquid 6, preferably a synthetic oil as defined above, and a chemically inert solid thermal storage material 7, consisting only of glass particles, preferably glass beads. The glass balls 7 rest on a support 7a ensuring their retention while allowing the passage of the heat-transfer liquid 6 throughout the tank 2.

The support 7a can be made in a single piece or be made up of several pieces to facilitate its mounting within the tank 2.

In FIG. 1, the glass balls 7 have an identical diameter. However, according to another preferred embodiment, the glass balls 7 have different sizes.

Preferably, the glass is borosilicate and has particularly the following composition by weight: from 70 to 80% by weight of silica (SiCh), from 7 to 13% by weight of boron oxide (B2O3), the rest of the composition being supplemented Na2O3 and / or AI2O3.

The heat transfer liquid 6 occupies, along the longitudinal axis AA, the upper part of the tank 2 at a first temperature (called temperature TC), the lower part of the tank at a second temperature (called temperature TF), the middle part of the tank 2, corresponding to an intermediate region called thermocline, interposed between the upper part and the lower part. The first temperature (TC) is higher than the second temperature (TF).

The heat transfer liquid 6 therefore includes a hot zone 6C (at a temperature TC) located at the top of the tank 2, a cold zone 6F (at a temperature TF) located at the bottom of the tank 2 and an intermediate zone 6T, interposed between the hot zone 6C and the cold zone 6F, called a thermocline and constituting a thermal gradient.

In other words, the heat transfer liquid 6 is thermally stratified in the tank 2, these strata forming layers having different temperatures which are superimposed on each other, from the coldest zone to the warmest in accordance with the axis. longitudinal AA.

The TC temperature can vary from 110 ° C to 650 ° C and the TF temperature can vary from 100 ° C to 640 ° C.

The temperature in the intermediate zone 6T is lower than the temperature TC of the hot zone 6C and higher than the temperature

TF of cold zone 6F.

Preferably, the heat transfer fluid 6 is an oil, in particular a synthetic oil, corresponding to a mixture of isomers of dibenzyletoluene, in particular that sold under the trade name Jarytherm DBT®.

FIG. 1 represents the storage phase, that is to say the stage during which the heat transfer liquid 6 is stored in the tank 1 and the thermocline is in equilibrium in the center of the tank 1.

As indicated above, FIG. 2 schematically describes the storage tank according to the invention, in particular by illustrating the direction of circulation of the heat-transfer liquid 6 within the tank 2, during the charging phase.

During this charging phase, the hot heat transfer liquid 6, coming from a solar collection system (not shown in FIG. 2), is introduced into the upper part 2a through the orifice 4 and s' flows downwards (along the longitudinal axis AA) through the glass balls 7 inducing a displacement of the thermocline 6T downwards. During its circulation through the glass balls 7, the heat transfer liquid 6 is cooled to reach the temperature TF and is discharged through the orifice 5 from the lower part 2b of the tank 1 to the solar collection system.

In Figure 2 has been shown, by arrows, the direction of circulation of the heat transfer liquid 6 through the tank 1, namely from top to bottom along the longitudinal axis A-A. The intermediate zone 6T moves axially downwards during the charging phase.

As indicated above, FIG. 3 schematically illustrates the storage tank according to the invention, in particular by illustrating the direction of circulation of the heat-transfer liquid 6 within the tank 2, during the discharge (or destocking) phase. ).

During this discharge phase, the cool coolant 6, from a thermodynamic conversion system (not shown in Figure 3), is introduced through the orifice 5 of the lower part 2b of the tank 2 and s 'flows upwards (along the longitudinal axis AA) through the glass balls 7 inducing a displacement of the thermocline 6T upwards. During its circulation through the glass balls 7, the heat transfer liquid 6 is heated to reach the temperature TC and is evacuated through the orifice 4 of the upper part 2a of the tank 1 towards the thermodynamic conversion system, namely the turbine.

In Figure 3 has been shown, by arrows, the direction of circulation of the heat transfer liquid through the tank 1, namely from the bottom up along the longitudinal axis A-A. The intermediate zone 6T moves axially upwards during the discharge phase.

Figures 1 to 3 therefore describe an embodiment of a single tank thermal storage system capable of containing a heat transfer fluid and containing at least one solid thermal storage material comprising at least glass particles.

As a variant, the reservoir 2 can be divided into several compartments overlapping along the longitudinal axis AA, each compartment comprising the glass particles 7, arranged in the form of a bed, covered by the heat transfer liquid 6 capable of circulating through all of the compartments.

Still alternatively, the glass particles 7 may have the shape of spheres, of flakes and / or have completely free shapes.

The following example relates to the thermal stability tests of the heat transfer fluid as a function of the nature of the solid storage material used.

Example of thermal stability

In this example, the thermal stability of a synthetic oil sold under the trade name Jarytherm ® DBT by the company Arkema was studied, in a thermal storage tank, alone or in the presence of different types of chemically solid thermal storage materials inert at a temperature of 340 ° C for a period of 500 hours.

The amount of non-degraded synthetic oil was measured at the end of the study period.

The results are grouped in the following table:

Operating conditions DBT content in the oil New oil 98 Oil only / 500 hours at 340 ° C 94.3 Oil + glass beads / 500 hours at 340 ° C 93.4 Oil + rock / 500 hours at 340 ° C 83.9 Oil + sand / 500 hours at 340 ° C 81.2

The results show that the DBT content in the oil is significantly higher with glass beads compared to that measured in the presence of rocks or sand after a period of 500 hours at a temperature of 340 ° C.

These results also show that the DBT content in the oil is similar when the oil is used alone or in the presence of glass beads. This implies that the oil used can be partially advantageously replaced by glass beads without negatively impacting its quality and the functioning of the storage system.

Thanks to the savings made with the use of glass particles, the thermal storage tank is financially more advantageous than a tank comprising synthetic oil alone. Indeed, synthetic oil is more expensive than glass particles.

Claims (17)

1. Thermal storage tank (1) comprising at least one chemically inert solid thermal storage material (7) containing at least glass particles. 2. Thermal storage tank (1) according to claim 1, characterized in that the glass particles are glass beads. 3. Thermal storage tank (1) according to claim 1 or 2, characterized in that the glass particles (7) have a size distribution having a diameter dso of 500 to 20,000 microns, in particular from 1000 to 10,000 microns. 4. Thermal storage tank (1) according to any one of the preceding claims, characterized in that the glass particles (7) have at least two different particle sizes. 5. Thermal storage tank (1) according to any one of the preceding claims, characterized in that the glass in the form of particles has a weight composition comprising from 70 to 80% by weight of silica (SiCh), relative to the weight total of the composition, the remainder being supplemented by other compounds chosen from Na ₂ O, CaO, MgO, AI2O3 and / or B2O3 in variable proportions. 6. Thermal storage tank (1) according to any one of the preceding claims, characterized in that the glass is borosilicate. 7. Thermal storage tank (1) according to any one of the preceding claims, characterized in that the glass has the following composition by weight: from 70 to 80% by weight of silica (S1O2), from 7 to 13% by weight boron oxide (B2O3), the rest of the composition being supplemented Na ₂ O3 and / or AI2O3; the contents by weight being calculated relative to the total weight of the composition. 8. Thermal storage tank (1) according to any one of the preceding claims, characterized in that it further comprises at least one heat transfer fluid (6). 9. thermal storage tank (1) according to claim 8, characterized in that the heat transfer fluid (6) is liquid at room temperature. 10. Thermal storage tank (1) according to claim 8, characterized in that the heat transfer fluid (6) is chosen from molten salts and oils. 11. A thermal storage tank (1) according to claim 10, characterized in that the molten salts can be chosen from nitrate salts, carbonate salts or a mixture of these salts, in particular a mixture of nitrate salts. 12. Thermal storage tank (1) according to claim 10, characterized in that the oil is chosen from synthetic oils, mineral oils, vegetable oils and their mixtures. 13. A thermal storage tank (1) according to claim 10 or 11, characterized in that the oil is a mixture of diphenyl oxide and diphenyl or a mixture of isomers of dibenzyletoluene. 14. Thermal storage tank (1) according to any one of the preceding claims, characterized in that it comprises a tank (2) filled with a heat-transfer fluid (6) and with a solid chemically inert thermal storage material (7) comprising at least glass particles, a first longitudinal end (2a), located at its upper part, and a second longitudinal end (2b) located at its lower part; the fluid (6) being able to circulate between the first longitudinal end (2a) and the second longitudinal end (2b). 15. A thermal storage tank (1) according to claim 14, wherein the first longitudinal end (2a) is provided with means for collecting and supplying the heat transfer fluid (6) at a first temperature (6C) varying from 110 ° C at 650 ° C and the second longitudinal end (2b) is provided with means for collecting and supplying the heat transfer fluid (6) at a second temperature (6F) varying from 100 ° C to 640 ° C; the first temperature (6C) being higher than the second temperature (6F). 16. Solar power station comprising at least one thermal storage tank (1) containing at least one heat transfer fluid (6), as defined according to any one of claims 8 to 13, and at least one solid thermal storage material, chemically inert 5 (7), as defined in any one of claims 1 to 7. 17. Use of at least one chemically inert solid thermal storage material (7) comprising at least glass particles to limit the rate of degradation of a heat transfer fluid (6) capable of circulating in a thermal storage tank (1 ) such as 10 defined according to any one of claims 1 to 15. 1/2