FR3050263A1 - THERMAL ENERGY STORAGE DEVICE THROUGH PHASE CHANGE MATERIAL COMPRISING AN ELEMENT FOR CREATING LOAD LOSS - Google Patents

Abstract

The invention relates to a thermal energy storage device by means of a Phase Change Material (MCP) comprising at least one MCP, a tank and several thermal fluid heat exchangers, each exchanger comprising: a plurality of tubes and a distributor, the distributor connecting the tubes together and distributing a coolant to the plurality of tubes; and a collector, the manifold connecting the tubes to one another and collecting the coolant of the plurality of tubes, the distributor and the manifold respectively comprising a pipe suitable for introducing or discharging the coolant, the coolant is two-phase liquid-gas and an exchanger comprises at least one element arranged at the level of the manifold pipe to create a pressure drop in the circulation of the coolant .

Description

TECHNICAL AREA

The present invention relates to a heat exchanger heat transfer fluid and a thermal energy storage device by phase change material comprising said exchanger.

The field of the invention relates to Thermal Storage Systems (SST) by Materials Phase Change (MCP). The invention relates more particularly to the integration of a thermal storage system in concentrating solar power plants, for example for plants with direct steam generation, or the recovery of fatal heat industries.

STATE OF THE ART

Thermal storage systems offer many benefits for the management of industries. For example, in concentrating solar power plants, there is a time gap between the available solar resource and the energy demand. This problem arises for all intermittent heat production units. The development of storage systems makes it possible to defer the use of heat production by collecting heat during periods of strong solar irradiation in order to restore it later during periods of non-sunshine or during the night.

In the process industry, thermal storage systems are a means of valuing fatal heat. This heat, resulting from industrial heat discharges, is available at temperature levels between 30 and 90 ° C in the food industry, paper-cardboard, chemistry and even between 200-500 ° C for the metal, glass and cement industries . However, in most cases, the periods of availability differ from the periods of use, and without a storage solution, all the energy in excess, unusable at the time of its production, is simply thrown into the outside environment (at the time of its production). atmosphere in the form of gaseous effluents or in natural water circuits in the form of liquid effluents). With a storage system, excess energy produced during the day could be injected into an urban heat network at the peak of consumption in the morning and evening. The storage of heat would also transport this energy to another industrial site that would need a heat input.

There are different types of storage; sensitive, latent and thermochemical.

Latent storage uses Phase Change Materials (PCMs) to store heat. The thermal storage is performed by storage enthalpy change of state. It is the enthalpy of phase change, most often during the change of solid / liquid state, which is stored. This energy, which is absorbed during melting and released during solidification, results from the establishment or rupture of interatomic or intermolecular bonds. The charge of the storage system is accompanied by the melting of the storage material, while the discharge is achieved by the solidification of said material. The material should be carefully chosen according to the target temperature of the storage system so that its melting temperature is within the operating temperature range. The change of liquid-gas phase is much more energetic but the implementation difficulties related to the management of large volumes of gas under pressure and at high temperature limit their development.

The exchanged heat is called phase change enthalpy or latent heat and the amount of energy is of the order of 200 J / g so that by using such solid-liquid MCP it is possible to reduce the volumes of storage. As a result, the materials are reduced, which decreases the price of the system, and limits heat losses which are proportional to the external surface of the tank.

The energy density can thus be doubled compared to sensitive systems. It is, in fact, of the order of 15-60 kWh / m ^ for sensitive storage systems and 60-120 kWh / m® for latent storage systems. One of the major advantages of this technology is that the phase change can be done at constant pressure and temperature. Therefore, the discharge of the stored energy is at a constant temperature.

However, the low thermal conductivity of the MCP, of the order of 0.2 to 0.5 W / (m.K) limits the heat transfer within these materials. MCPs are then inserted into vessels with increased surface exchangers, such as circular or longitudinal finned tubes to maximize heat transfer.

We know in particular the tube-shell heat exchanger technology. A shell in which a fluid circulates is traversed by a bundle of tubes in which another fluid flows. Both fluids exchange energy by conduction through the thickness of the tubes. In the case of thermal storage this technology is adapted, there is no longer exchange between two fluids in motion, but between a heat transfer fluid circulating in the tubes and a MCP which is fixed in the shell (apart from the movements of natural convection in the liquid phase). During charging, the coolant reaches a temperature above the melting temperature of the PCM and gives energy to it, which causes its melting; during the discharge, the heat transfer fluid enters at a temperature below the melting temperature of the MCP and recovers the previously stored energy, which causes the solidification of the MCP.

For the optimization of the storage devices, it may be advisable to install several exchangers in the same tank containing the MCP, thereby improving the overall thermal insulation, the reduction of the surface to be insulated; a single volume of MCP is planned, limiting the problems related to the filling of the tanks. Finally, since only one tank is needed, the costs are reduced.

However, the arrangement of several exchangers in the same tank poses problems as to the distribution of the heat transfer fluid in the different exchangers.

There is a need for a thermal energy storage device by MCP comprising a plurality of heat exchangers solving the problem of the distribution of the coolant in the different heat exchangers.

SUMMARY OF THE INVENTION

The present invention proposes for this purpose a thermal energy storage device by Phase Change Material (MCP) comprising at least one MCP, a vessel containing the at least one MCP and several thermal fluid heat exchangers plunging at least partially in the tank containing the at least one MCP, each exchanger comprising: a plurality of tubes, a distributor arranged at a first end of the tubes arranged in the upper part of the tank, the distributor connecting the tubes to one another and distributing a heat transfer fluid to the plurality of tubes, and a collector arranged at a second end of the tubes arranged in the lower part of the tank, the collector connecting the tubes to one another and collecting the coolant of the plurality of tubes, the distributor and the collector respectively comprising a pipe suitable for introducing or evacuating the coolant.

Advantageously, the heat transfer fluid is a two-phase fluid in a liquid state and gaseous state able to circulate in the exchanger.

Advantageously, the device comprises at least one element arranged at least partially at the duct of the manifold configured to create a pressure drop in the circulation of the coolant.

The duct of the manifold comprises an element for controlling the distribution of the heat transfer fluid flow in each of the exchangers. Indeed, the setting in parallel of several exchangers requires a management of the distribution of the coolant. The exchangers are arranged in a tank filled with MCP, forming part of the storage device. At the arrival of the coolant, the latter will enter the exchangers through the pipes leading to the distributors. The coolant filling the exchangers located at the periphery of the storage device is therefore subject to greater physical loads because the latter must travel a greater distance. This reasoning is also valid for the tubes located at the periphery of the exchangers, also subject to greater physical loads. For example, if at the end of the heat load, a heat exchanger was completely filled with steam, then this steam could go up in the central smooth tube and create a preferential circulation in this exchanger, due to a lower pressure drop than in the other exchangers still filled with liquid. This imbalance of flow could limit the storage load. It is therefore advantageous to have a system for managing the pressure losses related to the circulation of the heat transfer fluid within the exchanger. Indeed, these pressure losses directly influence the amount of heat transfer fluid in the liquid state within the exchanger, and at the same time the filling of the latter heat transfer fluid in the vapor state. The invention advantageously makes it possible to control the distribution of the coolant flow rate in each of the exchangers.

This control can be achieved in two ways, not exclusive of each other, several elements may be present: Passively by the addition of a pressure drop at the manifold pipe of each exchanger , thus limiting the outflow of heat transfer liquid in liquid form. This added pressure drop then makes the pressure losses related to the circulation of the coolant negligible and therefore allows to have a substantially identical amount of heat transfer fluid between the different exchangers of the storage device. In an active way, by a management of liquid in each exchanger. This management involves for each exchanger a differential pressure measurement between the manifold and manifold pipes allowing the deduction of the heat transfer liquid level, and a regulation of the output flow by a control valve placed on the manifold pipe.

According to another separable aspect, the device according to the invention comprises a plurality of exchangers.

Advantageously, the device comprises expansion compensators disposed between the exchangers and between the exchangers and the vessel, so that it is advantageous firstly to seal the vessel and advantageously to compensate for the different expansions of the exchangers. The exchanger according to the invention allows the latter to be arranged in support on the bottom of the tank, without requiring connection in this area.

In another aspect, the invention relates to a thermal energy storage method comprising a charging step and / or a discharge step. For each step, the heat transfer fluid is introduced into the upper part of the tank and is evacuated in the upper part as well.

BRIEF DESCRIPTION OF THE FIGURES

The objects, objects, as well as the features and advantages of the invention will emerge more clearly from the detailed description of an embodiment of the latter which is illustrated by the following accompanying figures in which:

Figure 1: Schematic diagram of a multi-exchanger phase change material storage device

2: Management of the distribution of heat transfer fluid flow rates according to a first embodiment using passive management.

Figure 3: Management of the distribution of coolant flow rates according to a first embodiment using active management.

FIGS. 4: Management of the distribution of the flows of coolant according to a second embodiment using passive management

Figure 5: Management of the distribution of heat transfer fluid flows according to a second embodiment using active management

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Before beginning a detailed review of embodiments of the invention, are set forth below optional features that may optionally be used in combination or alternatively.

It is recalled first of all that the invention relates to a thermal energy storage device by Phase Change Material (PCM) comprising at least one element configured to create a pressure drop in the circulation of the coolant.

Advantageously, according to preferred but non-limiting variants, the invention comprises at least one element making it possible to control the distribution of the heat transfer fluid flow rate in each of the exchangers, said element being arranged at least partially at the level of the ducting of the collector.

Advantageously, the element creates a pressure drop by reducing the passage section of the heat transfer fluid.

Preferably, the reduction of the passage section of the heat transfer fluid by the element is located on a single portion of the manifold pipe.

According to one embodiment, the control of the distribution of the heat transfer fluid flow is passive.

Advantageously, the element comprises a narrowing of the duct of the collector.

Advantageously, the element consists of a pierced plate, or a membrane, or a reduction in the diameter of the pipe.

According to another embodiment, the control of the distribution of the heat transfer fluid flow is active.

Advantageously, said element is configured to manage the liquid level of the coolant in the heat exchanger.

Advantageously, the device comprises an element for measuring the differential pressure between the distributor and the manifold and in which the element consists of a control valve for the outlet flow rate of the coolant arranged at the level of the manifold pipe.

Advantageously, the coolant is configured to be in a liquid state at the second end of the tubes, in the lower part of the tank, and a vapor state at the first end of the tubes, in the upper part of the tank.

Advantageously, the tubes extend longitudinally between the distributor and the collector.

Advantageously, the tubes are straight and parallel to each other.

Advantageously, the device is adapted to be arranged in a tank containing a MCP so that the tubes extend vertically in the tank.

Advantageously, the pipes respectively of the distributor and the collector open at the upper part of the tank.

Advantageously, the ducting of the collector extends from the collector towards the distributor and is able to be immersed in the MCP.

Advantageously, the duct of the collector is thermally insulated.

Advantageously, the heat transfer fluid is in the liquid state in the duct of the collector.

Advantageously, the tank comprises a bottom wall, side walls and an upper wall defining an interior volume receiving the at least one MCP.

Advantageously, the pipe of the distributor and the pipe of the collector pass through the upper wall of the tank to open out of the tank.

Advantageously, at least one exchanger is arranged in support on the lower wall of the tank.

Advantageously, the side walls of the tank are of hexagonal cross section.

Advantageously, the device comprises expansion compensators configured to ensure a seal between the distributor of each exchanger, and between the distributors of the exchangers and the tank.

Advantageously, the MCP is a solid-liquid MCP.

According to another aspect, the invention relates to a method for storing thermal energy in a device comprising a charging phase during which for each exchanger: the heat transfer fluid enters each exchanger in the upper part through the ducting of the distributor opening in the upper part of the tank, the distributor in the upper part of the exchanger distributes the coolant in the gaseous state to the plurality of tubes, the coolant in the gaseous state condenses in the tubes causing the melting of the MCP, - the heat transfer fluid in liquid form is collected by the collector in the lower part of the exchanger - The heat transfer fluid in liquid form passes through the element

The coolant is evacuated from the exchanger through the manifold pipe. The invention also relates to a storage method comprising a discharge phase during which, for each exchanger: the heat transfer fluid enters the exchanger in the upper part through the duct of the manifold opening into the upper part of the vessel; coolant in liquid form passes through the element - the manifold at the bottom of the exchanger distributes the coolant in the liquid state to the plurality of tubes. - The heat transfer fluid in the liquid state vaporizes in the tubes causing solidification of the MCP, - the heat transfer fluid in the gaseous state is collected by the distributor in the upper part and is removed from the heat exchanger by the distributor pipe.

Advantageously, the invention relates to a method in which the coolant is in the liquid state throughout the duct of the collector. The invention also relates to a storage method comprising the following steps: - Differential pressure measurement - Determination of the liquid level of the heat transfer fluid in the exchanger - Control of the control valve arranged on the pipe of the collector. The invention relates to a heat exchanger 1 comprising a heat transfer fluid. The heat exchanger 1 according to the invention is intended to be arranged in a tank 14 to form a thermal energy storage device. The tank comprises at least one MCP 13 and the exchanger 1 is advantageously at least partially immersed in the MCP 13 contained in the tank 14.

The heat transfer fluid is preferably a two-phase fluid that is to say that it is configured to take alternately two phases or states under the operating conditions of the invention. According to the invention, the heat transfer fluid is in the liquid state and in the gaseous state under the operating conditions, that is to say temperature and pressure, of the heat exchanger 1 and the storage device. thermal energy of the invention.

The change of phase or state of the coolant is made during the charging and discharging of the thermal energy storage device within the heat exchanger 1 by transfer of thermal energy between the coolant and the MCP 13 .

Advantageously, in charge, the heat transfer fluid enters the exchanger 1 in gaseous form, the energy transfer is in favor of the MCP 13 thanks to the heat transfer fluid which gives up its thermal energy. The coolant then decreases in temperature and changes state to be in the liquid state at the outlet of the exchanger 1. In discharge, the heat transfer fluid enters the exchanger 1 in liquid form, the energy transfer is made in favor of the heat transfer fluid thanks to the MCP 13 which gives up its thermal energy. The heat transfer fluid then increases in temperature and changes state to be in the gaseous state at the outlet of the exchanger 1.

The latent energy storage absorbs the condensation energy of the heat transfer medium vapor during charging, and restores the latent heat to evaporate the liquid heat transfer fluid during the discharge. This process is advantageously carried out without any significant variation in the temperature level, nor advantageously in the quality of the energy.

The tank 14 contains at least one MCP 13. It can be used mixtures of MCP 13. In the remainder of the description, the reference to a MCP 13 is not limiting. Different MCP may be used in particular solid / solid transition MCP or preferably solid / liquid transition MCP. The invention is suitable for a wide variety of MCPs and therefore a wide range of storage temperatures. The two main categories of MCP that can be used are organic (paraffin, fatty acid, alcohol, ...) and inorganics (salts, salt hydrates, metal alloys, ...). For steam heat networks (~ 180 ° C) the MCP used will have a melting temperature of the order of 100-120 ° C, for example: erythritol, sebacic acid, paraffin ,. It is preferred to target a material which does not oxidize and which does not oxidize the metal structure of the exchanger 1 or the vessel 14 and which has a good mass change phase enthalpy and which is not toxic. Preferably, the MCP 13 will have a good heat capacity and the highest possible thermal conductivity.

MCP 13 is a preferably solid two-phase material whose passage between these two phases stores or releases energy. Preferably, the transition from a first phase to a second phase will require heat which is stored in the MCP in its second phase. On the other hand, the transition from the second phase to the first phase is exothermic and releases the stored heat.

When the energy storage device operates to store thermal energy, that is to say in charge, the heat exchanger 1 brings heat into the tank 14, there is a heat exchange of the heat transfer fluid to the MCP 13 through the exchanger. This heat will allow the transformation of the MCP 13 from the first phase to the second phase, which will then store the heat from the coolant. When the device operates to restore thermal energy, that is to say in discharge, the heat exchanger 1 cools the MCP 13, there is a heat exchange from the MCP 13 to the heat transfer fluid through the exchanger 2, which allows the transition from the second phase to the first phase. This transformation is exothermic. The heat released is recovered by the coolant. The exchanger 1 comprises a plurality of tubes 2. Advantageously, the coolant circulates in the exchanger 1 and more particularly in the tubes 2. It is within the tubes 2 of the exchanger 1 that the change of phase of the coolant. The exchanger 1 according to the invention is intended to be at least partially immersed in a tank 14 containing at least one MCP 13.

The tubes 2 comprise a first end 3 and a second end 4. Advantageously, the first end 3 is adapted to be arranged in the upper part of the exchanger 1 while the second end 4 is adapted to be arranged in the lower part of the exchanger 1. This arrangement is thus found when the exchanger 1 is arranged in the tank 14 of the device, that is to say that the first end 3 of the tubes 2 is disposed in the upper portion 17 of the tank 14 and the second end 4 of the tubes 2 is disposed in the lower part 18 of the tank 14.

The upper part is the area above, along a vertical axis, of a horizontal median plane. The upper part is preferably the upper third respectively of the tank 14 or the exchanger 1.

By lower part is meant the area below, along a vertical axis, a horizontal median plane. The lower part is preferably the lower third respectively of the tank 14 or the exchanger 1. The exchanger 1 comprises a distributor 5 putting in fluid communication the first ends 3 of the tubes 2 and a collector 6 putting in fluid communication the second ends 4 of the tubes 2. The distributor 5 and the collector 6 have a functional role of formation of the fluidic network for the circulation of the coolant in the exchanger 1.

The distributor 5 and the collector 6 provide an advantageously uniform distribution of the coolant to the tubes 2.

Advantageously, the tubes 2 are integral with the body 24 of the distributor 5 and the body 25 of the collector 6 respectively by their first ends 3 and by their second ends 4 which are for example welded to the bodies 24, 25.

The distributor 5 comprises a pipe 7 intended for the introduction or the outlet of the heat transfer fluid of the exchanger 1, more specifically tubes 2.

The collector 6 comprises a pipe 8 intended for the introduction or the outlet of the heat transfer fluid of the exchanger 1, more precisely tubes 2.

In a particular embodiment, illustrated in Figures 4 and 5, the pipe 8 of the manifold 6 extends towards the distributor 5. The pipe 8 is integral with the manifold 6 and is arranged on the same side as the tubes 2 relative to the body 25 of collector 6.

The tubes 2 can be of any section, with a marked preference for the circular section tubes which are the simplest to design and which are most resistant to pressure. The arrangement of the tubes 2 can also vary, they can be in square, in triangle, ...

The tubes 2 may be steel, the conventional grades for a pressure wall are P235GH, P265GH, P355GH; in the absence of pressure, stainless steels 304, 316 may be used, aluminum, copper, or other metal or alloy. With a preference for low cost steel, which is strong and pressure resistant and aluminum, easy to work, good thermal conductor.

Conventionally, the tubes 2 are surrounded by circular fins increasing the heat exchange surface or inserts of larger dimensions in addition to maintaining the tubes integral with each other.

The distributor 5 and the collector 6 respectively comprise a body (24 and 25). This body is delimited by two plates. In the case of the distributor 5, the upper plate is drilled having two orifices communicating with the pipes 7 and 8, the lower plate is drilled having several orifices communicating with the tubes 2. In the case of the manifold 6, the upper plate is drilled with several orifices communicating with the tubes 2 and an orifice communicating with the channel 8, the lower plate is not drilled. For the distributor 5, as the collector 6, the upper and lower plates are perpendicular to the tubes 2. The distributor 5 and the collector 6 are also delimited by side walls having no orifice. The pipes 7 and 8 may have the same dimensions in section as the tubes 2 and have the same composition.

The tubes 2 extend advantageously vertically. The tubes 2 extend longitudinally between the collector 6 and the distributor 5, preferably the tubes 2 are straight and parallel to each other.

According to a first embodiment, described in FIGS. 2 and 3, the duct 8 of the collector 6 is configured to open at the bottom of the exchanger 1.

According to a second embodiment, described in FIGS. 4 and 5, the duct 7 of the distributor 5 and the duct 8 of the collector 6 are configured to open into the upper part of the exchanger 1. The duct 8 opens out beyond the face The duct 8 passes through the dispenser 5 without being in fluid communication with it. The pipes 7 and 8 then open on the upper face of the heat exchanger 1. The upper surface means the surface of the heat exchanger 1 located above the first end of the tubes 2. The upper face of the heat exchanger 1 preferably corresponds to the upper face of the body 24 of the distributor 5. The exchanger 1 being arranged in a tank 14, the pipes 7, 8 open into the upper part of the tank 14. Preferably at the upper face of the tank 14. The connections of the exchanger 1 are thus made from the top which facilitates the assembly of the exchanger 1 in the tank 14 and its extraction for repair or replacement.

In one embodiment, as in the other, the coolant circulating in the exchanger 1 is subjected to different physical loads disturbing its distribution within the exchanger 1.

FIG. 3 illustrates an embodiment where the distribution of the coolant flow rate is managed passively. A restriction element 23 is added at the manifold pipe 8.

The term "restriction element" means any element allowing the section of the duct of the collector 8 to be narrowed. By way of non-limiting example, this element may correspond to a plate, from the diameter of the pierced pipe 8, to a membrane, to a reduction in the diameter of the pipe ...

Passive management of the heat transfer fluid means management using a restriction element able to adopt a single state. Indeed, in the case of passive management, the restriction element comprises a non-variable structure, resulting for a given heat transfer fluid flow at a corresponding pressure drop. By way of example, when the restriction element corresponds to a decrease in the section size of the channel 8, this reduction is fixed and can not be modified.

During the charging step, the coolant in gaseous form will enter the exchanger 1 through the channel 7 of the distributor. It then circulates in the distributor 5 arranged in the upper part 17 of the tank 14. The heat transfer fluid enters through the upper face of the body 24 of the distributor 5 through the pipe 7. The distributor distributes homogeneously the coolant in the tubes 2 , where it condenses by causing the melting of the MCP 13. The heat transfer fluid in the liquid state is collected in the lower part 18 of the tank 14 by the collector 6. The heat transfer fluid to exit the tank through the collector 6 and goes up in the pipe 8. The restriction element 23 will be located at the pipe 8 of the collector.

Preferably, the element 23 is located at the junction between the collector 25 and the pipe 8 of the collector 6.

This restriction element will cause a large and sudden pressure drop, limiting the heat transfer fluid flow at the outlet of this restriction element 23.

This pressure drop due to the element 23 makes negligible the pressure losses related to a normal circulation of the heat transfer fluid and thus allows a substantially equal distribution of heat transfer fluid flows within the exchangers and tubes 2.

By normal circulation is meant the circulation of the coolant during the use of the device without the addition of a restriction element for the diameter of the tubes 2 or in the channels of the distributor or the collector.

Advantageously, the ratio between the pressure drops related to the normal circulation of the heat transfer fluid in the collector and the pressure losses related to the restriction element is at least 5. Conversely, the discharge step, the heat transfer fluid under liquid form enters the exchanger 1 through the pipe 8 of the manifold 25. The heat transfer fluid will flow through the restriction member 23. The heat transfer fluid enters through the upper face of the body 25 in the lower part 18 of the tank 14. The collector 6 homogeneously distributes the coolant in the tubes 2, where the solidification of the MCP 13 allows the vaporization of the coolant. The coolant in the gaseous state is collected in the upper part 17 of the tank 14 by the distributor 5. The heat transfer fluid, to exit the tank, passes through the distributor 5 and back into the channel 7 of the distributor 5 before being extracted from the tank 14.

Advantageously, the exchanger 1 comprises a level of liquid 12 in the tubes 2 variable according to the charging or discharging step but always located above the collector 6. The liquid level 12 illustrates the separation of the two phases of the fluid coolant, the gaseous phase, the steam 11 being above the liquid phase 10. Thus, the heat transfer fluid is always in the liquid state in the manifold 6 and therefore in the pipe 8 and still in the gaseous state in the body of the distributor 24 and in the channel 7 of the distributor.

FIG. 3 illustrates an embodiment in which the distribution of the heat transfer fluid flow is actively managed. A restriction element 23 is added at the manifold pipe 8. This restriction element is a control valve 26 of the coolant outlet flow rate within the duct 8 of the collector.

An active management of the heat transfer fluid means a management using a restriction element able to adopt several states. Indeed this restriction element 23 can adopt a state where the pressure drop generated by its presence is zero, this is the case where the control valve 26 is fully open. This restriction element 23 can also adopt different states corresponding to different openings of the control valve 26, resulting in a restriction of the duct 8 of the more or less important collector. The more the restriction of the duct 8 of the collector is important plus the pressure losses are too.

This active management involves for each exchanger 1, a differential pressure measurement between the distributor 5 and the collector 6, by means of a pressure sensor 22, to deduce the level of liquid coolant 10. A regulation of this liquid heat-transfer fluid 10 will be performed through a control valve 26 placed on the pipe 8 of the collector.

During the charging step, the coolant in gaseous form will enter the exchanger 1 through the channel 7 of the distributor. It then circulates in the distributor 5 arranged in the upper part 17 of the tank 14. The coolant penetrates through the upper face of the body 24 of the distributor 5 through the pipe 7. The distributor distributes homogeneously the coolant in the tubes 2 , where it condenses by causing the melting of the MCP 13. The heat transfer fluid in the liquid state is collected in the lower part 18 of the tank 14 by the collector 6. The coolant to exit the tank passes through the collector 6 and goes back in the pipe 8. A pressure sensor 22 will measure the pressure difference between the distributor 5 and the manifold 6. Depending on this pressure difference, the opening of the control valve 26 will be more or less important for the regulation the flow of the coolant. The opening of the valve can be done manually or electronically.

Conversely, the discharge step, the heat transfer fluid in liquid form enters the exchanger 1 through the pipe 8 of the manifold 25. A pressure sensor 22 will measure the pressure difference between the distributor 5 and the collector 6. The fluid coolant will flow through the control valve 26 whose opening will depend on the pressure difference. The heat transfer fluid enters through the upper face of the body 25 in the lower part 18 of the tank 14. The manifold 6 homogeneously distributes the coolant in the tubes 2, where it solidifies the MCP 13 allows the vaporization of the heat transfer fluid. The coolant in the gaseous state is collected in the upper part 17 of the tank 14 by the distributor 5. The heat transfer fluid to exit the tank passes through the distributor 5 and back into the pipe 7 of the distributor 5 before being extracted from the tank 14.

Figures 4 and 5 respectively relate to the management of the distribution of the heat transfer fluid flow passively for Figure 4 and actively for Figure 5, according to a second embodiment. The pipes 7, 8 open into the upper part of the tank 14. Preferably at the upper face 17 of the tank 14.

The connections of the exchanger 1 are thus made from the top which facilitates the assembly of the exchanger 1 in the tank 14 and its extraction for repair or replacement.

In the case of passive management, the restriction element 23 is located within the pipe 8 of the collector, preferably at the junction between the collector 25 and the pipe 8.

In the case of active management, the pressure sensor measures the pressure difference between the distributor and the manifold, and the control valve 26 is located within the pipe 8 of the manifold.

In one embodiment, as in the other, during passive management, the added pressure drop facilitates the boiling of the coolant in discharge. In the case of active management, the control of the level 12 of liquid heat transfer fluid is a means of adjusting the latent energy storage capacity. Indeed, in charge, the melting of the MCP is only done on the height of the exchanger on which condensation takes place, that is to say above the liquid level 12 in the tubes 2. In discharge, the solidification of the MCP is only done on the height of the exchanger on which the boiling takes place, that is to say below the level of liquid 12 in the tubes 2.

Passive management of the flow distribution thus has the advantage of simplicity of use, no additional component or control loop being necessary for its implementation. Active management is more complex (addition of a control valve, a differential pressure measurement, and a control loop), but allows to manage in a differentiated way each exchanger of the storage, either by the management of level liquid by simply condemning one or more exchanger by closing the valve.

Several exchangers 1 can be placed in a tank 14, advantageously low pressure (that is to say a pressure less than 1.5 bar abs) containing at least one MCP 13. Advantageously, expansion compensators 20 are also arranged between 5. The expansion compensators 20 advantageously allow differential thermal expansion between the distributors 5 and the tank 14. According to one advantageous possibility, the expansion compensators 20 also make it possible to guarantee the tightness of the gaseous atmosphere of the tank 14.

The expansion compensators 20 are advantageously sealed joints and preferably have an elasticity to absorb the thermal expansion between the exchangers 1.

According to this arrangement illustrated in FIG. 1, the distributors 5 of the exchangers 1 form the upper face of the tank 14.

The upper portion 17 of the tank 14, advantageously above the MCP 13 may advantageously be occupied by a gas sky 19 comprising an inert gas to limit the corrosion process.

In FIG. 1, illustrating a device according to the invention with a tank 14 in which exchangers 1, of which 3 are entirely represented, and an MCP 13, are placed, the arrows indicate the direction of flow of the coolant during the charging phase. (condensation of the coolant, fusion of the MCP). The arrows with a solid line correspond to the coolant in the vapor state while the arrows with a dashed line correspond to the heat transfer fluid in the liquid state. The direction of flow is reversed in the discharge phase (evaporation of the coolant, solidification of the MCP).

Example:

A thermodynamic solar power plant operates at a nominal pressure of 110 bar. To be able to return the amount of steam corresponding to 6 hours of operation at full load, the storage must have a capacity of 900 MWht. At the temperature and pressure levels targeted by this application, MCP storage is about 50% of the total storage capacity, and NaN03 is an interesting MCP. Under these conditions the total volume of NaNO3 required for the plant would be about 4400 m3.

However, an optimized size storage device, comprising 217 tubes of 9 m long, for example, would require a volume of NaNO 3 of 60 m 3 per exchanger. It therefore takes 74 heat exchangers 1 to reach the storage capacity required by the solar power station.

Table: Characteristics of the MCP storage for a direct generation steam plant (without the use of an intermediate heat transfer fluid) of 50 MWe

These 74 exchangers could ideally be divided into 2 tanks of 37 exchangers, which would optimize the hexagonal shape of the tank 14.

In this case, during passive management of the flow distribution, the restriction element is in particular a pipe, or a smaller diameter bore in the manifold.

During an active management of the flow distribution, this management makes it possible to adapt the capacity of the storage to the thermal energy available. Indeed, the amount of steam produced in a direct-generation solar power plant depends very heavily on the daily sunshine, and therefore the time of year. If the storage is sized for a sunny summer day, it often happens that the daily steam output is not nominal. If, for example, this production can store only half of the nominal capacity of the storage (450 MWht), active management of the distribution of flows makes it possible to mobilize only half of the storage exchangers (preferably those located at tank) by condemning the other exchangers by closing their control valve.

REFERENCES 1. Exchanger 2. Tube 3. First end 4. Second end 5. Dispenser 6. Manifold 7. Channel 8. Channel 9. Thermal insulation 10. Liquid 11. Steam 12. Liquid level

13. MCP 14. Tank 15. Bottom wall 16. Side walls 17. Upper part 18. Bottom part 19. Gaseous stage 20. Expansion compensator 21. Foot 22. Pressure sensor 23. Restrictor element 24. Valve body 25 Manifold body 26. Control valve

Claims (22)

1. Thermal energy storage device by Phase Change Material (PCM) comprising at least one MCP (13), a tank containing the at least one MCP (13) and several heat exchangers (1) with a heat transfer fluid least partially in the tank (14) containing the at least one MCP (13), each exchanger (1) comprising: • a plurality of tubes (2), a distributor (5) having a body (24) arranged at a first end tubes (2) arranged in the upper part (17) of the tank, the distributor (5) connecting the tubes (2) between them and distributing a coolant to the plurality of tubes (2), • and a collector (6) comprising a body (25) arranged at a second end of the tubes arranged in the lower part (18) of the tank, the manifold connecting the tubes (2) between them and collecting the coolant of the plurality of tubes (2), the distributor (5) and the collector (6) respectively comprising a pipe (7, 8) suitable at the introduction or the evacuation of the coolant, characterized in that the coolant is two-phase liquid-gas and in that at least one exchanger (1) comprises at least one element (23, 26) arranged at least partially at the level of the duct (8) of the manifold configured to create a pressure drop in the circulation of the coolant. 2. Device according to the preceding claim wherein the element (23, 26) creates a pressure drop by decreasing the passage section of the heat transfer fluid. 3. Device according to the preceding claim, wherein the reduction of the heat transfer fluid passage section by the element (23, 26) is only on a portion of the manifold pipe. 4. Device according to any one of the preceding claims wherein the control of the distribution of the heat transfer fluid flow is passive. 5. Device according to the preceding claim wherein the element (23) consists of a pierced plate, or a membrane, or a reduction of the diameter of the pipe. 6. Device according to claims 1 or 2 or 3 wherein the control of the distribution of the heat transfer fluid flow is active. 7. Device according to the preceding claim wherein said element (26) is configured to manage the liquid level of the coolant in the heat exchanger (1). 8. Device according to one of the two preceding claims comprising a differential pressure measuring element (22) between the distributor (5) and the collector (6) and wherein the element (26) consists of a control valve the outlet flow of the heat transfer fluid arranged at the duct (8) of the collector. 9. Device according to any one of the preceding claims wherein the heat transfer fluid is configured to be in a liquid state (10) at the second end of the tubes (2), in the lower part (18) of the tank, and at a vapor state (11) at the first end of the tubes (2), in the upper part (17) of the tank. 10. Device according to any one of the preceding claims wherein the tubes (2) extend longitudinally between the distributor (5) and the collector (6). 11. Device according to any one of the preceding claims wherein the tubes (2) are straight and parallel to each other. 12. Device according to any one of the preceding claims wherein the pipes (7, 8) respectively of the distributor (5) and the manifold (6) open at the upper part (17) of the tank. 13. Device according to any one of the preceding claims wherein the pipe (8) of the manifold extends from the manifold (6) towards the distributor (5) and is capable of being immersed in the MCP (13). 14. Device according to the preceding claim, wherein the heat transfer fluid is in the liquid state (10) in the pipe (8) of the collector. 15. Apparatus according to any one of the preceding claims wherein the vessel (14) comprises a bottom wall (15), side walls (16) and an upper wall defining an interior volume receiving the at least one MCP (13). 16. Device according to the preceding claim wherein the pipe (7) of the distributor and the pipe (8) of the collector through the upper wall of the tank (14) to open out of the tank. 17. Device according to any one of the two preceding claims wherein at least one exchanger (1) is arranged in abutment on the bottom wall (18) of the vessel. The device of any of the claims wherein the MCP (13) is a solid-liquid MCP. 19. A method for storing thermal energy in a device according to any one of claims comprising a charging phase during which for each exchanger: - the heat transfer fluid enters each exchanger (1) in the upper part through the pipe ( 7) of the distributor (5) opening into the upper part (17) of the tank (14), - the distributor (5) in the upper part of the exchanger (1) distributes the heat transfer fluid in the gaseous state to the plurality of tubes (2), - the heat transfer fluid in the gaseous state condenses in the tubes (2) causing the melting of the MCP (13), - the heat transfer fluid in liquid form is collected by the collector (6) in the lower part of the the exchanger (1) - The coolant in liquid form passes through the element - The coolant is removed from the exchanger (1) through the pipe (8) of the manifold (6). 20. Method according to the preceding claim comprising a discharge phase during which for each exchanger: - the heat transfer fluid enters the exchanger (1) in the upper part (17) through the pipe (8) of the collector (6) opening in the upper part (17) of the tank (14), - The coolant in liquid form passes through the element - the collector (6) in the lower part of the exchanger (1) distributes the heat transfer fluid in the liquid state to the plurality of tubes (2), - the coolant in the liquid state vaporizes in the tubes (2) resulting in the solidification of the MCP (13), - the coolant in the gaseous state is collected by the distributor (5). ) in the upper part and is removed from the exchanger (1) through the pipe (7) of the distributor (5). 21. Method according to any one of the two preceding claims wherein the coolant is in the liquid state throughout the pipe (8) of the manifold (6). 22. A method according to any one of the three preceding claims comprising the following steps: - Differential pressure measurement - Determination of the liquid level of the coolant in the exchanger - Control of the control valve (26) arranged on the pipe (8) ) of the collector.