Device for determining the charge level of a Thermal Storage System

Abstract

Device for Determining the Loading Rate of a Thermal Storage System. The invention relates to a latent heat storage system comprising a tank (101), a solid / liquid PCM (103, 104), a gas gap (102), and a heat exchanger. The storage system (100) is configured such that a portion of a separation front (110) between the gas gap and the PCM has a position representative of the storage system's loading rate. The system includes a vibrating fork sensor (200) for mounting on a side wall (113) of the tank, at a predefined height, within a measuring zone (203) so as to be in contact alternately with the gas gap or the liquid PCM depending on the volumetric variation of the PCM, and to provide a signal based on its contact with the gas gap or the liquid PCM. An electronic board connected to at least one sensor determines the storage system's loading rate based on the signal provided by the sensor. and its predefined height. Figure for the abbreviation: Fig. 2B

Description

Title of the invention: Device for determining a charge rate of a Thermal Storage System Technical field

[0001] The invention relates to the field of Thermal Storage Systems (TSS) using Phase Change Materials (PCMs), and more particularly, the integration of a device for measuring the state of charge of the system. The invention will find its application more particularly for all SSTs having an interface between the PCM and a gas canopy.

[0002] The invention will find its application for example in urban, rural or industrial heating and / or cooling networks as well as in the storage of solar energy. The invention may also find applications in housing or even off-grid thermal transport (trucks, boats, etc.). STATE OF THE ART

[0003] Thermal storage can be achieved by a change of state characterized by a transformation enthalpy. In this case, storage is done by phase change material. It is the phase change enthalpy that is stored. The charging of the heat storage system is accompanied by the melting of the storage material, while the discharge is achieved by the solidification of said material. It is the opposite when considering storage of frigories for a cold network.

[0004] One of the major advantages of this technology is that the phase change occurs at a constant temperature. Therefore, the discharge of the stored energy can occur at a virtually constant temperature and close to the phase change temperature of the material.

[0005] The phase change enthalpy is relatively large compared to the sensible energy variation of a material. Therefore, storage systems with MCP are interesting, because the amount of energy stored per unit of volume (and mass) is greater than that obtained by a sensible system (better storage density). As a result, the storage and material volumes are reduced, which makes it possible to limit thermal losses which are proportional to the external surface of the tank.

[0006] One system for implementing latent heat storage is the use of shell and tube exchangers. A shell in which a fluid circulates is traversed by a bundle of tubes in which another fluid flows. The two fluids exchange energy by conduction through the thickness of the tubes. In the case of thermal storage, this technology is suitable; there is no longer any exchange between two fluids in motion, but between a heat transfer fluid which circulates in the tubes and the MCP which is fixed in the shell (apart from natural convection movements in the liquid phase). During charging, the heat transfer fluid reaches a temperature higher than the melting temperature of the MCP and gives up energy to it, which causes it to melt; during discharging, the heat transfer fluid enters at a temperature lower than the melting temperature of the MCP and recovers the previously stored energy, which causes the MCP to solidify.

[0007] As presented above, the interest of thermal storage is obvious, particularly in the field of heating and cooling networks. However, a relevant use of such a device depends largely on the capacity of the network manager to be able to implement a real energy strategy based on technical and economic data of consumption / production in real time, as well as on adapted forecasts. In this logic, the manager will thus be able to choose rationally when to charge or discharge his storage means. The implementation of this usage strategy is only feasible if the state of charge or the charge rate (i.e. the quantity of calories or frigories stored) of the storage system is known.However, measuring the state of charge of a thermal storage by latent heat is problematic, because the heat is stored at a constant temperature, so it is difficult to quantify it using temperature detectors.

[0008] Several solutions for knowing the charge rate have been developed in the past.

[0009] One way to know the state of charge of a thermal storage system is to record its operating history. To do this, the quantity of energy injected or withdrawn from the storage system is measured using a flow meter and temperature detectors placed in the heat transfer fluid circuit, at the inlet and outlet of the thermal storage system. By knowing the initial state of charge when the storage system is put into service, it is therefore theoretically possible to know the state of charge of the storage system following different operations.

[0010] This method has many disadvantages: thermal losses at the level of the external surfaces must be finely simulated, or measured and taken into account, the precision of the estimation of the charge rate will deteriorate over time due to the accumulation of errors, many expensive and unreliable electronic acquisition, memory and calculation elements are necessary.

[0011] The Austrian laboratory ASiC proposes to measure the charge rate of a latent storage tank by measuring the pressure of the tank's sky. This idea is based on the fact that the MCPs used exhibit a strong volume expansion during their fusion (from 5% to 15%). A pressure increase therefore takes place in the sky between the state entirely solid and the entirely liquid state. It is thus possible to correlate the pressure measured in the headspace with the fraction of liquid formed and therefore to determine the charge rate. In practice, this method has many disadvantages. Firstly, it requires perfect sealing of the storage volume in order to be able to observe the pressure variation. In addition, these pressure variations subject the tank to strong pressure increases which have an impact on the design of the tank. Furthermore, the influence of temperature on the pressure of the gas headspace must also be taken into account, as its impact can be significant. This aspect can have a significant impact on the cost of the device.

[0012] Measuring the charge rate by measuring the gas flow rate that leaves / enters the gas head during the melting / solidification cycles has also been proposed. This measurement method has the advantages of being non-intrusive and not being disturbed by thermal losses from storage. However, this device has several disadvantages: the estimation of the charge rate is based on the integration over time of a flow rate that will necessarily have a measurement uncertainty, it is necessary to ensure costly and complex sealing of the tank.

[0013] The scientific publication Zsembinszki, G.; Orozco, C.; Gasia, J.; Barz, T.; Emhofer, J.; Cabeza, LF Evaluation of the State of Charge of a Solid / Liquid Phase Change Material in a Thermal Energy Storage Tank. Energies 2020, 13, 1425, provides a summary of the techniques for measuring the state of charge of a MCP storage referenced in the literature, including: - measurements by difference in electrical conductivity of the MCP between liquid and solid, which prove to be too intrusive and complex to implement in large SSTs; - a method based on sound propagation (a kind of radar), which requires complex calibration and could be very disturbed for tube and shell storage with many metal tubes and fins; - the measurement of the change in electrical resistance of a silicone membrane, which changes with mechanical stress.This membrane is placed on a tapping on the storage wall, which could cause sealing problems. Furthermore, this method only works for closed-shell systems.

[0014] It is also known that the charge rate (or state of charge) of a thermal storage corresponds to the portion of useful thermal energy still available divided by the total storable thermal energy.

[0015] The useful thermal energy available in a so-called latent storage means is the sum of the sensible and latent energies of the system.

[0016] The portion of sensible energy available in a latent storage system is easily measurable by one or more temperature probes. The importance of this portion of energy depends on the heat capacity of the material used and the difference between the temperature of the system and that of the source (hot or cold) of the application. The greater this gap, the higher the proportion of sensible energy stored will be.

[0017] The latent thermal energy available in a latent storage system corresponds, for its part, to the mass of the liquid MCP present multiplied by its latent heat of phase change (solid-liquid). Latent thermal energy total storable heat corresponds to the total mass of MCP multiplied by its latent heat. Finally, in the case where the share of sensible energy from storage is negligible, the The charge rate of a latent storage can therefore be defined by:

[0018] [Math.l] Load rate = liquid mass of MCP total mass of MCP

[0019] The total mass of MCP is constant and known since it is one of the design and sizing parameters of the thermal energy storage system. It is therefore sufficient to be able to determine the mass of liquid. However, the mass of liquid can be easily determined from the volume occupied by this liquid if its liquid density is known.

[0020] In the case of storage of colds, it is the mass of solid over the total mass which will be equal to the charge rate.

[0021] Thus, several solutions have been sought to determine the liquid mass of MCP.

[0022] Document EP 3 264 018 discloses a method which proposes to measure the charge rate by estimating the height of solid in the tank using the frequency measurement of a vibrating cord. The cord is fixed at the top of the storage, and the solid level of the MCP constitutes its second fixed point. The free length of the cord therefore depends on the height of solid. In a storage where the MCP is entirely solid, the free length of the cord is very short, in an entirely liquid storage the free length of the cord is at its maximum. Since the vibration frequency of a cord depends on its length, the charge rate of the storage is directly the image of the vibration frequency. Thus, by exciting the cord, it is possible to directly obtain the charge rate of the storage by measuring the vibration frequency. This method, although certainly very precise, is nevertheless very intrusive and would therefore be expensive and complex to implement.

[0023] There is also a measuring method described in document WO 2016 / 051377 consisting of adding a liquid compatible and immiscible with the MCP contained in the storage volume. The quantity of measuring fluid must be sufficient to ensure that the apparent surface in the upper part of the tank is flat when the tank is completely discharged. Any increase or decrease in the level of this fluid is caused by the melting / solidification of the MCP, due to the variation volume of the phase change. It is therefore possible to establish a law providing the state of charge as a function of the level of the measuring fluid. The system uses an optical or laser detector introduced into the tank to monitor the displacement of the height level of the measuring fluid. The main disadvantage of the system is the quantity of measuring fluid required to cover the entire MCP regardless of the configuration. The impact on the density of the system is direct and possibly non-negligible. This method is also very intrusive, because the detector is internal to the tank.

[0024] There is therefore a need to propose a device for determining the charge rate of a thermal storage system that resolves all or part of these disadvantages. SUMMARY

[0025] To achieve this objective, according to one embodiment, the invention provides a device for determining a charge rate of a thermal storage system (TSS) by latent heat, - the SST comprising a tank comprising at least one side wall and receiving a solid / liquid MCP whose phase change is accompanied by a volume variation, and a gas ceiling, with a heat exchanger immersed in the tank and capable of receiving a heat transfer fluid, - the SST being configured so that part of a separation front between the gas ceiling and the MCP has, in the tank, a position representative of the SST loading rate, - the SST being in a completely discharged state when the phase change material is substantially totally in a solid state defining a first level of height of the separation front and in a completely charged state, when the phase change material is substantially totally in a liquid state defining a second level of height of the separation front, - comprising at least one detector intended to be arranged on a side wall of the tank and advantageously an electronic card connected to at least one detector and intended to determine the charge rate of the SST, advantageously at a given moment of its operation, characterized in that: - the at least one detector is a vibrating blade detector intended to be arranged at a predefined height in a measurement zone whose height is defined between the first height level and the second height level, and to be in contact alternately with the gas canopy or the liquid MCP depending on the volume variation of the MCP, and to provide a signal depending on its contact with the gas canopy or the liquid MCP, - advantageously the electronic card determines the charge rate of the SST, advantageously at a given moment of its operation, according to of the signal provided by the at least one vibrating blade detector and its predefined height in the measurement area.

[0026] The device according to the invention presents a determination of the charge rate which is more precise in particular than the prior art taking into consideration the liquid / solid interface. With the device according to the invention the risks of false measurements are limited since the vibrating blade detects the liquid / gas head MCP separation front, there is therefore no contact with the solid MCP and there is therefore no risk that the solid MCP, by detaching from the wall of the tank, induces measurement errors. Furthermore, the device according to the invention allows a direct physical measurement without integration over time. There is therefore no drift of the determination device over time. The device is applicable to tanks whose gas head is closed or open. Finally, the determination device is very slightly intrusive, facilitating its implementation and limiting the impacts on the operation of the SST.The vibrating blade is for example screwed from the outside of the tank onto the side wall, so it can be inspected and removed in the event of a breakdown or for replacement. Advantageously, the accuracy of the load rate determination can be easily increased by modulating the number of vibrating blades.

[0027] According to another aspect, the invention relates to a thermal storage system (TSS) by latent heat comprising a tank comprising at least one side wall and receiving a solid / liquid MCP whose phase change is accompanied by a volume variation, and a gas ceiling, and a heat exchanger immersed in the tank and capable of receiving a heat transfer fluid, - the SST being configured so that part of a separation front between the gas ceiling and the MCP has, in the tank, a position representative of the SST loading rate, - the SST being in a completely discharged state when the phase change material is substantially totally in a solid state defining a first level of height of the separation front and in a completely charged state, when the phase change material is substantially totally in a liquid state defining a second level of height of the separation front, - comprising at least one detector intended to be arranged on a side wall of the tank and advantageously an electronic card connected to the at least one detector and intended to determine the charge rate of the SST, advantageously at a given moment of its operation, Characterized in that: - the at least one detector is a vibrating blade detector intended to be arranged at a predefined height, in a measurement zone whose height is defined between the first height level and the second height level, and to be in contact alternately with the gas sky or the liquid MCP depending on the volume variation of the MCP, and to provide a signal depending on its contact with the gas sky or the liquid MCP, - the electronic card determines the charge rate of the SST, advantageously at a given moment of its operation, according to the signal provided by the at least one vibrating blade detector and its predefined height in the measurement zone.

[0028] Advantageously, the device or SST comprises a plurality of vibrating blade detectors arranged at different heights in the measurement zone.

[0029] This device thus makes it possible to determine the charge rate, whatever the state of charge of the latent heat energy storage means.

[0030] According to yet another aspect, the invention relates to a method for setting up a device for determining a load rate of an SST comprising: - The definition of the measurement zone in which to place the at least one vibrating blade detector, including for example the steps below: • carry out a complete discharge of the SST, • measure the first level of height of the separation front when the storage SST is in this fully discharged state, • carry out a full charge of the SST, • measure the second level of separation front height when the storage SST is in this fully charged state, - Positioning at least one vibrating blade detector in the measurement area on a side wall of the tank at a predefined height.

[0031] According to yet another aspect, the invention relates to a method for determining a charge rate of an SST comprising receiving the signal provided by the at least one vibrating blade detector, then determining the charge rate, advantageously at said determined moment, as a function of the signal provided by each vibrating blade detector and their predefined height in the measurement zone.

[0032] The determination device, the associated SST and the determination method according to the invention are particularly effective since they make it possible to directly obtain the liquid mass of MCP and they do not need to go through theoretical calculations taking into account the expansion coefficient of the MCP and / or the volume occupied by a measuring fluid. The determination is therefore simple and rapid with optimized precision and a very limited risk of error without risk of drift of the measurement over time. BRIEF DESCRIPTION OF THE FIGURES

[0033] The aims, objects, as well as the characteristics and advantages of the invention will emerge better than the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0034] [Fig.l] [Fig.l] represents a sectional view of a thermal storage system according to the invention.

[0035] [Fig.2A] Figures 2A to 2D represent a tank equipped with a determination device according to the invention during a discharge phase (solidification of the MCP).

[0036] [Fig.2B]

[0037] [Fig.2C]

[0038] [Fig.2D]

[0039] [Fig.3A] Figures 3A to 3D represent a tank equipped with a determination device according to the invention during a loading phase (liquefaction of the MCP).

[0040] [Fig.3B]

[0041] [Fig.3C]

[0042] [Fig.3D]

[0043] [Fig.4] [Fig.4] shows a vibrating blade detector used in the device of determination according to the invention.

[0044] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of the applications practices. DETAILED DESCRIPTION

[0045] Before commencing a detailed review of embodiments of the invention, are listed below are optional features that may be used in combination or alternatively: according to one example, the plurality of vibrating blade detectors 200 being arranged so that the height 206 separating two successive vibrating blade detectors 200 is identical; According to one example, the device or SST comprises from 2 to 10 vibrating blade detectors 200; In one example, the device or SST does not include additional measuring fluid; According to one example, the signal provided by the at least one vibrating reed detector 200 is an all-or-nothing (ON) signal; According to one example, the SST is configured so that the separation front 110 is substantially planar parallel to the horizontal during operation of the SST; According to one example, the heat exchanger comprises a lower distributor 108 arranged in the lower part of the tank 101 and an upper distributor 109 arranged in the upper part of the tank 101, the lower distributor 108 and the upper distributor 109 being respectively intended for the introduction and evacuation of the heat transfer fluid in the heat exchanger; - According to one example, the heat exchanger comprises a single-phase heat transfer fluid and the exchanger is configured to ensure the circulation of the heat transfer fluid from the upper distributor 109 to the lower distributor 108 under load and from the lower distributor 108 to the upper distributor 109 under discharge.

[0046] According to one example, the method comprises placing a plurality of vibrating blade detectors 200 in the measurement area 203 at different predefined heights.

[0047] For the remainder of the description, 'top' and 'bottom', or their derivatives, are understood to mean a quality of relative positioning of a device element for determining a charge rate or of the thermal storage system when the latter is installed functionally, the 'top' being oriented away from the ground and the 'bottom' being oriented towards the ground. The upper end is located at the top and the lower end is located at the bottom.

[0048] Vertical means that which is parallel to the direction of gravity given in particular by the plumb line and horizontal that which is perpendicular to the vertical. The top and the bottom being vertically opposed.

[0049] By horizontal we mean that which is perpendicular to the vertical.

[0050] Transverse means a direction perpendicular to a longitudinal direction. A transverse section is a section perpendicular to the longitudinal axis.

[0051] Upstream and downstream, inlet, outlet, at a given point are taken in reference to the direction of circulation of the fluid.

[0052] A parameter "substantially equal / greater / less than" or "of the order of" a given value means that this parameter is equal / greater / less than the given value, to within plus or minus 10%, or even to within plus or minus 5%, of this value.

[0053] Fluidly connected or in fluidic connection means when a line provides a connection by or in which a fluid circulates.

[0054] In the present description, the expression "A fluidically connected to B" is synonymous with "A is in fluidic connection with B" and does not necessarily mean that there is no member between A and B. The expressions "arranged on" or "on" are synonymous with "fluidically connected to".

[0055] Hot, cold, cooled means a temperature relative to another point in the system.

[0056] The use of the indefinite article "a" or "an" for an element or a step does not exclude, unless otherwise stated, the presence of a plurality of such elements or steps.

[0057] The invention relates to a system for determining a charge rate of a Thermal Storage System (TSS). The invention also relates to a thermal storage system (TSS) comprising the device for determining the charge rate.

[0058] The device for determining the charge rate is applicable to a latent heat thermal storage system.

[0059] Storing thermal energy allows heat to be used later. Heat can be stored in several forms. The invention focuses on storage in the form of latent heat with the use of phase change materials that store energy as they change phase. When the material reaches its phase change temperature, it absorbs a quantity of heat to carry out the transformation, known as the latent heat of fusion or vaporization as the case may be. Conversely, when the liquid or gas material is cooled, it returns to the solid or liquid phase, releasing its latent heat.

[0060] Although the latent heat of fusion is lower than the latent heat of evaporation, the solid-liquid transition is the most promising since it makes it possible to limit the volume expansion and thus the increase in pressure due to the phase change.

[0061] The invention applies to all solid / liquid MCPs. Solid / liquid MCPs are understood to be materials that change phase between a solid state and a liquid state depending on its temperature. When its temperature is above its melting temperature, the MCP is in the liquid state and when its temperature is below its melting temperature, the MCP is in the solid state.

[0062] Preferably, the MCPs are chosen from solid / liquid MCPs exhibiting a volume variation during the phase change. Preferably, the volume variation is at least of the order of 5%, preferably of the order of 10 to 20%.

[0063] Preferably, the MCPs are chosen from organic compounds and in particular fatty alcohols, fatty acids and paraffins or from inorganic compounds such as molten salts, liquid metals or salt hydrates.

[0064] The MCP may be a single MCP or a mixture of several MCPs. In the remainder of the description, the use of the term an MCP is not limiting.

[0065] The thermal energy storage system according to the invention comprises a storage tank 101 intended to receive the MCP, as described above. The tank 101 is also called a calender. The tank 101 is preferably cylindrical for reasons of mechanical strength. The tank 101 comprises at least one side wall 113, in particular when the tank is cylindrical. The tank 101 may comprise several side walls 113 when it has another geometry, for example of the parallelepiped type. The tank 101 also comprises a lower wall 112 and possibly an upper wall 111, depending on whether the tank 101 is open or closed.

[0066] The thermal storage system according to the invention also comprises a heat exchanger immersed in the tank 101. The heat exchange is intended for the circulation of a heat transfer fluid from an external heat transfer fluid circulation network to store and extract heat from the MCP. Preferably, the heat transfer fluid is a single-phase fluid under the operating conditions of the SST, most often water or pressurized water, but it can also be air, a thermal oil or even a molten salt.

[0067] The thermal energy storage system according to the invention is thus of the shell-tube type.

[0068] The heat exchanger preferably comprises a bundle of tubes 105, in particular with fins 106, assembled between a lower distributor 108 and an upper collector 109. In operation, the heat transfer fluid circulates inside the tubes 105 and exchanges its heat with the MCP 103, 104 contained in the tank 101.

[0069] Advantageously, the tank 101 extends in a main vertical direction. Advantageously, the heat exchanger extends in a vertical direction, the bundle of tubes 105 extends vertically between the lower distributor 108 and the upper distributor 109, preferably respectively arranged at the lower and upper ends of the tank 101. The lower distributor 108 and the upper distributor 109 are connected to an external heat transfer fluid circulation network respectively by an inlet or outlet pipe for the heat transfer fluid.

[0070] The upper distributor 109 and the lower distributor 108 may respectively form at least partially the upper wall 111 and the lower wall 112 of the tank 101. The upper wall 111 of the tank 101 is advantageously formed by a cover. Advantageously, the tank 101 is configured to allow it to be filled. For example, the tank 101 may comprise a removable cover to allow it to be filled or a cover provided with filling hatches or the tank comprises a hatch on a shell on the side of the system.

[0071] The tank 101 of the SST comprises a gas ceiling 102. Advantageously, the gas ceiling 102 is arranged above the MCP 103, 104. According to one possibility, the gas ceiling 102 is located between the upper surface of the MCP 103, 104 and the upper wall 111 of the tank 101, which may be formed by the upper distributor 109, in particular by the lower plate of the upper distributor 109.

[0072] The device for determining the charge rate according to the invention takes into consideration the separation front 110 of the MCP 103, 104 with the gas canopy 102. The separation front 110 of the MCP 103, 104 with the gas canopy 102 is understood as the interface between the gas canopy 102 and the MCP 103, 104 in contact with the gas canopy 102, that is to say either the MCP 104 in the liquid state, or the MCP in the solid state 103 depending on the operating phases of the SST.

[0073] The position, in the tank, of the separation front 110 is intended to be representative of the loading rate of the SST.

[0074] Advantageously, the device for determining the charge rate does not require the presence of an additional measuring fluid other than the liquid / solid MCP. It has in fact been surprisingly found that the measuring fluid is not necessary to enable the monitoring of the separation front 110 of the MCP with the gas ceiling.

[0075] The separation front 110 of the MCP 103, 104 with the gas ceiling 102 is substantially flat, advantageously parallel to the horizontal, advantageously over the entire cross-section of the tank 100.

[0076] The position of the separation front 110 in the tank varies according to the variations in volume of the MCP. These variations in volume are mainly due to the phase change of the MCP: that is to say due to the melting or solidification of the MCP. It is thus understood that the position of the separation front 110 makes it possible to determine the volume and therefore the mass of liquid MCP at a time T.

[0077] According to an embodiment of thermal energy storage in the form of calories, when the MCP is substantially entirely in a solid state, the SST is then completely discharged, the separation front 110 then taking a position defining a first height level 201. Conversely, when the MCP is substantially entirely in a liquid state, the SST is then completely charged, the separation front 110 then taking a position defining a second height level 202.

[0078] The first height level 201 corresponds to the lowest level of the separation front 110 in the tank 101 while the second height level 202 corresponds to the highest level of the separation front 110. During operation, the separation front 110 therefore takes a position between the first height level 201 and the second height level 202. The height between the first height level 201 and the second height level 202 defines a measurement zone 203. The measurement zone 203 therefore corresponds to the positioning amplitude of the separation front 110 during operation of the SST 100.

[0079] Preferably, the thermal storage system and the device for determining a charge rate are configured so that the measurement zone 203 is at least 25 cm high. For example, the measurement zone 203 which alternately sees liquid MCP 104 and gas ceiling 102 in the top of a tank 101 comprising 10 m of MCP, has a height of 1 to 1.5 m, considering a volume expansion of the MCP typically of the order of 10-15%.

[0080] According to the invention, the determination device comprises at least one vibrating blade detector 200. In the remainder of the description, reference is made to a vibrating blade to speak of a vibrating blade detector. The vibrating blade 200 is intended to be arranged in the measurement zone 203. Advantageously, the vibrating blade 200 intended to be alternately in contact with the gas ceiling 102 or the liquid MCP 104. Advantageously, the vibrating blade intended to be arranged in the measurement zone 203 with the exception of the first height level 201, so that the vibrating blade 200 is alternately in contact with the liquid MCP 104 and the gas ceiling 102 without coming into contact with the solid MCP 103.

[0081] The vibrating blade detector 200 is advantageously a detector making it possible to detect the presence of the gas canopy 102 or the liquid MCP 104, preferably by an all-or-nothing binary signal TOR on the basis of a signal equal to zero for the presence of the gas canopy 102 and a signal equal to one for the presence of the liquid MCP 104.

[0082] The vibrating blade detector 200 is advantageously a point detector intended to detect the presence of the gas ceiling 102 or the liquid MCP 104 continuously.

[0083] According to a preferred possibility, the device for determining a charge rate comprises a plurality of vibrating blade detectors 200 arranged at different heights in the measurement zone 203.For example, the device comprises 5 vibrating blade detectors arranged as described below, the position of each vibrating blade 200 in the measurement zone 203 corresponds to a certain charge rate of the SST, the position of the vibrating blade 2001 corresponding to the first height level 201 makes it possible to determine a charge rate of the order of 0%; the position of the vibrating blade 2005 corresponding to the second height level 202 makes it possible to determine a charge rate of the order of 100%; the position of the vibrating blade 2003 corresponds to 50% of the height of the measurement zone 203 makes it possible to determine a charge rate of the order of 50%; the position of the vibrating blade 2002 corresponds to 25% of the height of the measurement zone 203 makes it possible to determine a charge rate of the order of 25%; the position of the vibrating blade 2004 corresponds to 75% of the height of the measuring zone 203 makes it possible to determine a load rate of the order of 75%.

[0084] The height of the measuring zone 203 corresponds to a 100% load rate and the positioning of the vibrating blade 200 in the measuring zone 203 thus corresponds to a corresponding load rate.

[0085] Advantageously, the device for determining the charge rate and the associated SST comprise a plurality of vibrating blades 200. Preferably, the device for determining the charge rate comprises two or more vibrating blades 200. Preferably, the determination device comprises 3 vibrating blade detectors 200, more preferably 4 vibrating blade detectors 200, preferably 5 vibrating blade detectors 200, preferably 6 vibrating blade detectors 200, preferably 7 vibrating blade detectors 200, preferably 8 vibrating blade detectors 200, preferably 9 vibrating blade detectors 200, preferably 10 vibrating blade detectors 200. The more vibrating blades 200 the device for determining the charge rate comprises, the greater the accuracy of the determination is high. For example, with 5 200 vibrating fork detectors, the charge rate will be known to within 20%, whereas with 10 200 vibrating fork detectors, the charge rate will be known to within 10%.

[0086] In the embodiment where the device for determining the charge rate comprises a plurality of vibrating blades 200, the vibrating blades 200 are all arranged in the measurement zone 203 and preferably with a regular gap 206 between 2 successive vibrating blades 200.

[0087] The vibrating blade 200 is of the type of piezoelectric detector intended for the detection of a liquid or a gas.

[0088] The vibrating blade 200 is advantageously arranged in the tank 100 at a side wall 113. Advantageously, the vibrating blade 200 is arranged so as to pass through a side wall 113. For example, a tank 100 conventionally comprises bosses in the upper part. The vibrating blade 200 is advantageously arranged through bosses of this type. This positioning allows easy installation of the determination device since it does not require intrusive penetration into the tank, and it is thus easy to repair or maintain the vibrating blade 200.

[0089] The vibrating blade 200 is a detector comprising a first blade 403 and a second blade 404 arranged face to face like a tuning fork. The blades 403, 404 are brought to their resonant frequency, for example of the order of a hundred Hertz, by piezoelectric effect. The vibration of the blades 403, 404 is different depending on the medium in which the vibrating blade 200 is located. When the vibrating blade 200 is in contact with the gas ceiling 102, the blades 403, 404 vibrate at their own resonant frequency. When the vibrating blade 200 is in contact with the liquid MCP 104, the blades 403, 404 have an attenuated vibration frequency and amplitude. Depending on the frequency and amplitude of vibrations of the blades 403, 404, the vibrating blade 200 produces an electrical signal causing a relay to switch. The signal produced by the vibrating blade detector 200 is advantageously an all-or-nothing signal.For example, when the vibrating blade detector 200 is in contact with the gas canopy 102, the blades 403, 404 vibrate at their own resonant frequency, the vibrating blade detector 200 transmits a signal equivalent to zero. Conversely, when the vibrating blade detector 200 is in contact with the liquid MCP 104, the blades 403, 404 vibrate at a frequency and amplitude attenuated relative to the resonant frequency, the vibrating blade detector 200 transmits a signal equivalent to 1.

[0090] The vibrating blade detector 200 comprises a first portion 400 comprising the 2 blades 403, 404 and intended to be arranged inside the tank 101, a second portion 401 intended to ensure the connection of the vibrating blade detector 200 to the tank 101, in particular by a screw thread, and a third portion 402 intended to be arranged outside the tank 101 and advantageously comprising an electrical module comprising the piezoelectric element allowing the blades 403,404 to vibrate and an integration means intended to transform the signal of the vibrations of the blades 403,404 into an advantageously all-or-nothing signal.

[0091] Advantageously, the determination device comprises an electronic card intended to determine the charge rate as a function of the signal provided by the vibrating blade detector(s) 200 and their position in the measurement zone 203.

[0092] In Figures 2A, 2B, 2C and 2D the tank 101 is illustrated during a discharge of an SST comprising a determination device according to the invention comprising five vibrating blade detectors 200. The vibrating blade detectors 200 are arranged in the measurement zone 203. During a discharge phase of the SST, the MCP 104 undergoes solidification, that is to say it passes from the liquid state to the solid state.

[0093] In Figures 2A, the SST is fully charged, the MCP 104 is entirely in the liquid state. The separation front 110 between the liquid MCP 104 and the gas ceiling 102 is substantially flat and advantageously horizontal. The separation front 110 is located at a first height level of 201 relative to the lower wall 112 of the tank 101.

[0094] In [Fig.2B], the tube bundle 105 is supplied from the lower distributor 108 with a cold heat transfer fluid 301. By cold is meant that the heat transfer fluid is at a temperature lower than the melting temperature of the MCP. The solidification of the liquid MCP 104 begins. The liquid MCP 104 transfers its thermal energy to the cold heat transfer fluid 301 which emerges at the upper distributor 109 at a higher temperature level as the heated heat transfer fluid 302. The level of liquid MCP 104 begins to drop by volume contraction of the MCP in the lower part of the tank 101. The separation front between the MCP and the gas ceiling 102 remains a flat and horizontal liquid / gas interface.

[0095] In [Fig.2C], the SST continues to discharge with the same heat transfer fluid circulations in [Fig.2B]. The MCP is almost entirely solidified. The separation front 110 between the MCP and the gas ceiling 102 remains a flat and horizontal liquid / gas interface.

[0096] In [Fig.2D], the SST is completely discharged. The MCP 103 is entirely in the solid state. The separation front 110 between the MCP and the gas ceiling 102 is a substantially flat and advantageously horizontal solid / air interface due to progressive solidification from bottom to top. The separation front 110 is located at a second height level 202 relative to the lower wall 112 of the tank 101.

[0097] The change in height of the separation front 110 between the first height level 201 and the second height level 202 is representative of the fraction of liquid MCP 104 in the tank 101 and therefore of the state of charge of the SST.

[0098] In Figures 3A, 3B, 3C and 3D the tank 101 is illustrated during a charging of the SST comprising a determination device according to the invention comprising five vibrating blade detectors 200. During a charging phase of the SST, the MCP 103 undergoes a melting, that is to say it passes from the solid state to the liquid state.

[0099] In [Fig.3A], the SST is fully discharged, the MCP 103 is entirely in the solid state. The interface between the solid MCP 103 and the gas ceiling 102 comes from the previous discharge and is therefore advantageously flat and horizontal. The separation front 110 is located at a first level of height 201 relative to the lower wall 112 of the tank 101.

[0100] In [Fig.3B], the tube bundle 105 is supplied from the upper distributor 109 with a hot heat transfer fluid 303. By hot is meant that the heat transfer fluid is at a temperature higher than the melting temperature of the MCP. The melting of the solid MCP 103 begins. The hot heat transfer fluid 303 transfers its thermal energy to the solid MCP 103. The cooled heat transfer fluid 304 leaves the tank 101 at the lower distributor 108 at a temperature level lower than that of its inlet. The solid MCP 103 transforms into liquid MCP 104 in the upper part of the tank 101. This phase change of the MCP creates the separation front 110 between the MCP and the gas ceiling 102 with a flat and horizontal liquid MCP 104 / air interface. The level of liquid MCP 104 begins to increase by volume expansion of the liquefying MCP 103. The separation front 110 begins to move.

[0101] In [Fig.3C], the SST continues to be charged with the same heat transfer fluid circulations as in [Fig.3B]. The MCP is almost entirely liquefied. The separation front 110 between the MCP and the gas ceiling 102 remains a flat and horizontal liquid / gas interface.

[0102] In [Fig.3D], the SST is fully loaded. The separation front 110 between the MCP, the gas ceiling 102 and a flat and horizontal liquid / air interface. The separation bottom 110 is located at a first height level of 202 relative to the lower wall 112 of the tank 101.

[0103] Advantageously, the melting / solidification profile contributes to the fact that the determination device according to the invention and the associated SST do not require the presence of a measuring fluid since the separation front between the MCP and the gas ceiling 102 is naturally flat and horizontal.

[0104] In Figures 2 and 3, five vibrating blade detectors 2001, 2002, 2003, 2004, 2005 are arranged in the measurement area 203. For example, the vibrating blades are arranged so that the first vibrating blade 2001 is arranged at a height level above the first height level 201 corresponding to 10% of the height of the area 203, the second vibrating blade 2002 is arranged at a height level height above the first height level 201 corresponding to 30% of the height of the zone 203, the third vibrating blade 2003 is arranged at a height level above the first height level 201 corresponding to 50% of the height of the zone 203, the fourth vibrating blade 2004 is arranged at a height level above the first height level 201 corresponding to 70% of the height of the zone 203, the fifth vibrating blade 2005 is arranged at a height level above the first height level 201 corresponding to 90% of the height of the zone 203.

[0105] In Figures 2A and 3D, all the vibrating blades are in contact with the gas canopy 102 and therefore return a signal of zero value, the SST is discharged, the charge rate of the SST is less than 10%. The charge rate is determined by the electronic card which processes the signal from the vibrating blade detectors.

[0106] In [Fig.2C] and 3B, two vibrating blades, the first vibrating blade 2001 and the second vibrating blade 2002 are in contact with the liquid MCP 104 and therefore return a signal of value 1 and 3 vibrating blades, the third vibrating blade 2003, the fourth vibrating blade 2004 and the fifth vibrating blade 2005 are in contact with the gas canopy 102 and therefore return a signal of value zero. The SST is charged at a charge rate of between 30 and 50%.

[0107] In [Fig.2D] and 3A, all the vibrating blades are in contact with the liquid MCP 104 and therefore return a signal of value 1, the SST is charged, the charge rate of the SST is greater than 90%.

[0108] According to one aspect, the SST according to the invention operates by carrying out the melting of the solid MCP 103 by the circulation of a hot heat transfer fluid 303 from the upper distributor 109 to the lower distributor 108, that is to say from the top to the bottom of the tank 101. Conversely, the solidification of the liquid MCP 104 is carried out by the circulation of a cold heat transfer fluid 301 from the lower distributor 108 to the upper distributor 109, that is to say from the bottom to the top of the tank 101. Advantageously, in this configuration, the melting of the MCP 103 takes place along a plane and horizontal separation front 110 from the top to the bottom of the tank 101, with a piston effect. Conversely, the solidification takes place along a plane and horizontal separation front 110 from the bottom to the top. of the tank 101.

[0109] According to one aspect, the invention relates to a method for setting up a device for determining a load rate of an SST.

[0110] This method of setting up the determination device comprises a first phase of defining the measurement zone 203 in which at least one vibrating blade detector 200 must be arranged.

[0111] According to a preferred possibility, this first phase of defining the measurement zone 203 is carried out by calculation. According to another possibility, this first phase of definition of the measurement zone 203 is carried out on the installed SST. In this possibility, this first definition phase comprises several successive steps. First, the SST is completely discharged. The MCP 103 is entirely in the solid state. Then, the first height level 201 of the separation front 110 is measured. The height of the interface between the solid MCP 103 and the gas ceiling 102, corresponding to the separation front 110 in this discharged state, is measured from the upper wall 111 of the tank, preferably, that is to say from the bottom of the tank 101. This height 201 corresponds to the height of the solid MCP 103 in this discharged state. Then, the SST is completely loaded. The MCP 104 is substantially entirely in the liquid state. Finally, the second height level 202 of the separation front 110 is measured.The height of the interface between the liquid MCP 104 and the gas ceiling 102, corresponding to the separation front 110 in this charged state, is measured from the upper wall 111 of the tank preferably, that is to say from the bottom of the tank 101. This height 202 corresponds to the height of the liquid MCP 104 in this charged state. The measurement zone 203 is located between the first height level 201 and the second height level 202.

[0112] The method for positioning the determination device according to the invention advantageously comprises a second phase of positioning at least one vibrating blade detector 200 in the measurement zone 203 on a side wall 113 of the tank 101 at a predefined height.

[0113] According to a preferred embodiment, the method of positioning the determination device comprises repeating the second phase of positioning at least one vibrating blade detector 200 for each other vibrating blade detector 200 intended to be arranged in the measurement zone 203 at a different height.

[0114] According to another aspect, the invention relates to a method for determining a charge rate of an SST. According to the invention, the method for determining the charge rate of the SST comprises receiving the signal provided by one or more vibrating blade detector(s) 200, advantageously by the electronic card, then determining the charge rate as a function of the signal provided by each vibrating blade detector 200 and their height in the measurement zone 203. Advantageously, the electronic card provides a charge rate as a percentage preferably between 10 and 90%, preferably between 5 and 95%. According to a preferred embodiment, the determination of a charge rate of an SST is carried out continuously.

[0115] According to one possibility, the first phase of defining the measurement zone 203 can be carried out again after a certain number of charge-discharge cycles to ensure that the first height level 201 and the second height level 202 have not varied due to the degradation of the quality of the MCP.

[0116] An example of implementation is given below. A thermal storage system

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123] 100 consists of a bundle of tubes 105 included in a calender, or tank, 101 mounted on a stand. The calender is closed at the top and bottom by domed bottoms. The tank 101 is intended to receive the MCP 103,104 from the fatty alcohol family. The tank 101 contains around 8.8 tonnes of MCP 103,104. The bundle of tubes 105 consists of 361 finned tubes with a total length of 9000 mm for a length of tubes with fins of 8600 mm. The SST has a total overall height of 12 m for a diameter of 1.40 m. The SST is configured for the storage of 800 kW.h. The first height level 201 when the MCP 103 is fully solid is 7600 mm. The second height level 202 when the MCP 104 is fully liquid is 8600 mm. The first height level 201 and the second height level 202 are measured from the bottom distribution plate of the tank in contact with the MCP. Ten vibrating fork detectors 200 are arranged in the measuring area 203 defined between the first height level 201 and the second height level 202. The vibrating fork detectors 200 are arranged at the following predefined heights relative to the top of the lower collector plate 108: - 7650 mm - 7750 mm - 7850 mm 7950 mm - 8050 mm - 8150 mm - 8250 mm - 8350 mm 8450 mm - 8550 mm In this configuration, when all the vibrating reed detectors 200 transmit a signal of zero value, the charging rate of the SST is less than 5%. When all the vibrating reed detectors 200 transmit a signal of one value, the charging rate of the SST is greater than 95%. When half of the vibrating reed detectors 200 transmit a value of one and the other half transmit a value of zero then the charging rate is between 45 and 55%. The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. List of references 100. SST 101. Tank 102. Gas Sky 103. Solid MCP 104. Liquid MCP 105. Tube bundle 106. Fins 108. Lower distributor 109. Upper distributor 110. MCP / gas separation front 111. Upper wall 112. Lower wall 113. Side walls 200. Vibrating blade detector 201. First level of height 202. Second level of height 203. Measurement area 206. Height between two successive vibrating blades 301. Introduction of cold heat transfer fluid during discharge (= temperature lower than the melting temperature of the MCP) 302. Evacuation of heat transfer fluid heated during discharge (temperature higher than the temperature of the cold heat transfer fluid) 303. Introduction of hot heat transfer fluid during charging (= temperature higher than the melting temperature of the MCP) 304. Evacuation of cooled heat transfer fluid during discharge (temperature lower than the temperature of the hot heat transfer fluid) 400. First portion of vibrating blade intended to be arranged inside the tank and in contact with the liquid MCP or the gas ceiling 401. Second portion of vibrating blade intended to pass through the tank 402. Third portion of vibrating blade intended to be outside the tank 403. First Blade 404. Second blade 2001. First vibrating blade detector 2002. Second vibrating blade detector 2003. Third vibrating blade detector 2004. fourth vibrating detector 2005. Fifth vibrating blade detector

Claims

Claims

1. Device for determining a charging rate of a thermal storage system (TSS) (100) by latent heat, the SST (100) comprising a tank (101) comprising at least one side wall (113) and receiving a solid / liquid MCP (103,104) whose phase change is accompanied by a volume variation, and a gas canopy (102), with a heat exchanger immersed in the tank (101) and capable of receiving a heat transfer fluid, the SST (100) being configured so that a portion of a separation front (110) between the gas canopy (102) and the MCP (103,104) has, in the tank (101), a position representative of the charging rate of the SST (100), the SST (100) being in a completely discharged state when the phase change material is substantially totally in a solid state defining a first level height (201) of the separation front (110) and in a fully charged state,when the phase change material is substantially completely in a liquid state defining a second height level (202) of the separation front (110), comprising at least one detector intended to be arranged on a side wall (113) of the tank (101) and an electronic card connected to the at least one detector and intended to determine the charge rate of the SST (100), at a given moment of its operation, Characterized in that:, • the at least one detector is a vibrating blade detector (200) intended to be arranged at a predefined height in a measurement zone (203) whose height is defined between the first height level (201) and the second height level (202), and to be in contact alternately with the gas canopy (102) or the liquid MCP (104) depending on the volume variation of the MCP, and to provide a signal depending on its contact with the gas canopy (102) or the liquid MCP (104), • the electronic card determines the charge rate of the SST (100), based on the signal provided by the at least one vibrating blade detector (200) and its predefined height in the measurement zone (203).

2. Thermal storage system (TSS) by latent heat comprising a tank (101) comprising at least one side wall (113) and receiving a solid / liquid MCP (103,104) whose phase change is accompanied by a volume variation, and a gas canopy (102), and a heat exchanger immersed in the tank (101) and capable of receiving a heat transfer fluid, the SST (100) being configured so that a portion of a separation front (110) between the gas canopy (102) and the MCP (103,104) has, in the tank (101), a position representative of the charge rate of the SST, the SST (100) being in a completely discharged state when the phase change material is substantially totally in a solid state defining a first height level (201) of the separation front (110) and in a fully charged state,when the phase change material is substantially completely in a liquid state defining a second height level (202) of the separation front (110), the SST comprising a device for determining a loading rate of the SST (100) comprising at least one detector intended to be arranged on a side wall (113) of the tank (101) and an electronic card connected to at least one detector and intended to determine the loading rate of the SST (100) Characterized in that:, • the at least one detector is a vibrating blade detector (200) intended to be arranged at a predefined height, in a measurement zone (203) whose height is defined between the first height level (201) and the second height level (202), and to be in contact alternately with the gas canopy (102) or the liquid MCP (104) depending on the volume variation of the MCP, and to provide a signal depending on its contact with the gas canopy (102) or the liquid MCP (104), • the electronic card determines the charge rate of the SST (100) based on the signal provided by the at least one vibrating blade detector (200) and its predefined height in the measurement zone (203).

3. A device according to claim 1 or SST according to claim 2 comprising a plurality of vibrating blade detectors (200) arranged at different heights in the measuring area (203).

4. Device according to any one of claims 1 or 3 or SST according to any one of claims 2 or 3 in which the plurality of vibrating reed detectors (200) being arranged so that the height (206) separating two successive vibrating reed detectors (200) is identical.

5. A device according to any one of claims 1 or 3 to 4 or SST any one of claims 2 to 4 comprising from 2 to 10 vibrating blade detectors (200).

6. Device according to any one of claims 1 or 3 to 5 or SST any one of claims 2 to 5 not comprising additional measuring fluid.

7. Device according to any one of claims 1 or 3 to 6 or SST any one of claims 2 to 6 in which the signal provided by the at least one vibrating blade detector (200) is an all-or-nothing (TOR) signal.

8. Device according to any one of claims 1 or 3 to 7 or SST any one of claims 2 to 7 configured so that the separation front (110) is substantially plane parallel to the horizontal during operation of the SST.

9. Device according to any one of claims 1 or 3 to 8 or SST any one of claims 2 to 8 in which the heat exchanger comprises a lower distributor (108) arranged in the lower part of the tank (101) and an upper distributor (109) arranged in the upper part of the tank (101), the lower distributor (108) and the upper distributor (109) being intended for the introduction and evacuation of the heat transfer fluid in the heat exchanger.

10. Device according to any one of claims 1 or 3 to 9 or SST any one of claims 2 to 9 in which the heat exchanger comprises a single-phase heat transfer fluid and the exchanger is configured to ensure the circulation of the heat transfer fluid from the upper distributor (109) to the lower distributor (108) under load and from the lower distributor (108) to the upper distributor (109) under discharge.

11. Method for setting up a device for determining a load rate of an SST according to any one of claims 1 or 3 to 9 comprising:

1. Defining the measurement area (203) in which to place the at least one vibrating blade detector (200) 2. Positioning the at least one vibrating blade detector (200) in the measurement area (203) on a side wall (113) of the tank (201) at a predefined height.

12. A method according to the preceding claim comprising placing a plurality of vibrating blade detectors (200) in the measurement area (203) at different predefined heights.

13. A method for determining a charge rate of an SST according to any one of claims 3 to 9 comprising receiving the signal provided by the at least one vibrating blade detector (200), then determining the charge rate at said determined time as a function of the signal provided by each vibrating blade detector (200) and their predefined height in the measurement zone (203).

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