WO2024141680A1 - Thermal storage module and associated method - Google Patents

Abstract

The invention relates to a thermal storage and transfer module (1) of the type that uses a phase change material (1) to take advantage of the latent heat of fusion of the same, wherein the module comprises a container (4) provided internally with a set of tubes (2) extending longitudinally through the container (3) from a proximal portion to a distal portion thereof and being intended to channel a heat transfer fluid, said module comprising a composite material (3) which, in turn, comprises a matrix provided with metal wool that is both electrically and thermally conductive, and a phase change material in the temperature range comprised between 50° and 550°C, wherein the metal wool is arranged in the form of blankets inside the container (4).

Description

THERMAL STORAGE MODULE AND PROCEDURE ASSOCIATED WITH IT

OBJECT OF THE INVENTION

The present invention can be included within the technical field of thermal storage modules, in particular those modules or equipment of the type that comprise phase change materials to take advantage of their latent heat by fusion. More specifically, the object of the invention refers to a module, as well as a manufacturing and assembly procedure thereof, which comprises a conductive matrix provided with metal wool and heating elements that can be or form part of them. metal wools, for example by induction or resistive heating, giving rise to a particularly advantageous configuration for the storage, transmission and management of thermal energy, for example, for use in industrial plants or in solar thermal plants.

BACKGROUND OF THE INVENTION

Currently, commercial solar thermal plants are characterized by the possibility of introducing thermal storage systems that allow the production of electrical energy during hours without sun. These plants are characterized by having a heat transfer fluid or working fluid that is responsible for transferring the heat received from the sun to the storage systems and/or to the power block that generates electrical energy subsequently through a steam cycle.

The thermal storage materials that function as storage media most commonly used in this industry are inorganic salts, due to their low cost and high thermal capacity. These salts (normally nitrates) can be used in their liquid state (melted) or also at their phase change point from solid to liquid. In the first case the sensible heat contained in a certain temperature range is used; In the second, the latent heat at its melting point is used, delivering and storing thermal energy at a certain constant temperature. They are also characterized by having a low thermal conductivity of the order of 0.5 W/m K.

In the case in which its sensible heat is used, in which the salts are molten, they exchange heat with the heat transfer fluid (HTF) thanks to a heat exchanger where both materials flow. (inorganic salts and HTF). Due to the liquid state of both materials that flow through the heat exchanger, an acceptable heat transfer is achieved for the plants that improves as the thermal temperature jump of the fluids in the exchange increases. In the second case, in which latent heat is used, the inorganic salts remain static at their melting point and the heat exchange occurs between the HTF (which circulates through the tubes) and the salts themselves, which change liquid phase. to solid and vice versa in the loading and unloading processes. It is of special mention that the HTF circulating through the tubes must exchange heat with the phase change material (MCF - “phase change material”) through the external surface of the tubes and demands most of the heat flow. in the radial direction (transverse to the axis of the tubes). The transfer at the point where fusion occurs is controlled by a high transfer coefficient due to the phase change, while the transfer in the already melted or solidified part depends on the effective conductivity of the MCF. If the thermal conductivity of the MCF is low, this represents a limiting factor in the exchange by generating a thermal resistance of the heat flow towards the fusion front. That is why MCFs use different techniques to increase the effective conductivity of the medium used in the phase change.

One of the proposed solutions lies in doping the MCF with highly conductive elements such as graphite particles (US 2004- 084658) in order to obtain greater conductivity in the generated compound. From this system it is concluded that the conductivity of the MCF is effectively increased, but in all directions equally, without excessively improving the conductivity in the direction of interest (transverse to the axis of the tube).

Another proposed solution (LIS2010/0276121 A1) is to insert conductive elements in a tank or container in the desired direction for heat exchange, which act as a random finned surface. However, the space between fins is relevant and there are empty spaces without conductive material. This again represents resistance to transfer and an attempt is made to remedy it by adding other elements in other directions in order to also increase the conductivity of these intermediate spaces. In the same way as in the previous solution, a large amount of material is wasted because it is not thermally conducted only in the desired direction.

Document WO2013/059467 A2 also proposes the installation of thermally conductive elements between the plates of an exchanger, the application being impossible with tube exchangers.

Finally, and in the same sense, it is also proposed (US2007/0175609A1) to provide the tubes through which the heat transfer fluid circulates with highly conductive fins. In this case, all the conductive material is used in the desired direction of heat transfer, but it results in average heat transfers that are not very high. This is mainly due to the low transfer in the areas furthest from the fins. This solution also requires the installation of an excessive number of fins, implying excessive material costs as well as excessive manufacturing costs. DESCRIPTION OF THE INVENTION

The present invention aims to solve some of the problems mentioned in the state of the art. More particularly, a first aspect of the present invention describes a thermal storage module of the type that uses a phase change material to take advantage of the latent heat of fusion thereof, where said module comprises a container provided internally with a set of tubes. that longitudinally traverse said container from a proximal portion to a distal portion thereof, and where the tubes are intended to channel a heat transfer fluid.

Note that the module can act as an evaporator using water as the transfer fluid. Alternatively, you can use any other known heat transfer fluid.

Preferably, the module comprises a composite material comprising a matrix that is both electrically and thermally conductive, where the metal wools are arranged in the form of blankets inside the container and whose metal fibers are arranged in at least a first preferential direction that is transverse to the tubes, said conductive matrix of metanic wool being in intimate contact with the tubes.

The composite material comprises the phase change fluid and the conductive matrix formed by the wool, this material is arranged between the tubes. Preferably, this crosses the container longitudinally.

Likewise, resistive heating elements may be connected to an electrical power source and arranged within the assembly, or as part of the same composite material, and are configured to melt the phase change material and exchange heat with the phase transfer fluid. heat circulating through the tubes. Preferably, the composite material is the heat storage medium and is formed by the MCF plus the metal wool. This MCF is made up of salts that melt when they receive heat from the transfer fluid or an electrical power supply. The storage medium freezes when it transfers thermal energy to the transfer fluid. The device allows electrical charging and thermal discharge of the module simultaneously.

The metal wools with the configuration described above, on the one hand, substantially improve heat transfer, and, furthermore, in a preferred embodiment, they can be used in themselves as resistive elements connected to a power source to provide heat to the system. Alternatively, metal wool can be used for induction heating.

The phase change material may comprise organic and inorganic fluids having a latent heat of fusion greater than 100 kJ/kg and a thermal conductivity less than 1.5 W/m K.

The thermal storage and transfer module described above allows the use of phase change materials (MCF) with a metal matrix that increases the thermal conductivity and electrical conductivity of the composite material (MCF plus metal wool).

Metallic fiber is a fiber that can be composed of metal, plastic-clad metal, metal-clad plastic, or a completely metal-clad core. The compounds used include metals and metal oxides, alloys or mixtures of these and carbon derivatives. Recycled materials can be used to make the wool. Preferably, the fibers of the conductive metal wool matrix have a diameter of between 10 and 300 microns and are manufactured from a corrosion-resistant metal alloy of the phase change material.

The storage composite material made up of MCF and metal wool has greater heat transfer capacity and electrical and thermal conductivity, a stable chemical composition, and high heat transfer rates.

In a preferred embodiment of the present invention, the storage module is thermally charged through a circuit of heating elements, for example, materialized in electrical resistances inserted in said composite material that is formed by the phase change material (MCF). and metallic wool. In this way, from a supply of electric current applied directly inside the storage medium (composite material), the dissipation of energy in the form of heat occurs after the passage of an electric current, resulting in a power type embodiment. to heat (“Power to heat”).

The resistive elements can have mineral insulation and use an electric heating wire made of one or more alloys as a heat source. A layer of high-purity, high-temperature electrofused crystalline magnesium oxide can be used to provide dielectric insulating and heat-conducting properties.

Preferably, continuous seamless stainless steel, alloy steel or copper tubes are used as cladding. In case corrosive salts are used as phase change material (MCF), the resistors may have a jacket, coating or outer covering for the resistance wire. The mineral insulated inserted resistance wire works on the principle that once the line receives power, heat is generated. The amount of heat generated comes determined by the intensity and resistance that crosses the line. The current passes through the heating wire of the cable and its electrical energy is converted into efficient heat. Joule's law establishes that the heat generated Q depends on the electric current I that passes through a homogeneous conducting material with resistance R per unit of time t:

Q=I ² RP=I ² R

The total energy consumption P of a heater can be calculated using these electrical formulas. The electrical resistance R is the measure of opposition to the electric current and depends on the resistivity p, an inherent characteristic of the material, and the length L and the area A.

The storage module discharges the stored energy by exchanging heat with the heat transfer fluid (HTF) that circulates through the set of tubes that pass through the phase change material.

The proposed and described solution allows the storage to be charged through electric current, which dissipates the electrical energy in the form of heat, which is distributed to the composite material thanks to the high conductivity of the medium formed by the wool and salts, melting the material. The high effective thermal conductivity of the medium allows the thermal power per specific exchange surface of the tubes to be increased, which allows the values that can be achieved with systems without metal matrices to be reduced by half. This, in an exchanger, represents being able to reduce the number of tubes used by half without penalizing the thermal power exchanged.

Note that the described module can be charged both thermally through the transfer fluid that circulates through the tubes and through electrical resistances inserted in the storage medium, giving high-efficiency storage solution for a “Power to heat” and “heat to heat” concept.

In a preferred embodiment, the tubes have a linear configuration passing through the container, and the fibers of the metal wool are arranged at an angle of 45° to each other to ensure homogeneous effective thermal conductivity in the transverse or radial plane of the tubes. .

In another embodiment, the tubes may run helically through the container, in which case the metal wool fibers may be arranged at different angles to each other to ensure homogeneous thermal conductivity.

In this case, the metal wool fibers will continue to be arranged around the tubes distributed in longitudinal sections, and in each section the necessary rotation will be carried out to guarantee the uniformity of the conductivity in the axial plane. The plurality of different directions may be necessary to ensure homogeneous thermal conductivity.

The heating elements, preferably provided with resistive elements, are configured to heat the phase change material up to 700°C. Preferably, they are configured to heat in a range between 50°C and 600°C.

The resistive elements may comprise a resistive wire that is the active part of the heating element, a dielectric insulator that allows thermal conductivity, a jacketed tube that ensures mechanical and corrosion protection of the heating element, output connections, and terminals. connection that allows the electrical connection of the heating element. In a second aspect of the invention, the present invention relates to a process heat installation, where said installation comprises the module according to any of the described embodiments to improve thermal storage or controlled heat transfer, optimizing and maximizing izing the production of process heat, decoupling the generation of thermal energy from the availability of electrical energy and, consequently, being able to efficiently manage the thermal energy production of the plant. The module allows the hours of electrical charge and thermal discharge to be decoupled. In this way, charging can be carried out when the lowest cost of electrical energy is available, while unloading is controlled by the heat demand of the process.

In a third aspect, the present invention refers to a procedure for manufacturing and assembling the conductive metal wool matrix of the thermal storage module described above, where said procedure comprises:

- cutting a metal alloy cable with blades provided with a predetermined pitch configured to obtain fibers with a diameter of between 10 and 300 microns,

- group the set of fibers generating metallic wool blankets in a preferential direction,

- place the blankets in the container in a preferential direction that is transverse to the tubes.

Likewise, the procedure further comprises using the metal wool blankets as material for the composite storage medium inside the container and assembling them in the manner explained above.

In a preferred embodiment where the heating elements are resistive, the method further comprises connecting these to a source of electrical energy. In one embodiment, preferably where the set of tubes has a linear, homogeneous and parallel configuration within the container, the procedure further comprises placing the fibers of the metal wool at an angle of 45° from each other within the container to ensure a homogeneous effective thermal conductivity in the transverse or radial plane of the tubes.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, in accordance with a preferred example of its practical implementation, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1 shows a schematic perspective view of a preferred embodiment of the present invention, showing the container, the tubes, the conductive matrix of metal wool, the resistive elements and the phase change material.

Figure 1A.- Shows a section view illustrating the arrangement of the fibers of the conductive matrix of metal wool according to a preferred embodiment of the present invention.

Figure 2.- Shows a preferred embodiment where the fibers of the conductive metal wool matrix are oriented transversely to the tubes, showing different options according to preferred embodiments of the invention.

Figure 3.- Shows a top schematic view that illustrates a preferred embodiment of the arrangement of the resistive elements with respect to the tubes and the conductive matrix. PREFERRED EMBODIMENT OF THE INVENTION

Below, with the help of the attached figures 1-3 described above, a detailed description of an example of a preferred embodiment of the object of the invention is offered.

As Figure 1 illustrates, the object of the invention refers to a thermal storage module (1) of the type that uses a phase change material to take advantage of its latent heat of fusion, where said module comprises a container (4) provided internally with a set of tubes (2) that longitudinally traverses said container (4), where said tubes (2) are intended to channel a heat transfer fluid.

More specifically, the module (1) comprises a composite material (3) that acts as a storage medium, where the metal matrix that, together with the MCF, improves the effective axial conductivity of the medium both electrically and thermally. The composite material comprises metal wool arranged in the form of blankets inside the container (4) and whose metal fibers are arranged in a preferential direction that is transverse to the tubes (2), said conductive metal wool matrix being in intimate contact with the tubes. (2). The arrangement of these fibers can be seen in more detail in Figure 2.

Furthermore, the aforementioned composite material (3) comprises a phase change material in the temperature range between 50° and 550°C.

Likewise, as shown in Figure 1, the module has a container (4) and inside it the tubes (2) and the composite material (3) are arranged, and some heating elements (5) passing through the exchange material. phase and the metal wool matrix, in such a way that the heating elements (5) melt the phase change material and exchange heat with the heat transfer fluid circulating through the tubes (2).

In the preferred embodiment described, the heating elements (5) are resistive elements configured to heat the heat transfer fluid up to 700°C.

In an alternative embodiment, the heating elements (5) are resistive elements materialized by the metal wools themselves without external resistances. Furthermore, the module may comprise additional resistances and, in turn, at least part of the metal wools act as resistive elements to generate heat.

Preferably, the heating elements (5) comprise pure nickel and nickel-plated copper conductors and insulation impregnated with fiberglass or other composite resins.

Alternatively, the heating elements (5) comprise tungsten wires, preferably provided with dopants, and may, optionally, comprise insulation of fiberglass and/or other composite resins.

The storage material or also called composite material (3), comprises the phase change material and the metal wools of the conductive matrix described above. Therefore, the conductive matrix is arranged in the form of blankets in intimate contact with the tubes (2) and this acts in itself as a storage material where the phase change material melts by exchanging heat with the tubes (2). or the resistive heating elements (5), and freeze when giving energy to the transfer fluid that circulates through the tubes (2). In another preferred embodiment, the phase change material comprises inorganic salts provided with a latent heat of fusion greater than 100 kJ/Kg and a thermal conductivity less than 1.5 W/mK.

The fibers of the conductive metal wool matrix in the preferred embodiment have a diameter of between 10 and 300 microns and are manufactured from a metal alloy resistant to corrosion with respect to the phase change material.

The described thermal storage module is especially advantageous for any other plant that requires effective and high-performance means for the storage, management and transfer of thermal energy, both in its “power to heat” and “heat to heat” options. heat” (heat-heat).

A second aspect of the present invention refers to a manufacturing and assembly procedure of the conductive metal wool matrix of the storage and thermal transfer module (1) described above, where said procedure comprises the steps of:

- cutting a metal alloy cable with blades provided with a predetermined pitch configured to obtain metal fibers with a diameter of between 10 and 300 microns,

- group the set of fibers generating metallic wool blankets in a preferential direction,

- place the blankets in the container (4) in a preferential direction that is transverse to the tubes (2).

Claims

1.- Thermal storage and transfer module (1) of the type that uses a phase change material (1) to take advantage of its latent heat of fusion, where said module comprises a container (4) provided internally with a set of tubes (2) longitudinally traversing said container (3) from a proximal portion to a distal portion thereof, said tubes (2) intended to channel a heat transfer fluid, the module being characterized in that it comprises: - a composite material (3) which in turn comprises a matrix provided with metal wools that are both electrically and thermally conductive, and a phase change material in the temperature range between 50° and 550°C, where the wools The metallic fibers are arranged in the form of blankets inside the container (4) and whose metallic fibers are arranged in at least one preferential direction that is transverse to the tubes (2), said conductive matrix of metanic wool being in intimate contact with the tubes (2). ), - heating elements (5) that pass through or are part of the composite material (3), in such a way that they melt the phase change material and exchange heat with the heat transfer fluid that circulates through the tubes (2). 2.- The module (1) of claim 1, wherein the heating elements (5) are resistive elements of at least a portion of the metal wools of the composite material (3) configured to be connected to an electrical power source. . 3.- The module (1) of claim 1, wherein the heating elements (5) are induction heating elements using the metal wools of the composite material (3) for said induction heating. 4.- The module (1) according to any one of the preceding claims, wherein the heating elements (5) are configured to heat the phase change material up to 700°C. 5.- The module (1) according to any one of the preceding claims, wherein the heating elements (5) are resistors arranged within the composite material (3) passing through it. 6.- The module (1) of any one of the preceding claims, wherein the heating elements (5) comprise a jacket resistant to corrosion caused by the phase change material. 7.- The module (1) of claim 6, wherein the jacket is made of stainless or carbon steel. 8.- The module (1) of any one of the preceding claims, wherein the heating elements (5) comprise an intermediate insulation layer that comprises a dielectric insulating material that has a high thermal conductivity. 9.- The module (1) of claim 8, wherein the intermediate insulation comprises electrofused magnesium oxide. 10.- The module (1) of any one of the preceding claims, wherein the phase change material (1) comprises inorganic salts provided with a latent heat of fusion greater than 100 kJ/Kg and a lower thermal conductivity. at 1.5 W/mK. 11.- The module (1) of any one of the preceding claims, in which the set of tubes (2) have a linear configuration. 12.- The module (1) of any one of claims 1 to 9, in which the set of tubes (2) have a helical configuration inside the container (4). 13.- The module (1) of any one of the preceding claims, wherein the fibers of the metal wool are arranged at an angle of 45° from each other to ensure homogeneous effective thermal conductivity in the transverse or radial plane. of the tubes (2) that are arranged linearly. 14.- The module (1) of any one of claims 1 to 12, wherein the fibers of the metal wool, in a first portion of the container (4), are arranged in a first preferential direction that comprises a first angle , and, in a second portion of the container (4), are arranged in a second preferential direction that comprises a second angle that is different from the first angle. 15.- The module (1) of any one of claims 1 to 12, in which the metal wool fibers are arranged in a direction perpendicular to the tubes (2), with a random distribution in the radial plane, covering a plurality of radial angles in each axial or transverse section. 16.- The module (1) of any one of the preceding claims, wherein the fibers of the conductive matrix (3) of metal wool have a diameter of between 10 and 300 microns and are manufactured from a resistant metal alloy. to corrosion of the phase change material (1). 17.- Procedure for manufacturing and assembling the conductive matrix (3) of metal wool of the module (1) of any one of the preceding claims, comprising: - cutting a metal alloy cable with blades provided with a predetermined pitch configured to obtain fibers with a diameter of between 10 and 300 microns, - group the set of fibers generating metallic wool blankets in a single preferential direction, - place the blankets in the container (4) in a preferential direction that is transverse to the tubes (2). 18- The procedure of claim 16, which further comprises using the metal wool blankets as a resistive heating element (5) inside the container (3) by connecting them to an electrical power source. 19- The method according to any one of claims 17 or 18, further comprising placing the fibers of the metal wool at a different angle from each other within the container (4) to ensure homogeneous effective thermal conductivity. in the transverse or radial plane of the tubes (2).