Materials for thermal energy storage, methods of making and methods of use

Abstract

According to one aspect of the invention, there is provided a material for thermal energy storage, the material comprising one or more metallic substances selected from metals and / or metal alloys encapsulated in a structural host material, wherein the metallic substances have a melting point in the range of 300-900 °C, and wherein the structural host material comprises at least 90 mass% of a hardened inorganic binder comprising one or more of a hydraulic binder, an alkali-activated material and a phosphate binder. According to another aspect, the invention provides a method of manufacturing said material for thermal energy storage, the method comprising the steps of: - providing a mixture of a metallic substance in solid state and a dry unreacted binder capable of reacting with a specified liquid; - adding the specified liquid to the mixture, thereby creating a paste containing the binder of the metallic substance; - casting the paste into a desired shape; and - hardening the paste, including the reaction with the specified liquid, whereby the paste is transformed into a structural host material encapsulating the metallic substance. According to yet another aspect, there is provided a method of heating a process stream by electrical power, the method comprising: - directly or indirectly electrically heating an amount of a material for thermal energy storage; and - directly or indirectly heat exchanging the process stream with the amount of material, thereby heating the process stream with heat from the amount of material.

Description

Technical Field

[0001] In one aspect, the present invention relates to a material for thermal energy storage. In another aspect, the present invention relates to a method for manufacturing the material. In yet another aspect, the present invention relates to a method for using the material, particularly in a method involving electrically heated process flows. Background Technology

[0002] Sustainable energy is a growing concern in modern society. In this regard, latent heat-based thermal energy storage has shown great potential through the use of phase change materials (PCMs) with high heat capacity. However, in practical applications, using PCMs for thermal energy storage presents several practical challenges, such as material dispersion, potential chemical reactions with the environment, and low thermal conductivity. Embedding PCMs in shells or porous networks, known as micron- and nano-sized encapsulated PCMs (EPCMs), has been proposed as a promising solution to these problems. Kasra Ghasemi et al. published a review in Sustainable Energy Technologies and Assessments, Volume 52 (2022), entitled: “PCM, nano / microencapsulation and slurries: A review of fundamentals, categories, fabrication, numerical models and applications.”

[0003] Metals and their alloys have long been studied as PCMs (Polymerized Matrix Materials), and miscible interstitial alloys (MGAs) have been proposed as a solution for thermal energy storage. MGAs consist of a mixture of two immiscible materials, particularly metals or semi-metals with different melting points. The two materials are pressed and sintered together, so that the component with the lower melting temperature is encapsulated as discrete particles within a matrix of the component with the higher melting temperature.

[0004] WO2014063191 describes such materials, particularly those in which the higher-melting-point material is a metal, graphite, or SiC, and the lower-melting-point material is another metal, metal alloy, or silicon. The use of such materials containing a lower-melting-point metal (e.g., zinc) encapsulated within graphite is further described in “Scaling up Miscibility Gap Alloy Thermal Storage Materials” in *Transition Towards 100% Renewable Energy*, A. Sayigh (ed.), 2018, Springer International Publishing. The materials proposed in these systems are typically expensive and subject to processing constraints, resulting in limited freedom in composite molding and usable bulk sizes. Furthermore, the use of graphite as an encapsulation material requires an inert gas flow for heat transfer to prevent combustion.

[0005] Likesh Kumar Sahu et al. published a review on thermal and mechanical properties of concrete containing phase change material in the International Journal of Engineering and Technology (IRJET), Volume 4 (2017), pp. 2154-2165. The review cited PCM materials with melting points typically around room temperature and proposed their use in concrete walls of houses and buildings for energy conservation in non-industrial heating systems (e.g., residential and commercial spaces). Since these materials are primarily used in houses and buildings, structural strength is a primary requirement, limiting the volume percentage of PCM and thus restricting its energy storage capacity.

[0006] The system described, which uses concrete to embed the PCM, is not suitable for efficient thermal energy storage at high temperatures, such as above 600°C or 700°C.

[0007] There is still a need to produce adaptable PCMs for thermal energy storage at high temperatures. Summary of the Invention

[0008] According to one aspect of the invention, a material for thermal energy storage is provided, the material comprising one or more metallic substances selected from metals and / or metal alloys encapsulated in a structural host material, wherein the metallic substance has a melting point in the range of 300°C to 900°C, and wherein the structural host material comprises at least 90% by mass of a hardened inorganic binder, the hardened inorganic binder comprising one or more of hydraulic binders, alkaline activating materials, and phosphate binders.

[0009] According to another aspect, the present invention provides a method for manufacturing the material for thermal energy storage, the method comprising the following steps:

[0010] - A mixture of a solid metallic substance and a dry, unreacted binder capable of reacting with a specified liquid;

[0011] - Add a specified liquid to the mixture to produce a paste containing a binder of metallic substances;

[0012] - Cast the paste into the desired shape; and

[0013] - To harden the paste, including by reacting it with a specified liquid, thereby transforming the paste into a structural host material for encapsulating metallic substances.

[0014] According to another aspect, a method for electrically heating a process flow is provided, the method comprising:

[0015] - Direct or indirect electric heating of a certain amount of material used for thermal energy storage; and

[0016] - To allow the process flow to exchange heat directly or indirectly with the given amount of material, thereby heating the process flow with the heat from the given amount of material. Detailed Implementation

[0017] Those skilled in the art will readily understand that, although specific embodiments of the invention have been illustrated with reference to one or more embodiments, each embodiment having a particular combination of features and measures, many of these features and measures can be applied equally or similarly independently to other embodiments or combinations.

[0018] When describing the elements of various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements besides those listed may also be present. Furthermore, it should be understood that references to “an embodiment” or “an embodiment” of this disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the described features.

[0019] We propose a novel material for thermal energy storage comprising one or more metallic substances encapsulated within a structural host material. The structural host material consists of at least 90% by mass, preferably at least 98% by mass, of a hardened inorganic binder. The metallic substances have a melting point in the range of 300°C to 900°C.

[0020] This material has been found to provide an excellent low-cost material for thermal energy storage in an operating temperature range of about 300°C to about 1000°C, preferably about 400°C to about 1000°C, and more preferably about 600°C to 1000°C. In some cases, the operating temperature is preferably no more than 950°C or preferably no more than 900°C.

[0021] Metallic materials can be used as phase change materials (PCMs) within the structural bulk material, and therefore, at the phase change temperature, they can absorb or release latent heat depending on the direction in which the induced phase change occurs. When the melting point of the metallic material is within the operating range, heat can be stored either as latent heat or sensible heat.

[0022] It has been found that relatively large amounts of metallic material can be encapsulated within structural bulk materials. This contrasts with the encapsulation of PCM used in houses / buildings, where the required strength in the building material significantly reduces the amount of PCM that can be contained. Furthermore, the hardened inorganic binder can cycle at temperatures up to approximately 1000°C while remaining intact and without peeling or cracking. It has been found that when concrete, for example, is used as a structural bulk material, as is the case in some prior art house and building materials, peeling and cracking frequently occur, especially at temperatures above approximately 600°C, which can lead to salt leakage from the material, thus reducing its effectiveness. Concrete typically contains inorganic binders, but their amount is well below 90% by mass. The function of the binder in concrete is to bind large amounts of sand and / or gravel.

[0023] Furthermore, it has been discovered that mixtures of (unreacted) inorganic binder pastes containing metallic substances, prior to hardening (reaction), can be poured and cast in large volumes like ordinary concrete. This makes it an excellent material for practical applications and processing.

[0024] The inventors have discovered three types of inorganic binders that can be used in the materials proposed in this invention: hydraulic binders, alkali-activated materials, and phosphate binders.

[0025] Hydraulic binders typically harden by reacting with (liquid) water. Cement is a hydraulic binder. Cement is a finely ground inorganic powder that, when mixed with water, forms a paste that solidifies and hardens through a hydration reaction and process, and retains its strength and stability even underwater after hardening. In the case of Portland cement, the reactive material is formed by calcining limestone and clay. In the case of calcium aluminate cement, the reactive material is typically formed by sintering a mixture of limestone and bauxite. Hydraulic cements are suitable for the materials of this invention because they are generally less expensive. Examples of suitable hydraulic cements include Portland cement, blast furnace cement, pozzolanic cement, composite cement, and calcium aluminate cement.

[0026] "Alkali-activated material" is a general term applicable to any binder system derived from the reaction of solid silicate powder (referred to as the "precursor") with an alkali metal source (referred to as the "activator") to produce a hardened material. The precursor can be a calcium silicate-rich precursor or a more aluminosilicate-rich precursor, such as metallurgical slag, natural volcanic ash, fly ash, or bottom ash. The activator is any soluble substance capable of providing alkali metal cations, increasing the pH of the reaction mixture, and accelerating the dissolution of the solid precursor; this includes alkali metal hydroxides, silicates, carbonates, sulfates, aluminates, or oxides. Alkali-activated materials include, but are not limited to, geopolymers, mineral polymers, inorganic polymers, inorganic polymer glasses, alkali-bonded ceramics, alkali-ash materials, soil cement, soil silicates, SKJ binders, F concrete, water ceramics, zeolite cement, and zeolite ceramics. For example, geopolymers are a subset of alkali-activated materials in which the binder phase is a pseudo-zeolite network structure of highly coordinated aluminosilicates. Geopolymers are prepared by mixing an alkaline solution (usually an alkali metal hydroxide or silicate) with a solid aluminosilicate material (usually low-calcium fly ash or calcined clay).

[0027] Phosphate binders, such as phosphate cement or phosphate-bonded cement, are products of an acid-base reaction between a concentrated aqueous solution of orthophosphoric acid, typically containing a metal salt, and an acid or basic metal oxide or aluminosilicate. The basic metal oxide preferably contains magnesium or aluminum as the metal.

[0028] The phosphoric acid liquid that forms cement almost always contains cations. The most important of these are aluminum and zinc, but other metals can also be used. The modified metals must be moderately soluble in oxide solutions and possess high ionic potentials. They must have low coordination numbers, multiple charges, and small ionic radii. This is necessary to maintain a glassy form in the cement gel. Amphoteric or weakly basic metals such as aluminum, zinc, beryllium, and magnesium ions meet this requirement.

[0029] Metallic substances comprise one or more metals and / or metal alloys. Suitable metals include aluminum, lead, magnesium, zinc, and their alloys. Aluminum is a particularly preferred metallic substance. A metal alloy is a combination of two or more elements, one of which must be a metal, producing an additive with metal-like properties. An alloy suitable for this document is an aluminum / silicon alloy. Therefore, metallic substances preferably comprise aluminum and / or its alloys.

[0030] All the key components of the new material can be low-cost, making it a very attractive improvement over existing solutions that either do not contain a significant amount of phase change material, thus limiting their thermal storage capacity, or lack the structural strength required to provide self-supporting materials.

[0031] It has been found that the amount of metallic material incorporated into a material can be much higher than anticipated in prior art references. The higher the metallic content in a material, the more heat can typically be stored per unit mass of material. However, the amount of metallic material should not exceed what would cause leakage from the material at higher temperatures. In this invention, it has been found that it is feasible for the total mass of metallic material encapsulated in the structural body material to be between 30% and 70%. Preferably, the total mass of the incorporated metallic material is between 40% and 70% of the total mass of the material, more preferably between 50% and 70%.

[0032] The remaining amount of the structural bulk material may also contain one or more admixtures, up to 10% by mass, excluding encapsulated salts. Admixtures, also known as "chemical admixtures," are materials added immediately before or during mixing to improve the manufacture or properties of the binder.

[0033] Typical admixtures are suitable for hydraulic binders, alkali-activated materials, and phosphate binders, and include retarders, accelerators, plasticizers, superplasticizers, and / or air-entraining admixtures. These admixtures are beneficial for reducing water content, which is helpful in cases with high salt content. Some admixtures can be considered to enhance the thermal conductivity of the material.

[0034] Novel materials for thermal energy storage can be manufactured by mixing finely crushed solid metallic substances with a dry, unreacted inorganic binder. For hydraulic binders, the specified liquid can be water. For alkali-activated binders, the specified liquid can be an alkaline solution. For phosphate binders, the specified liquid is a concentrated aqueous solution of orthophosphoric acid, wherein the dry, unreacted binder comprises an alkaline metal oxide or aluminosilicate.

[0035] Preferably, the fine solid metal material is a particle with an average diameter in the range of 2 mm to 12 mm.

[0036] In one embodiment of a method for manufacturing materials for thermal energy storage, particles of a metallic substance are first coated in a sacrificial material before being mixed with a dry, unreacted inorganic binder. The sacrificial material is preferably an organic material, and more preferably a wax or plastic. In this embodiment, the metallic substance is subdivided into appropriately sized solid particles and then coated with the sacrificial material. Once the thus-coated metallic particles are mixed with the dry, unreacted solid binder, the remaining steps of the manufacturing method can be completed. Upon initial heating of the material for thermal energy storage, the sacrificial material is burned off, thus providing space for the thermal expansion of the metal without damaging the main structural material.

[0037] A specified liquid can be added to the mixture to produce a paste containing metallic substances. The paste can be cast into desired shapes, such as blocks, and then allowed to harden to form the structural host material encapsulating the metallic substances. In this way, the hardened inorganic binder material (which functions to provide the structural properties of the novel material) can remain relatively free of metallic substances, while the material as a whole can still contain a significant amount of metallic substances.

[0038] For hydraulic binders, water is preferably added in a mass ratio of water to dried binder ranging from 0.20 to 0.55. If the water content is below 0.20, the paste lacks fluidity and cannot be molded in a mold, and it will easily contain trapped air bubbles and / or unreacted binder. If the water content is above 0.55, the paste is too fluid, creating a risk of agglomerates settling to the bottom. Furthermore, the hardened structure tends to be weak and prone to cracking during the drying process.

[0039] For alkali-activated materials, the alkaline solution is preferably added in an amount ranging from 0.20 to 0.55 by mass ratio of liquid to dry binder. This provides sufficient liquid for the necessary processability. If the liquid content is below 0.20, the paste lacks fluidity and cannot be molded in a mold, and it will easily contain trapped air bubbles and / or unreacted binder. If the liquid content is above 0.55, the paste is too fluid, creating a risk of agglomerates settling to the bottom. Furthermore, the hardened structure tends to be weak and prone to cracking during the drying process.

[0040] For phosphate binders, the concentrated aqueous solution of orthophosphate is preferably added in an amount ranging from 0.09 to 0.20 by mass ratio of liquid to dry binder. This provides sufficient liquid for the necessary processability. If the liquid content is below 0.09, the paste lacks fluidity and cannot be molded in a mold, and it will easily contain trapped air bubbles and / or unreacted binder. If the liquid content is above 0.20, the paste is too fluid, creating a risk of agglomerates settling to the bottom. Furthermore, the hardened structure tends to be weak and prone to cracking during the drying process.

[0041] The paste is cast into the desired shape and allowed to harden. During casting, additional conductive elements, such as metal rods or wires, can be incorporated into the material used for thermal energy storage. These metal rods or wires appropriately contain metals with high melting points and / or are permitted to remain intact throughout the use of the material for thermal energy storage. The use of such conductive elements helps to improve the thermal conductivity of the material used for thermal energy storage.

[0042] Manufacturing may also include a step of drying the structural host material of the encapsulated metallic substance. This step is carried out after the inorganic binder has fully reacted. Drying is preferably performed at a drying temperature between 70°C and 150°C before the structural host material of the encapsulated phase change material reaches its final operating temperature between 500°C and 1000°C. Drying at such temperatures avoids the accumulation of excessive pressure in the material, thereby preventing damage to the hardened binder structure.

[0043] Novel materials for thermal energy storage can be suitably used to heat process flows via electricity. This could involve electrically heating a quantity of such material and indirectly exchanging heat between the process flow and that quantity of material, thereby heating the process flow with heat from that quantity of material. The process flow can be a heat transfer fluid, such as oil or water / steam.

[0044] Referring to international publication WO2023012250 A1, which describes a thermal energy storage device, the thermal energy storage device includes:

[0045] - Powder bed with relatively high resistivity;

[0046] - At least two electrodes, said at least two electrodes being embedded in said powder bed and arranged to heat said powder bed by providing an electric current between said at least two electrodes;

[0047] - At least one heat transfer tube, the at least one heat transfer tube being arranged to contain a heat transfer fluid, the heat transfer tube having an inlet and an outlet capable of being connected to a heat energy consumption device, wherein the heat transfer tube and the powder bed are thermally coupled by an electrically insulating material.

[0048] The apparatus described in the application may further include a buffer layer thermally coupled to the powder bed and spaced from the heat transfer tube at least through the powder bed. One or both of the buffer layer and / or the electrical insulating material may comprise novel materials as described in this disclosure.

[0049] Electric heating power may fluctuate over time, which often occurs when the electric heating power comes from renewable energy sources such as solar and / or wind power. However, the electrical insulation material and optional buffer layer act as thermal buffers, which continue to heat the heat transfer fluid for a period of time during periods of interrupted electric heating power.

[0050] The encapsulated metallic material acts as a PCM (Polymerized Chemical Complex), exhibiting a phase transition between solid and liquid states at its melting point. The material's temperature can fluctuate within a certain range, typically increasing when more heat is added than extracted and decreasing when more heat is extracted than added, a result of adding or removing sensible heat from the material. However, if the predetermined melting point of the metallic material is within this temperature range, the material will absorb or release latent heat associated with the phase transition when the temperature reaches that point. This means that electrically heating the material will induce a first phase transition from solid to liquid. In the absence of sufficient electrical heating, a heating process flow can induce a second phase transition from liquid to solid.

[0051] The invention will now be described with reference to the following non-limiting embodiments.

[0052] Example

[0053] Example 1

[0054] The thermal storage material in Example 1 consists of a cementitious binder containing pure aluminum particles. To prepare the cementitious binder, an alkali-activated material comprising fly ash, water glass, 14M NaOH solution, deionized water, and a superplasticizer (SPL) was used. The SPL was MasterGlenium SKY 648 at a concentration of 20%. Aluminum particles comprised 30% by volume.

[0055] Weigh out all components (see Table 1). Weigh out and mix the water glass, NaOH solution, and deionized water together. Place the fly ash in the bowl of the Hobart mixer. While the mixer is operating at speed 1, slowly add approximately 90% of the liquid components to the cement over 30 seconds. Add the remaining 10% of the liquid components to the previously weighed SPL. Then add the liquid / SPL mixture to the bowl. Mix the fresh paste for another 30 seconds. Then stop the mixer, scrape the blades, bottom, and sides of the bowl to ensure complete mixing, and let the paste stand for 30 seconds. Then switch the Hobart to speed 2 and mix the paste for another 60 seconds. Next, add the aluminum particles to the fresh paste and mix at speed 1 for 60 seconds.

[0056] Table 1: Mass fraction of each component in (fresh) thermal storage material

[0057]

[0058] Fresh heat storage material is then poured into a mold. A 5×5×5cm silicone mold is used. The mold is placed on a vibration table (manufacturer: Tinpeng) and vibrated for 30 to 60 seconds to remove excess air and improve compaction. The mold is then covered and placed in a curing oven at 70°C for 14 days. Subsequently, the hardened material is removed from the mold. The cubes are weighed and their dimensions are measured. They are then placed in a 105°C oven (manufacturer: Binder) and left until all free water has been removed (11 days). Once a stable weight is reached, the weight and dimensions of the sample are recorded.

[0059] The samples were placed in a high-temperature oven (manufacturer: Western Oven) and slowly heated to 500°C over 12 hours. The samples were then held at 500°C for 12 hours to ensure complete removal of any remaining free water. The samples were then heated to 750°C and held for 8 hours to bring the entire sample to the target temperature, before being cooled back to 550°C. The four samples were then cycled 9 times between 750°C and 550°C (8 hours of heating and 16 hours of cooling, error! Reference source not found.), for a total of 10 thermal cycles. The four samples were then cycled 49 times between 750°C and 550°C, for a total of 50 thermal cycles. Finally, the four samples were cycled 99 times between 750°C and 550°C, for a total of 100 thermal cycles.

[0060] After heat treatment, the samples were visually inspected, weighed, and their dimensions were recorded. The compressive strength was determined. Additionally, aluminum particles were extracted from the heat storage material and studied using digital scanning calorimetry and thermogravimetric analysis.

[0061] The specimens remained stable in shape and size after 10 thermal cycles. The binder showed discoloration, changing from grayish-brown to reddish-brown. Based on the dry weight prior to thermal cycling, the specimens exhibited an average weight loss of 4.8%. The average compressive strength was 0.77 MPa.

[0062] The samples remained stable in shape and size after 50 thermal cycles. After 10 thermal cycles, the samples retained their observed reddish-brown color. Based on the dry weight prior to thermal cycling, the samples exhibited an average weight loss of 2.9%. The average compressive strength was 0.82 MPa.

[0063] The samples remained stable in shape and size after 100 thermal cycles. After 10 thermal cycles, the samples retained their observed reddish-brown color. Based on the dry weight prior to thermal cycling, the samples exhibited an average weight loss of 3.6%. The average compressive strength was 0.71 MPa.

[0064] Example 2

[0065] The thermal storage material in Example 2 consists of a cementitious binder containing aluminum particles. To prepare the cementitious binder, calcium aluminate cement (from Caltra Nederland BV) and deionized water were used. Water was used at a water-to-cement (w / c) ratio of 0.35. The aluminum particles comprised 30% by volume; the aggregate mass fraction is shown in Table 2.

[0066] Weigh out the three components. Place the calcium aluminate cement in the bowl of the Hobart mixer. While the mixer is operating at speed 1, slowly add water to the cement over 30 seconds. Mix the fresh paste for another 30 seconds. Then stop the mixer, scrape the blades, the bottom and sides of the bowl to ensure complete mixing, and let the paste stand for 30 seconds. Then switch the Hobart to speed 2 and mix the paste for another 60 seconds. Next, slowly add the aluminum granules to the fresh paste and mix at speed 1 for 60 seconds.

[0067] Table 2: Mass fraction of each component in (fresh) thermal storage material

[0068]

[0069] The fresh heat storage material is then poured into the mold. A 5×5×5cm silicone mold is used. The mold is placed on a vibration table (manufacturer: Tinpeng) and vibrated for 30 to 60 seconds to remove excess air and improve compaction. The mold is then covered and placed in a curing oven at 70°C for 24 hours. Subsequently, the hardened material is removed from the mold. The cubes are weighed and their dimensions are measured. They are then placed in a 105°C oven (manufacturer: Binder) and left until all free water has been removed (7 days). Once a stable weight is reached, the weight and dimensions of the sample are recorded.

[0070] The sample was placed in a high-temperature oven (manufacturer: Western Oven) and slowly heated to 500°C over 12 hours. The sample was held at 500°C for 12 hours to ensure complete removal of any residual free water. The sample was then heated to 750°C and held for 8 hours to bring the entire sample to the target temperature, before cooling to room temperature. Subsequently, the sample was heated to 550°C and then cycled between 750°C and 550°C, with heating for 8 hours and cooling for 16 hours, and this cycle was repeated twice.

[0071] After heat treatment, the samples were visually inspected and weighed. Additionally, aluminum particles were extracted from the thermal storage material and studied using digital scanning calorimetry and thermogravimetric analysis.

[0072] Following the first heat treatment, the samples exhibited an average weight loss of 11.1% based on their dry weight prior to heat treatment. The total weight loss of all samples was less than the weight of water added to the fresh paste, indicating the presence of a phase containing chemically bound water that remained stable at temperatures up to at least 750°C. Subsequent thermal cycling did not further reduce the sample weight. During the heat treatment, small aluminum droplets oozed from surface pores. During and after subsequent thermal cycling, the aluminum droplets remained consistent in shape, quantity, size, and location.

[0073] Example 3

[0074] The thermal storage material in Example 3 consists of a cementitious binder containing aluminum particles. To prepare the cementitious binder, anhydrite (Micro A) and deionized water were used. Water was used at a water-to-binder ratio of 0.40 (w / b). Aluminum particles comprised 30% by volume; the aggregate mass fraction is shown in Table 3. 1% by volume of basalt fiber was added.

[0075] First, the aluminum granules are coated with wax. This allows a buffer zone to form between the aluminum and the hardened binder to compensate for any stress caused by air entrapment due to their different coefficients of thermal expansion. The aluminum granules are weighed and placed in an SX105 wax cup in a 110°C oven. The aluminum granules are then sieved and cooled in a laboratory setting. While the aluminum granules are at room temperature, more molten wax is poured on top of them, and they are allowed to stand for one minute. The material is then sieved, and the mass of the wax is measured.

[0076] Weigh out the remaining four components. Place the hard plaster and fibers in the bowl of the Hobart mixer and mix at speed 1 for 60 seconds. While the mixer is operating at speed 1, slowly add water to the adhesive over 30 seconds. Mix the fresh paste again for 30 seconds. Then stop the mixer, scrape the blades, the bottom and sides of the bowl to ensure complete mixing, and let the paste stand for 30 seconds. Then switch the Hobart to speed 2 and mix the paste again for 60 seconds. Next, slowly add the wax-coated aluminum granules to the fresh paste and mix at speed 1 for 60 seconds.

[0077] Table 3: Mass fraction of each component in (fresh) thermal storage material

[0078]

[0079] The fresh heat storage material is then poured into the mold. A 5×5×5cm silicone mold is used. The mold is placed on a vibration table (manufacturer: Tinpeng) and vibrated for 30 to 60 seconds to remove excess air and improve compaction. The mold is then covered and placed in a curing oven at 70°C for 24 hours. Subsequently, the hardened material is removed from the mold. The cubes are weighed and their dimensions are measured. They are then placed in a 105°C oven (manufacturer: Binder) and left until all free water has been removed (7 days). Once a stable weight is reached, the weight and dimensions of the sample are recorded.

[0080] The sample was placed in a high-temperature oven (manufacturer: Western Oven) and heated to 750°C at a rate of 1°C / min, and held at this temperature for 8 hours. The sample was then cooled to room temperature. After observation, the sample was exposed to a second thermal cycle.

[0081] After the first heat treatment, the specimens retained their original shape and form. No cracking was observed, and the aluminum particles remained contained within the binder. Following the first heat treatment, the specimens exhibited an average weight loss of 5.0% based on their dry weight prior to heat treatment.

[0082] After the second heat treatment, the specimen retained its original shape and form. No cracking was observed, and the aluminum particles remained contained within the binder. Based on the weight of the specimen after the previous heat treatment, the specimen exhibited an average weight loss of 0.47%.

[0083] Example 4

[0084] Lead, magnesium, zinc, and aluminum-silicon were all tested as metal / metal alloys for use as phase change materials. They were tested using two different methods.

[0085] Sample Preparation #1

[0086] First, weigh out each phase change material to replace 30% by volume of the fresh binder. Then, prepare a fresh calcium aluminate cement paste by mixing calcium aluminate cement with water at a w / b ratio of 0.35. Cast 30 grams of the calcium aluminate paste around each PCM. Cover the samples and place them in a curing oven at 70°C for 24 hours. Subsequently, place them in an oven at 105°C and dry for 7 days.

[0087] Sample preparation #2

[0088] Alternatively, containers are made from calcium aluminate cement, water, and basalt sand according to the mass fractions in Table 4. The mixture is cast into 10×10×10cm cubes with an 8cm deep cavity and a 5×5cm area. The blocks are cured at 70°C for 24 hours and then dried at 105°C until a stable weight is achieved. Once the containers have cured and dried, 30g of each type of PCM is added to the container.

[0089] Table 4: Mass fraction of each component in the thermal storage material container

[0090]

[0091] The sample was placed in a high-temperature oven (manufacturer: Western Oven) and heated to 750°C at a rate of 1°C / min, and held at that temperature for 8 hours. The sample was then cooled back to room temperature.

[0092] Following heat treatment, the samples prepared using Preparation 1 were split open and the PCMs were examined. Melting was clearly observed in all PCMs. The lead and magnesium samples changed from silver and gray to white, respectively. The zinc sample exerted force on the hardened binder, and some cracks were observed. The aluminum-silicon sample showed smaller particles agglomerated within the hardened binder.

[0093] The sample from preparation 2 showed no negative impact on the binder container.

[0094] Example 4

[0095] The thermal storage material in Example 4 consists of a cementitious binder containing aluminum particles. To prepare the cementitious binder, CURAS 90 PF components A and B (Gouda Refractories) and deionized water were used. The aluminum particles comprised 30% by volume; the aggregate mass fraction is shown in Table 3.

[0096] Weigh out the four components. Place components A and B in the bowl of the Hobart mixer and mix at speed 1 for 60 seconds. While the mixer is operating at speed 1, slowly add water to the binder. Mix the fresh paste for another 30 seconds. Then stop the mixer, scrape the blades, the bottom and sides of the bowl to ensure complete mixing, and let the paste stand for 30 seconds. Then switch the Hobart to speed 2 and mix the paste for another 60 seconds. Next, slowly add the aluminum granules to the fresh paste and mix at speed 1 for 60 seconds.

[0097] Table 5: Mass fraction of each component in (fresh) thermal storage material

[0098]

[0099] The fresh heat storage material is then poured into the mold. A 5×5×5cm silicon mold is used. The mold is placed on a vibration table (manufacturer: Tinpeng) and vibrated for 30 to 60 seconds to remove excess air and improve compaction. The mold is then covered and cured at 20°C for 24 hours. Subsequently, the hardened material is removed from the mold. The cubes are weighed and their dimensions are measured. They are then placed in a 105°C oven (manufacturer: Binder) and left until all free water has been removed (7 days). Once a stable weight is reached, the weight and dimensions of the sample are recorded.

[0100] The sample was placed in a high-temperature oven (manufacturer: Western Oven) and heated to 750°C at a rate of 1°C / min, and held at that temperature for 8 hours. The sample was then cooled back to room temperature.

[0101] Following heat treatment, the specimens retained their original shape, form, and color. No cracking was observed, and the aluminum particles remained contained within the binder. Based on the dry weight of the specimens prior to heat treatment, the specimens exhibited an average weight loss of 0.7% after the first heat treatment.

[0102] Those skilled in the art will understand that the invention can be practiced in many different ways without departing from the scope of the appended claims.

Claims

1. A material for thermal energy storage, the material comprising one or more metallic substances selected from metals and / or metal alloys encapsulated in a structural host material, wherein the metallic substance has a melting point in the range of 300°C to 900°C, and wherein the structural host material comprises at least 90% by mass of a hardened inorganic binder, the hardened inorganic binder comprising one or more of hydraulic binders, alkaline activating materials, and phosphate binders.

2. The material according to claim 1, wherein the metallic substance has a melting point in the range of 600°C to 800°C.

3. The material according to claim 1 or claim 2, wherein the metallic substance is selected from the group consisting of aluminum, lead, magnesium, zinc and aluminum / silicon alloys.

4. The material according to any one of the preceding claims, wherein the total amount of metallic material encapsulated in the main structural material is in the range of 20% to 70% of the total volume of the material, preferably between 25% and 60%, and more preferably between 30% and 50%.

5. A method for manufacturing the material according to any one of claims 1 to 4, the method comprising the following steps: - Provide a mixture of the solid metallic substance and a dry, unreacted binder capable of reacting with the specified liquid; - Add the specified liquid to the mixture to produce a paste containing the binder of the metallic substance; - Cast the paste into the desired shape; as well as - Hardening the paste, including reacting with the specified liquid, thereby transforming the paste into a structural host material encapsulating the metallic substance.

6. The method of claim 5, wherein, prior to mixing with the dried unreacted inorganic binder, the refined particles of the metallic substance are first coated in a sacrificial substance, preferably a wax.

7. The method of claim 5 or claim 6, wherein additional conductive elements are incorporated into the material for thermal energy storage during casting.

8. The method according to any one of claims 5 to 7, wherein the dried unreacted inorganic binder comprises a hydraulic binder, and the designated liquid comprises water, wherein the water is added to the hydraulic binder, the mass ratio of the liquid to the hydraulic binder being in the range of 0.20 to 0.

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9. The method according to any one of claims 5 to 7, wherein the dried inorganic binder comprises an alkaline activated binder, and the designated liquid comprises an alkaline solution, wherein the alkaline solution is added to the alkaline activated binder, the mass ratio of the liquid to the alkaline activated binder being in the range of 0.20 to 0.

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10. The method according to any one of claims 5 to 7, wherein the dried inorganic binder comprises an alkaline metal oxide or aluminosilicate, and the designated liquid comprises a concentrated aqueous solution of orthophosphoric acid, wherein the concentrated aqueous solution of orthophosphoric acid is added to the alkaline metal oxide or aluminosilicate, the mass ratio of the liquid to the alkaline metal oxide or aluminosilicate being in the range of 0.09 to 0.

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11. The method according to any one of claims 5 to 10, further comprising the step of drying the structural body material encapsulating the metallic substance at a drying temperature in the range of 70°C to 150°C before bringing the structural body material encapsulating the phase change material to its final operating temperature, preferably wherein the final operating temperature is between 500°C and 1000°C, more preferably between 500°C and 900°C.

12. A method for heating a process flow by electric power, the method comprising: - Directly or indirectly electrically heat a certain amount of material for thermal energy storage according to any one of claims 1 to 5; as well as - Allow the process flow to exchange heat directly or indirectly with the given amount of material, thereby heating the process flow with heat from the given amount of material.

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