Powder phase change material (PCM) for thermal energy storage (TES)

Abstract

A method of producing expanded graphite where a commercially available oxidised expandable graphite undergoes, under vacuum, an initial heating up to 800 °C for a short period after which, the temperature is raised up to 1,500 °C. The graphite produced has particles of 30 microns in size, 45 mesh, and with a density of less than 0.001 kg / m3. The graphite may be impregnated with a phase change material which may be an organic material or a hydrated salt. The impregnated graphite may be used building materials such as mortar or concrete for use in construction materials.

Description

Field of Invention Thermal energy storage (TES) is a pivotal technology that addresses the challenge of efficiently managing and utilizing thermal energy for various applications. It involves the strategic capture, retention, and subsequent release of heat energy for later use, enabling better synchronization between energy generation and consumption. TES plays a vital role in optimizing energy systems, particularly in scenarios where there is a mismatch between the availability of energy and its demand. This imbalance is often seen in renewable energy sources like solar and wind, which produce energy intermittently. TES provides a solution by storing excess energy during peak production times and releasing it when demand surges or energy generation dips. There are several mechanisms through which thermal energy can be stored. Most commonly two common technologies are utilised by industry namely Sensible Heat Storage (This involves raising the temperature of a storage medium (usually a solid or liquid) to store thermal energy. The energy is released when the medium's temperature is lowered) or Latent Heat Storage (Phase change materials (PCMs) are used in this method. The material undergoes a phase change (like solid to liquid) at a specific temperature, absorbing or releasing latent heat during the process). The most common Latent Heat TES is the water-ice systems but if one wish to have a Latent Heat TES different than 0°C water ice one has to deal with chemicals. Most common Phase Change Materials (PCM) are either based on hydrated salt or organic materials such a paraffins and these materials must be encapsulated in airtight containers and this requirement adds considerable cost and design limits for any TES applications. PCM’s by nature having lowerthermal conductivity result in getting energy in and out takes longer. Graphite or other high conductive materials are added to PCM encapsulation in order to overcome this issue. Commercially the integration of expanded graphite with PCMs provided significant improvements across various industries, from energy-efficient buildings to advanced thermal storage systems. As we strive for more efficient and sustainable energy solutions, the synergy between expanded graphite and PCMs offers a novel pathway to address the challenges of energy storage and release. Background of the Invention: In essence, thermal energy storage is a versatile and transformative technology that not only optimizes energy utilisation but also contributes to the integration of renewable energy sources, grid stability, and overall energy efficiency. Thermal Energy Storage (TES) solutions have made significant strides in the built environment, contributing to improved energy efficiency, sustainability, and overall comfort. Here are some notable applications of thermal energy storage in the built environment: Incorporating thermal energy storage into the built environment as part of the building fabric offers multifaceted benefits, including energy cost savings, reduced environmental impact, and improved energy resilience. As technology continues to evolve, the integration of thermal energy storage is expected to play an increasingly crucial role in shaping the sustainable future of the built environment. Most commonly used TES systems tends to be either simple sensible water storage or Phase Change Materials (PCM) tanks are applied in the form of encapsulated containers placed in these tanks. Simple hot and cold storage water tanks manufactured and marketed for centuries and PCM based TES tanks are the latest addition to built environment applications. Manufacturers like PCM Products (ww.pcmproducts.net), Axiotherm WWW.AXsQTHERM.DE , Cowa Thermal Solutions AG www.cowa-is.com , Cristopia Hangzhou Phase Change Technology www.feijiepcmxom, Klara Energy Systems All of these manufacturers encapsulate the PCM in plastic or metal containers as a product which is placed in tanks to exchange heat between the surrounding fluids generally water or anti-freeze solutions. There are many patents covering various format of PCM based water TES systems such as KR20160035905A THERMAL STORAGE TANK USING PHASE CHANGE US2023082570A1 DENSITY CONTROLLED PHASE-CHANGING MATERIAL (PCM) GB2510375A Hot water system comprising a heat source and a tank including a PCM KR102151130B1 PVT Solar heat pump system with PVT collector connected CN204649049U Phase change material puck energy storage tanks and adopt cooling water system of energy storage tanks. However, most of these systems are based on either expensive and complicated encapsulated or heat exchangers. Furthermore, by nature PCM is a poor heat conductor and therefore efficiency of these systems are relatively poor. Although a number of manufacturers market micro-encapsulated which is a process in which tiny particles or droplets are surrounded by a coating to give small capsules, with useful properties. However, this process requires a very precise and complicated production system and therefore the basic PCM material cost is almost doubled once it converted to a micro-encapsulated PCM. Moreover, even if one ignores the low conductivity of the finished product, the loading level of these micro-encapsulation reduces the latent heat capacity of the finished product as much as 50% of the original PCM’s latent heat. One way to reduce these costs and complications could be utilising the absorbent quality of the highly expanded graphite which would also over come the limiting heat transfer conductivity of conventional encapsulation. In order to avoid costly plastic / metal encapsulation as well as micro-encapsulation options it is possible to manufacture PCM embedded expanded graphite solid materials. Expanded graphite, with its high surface area and porous structure, offers an ideal platform for enhancing PCM absorption. By incorporating expanded graphite into PCM formulations, one can open the door to several advantages: 1. Enhanced Absorption: The expanded structure of graphite provides a larger surface area for PCM interaction. This enables PCMs to be absorbed more efficiently, accelerating the phase transition process. 2. Improved Thermal Conductivity: Graphite's inherent thermal conductivity can enhance the heat transfer between the PCM and its surroundings, enabling faster charging and discharging cycles. 3. Stability and Compatibility: Expanded graphite is chemically stable and can be engineered to be compatible with a wide range of PCMs. This ensures long-term performance and mitigates any adverse interactions between the two materials. 4. Customizability: The porosity and interlayer spacing of expanded graphite can be tailored to match the specific requirements of different PCMs, optimizing the absorption kinetics. The integration of expanded graphite with PCMs holds immense potential across various industries, from energy-efficient buildings to advanced thermal storage systems. There are a large number of Patents in place highlighting covering the production of expanded graphite based PCM material and some of the well knows Patents are as follows; WO2021035820A1 • 2021-03-04 • ZHANG LIQIANG [CN] - A graphite adsorption phase change energy-storage powder. The graphite adsorption phase change energy-storage powder comprises the following components... worm-like expanded graphite. KR101538643B1 (A) • 2015-07-22 • INHA IND PARTNERSHIP INST [KR] - .The present invention relates to a composite heat storage material comprising expanded graphite and, more specifically, to a composite heat storage material which can be used as a material for phase variation with absorption and emission of latent heat in... heat storage material which can be used as a material for phase variation with excellent conductivity and regeneration. CN105018038A • 2015-11 -04 • SHANGHAI AIERPAIKE PACKAGING MATERIAL CO LTD-The invention provides an organic phase change thermal storage material and its preparation method. CN113736431A (B) • 2021-12-03 • UNIV SOUTH CHINA TECH - The invention discloses a modified expanded graphite-hydrated inorganic salt composite phase change material as well as a preparation method. CN114656939A (B) • 2022-06-24 • UNIV SOUTH CHINA SCIENCE &TECH - The invention provides an expanded graphite-based composite phase change material with anisotropic thermal conductivity and a preparation method of the expanded graphite-based composite phase change material. CN101239798A • 2008-08-13 • UNIV SOUTH CHINA TECH [CN] - Preparation method of expanded-graphite-base hydrated salt composite solid-solid phase-change energy storage material CN104531077A • 2015-04-22 • UNIV YUNNAN NORMAL - Organic phase change thermal storage material and preparation method thereof CN105018038A • 2015-11-04 • SHANGHAI AIERPAIKE PACKAGING MATERIAL CO LTD COMPOSITE HEAT-STORAGE MATERIAL COMPRISING EXPANDED GRAPHITE AND PCM AND PROCESS FOR PRODUCING IT WO2011124624A1 • 2011 -10-13 • SGL CARBON SE [DE] WO2022146267A1 • 2022-07-07 • CUKUROVA UNIV REKTORLUGU [TR] Despite of numerous patents describing the details of how to manufacture PCM embedded expanded graphite material there is no commercial products on the market for water TES applications and the only commercial applications remains in battery and electronic thermal management applications. Summary of the Invention: The present invention leverages PCM-embedded highly expanded graphite as part of the construction materials, enabling the efficient storage of both heat and cold energy in a flexible powder format. This innovation caters to practical Thermal Energy Storage (TES) applications, suitable for both new installations and retrofitting projects. Detailed Description of the Invention: The current innovation centers around an initial process of low cost and simple production of PCM embedded expanded graphite into powder format. Our custom-design production using a basic graphite material and expand to 25~30 micron / 350~500 mesh size extremely fine powder having a density of as low as 0.001 kg / m3 which enables us to load 85~90% loading of any PCM material. A simple reactor vessel is employed to impregnate this highly expanded graphite with organic or hydrated salt-based Phase Change Materials (PCMs). The degree of imprecation, ranging as high as 90% of PCM, plays a pivotal role, as it determines the PCM energy storage capacity of the PCM embedded expanded graphite. This inventive method of production a powder PCM version which contains 90% of the original PCM solution represents a significant advancement in thermal energy storage technology. The high loading of PCM powder not only optimizes its energy density but also creates a practical and versatile format for energy storage applications. The subsequent impregnation of highly conductive graphite with PCMs enhances its heat transfer capability, enabling efficient / fast heat absorption and release. The ability to varying the loading levels allows for fine-tuning the composite's PCM absorption capacity to suit specific requirements. Whether for building insulation, industrial processes, or renewable energy integration, this innovative approach provides a customizable solution that can be adapted to diverse applications. In essence, this invention opens new avenues for efficient and scalable thermal energy storage, with the potential to significantly improve energy management, reduce environmental impact, and advance sustainability goals. The present invention is described in following drawings; Figure 1 -Thermal Energy Storage (TES) Figure 2 illustrates current thermal energy storage materials Figure 3 illustrates thermal energy storage options Figure 4 illustrates the powder Phase Change Material (PCM) production line 5 Figure 5 illustrates powder PCM construction applications Figure 6 illustrates powder PCM balls addition for plastering for internal applications Figure 7 illustrates powder PCM balls addition for plastering for external applications Figure 8 illustrates powder PCM balls addition for floor applications Whether cooling or heating loads 1 against the time scale 2 are always vary and TES is a useful tool to shift 4 the peak loads 3 to off-peak periods 5 as illustrated in Figure 1. A simple visualisation of Phase Change Materials benefits for the Thermal Energy Storage (TES) can be demonstrated by a cold-water test whereby if one takes a cold water 7 and pour into a glass 6 it would reach in a short time to room temperature but if one adds ice cubes 8 into that glass it will take far longer to warm up and this cooling energy comes from the latent heat energy of the water ice. At present majority of the TES applications are around water ice 8 which is 0 °C and any other temperature applications one has to deal with various chemical combinations and most common materials widely used in industry can be highlighted as Organic (H-C Chains) 9 or hydrated salt-based (mixture of as water / salt combination) 10 as illustrated in Figure 2. Majority of the existing PCM based TES options covered in Figure 2 organic PCM’s 9 can be applied directly and exposed to air but hydrated salt must be encapsulated in various formats like rectangular 11, spherical 12 or tube 13 formats. Alternatively, both PCM options can be incorporated as part of a heat exchanger / tank concept 14. PCM’s can also be encapsulated using micro-encapsulation techniques 15 or converted into powder versions 16 using silica or other absorbent based materials as illustrated in Figure 3. At present any powder production techniques cannot exceed 50~60% loading of PCM into the finished powder PCM. The present invention is based developing a technique producing highly expanded graphite 16 closer to less than 45 mesh levels which can absorb and safety hold the PCM 10 closer to 85~90% and this very fine based materials can be impregnated in a simple reactor vessel as illustrated in Figure 4. The simplicity of this production using an atmospheric reactor vessel 17 complete with heated jacket 18 and a mixer 19 as highlighted in Figure 4 provides a very low manufacturing cost. The finished PCM loaded graphite powder 20 flows easily out of the reactor vessel and via conventional conveyor belts transferred into the conventional 25 kg bagging 21 format. 25 kg powder PCM bags 21 are identical to any other building material packaging and can be shipped in pallets to sites I production location to mix with the building materials such as asphalt 22, construction materials such as concrete 23, building blocks like breeze blocks / 6 bricks 24 in order to increase the thermal mass capacity of the finished product as illustrated in Figure 5. Alternatively, powder PCM bags 21 can be added to any plaster material during mixing of the original plaster material in a mixer 25 as illustrated in Figure 6. Plaster material 26 mixed with PCM powder 21 can be applied to walls 27 and ceiling 28 and as a result the building’s internal thermal loads can be increased as much as 10-fold. Powder PCM 21 can be also mixed with any external mortar 29 in order to provide external thermal protection. Alternatively, powder PCM 21 can be introduced to any fagade tiles 30 production and effectively both mortar and tiles applied to outside walls 32 provide a thermal buffer for the building 31 and effectively keep the internal building temperature under control and over-come over heating as illustrated in Figure 7. As powder PCM 21 can be easily introduced to screed mixture whether pumped screed 34 or dry mix screed 35 applied to flooring 33 with or without any underfloor heating 33 systems as illustrated in Figure 8. As the floor tends to be thicker than wall I ceiling plaster applications by adding up to 20~30% of the 90% loaded powder PCM 21 within the floor screed results in the increase of its thermal mass capacity as much as 20 folds. Advantages of the Invention: By nature, whether organic or hydrated salt based PCM materials are very poor for heat transfer due to very low thermal conductivity. Using plastic encapsulation or any micro-encapsulated PCM options makes it worse for heat transfer point of view and although this can be improved by using metal encapsulation butthat increases the cost 10-fold and makes them uneconomical. Hence, the proposed expanded graphite-based powder PCM provides a highly conductive TES material with superior heat transfer performance. Although there are number of patents incorporating PCM in expanded graphite like; CN101805591A Inorganic hydrated salt expanded graphite composite phase-changing heat storage material and preparation method thereof refers to expanded graphite with PCM CN111499312A Expanded graphite adsorption tetradecane low-temperature phase change cement concrete and preparation method thereof CN111499312A Expanded graphite adsorption tetradecane low-temperature phase change cement concrete and preparation method thereof CN113736431A Modified expanded graphite-hydrated inorganic salt composite phase change material as well as preparation method and application thereof CN113736431A Modified expanded graphite-hydrated inorganic salt composite phase change material as well as preparation method and application thereof CN113736431A Modified expanded graphite-hydrated inorganic salt composite phase change material as well as preparation method and application thereof Expandable graphite is a kind of intercalation compound that uses physical or chemical methods to insert foreign materials with different properties into graphite sheets. However, when it expanded it provides a very porous structure. There many different ways to expand the graphite and the most common techniques can be described as • Chemical oxidation; • The electrochemical method; • Gas-phase diffusion method (double-chamber method) • Mixed liquid phase method • Melting method • Pressurization method • Explosion method There are a number of Patents refers to these techniques in various forms and versions of production technologies CN101805591A Inorganic hydrated salt expanded graphite composite phase-changing heat storage material and preparation method thereof CN108276964A Expanded graphite composite phase change material and applications of expanded graphite composite phase change material in electronic heat dissipating devices CN111499312A Expanded graphite adsorption tetradecane low-temperature phase change cement concrete and preparation method thereof CN111592303A Preparation method of tetradecane expanded graphite low-temperature phase-change cement mortar CN111849425A Organic-inorganic nano composite phase change heat storage material and preparation method thereof CN113736431A Modified expanded graphite-hydrated inorganic salt composite phase change material as well as preparation method and application thereof CN116285905A Expanded graphite-based phase-change temperature-regulating humiditycontrolling material as well as dry-collagen in-situ synthesis method and application thereof ES2298056A1 Set of mortars incorporating phase change microcapsules comprises lining materials containing e.g. cement, for room temperature control US2007222112A1 Process for manufacture of a latent heat storage device Most common and commercially applied technique is the chemical oxidation. It is the traditional method to prepare expandable graphite whereby natural flake graphite is evenly mixed with the appropriate amount of oxidant and intercalation agent, controlled by a certain temperature, continuously stirred, washed, filtered, and dried to obtain expandable graphite. Oxidant material could be potassium permanganate, potassium dichromate, chromium trioxide, potassium chlorate, etc.), or some liquid oxidants (such as hydrogen peroxide, nitric acid, etc.). Under the action of oxidant, graphite is oxidized and the neutral network macromolecules of the graphite layer become planar macromolecules with positive charges. The present invention harnesses commercially available low-cost ready-made oxidised expandable graphite, produced cost-effectively through industrial-scale methods, thereby mitigating low volume higher cost associated with expanded graphite base materials. The readily accessible expandable graphite undergoes initial heating upto 800°C within vacuum chambers as the first stage expansion for short periods. This technique not only minimises energy consumption but also achieves significantly higher levels of graphite expansion compared to conventional methods. As part of the present invention, the first-stage expansion is complemented by a brief secondary heat treatment, subjected to temperatures of upto 1,500°C. This process results in an end product less than 45 mesh, 30 microns in size, with a density of 0.001 kg / m3— considerably lighter than conventional expanded graphite available in the market The present invention, significantly more porous than existing commercial alternatives, allows for the loading or impregnation of PCM at levels reaching 85~90%. This surpasses the loading capacities of any commercially available expanded graphite-based PCM powders. Hence, the present invention offers larger energy storage density and therefore 5 requires far less volume (20~30% less) to achieve the same energy storage density for a given application. Less quantity makes the present invention also far more economical than any commercially available expanded graphite-based PCM powders. Additionally, the invention presents notably improved flow characteristics post-impregnation 10 with PCM. This feature enables easy packaging in industry-standard paper bags without forming lumps or compacting, crucial for on-site utilisation or the production of both liquid and dry mix versions of the finished building materials. The combination of low-cost production combined with closer to 90% PCM loading which 15 requires 20~30% less material for a give energy density makes the present invention satisfying both CAPEX and OPEX requirements with a pay back period of 2~3 years.

Claims

1. . A method of producing porous graphite, comprising the steps of:introducing standard commercially available pre-oxidised graphite into pre-heating process using a microwave roaster up to 500°Candusing low temperature 750~850°C atmospheric heating oven expansion as a secondary process, resulting in an end product of less than 40 mesh, 30 microns, and a density of 0.001 kg / m3. This fine powder demonstrates significantly improved PCM absorption rates, ranging between 85~90%.Than cooling the solid, porous carbon artifact to room temperature at atmospheric / ambient pressure storage.

2. A powder material as claimed in claim 1 wherein the thermal energy storage impregnated by organic or hydrated salt based PCM materials at atmospheric pressure.

3. A system as claimed in claim 1 and 2 wherein the energy storage materials mixed with construction materials such as mortar, concrete, plaster for internal covering of the internal walls and ceiling.

4. A system as claimed in claim 1 and 2 wherein the energy storage materials applied for construction materials such as external mortar or facade tiles for external use in buildings.

5. A system as claimed in claim 1 and 2 wherein the energy storage materials applied for construction materials such as mortar, concrete, screed formats in under floor heating applications.

7. A system as claimed in any preceding claims comprising one or multiple heat / cooling sources associated for the thermal energy storage purposes.

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