Thermal energy storage (TES) materials based on compressed expanded graphite and phase change material (PCM)

Abstract

Expanded graphite (23, fig. 3) is shaped using a mold (22, fig 3) and cutting apparatus (20, fig 3) to form expanded graphite spheres which are submerged in liquid phase change material (PCM) (29, fig 4) to absorb the PCM forming a shaped expanded graphite PCM. The expanded graphite PCM is used in a heat storage system. The system comprises at least one heat source which may be solar, electrical heating elements or a heat pump, 12, 13, 33, 34, which feeds energy into a hot water tank, 15, and a buffer tank, 39, The tanks are filled with expanded graphite PCM spheres, 30, to increase the amount of heat that can be absorbed by the system. The two tanks are connected by pipes allowing heat to be transferred from the buffer tank to the hot water tank. The buffer tank may also be directly connected to an external load application. Alternatively, the PCM may be selected to be suitable for cooling applications and multiple different PCMs may be used. The system may be setup to use multiple buffer tanks.

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 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 (w / w. , Axiotherm WVW.AXIOTWERM.DE , Cowa Thermal Solutions AG www.cowa-ts.oom , Cristopia Hangzhou Phase Change Technology www.feiiiepcm.cpm, 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. One way to reduce these costs and complications could be utilising the absorbent quality of the expanded graphite which would also over come the limiting heat transfer conductivity of conventional encapsulation. In order to avoid costly plastic / metal encapsulation 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 expanded graphite within water tanks, enabling the efficient storage of both heat and cold energy in a moulded 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 shaping expanded graphite into spherical balls within a diameter range of 10mm to 100mm. Subsequently, a reactor vessel is employed to impregnate these graphite balls with organic or hydrated salt-based Phase Change Materials (PCMs). The degree of compression, ranging from 1 to 12 tons, plays a pivotal role, as it determines the PCM absorption capacity of the moulded expanded graphite, which can span from 60% to 90%. This inventive method represents a significant advancement in thermal energy storage technology. The initial moulding of expanded graphite into spherical shapes not only optimizes its surface area but also creates a practical and versatile format for energy storage applications. The subsequent impregnation with PCMs enhances its thermal energy storage capabilities, enabling efficient heat absorption and release. The ability to vary the compression 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 the domestic hot water storage Figure 3 illustrates expanded graphite ball production using a compression die process Figure 4 illustrates the absorption process of phase change material (PCM) Figure 5 illustrates PCM balls TES tank application Figure 6 illustrates PCM balls addition for an existing domestic how water tank application Figure 7illustrates PCM balls addition fora domestic hot water tank TES applications Figure 8 illustrates PCM balls addition for hot water and heating system buffer tank TES applications Figure 9 illustrates PCM balls addition for heating / cooling tank TES 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 15 and anti-freeze 11 systems whether city mains water intake or process intake 9 circulated via a storage tank 10 complimented with heat transfer surfaces such as solar 13 and external heating 12 as well as top up with heating elements 14. These TES tanks can serve to process such as hot water services 16. Tanks can be cylindrical or rectangular 15 with or without heat exchangers 17 compete with external heating or cooling source of inlet 18 and outlet 19 connections service 16 as illustrated in Figure 2. Majority of the existing TES tanks covered in Figure 2 may also contain plain and / or encapsulated PCM materials using either metal or plastic encapsulated formats. The present invention is based on the expanded graphite based PCM form shaped material placed in these tanks. Figure 3 illustrates then production of these balls whereby the powder expanded graphite 23 is poured into mold chamber 22 and lays on top of the base mold 21. Top plunger mold 20 is placed the into the mold chamber and the pressure applied between the top 20 and bottom 21 mold is contained within the pressure chamber 24. A hydraulic pressure applies the pressure to compress the expanded graphite and forms a shape stable solid material. Once the form stable solid shape is formed it is placed inside a reactor vessel 28 complete with an agitator 27 as illustrated in Figure 4. Having a heated jacket 28 PCM content 26 of the reactor vessel stirred by built in stirrer 29 and light weight solid shaped expanded graphite overtime absorbs the PCM 26 and becomes a PCM embedded I loaded solid formed product 30. Solid shaped PCM material 30 can be placed in water tanks 15 complete with process supply 31 and return 32 connections as illustrated in Figure 5. Alternatively, solid shaped PCM 30 can be placed in any existing heating and cooling tanks using any existing tank connections as a retrofit application. Figure 6 illustrated a typical domestic hot water tank application whereby adding the formed shape PCM could increase the TES capacity of an existing tank as much as 3~4 times. Any existing or new solar 33 and heat pump 34 hot water and buffer tank’s TES capacity can be increased 3~4 times for a given volume by simply adding the form shaped PCM 30 as illustrated in Figure 7. Whether heat pump 34 supplies heating or cooling via supply 37 and return 38 to system diversion of this energy source via flow 35 and return 36 to a TES tank provides a facility shift the loads for any existing or new installations. Heating I Cooling system described in Figure 7 may also have a buffer tank 39 as illustrated in Figure 8 whereby the system supply 37 can be used to charge the PCM 30 inside the buffer tank 39 and once the hot or cold energy stored the return 38 load variations can be handled utilising the stored energy in form shaped PCM 30. Heat and cold energy generated by heat pumps 34 can be stored in formed shape PCM 30 based either in horizontal or vertical TES tanks 40 as illustrated in Figure 9 and these tanks can be charged using the supply 37 whenever surplus energy is available and recovered via return 38 from the system. 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, it 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 formed shaped PCM provides a highly conductive TES option with superior heat transfer performance. Furthermore, the present invention provides a very low-cost encapsulation and mass production option. As these formed shaped PCM materials can be manufactured in shape and size it offers not only for a wide range of new products I application options but also a significant opportunity for any existing retrofit applications for wide range of heating and cooling TES applications.

Claims

1. A method of formed shape compressed expanded graphite based embedded PCM materials for fluid-based systems thermal energy storage systems utilising buffer storage tanks for any heating and cooling applications.

2. A system as claimed in claim 1 wherein the thermal energy storage systems may contain single or multiple temperature compressed expanded graphite based embedded PCM materials.

3. A system as claimed in claim 1 and 2 wherein the energy source includes a single or multiple temperature phase change material of different operating temperature applied for heating and cooling circuits.

4. A system as claimed in any preceding claims wherein the compressed phase change material is provided packaged in any shape and geometry like as ball, rectangular and tubular.

5. A system as claimed in any preceding claims wherein the thermal energy storage tanks applied in singular or multiple formats.

6. A system as claimed in any preceding claims wherein the phase change material is provided packaged in heat exchanger format.

7. A system as claimed in any preceding claims comprising one or multiple heat / cooling sources connected to the tank.

8. A system as claimed in any preceding claims wherein the heat sources include a solar thermal, electric heating element(s) and / or PV heat source.

9. A system as claimed in any preceding claims wherein the heat sources may include an air source heat pump.

10. A system as claimed in any preceding claims applied as a buffer tank applied for heat 5 pump and / or chilled water circulation systems.

11. A system as claimed in claims 1 to 10 wherein a thermal transfer fluid is provided for charging and discharging the thermal energy storage.10 12. A system as claimed in claims 1 to 11 wherein the fluid is water with or without antifreeze solutions and the tank is configured such that the water flows around the phase change material.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. A method for manufacturing a formed-shape expanded graphite composite for thermal5 energy storage, comprising:(a) compressing expanded graphite to form a structured shape; and(b) introducing phase change material (PCM) as a secondary process, wherein the composite is used in thermal energy storage systems with or without a buffer storage tank for heating and cooling applications ,102. A system as claimed in claim 1 wherein the thermal energy storage systems may contain single or multiple temperature compressed expanded graphite based embedded PCM rnatetials.15 3. A system as claimed in claim 1 and 2 wherein the energy source includes a single ormultiple temperature phase change material of different operating temperature applied for .. heating and cooling circuits.• •4. A system as claimed in any preceding claims wherein the compressed phase change* «20 material is provided packaged in any shape and geometry like as ball, rectangular and • • •tubular.• • • •‘ . j 5. A system as claimed in any preceding claims wherein the thermal energy storage tanks applied in singular or multiple formats.

256. A system as claimed in any preceding claims wherein the phase change 1material is provided packaged in heat exchanger format. ।I7. A system as claimed in any preceding claims comprising one or multiple heat I cooling 30 sources connected to the tank.

8. A system as claimed in any preceding claims wherein the heat sources include a solar thermal, electric heating element(s) and / or PV heat source.।9. A system as claimed in any preceding claims wherein the heat sources may include an air 5 source heat pump.

10. A system as claimed in any preceding claims applied as a buffer tank applied for heat pump and / or chilled water circulation systems.10 11. A system as claimed in claims 1 to 10 wherein a thermal transfer fluid is provided forcharging and discharging the thermal energy storage.

12. A system as claimed in claims 1 to 11 wherein the fluid is water with or without antifreeze solutions and the tank is configured such that the water flows around the phase 15 change material.»I t •• ••

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