WO2025032003A2

WO2025032003A2 - Thermal energy storage system and method of providing phase change material in liquid form

Info

Publication number: WO2025032003A2
Application number: PCT/EP2024/072048
Authority: WO
Inventors: Conny Andersson
Original assignee: Energyintel Services Ltd
Priority date: 2023-08-04
Filing date: 2024-08-02
Publication date: 2025-02-13
Also published as: SE2350942A1; WO2025032003A3

Abstract

A method of providing a container of a thermal energy storage system with phase change material in liquid form. The method comprises providing a first load of phase change material in solid form into the container of the thermal energy storage system. The provided first load is melted into liquid form in the container. A second load of phase change material in solid form is fed into the container. The second load is larger than said first load. The already molten phase change material in the container melts the second load as it is submerged into the already molten phase change material, thereby gradually increasing the volume of phase change material in liquid form in the container.

Description

THERMAL ENERGY STORAGE SYSTEM AND METHOD OF PROVIDING PHASE CHANGE MATERIAL IN LIQUID FORM

TECHNICAL FIELD

The present disclosure relates to a method of providing a container of a thermal energy storage system with phase change material in liquid form.

BACKGROUND ART

A thermal energy storage system may be used for converting thermal energy to electricity. A phase change material may be heated and liquefied in a container. The phase change, from solid state to liquid state, results in a large energy recovery. The temperature at which the phase change material is liquefied may, e.g. be just under 600 °C. Examples of suitable phase change materials are different aluminium alloys.

Current practice in providing the phase change material into the container is quite complex, and time consuming. Typically, the container is filled with the phase change material, for example in the form of bars, slowly and carefully so as to avoid damaging the protective coating commonly provided on the inner walls of the container. Then the container is sealed and the phase change material is heated to above its melting temperature.

It would be desirable to provide a method which is less complex and less time consuming.

SUMMARY OF THE INVENTION An object of the present disclosure is to provide a method which alleviates at least some of the drawbacks of the prior art. This and other objects, which will become apparent in the following, are accomplished by a method as defined in the accompanying independent claim. Non-limiting exemplary embodiments are presented in the dependent claims.

According to an aspect of the present disclosure, there is presented a method of providing a container of a thermal energy storage system with phase change material in liquid form, the method comprising:

- providing a first load of phase change material in solid form into the container of the thermal energy storage system,

- melting the provided first load into liquid form in the container, and

- feeding a second load of phase change material in solid form, which is larger than said first load, into the container, such that the already molten phase change material in the container melts the second load as it is submerged into the already molten phase change material, thereby gradually increasing the volume of phase change material in liquid form in the container. Thus, the general inventive concept is based on the insight that by initially melting a relatively small load of phase change material, the molten material can then, in its turn, be used for melting more material that is fed into molten material. The relatively small first load of material may advantageously be provided in the container already at the factory. Then the container holding this small amount of phase change material may be transported to the site where it will be used. At the site, the small amount of phase change material is melted, by means of any suitably process, such as starting an HTF-circuit (heat-transfer-fluid circuit). When the initial first load of the solid phase change material has been melted, the larger second load may be feed into the container at the site. Since there is already provided molten phase change material in the container, the following melting of the second load will become easier and more time-efficient then conventional methods of filling a container with phase change material. When all the phase change material of the second load has been fed into the container, then the thermal energy storage system may be set into operation. Thus, the present disclosure teaches a method of preparing such a thermal energy storage system, and is performed before starting the actual operation of the system. The second load of material may be fed into the container in a number of different manners. Suitably, the feeding is performed in a controlled way, so that the fed material has time to melt before it reaches the bottom of the container. In some exemplary embodiments, the second load of material may be provided in the form of pellets, wherein pellets may be fed at a controlled rate into the already molten first load of material. In the following, another example will be discussed, which is based on making use of a material in the form of a continuous elongate element.

According to at least one exemplary embodiment, the method further comprises, before feeding the second load into the container:

- feeding the second load in the form of a continuous elongate element from a holder towards the container.

By providing the second load in the form of a continuous elongate element, a controlled gradual melting of the second load can be achieved. In particular, by feeding a continuous element, the speed of the feeding may be adapted such that the continuous elongate element, or parts thereof, is submerged at a controlled rate for efficient melting of the second load, and reducing the risk of damaging any protective liner/coating of the container when the second load is dispensed into the container. Furthermore, the second load may efficiently be transported to the site independently of the first load, by means of a suitable holder. An advantageous example of such a holder will be discussed in the following.

According to at least one exemplary embodiment, the continuous elongate element is in the form of a wire or a band, and the holder is in the form of a roll, wherein said feeding of the second load from a holder towards the container comprises:

- unwinding the wire or band from the roll and feeding it towards the container. Having a wire or band wound onto a holder is convenient from a transportation perspective. Furthermore, it allows for a controlled feeding. The speed at which the wire or band is unwound from the roll may, for example, be adapted to the size of the container and/or the amount of already molten phase change material in the container. For instance, when the amount of liquid phase change material is rather low, the feeding speed may be relatively slow, whereas when a large amount of hot molten material is present in the container, then the feeding speed may be increased. Hereby, the wire or band that is submerged into the already molten phase change material will have time to melt before reaching the bottom of the container (thereby avoiding damaging the bottom of the container). It should be noted, however, that in many cases even if the elongate element has not melted completely before it reaches the bottom of the container, it will still have softened considerably as it has travelled through the already molten material, thus the risk of damaging the bottom of the container is very low.

According to at least one exemplary embodiment, the method comprises cutting the continuous elongate element into pieces, wherein said feeding of the second load into the container comprises:

- feeding cut pieces of said elongate element into the container.

By cutting the elongate element (e.g. cutting a fed wire or band) into pieces, the individual pieces will melt quicker, thus further reducing the risk of damaging the container.

Any suitably cutter may be used for cutting the continuous elongate element into pieces. If desired, it would be conceivable to use the same cutter to provide the first load of material on site, if the container is shipped empty from the factory to the site. In this connection it should be pointed out that the relatively small first load may be provided in any suitable solid form. For instance, cut pieces of wire or band, or in the form of pellets, or in the form of bars, or even a single block of phase change material.

According to at least one exemplary embodiment, said feeding of the second continuous elongate element from a holder towards the container, comprises:

- feeding the continuous elongate element through a sealed passage leading to the container, thereby reducing the risk of gas escaping from the container.

By enabling the feeding and the melting process to be performed in an inert environment, the risk of slag forming is reduced.

In exemplary embodiments using a cutter for cutting the continuous elongate element, such a cutter may suitably be provided after the seal creating the sealed passage, such that the cutter is also provided in the inert environment. According to at least one exemplary embodiment, the method comprises supplying an inert gas into the container so as to create a volume of pressurized inert gas above the molten phase change material. The inert gas may, for instance, be nitrogen. This also contributes to reducing slag formation.

According to at least one exemplary embodiment, the first load is less than 30 % by weight, preferably less than 20 % by weight, such as less than 15 % by weight of the sum of the first and second loads. As a purely illustrative example, assuming that the total load to be provided in the container is around 4300 kg, the first load may be around 300-500 kg.

According to at least one exemplary embodiment, the thermal energy storage system further comprises a jacket connected to the exterior of the container, wherein a space if formed between the jacket and a wall portion of the container, the jacket having an inlet to said space, wherein said melting of the first load comprises:

- supplying a heat transfer fluid through the inlet into said space formed between the jacket and the wall portion of the container, in order to cause thermal energy to be transferred between the heat transfer fluid and the phase change material via said wall portion.

Using such a heat transfer fluid provides an efficient way to melt the first load. The heat transfer fluid may suitably be circulated in a heat transfer circuit via a heat exchanger, so that it continues to provide thermal energy to the phase change material via said wall portion, also during the feeding of the second load into the container.

According to at least one exemplary embodiment, said first and second loads of phase change material are of aluminium. Aluminium is readily available and commonly used phase change material. Furthermore, aluminium wires or bands are also available, thus being advantageously used in the exemplary embodiments of the disclosed method.

According to another aspect of the invention a thermal energy storage system is provided, comprising a container for storing a phase change material in liquid form, further comprising a jacket connected to the exterior of the container and a heat transfer fluid, which is supplied from a tank via a heating chamber to a space formed between the jacked and a wall portion of said container, wherein a pump arrangement is configured to pump the heat transfer fluid from the tank, via the heating chamber, to the space between the jacket and the wall portion of the container, such that the heat transfer fluid is heated in the heating chamber and thermal energy is transferred to the phase change material.

According to an embodiment of the thermal energy storage system the heat transfer fluid is liquid sodium.

According to an embodiment of the thermal energy storage system the heat transfer fluid is contained in a closed circuit and the pump arrangement is adapted to move said heat transfer fluid in said closed circle, wherein preferably the jacket comprises an outlet, from which the heat transfer fluid, is pumped back into said tank.

According to an embodiment, the thermal energy storage system further comprises a feeding device, which is adapted to feed the second load in the form of a continuous elongate element into container, preferably in the form of a wire or a band.

According to an embodiment, the thermal energy storage system further comprises a box having a gas sealing, which is adapted to create an inert environment within the container, wherein a sealed passage is arranged between the box and the container.

According to an embodiment of the thermal energy storage system a cutter, preferably a wire chopper adapted to cutting the elongate wire or band into pieces, is provided in the sealed passage.

According to an embodiment, the thermal energy storage system further comprises an inert gas supply system which is adapted to provide an inert gas, into the container so as to create a volume of pressurized inert gas above the molten phase change material.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, arrangement apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, arrangement apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present inventive concept will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present inventive concept may be combined to create embodiments other than those described in the following, without departing from the scope of the present inventive concept.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1 a-1 d schematically illustrate a method according to at least one exemplary embodiment of this disclosure.

Fig. 2 schematically illustrates equipment that may be used for performing some exemplary embodiments of the method.

Fig. 3 illustrates a thermal energy storage system.

DETAILED DESCRIPTION

Figs. 1 a-1 d schematically illustrate a method according to at least one exemplary embodiment of this disclosure. In particular, Figs. 1 a-1 d illustrate a method of providing a container 2 of a thermal energy storage system with phase change material in liquid form. The method comprises, as illustrated in Fig. 1 a, providing a first load of phase change material 4 in solid form into the container 2 of the thermal energy storage system. In Fig. 1 a this is illustrated by providing pellets in the container 2, such as for instance aluminium pellets. However, in other exemplary embodiments, the first load may be in the form of bars, cut pieces of wire or band, or even one solid block of material, be it of aluminium or any other suitable phase change material. This first load of phase change material 4 may either be provided in the container 2 already in the factory, and shipped in this way to the site where the thermal energy storage system will be operated, or the first load may be introduced into the container 2 at the actual site.

As illustrated in Fig. 1 b, the first load of phase change material 4 is then melted into liquid form in the container 2. The melted liquid phase change material 4 has a high temperature. This can therefore be used for melting newly added solid phase change material, which is illustrated in Fig. 1c.

In Fig. 1c a second load of phase change material 6 in solid form is fed into the container 2. The second load is larger than the first load. The already molten phase change material 4 in the container 2 will melt the second load of phase change material 6 as it is gradually introduced and submerged into the already molten phase change material 4. Hereby, the volume of phase change material in liquid form is gradually increased in the container 2. The liquid phase change material is kept in liquid form in any suitable manner (for example by means of a heat-transfer-fluid circuit as will later be discussed in relation to Fig. 3). Although Fig. 2 illustrates that cut pieces of an unwound wire or band is supplied into the container, it should be understood that other options for supplying the second load are envisaged and encompassed by the present disclosure. For instance, a wire or band, or any other suitable continuous elongate element, can in a controlled manner be continuously fed into the already molten phase change material. The feeding may be done at a controlled pace, for example at such feeding speed that the portion of the continuous elongate element that is being submerged into the molten phase change material has time to melt before it reaches the bottom of the container.

Fig. 1d schematically illustrates the container 2 having been provided with both the first and the second load, which are now in liquid form, thus allowing the thermal energy storage system to start its intended operation.

Fig. 2 schematically illustrates equipment that may be used for performing some exemplary embodiments of the method. In particular, Fig. 2 illustrates that the second load may be provided in the form of a continuous elongate element, in particular in the form of a wire or a band 10 that may be delivered to a site in winded form on a roll 12. A feeding device 14 may be provided to feed the wire or band 10 from the roll 12 towards the container 2. Thus, the feeding device 14 will unwind the wire or band 10 from the roll 12. The wire or band 10 may suitably be fed through a box 16 having a gas sealing, in order to create an inert environment within the container 2. Thus, the continued feeding of the wire or band 10 after the box 16 will be through a sealed passage 18 leading to the container 2. In this sealed passage 18, there may be provided cutter 20, such as a wire chopper, for cutting the wire or band 10 into pieces, wherein pieces of wire or band 10 are dispensed into the already molten phase change material. An inert gas supply system 22 may be present for providing an inert gas, such as nitrogen, into the container 2 so as to create a volume of pressurized inert gas 24 above the molten phase change material. Hereby, slag formation may be counteracted, while a simple and time-efficient melting procedure is achieved.

Fig. 3 illustrates a thermal energy storage system 30, having a container 32 in which a phase change material may be provided in liquid form, in line with the method of the present disclosure. Thus, the schematic container 32 in Figs. 1 and 2 may correspond to the container 32 in Fig. 3. The thermal energy storage system 30 comprises a jacket 34 connected to the exterior of the container 32. A space is formed between the jacket 34 and a wall portion of the container 32, the jacket 34 having an inlet to said space. A heat transfer fluid may be supplied from a tank 36 via a heating chamber 38, which comprises a heating device. The heat transfer fluid may, for example, be liquid sodium. A pump arrangement 40 may be configured to pump the heat transfer fluid from the tank 36, via the heating chamber 38, to the space formed between the jacket 34 and the wall portion of the container 32. When passing through the heating chamber 38 the heat transfer fluid will become heated by the heating device. Thermal energy is transferred between the heat transfer fluid located in said space and the phase change material. More specifically, thermal energy is transferred from the heat transfer fluid to the phase change material via said wall portion of the container 32.

The jacket 34 may suitably have an outlet, from which the heat transfer fluid, is pumped back into the tank 36. Thus, the pump arrangement 40 may move the heat transfer fluid in a closed circuit. Because of the transfer of heat energy, the phase change material in the container 32 will melt and turn into liquid phase. This phase change charges the thermal energy storage system 30 with energy, which may be discharged at a later point in time. The energy may be discharged by making use of another heat transfer fluid cir- cuit to take up the thermal energy from the phase change material (which then shifts back to solid form). The discharge of energy and the various possible implementations of the discharged energy do not form part of the general inventive concept as such. However, it should be understood that the thermal energy storage system 30, and its container 32 which may be filled using the method of this disclosure, may be used in any suitable implementation as will be appreciated by the person skilled in the art. One such example is to energize a Stirling engine.

Claims

1 . A method of providing a container of a thermal energy storage system with phase change material in liquid form, the method comprising:

- melting the provided first load into liquid form in the container, and

- feeding a second load of phase change material in solid form, which is larger than said first load, into the container, such that the already molten phase change material in the container melts the second load as it is submerged into the already molten phase change material, thereby gradually increasing the volume of phase change material in liquid form in the container.

2. The method according to claim 1 , further comprising, before feeding the second load into the container:

3. The method according to claim 2, wherein the continuous elongate element is in the form of a wire or a band and wherein the holder is in the form of a roll, wherein said feeding of the second load from a holder towards the container comprises:

- unwinding the wire or band from the roll and feeding it towards the container.

4. The method according to any one of claims 2-3, comprising cutting the continuous elongate element into pieces, wherein said feeding of the second load into the container comprises:

- feeding cut pieces of said elongate element into the container.

5. The method according to any one of claims 2-4, wherein said feeding of the second continuous elongate element from a holder towards the container, comprises: - feeding the continuous elongate element through a sealed passage leading to the container, thereby reducing the risk of gas escaping from the container.

6. The method according to any one of claims 1-5, comprising supplying an inert gas into the container so as to create a volume of pressurized inert gas above the molten phase change material.

7. The method according to any one of claims 1-6, wherein the first load is less than 30 % by weight, preferably less than 20 % by weight, such as less than 15 % by weight of the sum of the first and second loads.

8. The method according to any one of claims 1-7, wherein the thermal energy storage system further comprises a jacket connected to the exterior of the container, wherein a space if formed between the jacket and a wall portion of the container, the jacket having an inlet to said space, wherein said melting of the first load comprises:

9. The method according to any one of claims 1-8, wherein said first and second loads of phase change material are of aluminium.

10. A thermal energy storage system (30), comprising a container (2, 32) for storing a phase change material (5, 6) in liquid form, further comprising a jacket (34) connected to the exterior of the container (2, 32) and a heat transfer fluid, which is supplied from a tank (36) via a heating chamber (38) to a space formed between the jacked (34) and a wall portion of said container (2, 32), wherein a pump arrangement (40) is configured to pump the heat transfer fluid from the tank (36), via the heating chamber (38), to the space between the jacket (34) and the wall portion of the container (2, 32), such that the heat transfer fluid is heated in the heating chamber (38) and thermal energy is transferred to the phase change material (5, 6).

11 . The thermal energy storage system (30) according to claim 10, wherein the heat transfer fluid is liquid sodium.

12. The thermal energy storage system (30) according to claim 10 or 11 , wherein the heat transfer fluid is contained in a closed circuit and the pump arrangement (40) is adapted to move said heat transfer fluid in said closed circle, wherein preferably the jacket (34) comprises an outlet, from which the heat transfer fluid, is pumped back into said tank (36).

13. The thermal energy storage system (30) according to one of claims 10 to 12, further comprising a feeding device (14), which is adapted to feed the second load (6) in the form of a continuous elongate element into container (2, 32), preferably in the form of a wire or a band (10).

14. The thermal energy storage system (30) according to claim 13, further comprising a box (16) having a gas sealing, which is adapted to create an inert environment within the container (2, 32), wherein a sealed passage (18) is arranged between the box (16) and the container (2, 32).

15. The thermal energy storage system (30) according to claim 14, wherein a cutter (20), preferably a wire chopper, adapted to cutting the elongate element (10) into pieces, is provided in the sealed passage (18).

16. The thermal energy storage system (30) according to one of claims 10 to 15, further comprising an inert gas supply system (22) which is adapted to provide an inert gas, into the container (2, 32) so as to create a volume of pressurized inert gas (24) above the molten phase change material (5, 6).