Patent Description:
In <CIT>, a heat storage device is described having a storage vessel, a fluid flow circuit external to and in fluid communication with the vessel, a heat storage mass in the vessel adapted to store heat in the course of its transition from a solid to a molten state, and a heat carrier liquid which is not or only slightly miscible with the melt of the storage mass, and where the specific gravity of the storage mass differs so considerably from the specific gravity of the melt that layers are formed. A pump or mixer rotor is so arranged in the heat carrier liquid layer that a vortex is formed, whereby a mixture of the storage mass melt and the heat carrier liquid is sucked up. The liquid storage mass penetrates into the vortex of the pump rotor into minute droplets which assume a spherical shape on account of the surface tension and which then give off their heat to the heat carrier liquid. After solidification, the small spheres are again moved back into the storage mass layer by gravity and by centrifugal forces. The lateral wall of storage vessel has a slightly downwardly narrowing, truncated conical shape. During solidifying the rotor cuts the solidified mass into small pieces so that during subsequent heating no forces due to expansion of the mass act on the lateral wall of the storage vessel.

During heating, the salt expands and consequently exerts large forces on the lateral wall of the storage container setting high demands concerning the strength of the lateral wall of the storage container. When the salt is however molten for the first time, there is space between the salt particles allowing the salt to expand without exerting forces on the lateral wall of the storage container, through which in known devices the molten salt is often kept in a liquid state once it has been molten. The same happens when melting and solidifying metals.

This problem is solved by providing a heat exchange system according to claim <NUM>, provided with a storage container wherein the lateral wall has a downwardly narrowing, truncated conical and circumferentially walled shape and having an inclination angle of at least <NUM> degrees versus a vertical plane. In this way, the expanding liquefying heat storage mass can rise up without getting stuck between the lateral wall and consequently without exerting big forces on the lateral wall of the storage container.

In order to even more reduce the forces on the lateral wall of the storage container, the inclination angle of the lateral wall versus the vertical plane is around <NUM> degrees.

A conical shape has no corners, as such the heat storage mass cannot get stuck nor leave residues in corners.

From <CIT> an energy storage and transfer system is known in which a molten salt is transferred by a railway car having a storage container. The salt is kept continuously in molten state so no problems occur with respect to solidifying and melting the salt. The storage container has a rectangular cross section. The longitudinal walls of the storage container converting downwards with an inclination angle of about <NUM> degrees versus a vertical plane.

From <CIT> a heat transfer system is known having a large first storage container and a small second storage container of which only a small part of the lateral wall has a downwardly narrowing shape, with an inclination angle of about <NUM> degrees versus a vertical plane. The larger part of the lateral wall of the second storage container has a cylindrical shape. After solidifying the mass is only heated in the small second storage container and during heating of the mass the molten outer layer of the mass is directly discharged.

From <CIT> heat storage container is known of which the lateral wall has a downwardly narrowing, truncated conical shape, with an inclination angle of about <NUM> degrees versus a vertical plane. This container is for storing water ice. Water ice shrinks when melted, so there occur no problems with respect to solidifying and melting the water/ice.

A further disadvantage of the device as described in <CIT> is that there is no possibility to let the liquid heat storage mass leave the storage container in order to transport it to a heat consumption system / device outside the storage container.

This problem is solved by providing a storage container according to the present disclosure, wherein an output opening is provided that, during operation, is constantly in fluid connection with the liquid heat storage mass. Being in fluid connection means that the output opening itself can be in direct contact with the liquid heat transfer mass or via an open end of a tube. This has the advantage that during operation, there is enough liquid heat storage mass to continuously leave the storage container.

In an optional embodiment of a storage container according to the present disclosure, the output opening is located in the bottom wall of the storage container.

In an embodiment of a storage container according to the present disclosure, the storage container comprises a valve which is operable to open and close the output opening.

According to another aspect of the disclosure, a heat storage system is provided comprising a storage container according to the present disclosure as described above, a shredder for shredding large pieces of solid heat storage mass into smaller pieces, as well as transport means for transporting the smaller pieces of solid heat storage mass to a filling opening provided in the storage container.

According to a further aspect of the present disclosure, a heat transfer system is provided comprising a storage container according to the disclosure as described above, heat exchange means and a circuit connecting the storage container to the heat exchange means and provided for circulating the liquid heat storage mass between the heat exchange means and the container. This circuit has an upper and a lower point and the storage container is situated at the lower point of the circuit.

According to an alternative or additional aspect of the heat transfer system disclosed herein, the heat exchanger (or a part thereof) is positioned inside the storage container according to the disclosure as described above. By for instance providing inside the storage container a heat exchanger or a liquid circuit of the heat exchanger, this circuit can be used to cool down the heat storage mass when needed. This provides a solution for situations where flexible timing is necessary, for instance when rapid cooling or heating is required. In a particular embodiment the heat transfer system is provided with a heat exchanger (or a part thereof) positioned inside the storage container as well as heat exchange means and a circuit connecting the storage container to the heat exchange means and provided for circulating the liquid heat storage mass between the heat exchange means and the container.

In a further aspect the present disclosure refers to a method for storing heat by using a storage container as disclosed herein. In particular the method provides in a storage container comprising a heat storage mass that is convertible from a solid to a liquid phase by adding heat and from a liquid to a solid state by releasing heat, wherein the method comprises the steps of:.

wherein the heating means are in the form of one or more electrical heating elements located at the inside of the storage container against the lateral wall thereof or inside the lateral wall of the storage container.

The cooling down step in particular occurs in a passive form, by switching of the heating means.

In particular, the method as disclosed herein uses salt or metal as heat storage mass.

In a particular embodiment the method as disclosed here further comprises the steps of shredding large pieces of solid heat storage mass into smaller pieces, transporting the smaller pieces of solid heat storage mass to the storage container, and introducing the smaller pieces of solid heat storage mass into the storage container.

In a further aspect, the present disclosure provides in a the method for transferring heat using the heat storage method as disclosed here, further comprising the steps of circulating the liquid heat storage mass between heat exchange means and the storage container, wherein heat from the liquid heat storage mass is extracted by the heat exchange means. Alternatively or additionally, the present disclosure provides in a the method for transferring heat using the heat storage method as disclosed here, further comprising the steps of exchanging heat between the liquid heat storage mass and the heat exchanger (or a part thereof) in the storage container according to the disclosure as described above. In particular the heat extracted by the heat exchange means is converted into energy.

The present disclosure will be further elucidated below on the basis of drawings. These drawings show embodiments of the heat storage system, the storage container and a heat transfer system according to the present disclosure. Although the present disclosure is elucidated above on the basis of the given drawings, it should be noted that this disclosure is not limited whatsoever to the embodiments shown in the drawings. The disclosure also extends to all embodiments deviating from the embodiments shown in the drawings within the context defined by the claims.

A heat storage system according to the present disclosure, as shown in <FIG>, comprises a storage container <NUM> for a heat storage mass that is convertible from a solid to a liquid phase by adding heat and from a liquid to a solid state by releasing heat. The heat storage mass can be a salt as well as a metal that can be molten and can solidify again. In the embodiment as shown in <FIG>, the heat storage mass is a salt that is typically used in heat storage applications. The heat storage system further comprises a shredder <NUM> for shredding large pieces of solid salt into smaller pieces. Further, the heat storage system comprises transport means <NUM> for transporting the smaller pieces of solid salt to a filling opening <NUM> arranged in the storage container. The storage container, the shredder and the transport means can be mounted on a plateau <NUM> which can be placed on a transport vehicle to be moved to a location where such a heat storage system is needed.

As shown in <FIG>, the storage container <NUM> has an upper wall <NUM>, a bottom wall <NUM> and a lateral wall <NUM> that is extending in between the upper and the lower wall. The lateral wall <NUM> has a downwardly narrowing truncated form and extends circumferentially such that a closed wall is obtained. The lateral wall has an inclination angle <NUM> of about minimum <NUM>, more in particular <NUM> and most in particular <NUM> degrees with respect to a vertical extending plane <NUM>. More in particular, the lateral wall has a truncated conical shape.

The storage container is provided with an output opening <NUM>, more in particular arranged in the bottom wall <NUM> of the storage container and more in particular being continuously in fluid connection with the molten salt <NUM>. This output opening <NUM> can be closed off by a valve <NUM> which is operable to open and to close off the output opening <NUM>.

The storage container furthermore comprises one or more electrical heating elements <NUM> that are arranged to melt solid salt when they are switched on and to let the liquid salt to cool down again and consequently release its heat in case they are switched off again. These electrical heating elements <NUM> can be placed either inside the storage container against the lateral wall <NUM> thereof or are arranged in the lateral wall. The electrical heating means can be arranged under the form of a resistance wire or under the form of resistance rods. In an embodiment, the bottom wall <NUM> is free from such heating means <NUM>. When a solid salt mass is heated, first, a layer <NUM> of the solid salt that is in contact with the lateral wall <NUM> starts melting. Once the salt <NUM> has been molten, one or more further electrical heating elements <NUM> arranged inside the storage container and spaced apart from the lateral wall can speed up the melting process. These further electrical heating elements are in particular parallel arranged with the lateral wall <NUM> and can be attached to the upper wall <NUM> of the storage container <NUM>.

The storage container <NUM> can form part of a heat transfer system comprising heat exchange means and a circuit connecting the storage container to the heat exchange means. The molten salt can circulate in this circuit between the heat exchange means and the storage container. Such a circuit has an upper and a lower point and the storage container situated at the lower point of the circuit. Alternatively or additionally the heat transfer system comprises a heat exchanger (or a part thereof) being positioned inside the storage container.

An energy generation system as shown in <FIG> comprises an energy generation system <NUM> that is provided with a thermal conversion system, in this example a combustion boiler <NUM> for burning biomass, and a heat transfer system <NUM> for transferring heat from a thermal conversion system to a steam production device <NUM>. The heat transfer system comprises a heat exchange system <NUM> inside the combustion boiler, which heats salt to a temperature in excess of <NUM> with heat produced by the thermal conversion system. A heat exchanger <NUM> utilizes the heat for heating water or overheating steam which is utilized for example for drying wet biomass which in its turn is then fed into the combustion boiler at <NUM>. The heat transfer system further comprises a circuit <NUM> connecting the storage container <NUM> to the heat exchange means <NUM> and <NUM> and is arranged for circulating molten salt between the heat exchange means and the storage container. The molten salt is pumped by a pump <NUM> from the storage container <NUM> to the combustion boiler <NUM> where it heated. Subsequently, the heated molten salt enters the heat exchanger <NUM> from which it leaves at a temperature of approximately <NUM> and returns to the storage container. The combustion boiler <NUM> is provided with a riser and a boiler wall <NUM> and a combustion space <NUM> situated inside the boiler wall <NUM>. The bottom of the combustion boiler is formed by a circulating fluidized bed <NUM>. An air blower <NUM> blows the required amount of air via an air chamber <NUM> into the fluidized bed <NUM>. For initiating the combustion process, a start burner <NUM> may be utilized. The riser has several levels which each are cooled to an optimal temperature by the heat transfer medium. The boiler wall <NUM> is double walled and is cooled by the heat transfer medium. Thus in fact, the boiler wall <NUM> forms the first heat exchange means <NUM>.

Claim 1:
Heat transfer system (<NUM>) for transferring heat from a thermal conversion system (<NUM>) to a heat consuming system (<NUM>), comprising:
- a heat storage salt,
- a heat storage system, comprising a storage container (<NUM>) for the heat storage salt,
- a heat exchange system (<NUM>) which heats the heat storage salt to a temperature in excess of <NUM> with heat produced by the thermal conversion system, - a circuit (<NUM>) connecting the heat storage system to the heat exchange system (<NUM>) and being arranged for circulating the molten heat storage salt between the heat exchange system (<NUM>) and the heat storage system, the circuit (<NUM>) comprising a pump (<NUM>) for pumping the molten salt from the storage container (<NUM>) to the heat exchange system (<NUM>),
- a heat exchanger (<NUM>) transferring the heat of the molten salt to the heat consuming system (<NUM>),
the heat storage mass being convertible from a solid to a liquid phase by adding heat and from a liquid to a solid state by releasing heat, wherein the storage container comprises
- an upper wall (<NUM>), a bottom wall (<NUM>) and a lateral wall (<NUM>) extending in between the upper and the bottom wall, the lateral wall (<NUM>) has a downwardly narrowing, truncated conical and circumferentially walled shape, with an inclination angle (<NUM>) of at least <NUM> degrees versus a vertical plane,
- heating means (<NUM>) comprising electrical heating elements that are switchable on and off and that are provided for converting the heat storage mass (<NUM>) in the storage container
• from the solid to the liquid phase by adding heat to the heat storage mass when the heating means are switched on, and
• from the liquid to the solid phase by cooling down the liquid heat storage mass when the heating means are switched off.