WO2020007792A1

WO2020007792A1 - A heat storage unit

Info

Publication number: WO2020007792A1
Application number: PCT/EP2019/067589
Authority: WO
Inventors: Ludvig CHRISTENSEN
Original assignee: Seas-Nve Holding A/S
Priority date: 2018-07-02
Filing date: 2019-07-01
Publication date: 2020-01-09

Abstract

The present invention relates to a heat storage unit with a heat storage chamber (11) for containing a heat storing medium (100), the unit (10) including a cover (14, 37) covering the chamber (11), and a peripheral wall (12, 35, 55) defining an outer contour of the unit (10) and extending to the cover (14, 37), the peripheral wall (12, 35, 55) having an inner face (F) defining at least a portion of the chamber (11) below the cover (14, 37), the inner face (F) having a contour corresponding to a portion of the surface of an ellipsoid, such as a sphere, a first axis (A) of symmetry of the ellipsoid extending from a bottom (B) of the chamber (11) to the cover (14, 37), and first and second piping (52, 60) for supplying and discharging a gas to and from the chamber (11), the first piping (52) extending along the first axis (A) of symmetry from the cover (14, 37) and having an entry and/or exit for the gas located at the bottom (B), and the second piping (60) having one or more entry and/or exit passages (P) for the gas located above the entry and/or exit for the gas located at the bottom (B), such as at or near the cover (14, 37).

Description

A heat storage unit

TECHNICAL FIELD

The present invention relates to a heat storage unit.

BACKGROUND ART

Energy system operators ensure that the system is balanced in situations with low power production from wind and solar by using heat storage units that go through thermal charging and discharging cycles using a heat transfer gas, such as air, passed through a granular solid thermal medium, i.e. a material in which heat can be stored. The thermal medium goes from a heat charged state, in which a heat storage unit's thermal medium is relatively hot, to a heat discharged state, in which this medium is relatively cold, with periods of heat charging and discharging in between.

When the thermal medium is made of a packed bed of a granular heat storing material/medium contained in a storage chamber, heat is transferred to the solid material during charging through contact with the relatively hotter heat transfer gas that flows through (interstitial) passages between the piled gran- ules. During discharging of such a heat storage unit, heat is transferred from the solid material (cooling it) through contact with relatively cooler heat transfer gas flowing through the interstitial passages between the granules.

DE 202009005097 discloses a heat storage unit for underground use, having a bulbous shape and configured for being filled with water.

DE 2949584 discloses a heat storage unit comprising a frusto-conical structure containing sand and water, with a lid and a pipe for supplying a fluid. US 2013/0206356 shows a heat storage with a packed solid medium. SUMMARY OF THE INVENTION

The present invention seeks to provide an improved heat storage unit which comply with the above-mentioned requirements with a high heat charging and discharging efficiency.

With this aim the present invention provides a heat storage unit with a heat storage chamber for containing a solid medium, such as gravel or a granular material, the unit including a cover covering the chamber, and a peripheral wall defining an outer contour of the unit and extending to the cover, the peripheral wall having an inner face defining at least a portion of the chamber below the cover, the inner face having a contour corresponding to a portion of the surface of an ellipsoid, such as a sphere, a first axis (A) of symmetry of the ellipsoid extending from a bottom of the chamber to the cover, and first and second piping for supplying and discharging a gas to and from the chamber, the first piping extending along the first axis (A) of symmetry from the cover and having a chamber entry and/or exit for the gas located at the bottom, and the second piping having one or more chamber entry and/or exit passages for the gas located above the entry and/or exit for the gas located at the bottom, such as at or near the cover.

The contour of the inner face is such that the stacking of the solid medium in the chamber combined with the piping having the gas exit located centrally of the chamber and at the bottom/in the proximity of the bottom of the chamber results in the heat transfer gas leaving the first piping being directed upwardly by the inner face to flow through a major part of the medium, thereby resulting in an efficient charging and discharging of the unit.

Moreover, the cover may be removable, allowing replacement of the heat stor- age medium; and the unit may be configured for being placed in the ground with the aforementioned first axis of symmetry oriented vertically and prefera- bly with only the cover being exposed. The first piping may include an elongated conduit having a central axis (A’) coincident with the aforementioned first axis A; the conduit may be heat insu- lated, may be protected by an elongated casing, and may include a plurality of apertures defining together the entry and/or exit for the gas. The plurality of apertures may be sideways oriented and located spaced apart around the cen- tral axis A’ The conduit/first piping may preferably be supported, such as by the peripheral wall, at the bottom of the chamber and/or at locations above the bottom, so that the position of the conduit/first piping is securely maintained during filling of the chamber with the solid heat storing medium.

Also, the second piping is arranged to have entry and/or exit passages located preferably immediately below the cover, i.e. above the heat storing medium, so that any flow of gas entering the chamber at the bottom thereof, via the first piping gas entry, and flowing through the solid medium guided in part by the inner face of the peripheral wall will combine at the top of the chamber above the medium and exit the chamber through the second piping exit passages. For this preferably the second piping includes a plurality of conduits, each hav- ing a respective gas exit passage; the conduits may be located at different angular positions around the first axis of symmetry A of the ellipsoid. This an- gular spacing between all the conduits may be same, eg. 120°.

It is noted that the gas flow may in some cases be reversed, such as when discharging the unit (compared to when charging the unit). Hence, the second piping may in some instances be used for charging the unit whereby the pas- sages of the second piping will act as gas entry passages while the first piping will define in that case an exit for the gas.

The heat storage unit may be a High-Temperature Thermal Energy storage unit using electricity from renewables, e.g. from wind and solar during periods of overproduction, to heat up the heat transfer gas, eg. air, to at least 600- 900°C, where after the heated gas is blown through the heat storage chamber comprising the heat storing medium. When electricity is needed again, the air- flow may be reversed, and heated gas from the unit may be lead through a heat recovery steam generator (HRSG) connected to a traditional power sta- tion turbomachinery producing electricity. The medium may be heated, such as to at least 600°C, with air using low-cost electricity, the heat may be stored for long period, such as for days or weeks, without significantly loss of energy and the unit may then be discharged in accordance with demand. The energy charge and discharge system may, besides the heat storage unit, use any con- ventional equipment known in the power generation industry, being considered as being suitable therefor.

The medium may by way of example only be a non-degradable material having a grain size of 30-40 mm and capable of storing energy at 400°C or more in the granules, preferably between 400°C and 1000°C. The granules may have a volumetric thermal expansion below 3%, preferably below 2.5%, when heated from 0-1000°C. The material for the granules may by way of example be Anorthosite or Magnetite.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 illustrates three variants of an ellipsoid,

Fig. 2 shows a plurality of heat storage units of the invention placed in the ground, only the covers being visible,

Fig. 3 is a perspective view of an embodiment of a heat storage unit of the invention,

Fig. 4 is a cross-sectional view of the heat storage unit of fig. 3 Fig. 5 is an exploded view showing the various components of the unit of fig. 3,

Fig. 6 is a cross-sectional view of an outer concrete part of the unit of fig. 3,

Fig. 7 is a side view of a reinforcing cage of the concrete part of fig. 5,

Fig. 8 is a side view of an exemplary assembly forming an internal structure of the unit of fig. 3,

Fig. 9 is a top view of the assembly of fig. 8,

Fig. 10 is a vertical cross-sectional view through the assembly of fig. 8, shown along line A-A marked in fig. 9,

Fig. 1 1 is a side view of a subassembly comprising a first piping with casing, as shown in fig. 10, and

Fig. 12 is an enlarged view of a lower section of the subassembly of fig. 1 1 .

Embodiments of the present invention will now be explained in more detail below, by reference to the drawings.

Reference will for background information first be made to fig. 1 which illus trates three variants of an ellipsoid. An ellipsoid has three pairwise perpendic- ular axes of symmetry a, b, c which intersect at a center of symmetry C, called the center of the ellipsoid. For the present invention, typically the heat storage unit will have an internal face having a contour corresponding to a portion of the surface of an ellipsoid with two (second and third) axes of symmetry ori- ented in a horizontal plane and with a first axis A of symmetry extending verti- cally. If two of the axes a, b, c of an ellipsoid have the same length, then the ellipsoid is called a spheroid (a sphere); for the present invention the two horizontal axes a of symmetry may in that case have a length of at least 0.5 metres, such as at least 0.75 metres (measured from the center C), such that the sphere has a diameter of at least 1 -1 .5 metres. If the three axes a, b, c have the same length, the ellipsoid is a sphere, in which case for the present invention the two horizontal axes may have a length of at least 0.5 metres, such as at least 0.75 metres (measured from the centre C). If the three axes have different lengths, the ellipsoid is said to be tri-axial; in that case, for the present invention the minor one a may have a length of at least 0.5 metres, such as at least 0.75 metres (measured from the centre C). In the context of the present invention various parameters may impact the choice of ellipsoid, such as building re- strictions/limitations or heat storage medium variations within the chamber.

The remaining drawings illustrate the inventive heat storage unit 10, and parts thereof, which has an internal chamber configured for being packed fully or partially with a granular heat storing medium; such a medium 100 filled into the unit 10 is shown schematically in fig. 4. The material for the granules may by way of example only be Anorthosite which is a low-cost material that has a low volumetric thermal expansion of about 1 .15% at 600°C and about 2.15% at 1000°C. Other materials may be used, such as Magnetite which has a rela- tively higher heat capacity. The medium 100 is packed to allow a gas (such as air) supplied to the unit 10 and defining a heat exchange fluid, to flow between the granules 100 from an inlet to one or more gas exit passages or from one or more gas entry passages to a gas exit.

Fig. 2 shows schematically a plurality of heat storage units 10 of the invention placed in the ground 1 , each unit 10 having a minor portion defining a circular cover 37 projecting above the ground 1 . Piping mounted to the covers and possibly connecting the units 10 with each other is not shown in fig. 2. A typical commercial scale diameter above ground of the covers may likely be in the order of 10 metres, i.e. with the aforementioned lengths a, b, c in the order of 5 metres.

Fig. 3 shows one unit 10 with various piping 15 connected to the aforemen- tioned cover for delivering a gas, normally air, to the unit 10 and for simultane- ously removing relatively colder or warmer gas from the unit 10, after the gas has flown between granules of a granular medium contained in the unit 10, to either absorb or give off heat energy in a discharging or charging process, respectively.

Fig. 4 is a cross-sectional view of the unit 10, illustrating by arrows a flow of the aforementioned gas resulting from the present invention. The gas is sup- plied to the unit 10 and introduced into the medium via a first piping 52 extend- ing along a first axis A of symmetry, from the cover to the inside bottom B of the unit 10.

The granular medium is shown schematically by numeral 100 in fig. 10. Fig. 5 is an exploded view of the unit 10 showing the various components.

An upper portion of the unit 20 is defined by the aforementioned cover and preferably comprises a top metal part 37 and a layer 14 of a heat insulating material, such as mineral wool, as well as a lower metal part 57. The cover 14, 37, 57 is preferably configured for allowing access to the chamber 1 1 inside the unit 10, i.e. the volume into which the medium 100 is filled, such as for facilitating exchange of the medium 100.

The cover 14, 37, 57 is provided with multiple pipe connections for a second piping 60 defining, depending on the use of the unit 10, gas entry or exit pas- sages P, as well as with a connection for the first piping 52 defining, again depending on the use, a gas entry or exit. The gas, which defines the heat transfer fluid, flows between the first and second piping 52, 60 during operation of the heat storage unit 10, e.g. during charging and discharging. The direction of flow may be reversed; hence, the second piping 60 may in some instances be used for charging the unit 10 whereby the passages of the second piping 60 will act as gas entry passages while the first piping 52 will in that case be used for discharging the gas.

The first piping includes an elongated conduit 52 having a central axis A’ coin- cident with the aforementioned first axis A and is heat insulated by means of a layer 13 of a heat insulating material, such as by a layer of such a material having been wrapped around the conduit 52 being a steel pipe. An elongated protective casing 70 extends around the heat insulating layer 13 and includes at a lower end thereof at the bottom B a plurality of sideways oriented apertures defining together an entry and/or exit for gas flowing through the conduit 52, and located spaced apart around the axis A’. The apertures 76 may as shown in fig. 12 be identical, or be configured differently, such as to vary around the axis A’, to provide a particular flow pattern through the chamber 1 1 , which may be desirable where the ellipsoid is not a sphere or where variations in the gran- ular medium is contemplated.

Turning now to the lower portion 30 of the unit 10, an outer second structural part 35 of the peripheral wall defines an outer contour of the unit 10 and pro- vides support for at least a portion of the cover 14, 37, 57. Figs. 4 and 5 show also an inner first structural part 55 of the peripheral wall. This first structural part 55 is bowl-shaped, typically of metal and has an inner face F defining in part the chamber 1 1 below the cover 14, 37. According to the invention this inner face F has a contour corresponding to a segment of the surface of an (imaginary) ellipsoid, in the shown embodiment a sphere, with a first axis A of symmetry of the ellipsoid extending from the lowermost part or bottom B of the chamber 1 1 towards the cover 14, 37, 57. Preferably, the unit 10 is arranged in the ground 1 such that this first axis A is vertical or essentially vertical. A heat insulating material 12 is located between the inner and outer peripheral parts 35, 55; the outer, second structural part 35 preferably is of reinforced concrete, the concrete reinforcement preferably being a cage-structure 36 hav- ing a contour corresponding essentially to a portion of the surface of the afore- mentioned ellipsoid, as shown in fig. 7, in which case also the outer, second 35 may have a contour similar to that of the bowl-shaped inner, first structural part 55.

The distance along the first axis A between the lower face of the cover 14, 37 and the inside bottom B may by way of example be between 100% and 150% of the distance along the first axis A between the center of symmetry C of the ellipsoid and the imaginary ellipsoid (i.e. between the center of symmetry C and the bottom B/lowest point of the chamber 1 1 ); in the shown example of fig. 4 the distance along the first axis A between the lower face of the cover 14, 37 and the bottom B is about 125% of the distance along the first axis A between the center of symmetry C and the bottom B, see also fig. 8.

As seen best in figs. 1 1 and 12 the first piping in the form of conduit 52 is heat insulated 13 and the elongated casing 70 extends around the (tubular) heat insulation and includes a plurality of sideways oriented apertures, preferably distributed evenly around the central axis (A’), defining together the chamber entry for the gas when the unit 10 is in one state of operation, such as for charging, where hot gas is supplied to the unit via the conduit 52 to enter the chamber 1 1 via the apertures 76 and to finally exit the chamber through the second piping 60, as shown in fig. 10.

As may be seen from figs. 4 and 10 where flow directions are marked by ar- rows, the contour of the inner face F and the arrangement of the first piping 52 is such that gas leaving the first piping 52 is directed, evenly distributed around the central axis A’, upwardly along the inner face F to flow through a major part of the medium 10, thereby resulting in an efficient charging and discharging of the unit 10.

One method of making the aforementioned unit 10 will be described in the following:

On the selected location for the storage unit 10 a hole with the shape of a half sphere is excavated, and a plastic foil is arranged to cover the sides of the hole to ensure that subsequently applied concrete for forming the outer portion 55 of the peripheral wall will not mix with the soil. A cage 36 containing the full reinforcement is located in the hole. Concrete may then preferably be applied in a spraying procedure.

Where the soil is of a type not capable of holding its shape formwork may be arranged upside down next to the hole, with the cage 36 also upside down placed around the formwork, whereafter concrete is applied by spraying from the outside. Once cured this concrete shell is then turned around and placed in the hole.

After the concrete has cured for 3-5 days, work for mounting the peripheral wall insulation 12 can start. Insulating works may be carried out by positioning multiple layers of Skamol™ bricks type Supra™, such as in size 220mm x 1 10mm with thickness from 38mm to 76mm, cut to fit. The bricks may be secured in place using a cement based mortar.

Once the insulation work is done the inner surface of the insulation 12 may be provided with a 15-20mm layer of“wet” cement based mortar, following which the metal inner first structural part 55 is lowered into the hole and placed in the mortar before it cures, ensuring a good connection to the mortar on the full contact surface. After the mortar is cured around the first structural part 55, the first piping 52 with the casing 70 is lowered into the first structural part 55. Then a centering tool, which could be made of wood, is mounted to maintain the position of the first piping 52.

A first larger size granules layer of the material 100 can then be placed, on top of which a perforated plate (not shown) may be placed to keep the remaining granules 100 from mixing with the larger granules at the bottom B. After this the remaining granules are filled into the chamber 11. At the same time tem- perature probes may be placed at desired locations.

Claims

1. A heat storage unit (10) with a heat storage chamber (11 ) for containing a solid heat storing medium (100), said unit (10) including:

- a cover (14, 37) covering said chamber (11 ), and

- a peripheral wall (12, 35, 55) defining an outer contour of said unit (10) and preferably extending to said cover (14, 37),

- - said peripheral wall (12, 35, 55) having an inner face (F) defining at least a portion of said chamber (11 ) below said cover (14, 37),

- - said inner face (F) having a contour corresponding to a portion of the surface of an ellipsoid, such as a sphere,

- a first axis (A) of symmetry of said ellipsoid extending from a bottom (B) of said chamber (11 ) to said cover (14, 37), and

- first and second piping (52, 60) for supplying and discharging a gas, such as air, to and from said chamber (11 ),

characterised in

- said first piping (52) extending along said first axis (A) of symmetry from said cover (14, 37) and having an entry and/or exit for said gas located at said bottom (B), and

- said second piping (60) having one or more entry and/or exit passages

(P) for said gas located above said entry and/or exit for said gas located at said bottom (B), such as at or near said cover (14, 37).

2. The unit of claim 1 , said unit being configured for placement in the ground with said first axis (A) of symmetry extending vertically.

3. The unit of claim 1 or 2, said first piping including an elongated conduit (52) having a central axis (A’) coincident with said first axis (A).

4. The unit according to any of the previous claims, said first piping (52) being heat insulated (13), such as by a surrounding layer of a heat insulating mate- rial.

5. The unit according to any of the previous claims, an elongated casing (70) extending around said first piping (52), said casing (70) including a plurality of apertures, preferably distributed around said central axis (A’), defining together said entry and/or exit for said gas.

6. The unit according to any of the previous claims, said first and said second piping (52, 60) extending through said cover (14, 37).

7. The unit according to any of the previous claims, said second piping (60) including a plurality of conduits (60’), each having a respective one of said entry and/or exit passages (P).

8. The unit according to any of the previous claims, said peripheral wall includ ing an outer peripheral portion (35) defining said outer contour of said unit (10), an inner peripheral portion (55) defining said inner face (F), a heat insulating material (12) located between said inner and outer peripheral portions (35, 55), said outer peripheral portion (35) preferably being of reinforced concrete and said inner peripheral portion (55) preferably being of metal plate, said rein- forcement of said concrete preferably being a cage (36) having a contour cor- responding essentially to a portion of the surface of said ellipsoid.

9. The unit according to any of the previous claims, said cover (14, 37) includ- ing a layer (14) of a heat insulating material.

10. The unit according to any of the previous claims, the distance along said first axis (A) between the lower face of said cover (14, 37) and said bottom (B) being 100%-180% of the distance along the first axis A between the center of symmetry C of the ellipsoid and the ellipsoid.

11. A heat storage facility comprising one or more of the units (10) according to any of the previous claims, placed in the ground (1 ), preferably with said first axis (A) of symmetry extending vertically, wherein preferably a plurality of said units (10) are in gas fluid connection.