Thermal energy storage with reduced internal natural convection

Abstract

A thermal energy storage is provided comprising a housing, a thermal energy storage structure arranged within the housing, the thermal energy storage structure comprising thermal energy storage elements and a plurality of dividing elements, the plurality of dividing elements being arranged such that the thermal energy storage elements are divided into a plurality of layers, a fluid inlet, the fluid inlet being in fluid communication with the housing and adapted to receive a working fluid and provide a flow of working fluid towards the housing, and a convection reducing structure arranged adjacent the thermal energy storage structure at a side of the thermal energy storage structure that faces the fluid inlet. Furthermore, a method of storing thermal energy and a steam power plant for producing electrical energy are described.

Claims

1. A thermal energy storage, comprising: a housing, a thermal energy storage structure arranged within the housing, the thermal energy storage structure including thermal energy storage elements and a plurality of dividing elements, the plurality of dividing elements being arranged such that the thermal energy storage elements are divided into a plurality of layers, a fluid inlet, the fluid inlet being in fluid communication with the housing and adapted to receive a working fluid and provide a flow of working fluid towards the housing, and a convection reducing structure arranged adjacent the thermal energy storage structure at a side of the thermal energy storage structure that faces the fluid inlet, wherein the convection reducing structure comprises at least one perforated plate for supporting a layer of convection reducing elements.

2. The thermal energy storage according to claim 1, further comprising a diffuser section arranged between the fluid inlet and the housing, wherein the diffuser section has in increasing cross section in a direction from the fluid inlet towards the housing.

3. The thermal energy storage according to claim 1, further comprising a fluid outlet, the fluid outlet being in fluid communication with the housing and adapted to receive a flow of working fluid from the housing.

4. The thermal energy storage according to claim 3, further comprising a further convection reducing structure arranged adjacent the thermal energy storage structure at a side of the thermal energy storage structure that faces the fluid outlet.

5. The thermal energy storage according to claim 4, wherein the further convection reducing structure comprises a layer of convection reducing elements extending in a direction perpendicular to the layers of thermal storage elements.

6. The thermal energy storage according to claim 1, wherein the thermal storage elements and the convection reducing elements comprise a material selected from the group consisting of stone, lava stone, brick, granite, basalt, and ceramics.

7. The thermal energy storage according claim 1, wherein the dividing elements comprise sheets or plates of material through which the working fluid cannot flow.

8. A power plant for producing electrical energy, comprising a thermal energy storage according claim 1.

9. A method of storing thermal energy, the method comprising providing a flow of working fluid through an inlet towards a housing of a thermal energy storage, wherein the thermal energy storage comprises a thermal energy storage structure arranged within the housing, the thermal energy storage structure comprising thermal energy storage elements and a plurality of dividing elements, the plurality of dividing elements being arranged such that the thermal energy storage elements are divided into a plurality of layers, wherein the fluid inlet is in fluid communication with the housing and adapted to receive a working fluid and provide a flow of working fluid towards the housing, and wherein the thermal energy storage comprises a convection reducing structure, including a bulk material, arranged adjacent the thermal energy storage structure at a side of the thermal energy storage structure that faces the fluid inlet, wherein the convection reducing structure comprises at least one perforated plate for supporting the layer of convection reducing elements.

10. A thermal energy storage comprising: a housing, a thermal energy storage structure arranged within the housing, the thermal energy storage structure including thermal energy storage elements and a plurality of dividing elements, the plurality of dividing elements being arranged such that the thermal energy storage elements are divided into a plurality of layers, a fluid inlet, the fluid inlet being in fluid communication with the housing and adapted to receive a working fluid and provide a flow of working fluid towards the housing, and a convection reducing structure made of the same material as the thermal energy storage elements and arranged adjacent the thermal energy storage structure at a side of the thermal energy storage structure that faces the fluid inlet, wherein the convection reducing structure comprises at least one perforated plate for supporting the layer of convection reducing elements.

11. The thermal energy storage according to claim 10, wherein the convection reducing structure includes bulk material.

12. The thermal energy storage according to claim 11, wherein the bulk material is selected from brick, stone, lava stone, granite, basalt or ceramic.

Description

BRIEF DESCRIPTION

(1) FIG. 1 shows a side-view of a known thermal energy storage; and

(2) FIG. 2 shows a side-view of a thermal energy storage.

DETAILED DESCRIPTION

(3) The illustrations in the drawings are schematic. It is noted that in different figures, similar or identical elements are provided with the same reference numerals or with reference numerals which differ only within the first digit.

(4) FIG. 1 shows a side-view of known thermal energy storage 100. The thermal energy storage 100 comprises a fluid inlet 102 for receiving a working fluid, such as water, hot or cold steam, air, nitrogen or argon, as indicated by arrow 112. The thermal energy storage 100 further comprises a diffuser section 104 for evenly distributing the working fluid and for reducing the flow speed of the working fluid. The thermal energy storage 100 further comprises a housing 106 comprising thermal storage elements 120, such as bricks, stone, lava stone, granite, basalt or ceramics provided as bulk material. The thermal storage elements 120 are separated into a layered thermal energy storage structure by dividing elements 122, such as steel plates or metal sheets. The thermal energy storage 100 further comprises a nozzle section 108 for increasing flow speed and pressure of the working fluid leaving the thermal energy storage structure in the housing 106 and forwarding it to fluid outlet 110 for ejection from the thermal energy storage 100, as indicated by arrow 114.

(5) The thermal energy storage system 100 may be charged with thermal energy by feeding a hot working fluid, such as hot steam, to the fluid inlet 102. The working fluid will flow through the layers of thermal energy storage elements 120 in the thermal energy storage structure and thereby heat up the thermal storage elements 120. The cooled working fluid leaves the storage 100 via the fluid outlet 110. After the charging is completed, the storage 100 may be left in a standstill period of hours or even days until the stored thermal energy is needed and discharged by feeding a cold working fluid, such as water, to the fluid inlet 102. After flowing through the thermal energy storage structure in housing 106, the heated working fluid is ejected from the

(6) The dividing elements 122 are provided to prevent a change in the temperature distribution within the thermal energy storage structure due to natural convection during the standstill period, i.e. that hot fluid surrounding thermal storage elements in the lower part of the housing 106 flows to the upper part of the housing 106. However, due to the open space within the diffuser section 104, some natural convection may still occur from the lower layers towards the upper layers as indicated by the arrows 116. Accordingly, after a longer standstill period, the temperature distribution within the thermal storage structure will nevertheless. This is undesirable, as it causes stress on the thermal storage elements 120 structure and makes it difficult to achieve an output flow with a desired temperature when discharging the storage.

(7) FIG. 2 shows a side-view of thermal energy storage 200 according to an embodiment of the present invention. The overall structure and function of the thermal energy storage 200 is similar to the thermal energy storage 100 discussed above. Accordingly, a repeated description of similar and identical elements is omitted, and only additional and different features specific to the thermal energy storage 200 are described in the following. The dividing elements 222 are provided to prevent a change in the temperature distribution within the thermal energy storage structure due to natural convection during the standstill period, i.e. that hot fluid surrounding thermal storage elements in the lower part of the housing 206 flows to the upper part of the housing 206.

(8) The thermal energy storage 200 comprises a convection reducing structure provided as a vertical layer of convection reducing elements 224 in front of the thermal energy storage structure in housing 206 on the side facing the fluid inlet 202. Furthermore, the thermal energy storage 200 also comprises a convection reducing structure provided as a vertical layer of convection reducing elements 228 behind the thermal energy storage structure in housing 206, i.e. on the side facing the fluid outlet 210.

(9) The convection reducing structures are arranged adjacent the thermal energy storage structure (respectively on the upstream and downstream side thereof) such that they prevent the problematic natural convection during standstill that was discussed above. In particular, the convection indicated by arrows 116 and 118 in FIG. 1 cannot occur (or is at least reduced to an insignificant amount) due to the convection reducing elements 224 and 228.

(10) The convection reducing elements 224 and 228 are made of the same or a similar bulk material as the thermal energy storage elements 220 but are preferably smaller than these. Where the average size of the thermal energy storage elements 220 may be about 2 cm to 3 cm, the average size of the convection reducing elements may be about 0.5 cm to 1 cm.

(11) The convection reducing elements 224 and 228 are kept in the desired positions (i.e. at the transition between the diffuser section 204 and the housing 206 respectively at the transition between the housing 206 and nozzle section 208) by perforated metal plates 230, 232. Furthermore, an opening (not shown) may be provided for adding convection reducing elements 224 and 228 as necessary after a certain time of operation in case the flow of working fluids through the convection reducing structures 224 and 228 blows away some of the convection reducing elements 224 and 228.

(12) The thermal energy storage 200 shown in FIG. 2 is capable of storing thermal energy for a long standstill period while maintaining a uniform temperature distribution within the structure. Thereby, an extended lifetime of the thermal energy storage elements 220 is achieved and a constant temperature of the output fluid from the storage can be provided.

(13) The thermal energy storage 200 may advantageously be used for temporarily storing excess energy at power production plants when production temporarily exceeds demand, e.g. in connected with a wind power plant which is susceptible to varying wind speeds and wind directions.

(14) It is noted that the term comprising does not exclude other elements or steps and the use of the articles a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It is further noted that reference signs in the claims are not to be construed as limiting the scope of the claims.