Element for a thermal energy storage

Abstract

An element for an easily scalable thermal energy storage, distinctive in that the element includes an outer shell being a combined casting form and reinforcement, a solid thermal storage medium in the form of hardened concrete, which concrete has been cast and hardened into said outer shell. A method for building and use of the element is also disclosed.

Claims

1. A method of building an element for a thermal energy storage, the method comprising: building an outer shell, with one open end and a closed opposite end, the outer shell comprising a steel wall and a closed steel shell bottom, both having a thickness of 0.1-1.0 mm, the outer shell being a combined casting form and ring reinforcement; arranging the outer shell in a vertical position, with the open end upwards and the closed end downwards; arranging a pipe heat exchanger in the form of an open end smaller diameter pipe section arranged inside a larger diameter closed end pipe section, coaxially inside the outer shell for heat input and output, with cross sectional area or a Reynold's number for flow in the inner pipe and between the inner and outer pipes being identical; filling thermal energy storage material in the form of grouting or concrete mixture up to a prescribed level at which the ends or connections of said heat exchanger extend up over the concrete or grouting of the element as standing vertical, wherein the outer shell functions as a combined casting form and reinforcement; and wherein the resulting hardened concrete solid continuous thermal storage medium completely fills a volume between the outer shell and the pipe heat exchanger and any spacers extending between and connecting the outer shell and the pipe heat exchanger, the volume extending from the closed outer shell bottom up to a prescribed level from where the pipe heat exchanger ends or connections extend up above the hardened concrete solid continuous thermal storage medium if seen with the element standing vertical, wherein said volume inside the outer shell consists of hardened concrete solid continuous thermal storage medium.

2. The method according to claim 1, wherein the outer shell is wound and formed into a circular cross-section shape from steel bands.

3. The thermal energy storage element, built according to the method of claim 1.

4. A method of building an element for a thermal energy storage, the method comprising: building an outer shell, with one open end and a closed opposite end, the outer shell comprising a steel wall and a closed steel bottom, both having a thickness of 0.1-1.0 mm, the outer shell being a combined casting form and ring reinforcement; arranging the outer shell in a vertical position, with the open end upwards and the closed end downwards; building and arranging two U-shaped pipe heat exchangers inside the outer shell, wherein each pipe heat exchanger is shaped as a U-shaped pipe section comprising a U-bend with two straight pipe leg sections, wherein each U-shaped pipe section is arranged as positioned in one plane with the U-bend in the plane, wherein the two U-shaped pipe sections are arranged in different, parallel planes, with the U-bends perpendicular to each other and with each straight part of the two U-shaped pipe sections into one quadrant different from the other straight parts with concrete or grouting between the straight parts, as seen in cross section of the elements, wherein each U-shaped pipe heat exchanger has an identical flow cross-sectional area along the full embedded length; filling thermal energy storage material in the form of grouting or concrete mixture up to a prescribed level at which the ends or connections of said U-shaped pipe heat exchangers extend up over the concrete or grouting of the element as standing vertical, wherein the outer shell functions as a combined casting form and reinforcement; and wherein the resulting hardened concrete solid continuous thermal storage medium completely fills a volume between the outer shell and the pipe heat exchangers and any spacers extending between and connecting the outer shell wall and the pipe heat exchangers, the volume extending from the closed outer shell bottom up to a prescribed level from where the pipe heat exchanger ends or connections extend up above the hardened concrete solid continuous thermal storage medium if seen with the element standing vertical, wherein said volume inside the outer shell consists of hardened concrete solid continuous thermal storage medium.

5. The method according to claim 4, wherein the outer shell is wound and formed into a circular cross-section shape from steel bands.

6. The method according to claim 4, wherein the U-shaped pipe heat exchangers are formed by bending individual pipes or joining sections of pipe of identical cross section area for flow.

7. The method according to claim 4, wherein the cross sectional area is identical along the full length of the embedded U-shaped pipe heat exchangers, implying an identical Reynold's number and thereby equal turbulence along the full embedded length of U-shaped pipe heat exchangers.

8. The method according to claim 4, wherein the U-shaped pipe heat exchangers are pipe heat exchangers, configured with diameter for turbulent flow at operating conditions.

9. The thermal energy storage element, built according to the method of claim 4.

Description

FIGURES

(1) The invention is illustrated by eight Figures, of which:

(2) FIG. 1 illustrates an element of the invention,

(3) FIG. 2 illustrates another embodiment of an element of the invention,

(4) FIG. 3 illustrates one possible way of performing the casting process of the invention,

(5) FIG. 4 illustrates a further embodiment of an element of the invention, and also a detail of a thermal storage of the invention comprising elements of the invention, and

(6) FIG. 5 illustrates an element of the invention with multiple rows of imbedded heat exchangers.

(7) FIG. 6 illustrates an embodiment of a thermally insulated housing,

(8) FIG. 7 illustrates an embodiment of a spiro pipe, and

(9) FIG. 8 illustrates an embodiment of a corrugated spiro pipe.

DETAILED DESCRIPTION

(10) Reference is made to FIG. 1, illustrating a double U-bend element 1 of the invention, in longitudinal section and cross section. The element 1 for a thermal storage comprises means for heat input and output 2, a solid thermal storage medium 3 inside an outer metal shell 4 being a combined casting form and ring reinforcement. The means for heat input is one or both of small diameter pipe heat exchangers 2 and an electric heating element 2E, and the means for heat output is said small diameter pipe heat exchangers 2. Arrows for heat transfer fluid (HTF) flow in or out are indicated, and the figure illustrates spacers 5, a (optional) steel hook 6 useful as a lifting lug, and a steel end cap 7. The double U-bend element is named so because two U-bends 5U are arranged in parallel but a distance apart in the concrete or grouting. Each small diameter pipe heat exchanger extends from over the concrete of the element, with upper ends extending over the concrete, to or close to the lower end of the element, where the U-bend connects two parallel straight sections. The bends 5U have been joined by welding or by other method to the straight thin pipe sections. Alternatively, a continuous thin pipe could have been bent into correct shape in a bending machine, such as an induction-bending machine, with several bends and several straight sections, with only the terminal ends extending up above the concrete. Optionally, one or more of the upper bends can extend above the concrete, to function as lifting lugs. Alternatively, two or more embedded U-bends in an element can be connected in series. The pipe diameter is sufficiently small to ensure turbulent flow, and the arrangement provide small heat conduction distance and large surface area, whilst still providing a relatively small, light element possible to lift and handle with simple cranes, which is considered a preferable embodiment.

(11) Reference is made to FIG. 2, where a pipe-in-pipe element of the invention is illustrated in longitudinal section and cross section. Similar or identical elements have the same reference numerical as in FIG. 1. The means for heat input and output is in this embodiment an inner pipe 2i arranged into an outer pipe 2o, which can be seen clearly in the Figure. The inner pipe 2i has an open lower end, when the element is standing vertical, such as during casting, and the inner pipe lower end has not been brought all the way down to the lower end of the outer pipe 2o. The lower end of the outer pipe is closed, either against the steel cap 4L in the lower end of the element or by a separate cap or lid 8. Similarly, the outer pipe is closed towards the inner pipe at the top 9. For this embodiment, inner spacers 5i and outer spacers 5o are provided, for holding the inner and outer pipe section during casting, respectively. The pipe-in-pipe embodiment is feasible where the thermally induced stress is extreme, such as at the terminal ends of stacks of elements in a large thermal storage comprising many elements connected in series. The flow cross sectional area of the inner pipe and the outer pipe with the inner pipe inserted, are similar or identical, or the Reynold's number of the inner pipe and outer pipe with the inner pipe inserted are similar or identical, providing turbulent flow, contrary to prior art solutions.

(12) FIG. 3 illustrates a method of the invention for building an element of the invention. More specifically, the casting step is illustrated, whereby the outer metal shell, into which the means for heat input and output have been arranged correctly (not illustrated specifically), is filled with grouting or concrete up to a prescribed level 3P (visible in Fig. Nos. 1 and 2) at which the ends or connections of said means extend up over the top of the element as standing vertical. Essential in this respect is using the outer shell as a combined casting form and ring reinforcement, so that no separate form is required and no additional reinforcement or armouring is required. Accordingly, the cost and work with separate casting forms and separate reinforcement are avoided, helping to simplify the method and reducing cost. Typical equipment for concrete mixing and delivery can be used, such as a dry mix silo 10, a compulsory concrete mixer 11 and concrete buckets 12 to be handled by a crane 13 for the casting operation. Alternative building site arrangements can be used, such as pumping the concrete mixture into the outer shells, or using a combined feeding and mixing device, such as a feeding and mixing screw or conveyor, or a conveyor belt. A typical element height, as standing vertical, is 4-12 m, a typical diameter is 0.20-0.35 m. A typical element weight is 0.4-2 metric tons. Scaling the storage up or down is simple, by adding or removing elements. Replacing damaged elements is simple by using a crane, facilitating maintenance. The elements can be cast directly as positioned in a storage of the invention.

(13) FIG. 4 illustrates a further embodiment of an element 1 of the invention, and a detail of a thermal storage of the invention comprising elements of the invention. More specifically, the element, illustrated in cross section C and longitudinal section L, has a flat rectangular like cross section shape, with half circle shaped short sides, as seen on the cross sectional view. Heat exchangers 2 have been cast in concrete 3 in the outer shell or lining 4 and thus imbedded. In a thermal storage of the invention, the elements can be arranged with vertical or horizontal orientation, or inclined orientation. A detail of a storage S of the invention, with staggered organisation of elements for improved heat transfer of a dynamic active heat transfer and storage fluid, is also illustrated.

(14) FIG. 5 illustrates an element 1 of the invention with multiple rows of imbedded head exchangers 2 into a rectangular like outer shell 4.

(15) FIG. 6 illustrates an example of a thermally insulated housing 20 that includes a layer of insulation 22. An arrangement of elements 1 is shown arranged within the thermally insulated housing 20.

(16) FIG. 7 illustrates a spiro pipe 30. In some embodiments, the element 1 discussed above may comprise the spiro pipe 30. The spiro pipe 30 is a wound pipe where metal bands 32 of steel or aluminium have been folded and/or fused together when the pipe was formed by winding. A bottom lid or cap or similar, is provided in the lower end. The strength of the shell, and hence the thickness thereof, must be sufficient to withstand the hydrostatic pressure when casting of the grout or concrete takes place. Alternatively, any pipe section being sufficiently strong at casting and operation can be used or the metal bands can be welded or joined in other ways. Electro welding the bands by arranging the bands with overlap between two compressing rotating electrodes is one example of an alternative feasible joining method. However, machines for winding Spiro type pipes or ventilation ducts are commercially available on the market from several vendors, such machines are useful for producing the outer shell of the elements of the invention.

(17) FIG. 8 illustrates a corrugated spiro pipe 34. In some embodiments, the element 1 discussed above may comprise the spiro pipe 34. The corrugated spiro pipe 34, similar to the spiro pipe 30, is a wound pipe where metal bands 36 of steel or aluminium have been folded and/or fused together when the pipe was formed by winding. The corrugated spiro pipe 34 is corrugated with regular corrugations 36 along a length of the corrugated spiro pipe 34.

(18) The element of the invention is designed for any operating temperature ranging from subzero to 1000 C. or more. Operating temperature is limited by material and fluid properties and adapted to the specific application of the TES; typically 200-550 C. for thermal storages connected to steam turbines or organic rankine cycles. However, if used for district heating, freezing storage or air conditioning purposes, the element temperature can be below freezing, e.g. 40 C., or below 100 C. Very low temperatures may require special fluid for circulation in the pipes for heat input and output. It is to be noted that the fluid inside the heat exchanger is not in direct contact with the concrete; this means that there will be no problem with using fluids under pressure or fluids with chemical composition that can be damaging for the concrete for heat transfer means.