ES2414310B1 - HOT HEAT-BASED THERMAL STORAGE MODULE WITH HIGH HEAT TRANSFER RATES - Google Patents

Abstract

Thermal storage module based on latent heat with high heat transfer rates. # Thermal storage module based on the heat transfer of a heat transfer fluid to a phase change material comprised in a channel delimited by spiral-shaped metal plates that form an internal element of the module. The heat transfer fluid is circulated through the channel outside the channel comprising the phase change material. The internal element has a conical spiral longitudinal section in the upper and lower parts. This means that once the fluid travels through the module from the top to the bottom, the condensate is at the bottom, automatically separating from the steam, which can be recirculated.

Description

Thermal storage module based on latent heat with high heat transfer rates

FIELD OF THE INVENTION

The present invention relates to an energy storage module in the form of latent heat, which is designed to obtain high rates of heat transfer between a two-phase heat transfer fluid and a storage medium that changes from solid phase to liquid phase, when There is no direct contact between them.

BACKGROUND OF THE INVENTION

Currently there are many industrial applications where it is required to take advantage of process heat and in which the use of storage systems that allow the use of heat at times after its generation is very common.

A clear example of the importance of thermal storage systems is in solar thermal plants (in English Concentrating Solar Power-CSP-Plants), which generate electricity from concentrated solar radiation. In them, the presence of a storage system allows them to be kept in operation also during the hours of absence of solar radiation.

In general, the storage systems of commercial CSP plants are based on sensible heat since the heat transfer fluid (in English, Heat Transfer Fluid or HTF) is a single-phase fluid.

However, in plants with direct steam generation (in English Direct Steam Generation or DSG) the heat transfer fluid is a biphasic fluid, whose thermal potential is acquired mainly through evaporation. Therefore, to store and later recover this potential efficiently, it is advisable to use a substance that changes phase (Phase Change Material or PCM).

In order to develop a thermal storage system based on latent heat it is essential that the PCM used is well suited to the working conditions of HTF, especially in terms of temperature. In addition, it is desirable that it presents a good behavior from the point of view of heat transfer and thermal storage under such working conditions, which are safe, durable after thermal and economic cycling.

In a DSG plant the working temperature range (i. E. Steam / water saturation temperature of 210º C310º C) is determined by the pressure range in which the turbine and the hydraulic circuit can operate (i.

and. 20 bar-100 bar)

The solid-liquid phase change temperature of a large number of anhydrous salts and eutectic mixtures is within this range, in addition, in general, they all have a low cost, so they can be good candidates for storage systems. But, its main drawback is the low thermal conductivity (less than 1W / mK), which greatly limits the power of the storage system.

For this reason, the development of a thermal storage system based on this type of phase change materials must focus on concepts that allow compensating for the limitation imposed by its low conductivity on heat transfer rates.

From this perspective, there are two main lines of action: either on the PCM itself trying to improve its intrinsic thermal conductivity, or on the design of the thermal storage system trying to maximize the effective area of heat transfer between HTF and PCM .

US Patent 2933885 describes a thermal storage system based on latent heat where the module is composed of a PCM container and a set of tubes embedded therein placed either vertically or in the form of downward spirals through which a heat transfer fluid circulates biphasic

Also, in the article published in Applied Thermal Engineering, 30 (2010) p. 2643-2651, a latent heat storage module consisting of horizontal tubes is described, through which a biphasic heat transfer fluid circulates, and a mass of PCM (eutectic mixture NaNO3 / KNO3). In it, the thermal conductivity is improved by graphite fins attached to the tubes.

In both cases, during charging, the HTF is circulated through the tubes from the top of the module to the bottom, so that, during its course, most of the HTF condenses by transferring energy in the form of latent heat to the PCM With these configurations of tubes embedded in the PCM both the condensed and non-condensed HTF are forced to flow in the same direction, so that at the exit of said modules there is still a two-phase fluid. These types of fluids should not be recirculated as they could damage the circuit pumps due to cavitation phenomena. On the other hand, the vapor in suspension within the condensate at the exit of such modules cannot be reused, so its thermal potential is wasted. That's why these modules

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Thermal storage that cannot separate the condensed HTF from the non-condensed, require an additional separation system.

OBJECT OF THE INVENTION

The invention aims to alleviate the technical problems mentioned in the previous section. To do this, it proposes a thermal storage module comprising a substantially cylindrical container with a longitudinal axis, upper and lower lids at its ends, at least three inlet and outlet holes located in the lids and in the container body, a material of phase change and an internal element surrounded by said container. The internal element is formed by two spiral-shaped plates that together with the container delimit an outer channel and an inner channel and where said element, at its upper and lower ends, has a conical spiral geometry, the phase change material being found In the inner channel. Preferably, the module further comprises an interconnection piece provided with an opening adapted to cooperate with the internal element so that the phase change material does not invade the lower cover and the outer channel can pass through said piece. The lower cover will preferably be conical, that is, in the same way as the piece. PCM is one or a eutectic mixture of the following compounds: nitrites, nitrates, chlorites, chlorates, fluorites, fluorates, hydroxides

or alkali metal carbonates. Preferably, the module comprises an insulating layer between the container and the outer channel and in the spaces between the upper and lower covers and the internal element. An additional plate can also be provided attached to the upper end of the internal element that extends the internal channel vertically to the upper cover and supports within the internal channel perpendicular to the internal element plates.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the features of the invention in accordance with a preferred example of practical realization thereof, the following description of a set of drawings is attached, where the following has been represented by way of illustration:

Figure 1: shows an external front view of the module.

Figure 2: is a top view of the container.

Figure 3: is a cross section of the container along line I.

Figure 4: shows a cross section along line II.

Figure 5: It is an external front view of the internal element that forms a double spiral channel.

Figure 6: shows a mid-section cross section of the double spiral channel.

Figure 7: It is a longitudinal section of the thermal storage module through the center.

Figure 8: shows a cross section of the thermal storage module along line III.

Figure 9: Detailed view of the scratched areas at the top and bottom of the module of Figure 7.

Figure 10: shows the double unwound spiral channel and the positions of the structural supports.

DETAILED DESCRIPTION OF THE INVENTION

The thermal storage module is designed so that, during the charging process, the latent heat from the condensation of HTF is stored by the PCM in the form of latent heat of fusion and, during the discharge process, the latent heat of solidification released by the PCM is absorbed by the HTF in the form of latent heat of vaporization.

The thermal storage module (figure 1) is formed by a container 1, an upper lid 2, a lower lid 3, an internal element 4 (figure 5) formed by two spiral-shaped plates that delimit an outer channel 5 and a channel interior 6 and, finally, an interconnection piece 7 (figure 4) provided with a spiral opening 8.

The outer channel 5, through which the HTF circulates, is completely closed at its upper and lower ends, as shown in Figure 9, forming a cavity with conical spiral geometry, both at the top and bottom, to favor the drain of the condensed flow and the suction of the non-condensed fluid during the loading and the discharge of the steam flow generated during the discharge. In this way, the HTF is in indirect contact with the PCM (which is in the inner channel 6) always in the best possible conditions from the point of view of heat transfer.

The loading and unloading process, once the module of the invention comes into operation, is as follows: under load, a certain saturated steam flow (heat transfer fluid) is injected into the thermal storage module whose saturation temperature should be slightly higher than the PCM melting temperature; in

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discharge, a certain flow of saturated liquid is injected whose saturation temperature must be slightly lower than the solidification temperature of the PCM.

In this way, the saturated steam that feeds the thermal storage module during charging condenses by giving latent heat to the PCM which, from solid to liquid state, stores energy in the form of latent heat of fusion. On the other hand, during the discharge, the heat transfer fluid, now in the form of a saturated liquid, evaporates, absorbing the latent heat that the PCM gives it when it passes from a liquid state to a solid state. It is therefore a module that works both ways.

Figure 1 shows the positions of the inlet and outlet ducts of the storage module 9, 10, 11. During the module loading process, the heat transfer fluid (saturated steam) is injected into the interior through the duct 9 and the condensed flow resulting from the heat transfer of this saturated steam to the PCM exits through the lower duct 10. The upper duct 11 acts as an outlet for the uncondensed steam flow during this process, giving the thermal storage module the character of separator between steam and condensate.

During the module discharge process, the heat transfer fluid (saturated liquid) is injected into the interior through 10 and the steam flow resulting from the heat transfer of the PCM to this heat transfer fluid exits through 11 while keeping 9 closed .

The internal element 4 must be accessible from the top and from the bottom to facilitate its assembly and future maintenance, hence the upper and lower covers 3 are preferably flanged.

Figure 3 indicates, in an indicative way, the way in which the thermal insulation 12 should be placed inside the module to minimize lateral thermal losses. Its asymmetric shape is due to the need to adapt it to the development of element 4 and to thermally reinforce the wall 13. On the other hand, in figure 7, it is shown how thermal insulation 12 also fills the upper dead spaces 13 and lower 14 to prevent thermal losses to the outside in these areas and to buffer thermal bridges that may exist in the lower part of the storage module. Likewise, the contours of 9, 10 and 11 must be adequately coated with thermal insulation 12 since they are crucial points from the point of view of heat losses.

Figure 4 represents a cross-section along the line II of Figure 1 of the interconnection piece 7 which is located between the lower cover 3 and the container 1. In this interconnection part 7 a spiral opening has been made 8, to allow the internal element 4 of Figure 5 to pass through it. The internal element 4 and the interconnection piece 7 must be welded so that the inner channel 6 is closed at its bottom.

Figure 5 shows the asymmetry of the internal element 4 with respect to the main vertical axis. Because the internal element 4 is asymmetric with respect to the main axis, the inlet holes 10 and 11 are not in the exact center of the container.

Figure 5 also shows the channels 5 and 6 of the internal element 4 before being placed inside the container 1 and being welded to the part 7. In this case the channels 5 and 6 form two equally spaced spirals, but these They could also have configurations with variable spacing.

The outer channel 5, through which the HTF circulates, is closed at its upper and lower ends, which have a conical spiral shape. In this way, both the drainage of the resulting condensate flow in the load and the suction of the resulting steam flow in the discharge is favored. Thus, the closed channel 5 performs, during the loading process, the separator mission.

The inner channel 6, which houses the PCM 16, is closed in its lower part by the interconnection piece 7 which is welded to the internal element 4. This channel is delimited laterally by the plate that forms it, the outer channel plate 5 and by an additional plate 15 welded vertically to the latter, as shown in the figure

9. The internal channel height 6 must be such that it allows the volume changes of the PCM during thermal cycling and, in turn, prevents the dilated PCM from overflowing.

It is important to note that the maximum height of the inner channel 6 is a design parameter of the module

thermal storage that will depend on the value "e", the diameter "D" and the height "H", as well as the type of PCM

employee. Examples of PCM materials that can be used to fill the inner channel 9 are: nitrites, nitrates, chlorites, chlorates, fluorites, fluorates, hydroxides or carbonates of alkali metals as well as eutectic mixtures thereof.

It is important to mention that the internal element 4, preferably, must not be welded to the upper lid 2 of the container to allow free thermal expansion thereof and thus avoid possible torsion problems.

Figures 7 and 8 show the arrangement of the phase 16 change material inside the thermal storage module, noting how it occupies the interior of the inner channel 6, which is closed at the lower end thanks to the interconnection piece 7 of Figure 4. This optimizes the amount of PCM

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therefore, the condensed fluid accumulates in the area between the interconnection part 7 and the lower cover 3.

The height that the PCM reaches in the thermal storage module before its expansion (ie in solid state) must coincide with the position of 9, that is, with the height at which saturated steam is injected in charge (as is 5 indicated in figure 7).

Figure 8 also shows that PCM 16 is always surrounded by heat transfer fluid 17, except in dead spaces 13, where thermal insulation 12 is reinforced. In turn, the channel through which the heat transfer fluid, 5, will always be surrounded by thermal insulation 12 that is necessary to prevent thermal losses to the outside. In figure 9 the insulator 12 introduced in the spaces can be observed in more detail

10 13 and 14.

To avoid structural damage to the inner channel 6 when the working pressures of the heat transfer fluid are raised, optionally, the inlet 9 of the heat transfer fluid 17 can be tangential to the lateral surface of the container 1 instead of perpendicular as indicated in the figures.

For this reason they can also be placed inside the inner spiral channel 6 that contains the PCM 16, true

15 number of supports 18 welded perpendicularly to the surface of the channel as shown by way of example in Figure 10, with a length equal to the equalizing "e" and of the same material as element 4. The calculation of the number of supports per unit of area and the thickness of the same should be done depending on the working conditions of the heat transfer fluid, the nature of the PCM and the type of structural material of element 4.

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Claims (9)

one.

 Thermal storage module comprising a substantially cylindrical container (1) with a longitudinal axis, upper (2) and lower (3) caps at its ends, at least three inlet and outlet holes (9, 10, 11) located in the lids and in the body of the container and a phase change material (PCM), characterized in that it further comprises an internal element (4) surrounded by said container (1), where the internal element (4) is formed by two shaped plates of spiral which together with the container (1) delimit an outer channel (5) and an inner channel (6) and where said element, at its upper and lower ends, has a conical spiral geometry, the phase change material being found in the inner channel (6).

2.

 Module according to claim 1 characterized in that it further comprises an interconnection piece (7) provided with an opening (8) adapted to cooperate with the internal element (4) so that the phase change material does not invade the lower cover (3) and the outer channel can pass through said piece (7).

3.

 Module according to claims 1 or 2 characterized in that the lower cover (3) is conical.

Four.

 Module according to any of the preceding claims, characterized in that the PCM is one or a eutectic mixture of the following compounds: nitrites, nitrates, chlorites, chlorates, fluorites, fluorates, hydroxides or carbonates of alkali metals.

5.

 Module according to any of the preceding claims characterized in that it comprises an insulating layer

(12) between the container (1) and the outer channel (5).

6.

Module according to any of the preceding claims characterized in that the spaces (13, 14) between the upper and lower covers and the internal element (4) are provided with a thermal insulator (12).

7.

 Module according to any of the preceding claims characterized in that it is provided with an additional plate (15) attached to the upper end of the internal element (4) that extends the internal channel (6) vertically to the upper cover (2).

8.

 Module according to any of the preceding claims characterized in that it comprises supports (18) within the inner channel (6) perpendicular to the plates of the internal element (4).

SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201131378 SPAIN Date of submission of the application: 11.08.2011 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: F28D20 / 00 (2006.01) F28D20 / 02 (2006.01) RELEVANT DOCUMENTS

Category

56 Documents cited Claims Affected

Y

EP 1431694 A1 (HONDA MOTOR CO LTD) 06/23/2004, page 13, column 23, line 34 - 1-8

page 43, column 83, line 32; Figures 1, 2, 5-9, 16-27.

Y

US 3303877 A (TORSTEN RAMEN) 02/14/1967, column 1, line 11-column 2, line 40; 1-8

Figure 1.

TO

EP 1426720 A1 (HONDA MOTOR CO LTD) 06/09/2004, page 4, column 5, line 15 -page 7, 1-8

column 12, line 2; Figures 1-8, 12.

TO

US 2004 194908 A1 (TOMOHIDE KUDO) 07/10/2004, column 4, line 53 - column 9, 1-8

line29; Figures 1-10.

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 05.06.2013

Examiner O. Fernández Iglesias Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201131378 Minimum documentation sought (classification system followed by classification symbols) F28D Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201131378 Date of Written Opinion: 05.06.2013 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 1-8 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-8 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201131378  1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

EP 1431694 A1 (HONDA MOTOR CO LTD) 06-23.2004

D02

US 3303877 A (TORSTEN RAMEN) 02/14/1967

D03

EP 1426720 A1 (HONDA MOTOR CO LTD) 06.09.2004

D04

US 2004194908 A1 (TOMOHIDE KUDO) 07.10.2004

 2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The invention consists of a thermal storage module comprising a cylindrical container with upper and lower lids, at least three inlet and outlet holes located in the lids and the body, and a phase change material (called PCM). This module also has an internal element surrounded by the container, said internal element is formed by two spiral-shaped plates that together with the container delimit two channels, one internal and one external; the internal element at its upper and lower ends has a conical spiral geometry, the phase change material being in the inner channel. Document D01, to which the following reference numerals belong, is considered the state of the art closest to the invention, as set forth in claim 1 of the application. This document discloses a thermal storage module (1011) comprising a cylindrical container (1016) with upper (1013) and lower (1014) lids, at least three inlet holes (2124, 2126, 2128) located in the lids and in the body, and a phase change material (called PCM) (4029, 5026). This module also has an internal element (1025, 1026, 1027) surrounded by the container (1016), said internal element (1025, 1026, 1027) is formed by two plates (1025, 1027) that together with the container (1016) They delimit two channels, one internal (1021) and the other external (1020), the phase change material (4029, 5026) being in the inner channel (1021). (See document D01 page 13, column 23, line 34 -page 43, column 83, line 32; figures 1, 2, 5-9, 16-27). Document D01 differs from the technical object of claim 1 of the application in that the internal element does not have a conical spiral geometry at its upper and lower ends. This difference, however, is already mentioned in document D02. This document discloses a heat exchanger provided with cone-shaped elements (1) that assembled create conical spiral geometry ducts (20), through these ducts run the liquids that carry out the heat exchange without coming into contact direct (see document D02 column 1, line 11 - column 2, line 40; figure 1). Therefore, it is obvious to one skilled in the art to apply these characteristics with their corresponding effect to document D01, so that the module of the invention is obtained. Consequently, claim 1 of the application lacks inventive activity in view of what is disclosed in documents D01 and D02. This is in accordance with the provisions of article 8.1 of Law 11/86. The characteristics disclosed by dependent claims 2-5 and 7 are set out in documents D01 and D02. Dependent claim 6, which specifies the presence of insulating material between the upper and lower covers and the inner element, is considered an alternative to the arrangement of the insulation described in documents D01 and D02, while the detail disclosed in dependent claim 8 It is considered common knowledge in the state of the art as can be seen in documents D03 and D04. Therefore it is considered that claims 2-8 lack inventive activity in accordance with the provisions of article 8.1 of Law 11/86. State of the Art Report Page 4/4