HEAT STORAGE DEVICE FOR SENSIBLE HEAT STORAGE IN MOLTEN SALTS

Abstract

A heat accumulator device for accumulating sensible heat in molten salts, including: -a heat accumulator vessel for receiving molten salt, a separating layer being disposed in the heat accumulator vessel in order to separate a cold region, in which cold molten salt is present, from a hot region, in which hot molten salt is present, and the cold region being located below the hot region; - a device for loading and unloading the heat accumulator vessel, which device is connected to the cold region and to the hot region; and - a volume compensation device for compensating a temperature-related change in the volume of the molten salt, the volume compensation device interacting with the cold region and/or with the separating layer.

Claims

1-19. (canceled)

20. A heat storage device for sensible heat storage in molten salts comprising a heat storage reservoir for receiving molten salt, wherein a separating layer is arranged in the heat storage reservoir for separating a cold region, in which cold molten salt is arranged, and a hot region, in which hot molten salt is arranged, wherein the cold region is arranged below the hot region, comprising a device for charging and discharging the heat storage reservoir, which is connected to the cold region and the hot region, and comprising a volume compensation device for compensating for a temperature-related volume change of the molten salt, wherein the volume compensation device cooperates with the cold region and/or the separating region.

21. The heat storage device according to claim 20, wherein the volume compensation device comprises a compensation reservoir, wherein the compensation reservoir is connected to the cold region and/or the separating region, and wherein a compensation fluid is disposed in the compensation reservoir and cooperates with the cold region and/or the separating layer for volume compensation.

22. The heat storage device according to claim 21, wherein the compensation fluid can be introduced into the cold region and/or the separating layer for volume compensation.

23. The heat storage device according to claim 22, wherein the compensation fluid is cold molten salt.

24. The heat storage device according to claim 23, wherein the compensation reservoir is arranged above the heat storage reservoir and is connected to the cold region via a riser.

25. The heat storage device according to claim 23, wherein the device for charging and discharging the heat storage reservoir is connected to the cold region via the compensation reservoir.

26. The heat storage device according to claim 25, wherein the device for charging and discharging the heat storage reservoir has a discharge pump connected to the hot region or arranged in the hot region and a charge pump connected to the compensation reservoir or arranged in the compensation reservoir.

27. The heat storage device according to claim 22, wherein the compensation fluid is a gas.

28. The heat storage device according to claim 27, wherein a gas retention device is arranged in the heat storage reservoir, which retains the gas in a predetermined section in the heat storage reservoir after it has been introduced into the cold region or into the separating layer.

29. The heat storage device according to claim 27, wherein a gas retention device is formed as a plate having a side edge projecting downwardly, wherein a diffuser is arranged at the edge region of the gas retention device to stabilize the stratification in the molten salt.

30. The heat storage device according to claim 27, wherein the compensation reservoir has a connection to the atmosphere, wherein the gas can be transferred to the atmosphere in the event of temperature-related expansion of the molten salt.

31. The heat storage device according to claim 27, wherein a volume changing device is arranged on the compensation reservoir for changing the volume of the gas.

32. The heat storage device according to claim 31, wherein the volume changing device has a heating element and/or a cooling device, wherein the temperature of the gas can be changed by means of the heating element and/or the cooling device to change the volume.

33. The heat storage device according to claim 31, wherein the volume changing device has a thermal energy storage on the compensation reservoir by means of which the gas can be heated of cooled.

34. The heat storage device according to claim 31, wherein the volume changing device has a device for mechanical volume change of the gas.

35. The heat storage device according to claim 27, wherein the compensation reservoir has a variable volume.

36. The heat storage device according to claim 35, wherein the compensation reservoir has an elastic, movable or flexible wall or an elastic, movable or flexible wall section.

37. The heat storage device according to claim 20, wherein the volume compensation device has a compensation chamber in the cold region with a variable volume, wherein the compensation fluid can be introduced into the compensation chamber.

38. The heat storage device according to claim 20, wherein the heat storage reservoir has a movable wall or a movable wall section.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0044] In the following, the invention is described in more detail with reference to the following figures. In the drawings:

[0045] FIG. 1 is a schematic sectional view of a heat storage device according to the invention,

[0046] FIG. 2a shows the heat storage device of FIG. 1 in the charged state,

[0047] FIG. 2b shows the heat storage device of FIG. 1 in the discharged state,

[0048] FIG. 3 is a schematic view of a second exemplary embodiment of the heat storage device according to the invention,

[0049] FIG. 4a is a schematic view of the third exemplary embodiment of a heat storage device according to the invention in a charged state,

[0050] FIG. 4b is a schematic view of the third exemplary embodiment of a heat storage device according to the invention in a discharged state,

[0051] FIG. 5a is a schematic view of the volume compensation device of the exemplary embodiment of the FIG. 4a.

[0052] FIG. 5b is a schematic view of the volume compensation device of the exemplary embodiment of the FIG. 4a.

[0053] FIG. 5c is a schematic view of the volume compensation device of the exemplary embodiment of the FIG. 4a.

[0054] FIG. 6a is a schematic view of the volume compensation device of the exemplary embodiment of the FIG. 4b.

[0055] FIG. 6b is a schematic view of the volume compensation device of the exemplary embodiment of the FIG. 4b.

DETAILED DESCRIPTION

[0056] In FIG. 1, a heat storage device 1 according to the invention in schematically shown in a sectional view. Since only the principle of the heat storage device 1 according to the invention is to be illustrated initially on the basis of FIG. 1, some partial areas of the heat storage device 1 according to the invention have not been illustrated.

[0057] The heat storage device 1 has a heat storage reservoir 3 formed as a tank, for example. The heat storage device 1 according to the invention serves for heat storage of sensible heat in molten salts and can be used, for example, for heat storage of thermal energy of a solar power plant.

[0058] The heat storage reservoir 3 of the heat storage device 1 according to the invention is designed as a so-called single-tank system, in which three different temperature layers of the molten salt located in the reservoir are present in the heat storage reservoir 3. Said tank is a tank according to the so-called thermocline principle.

[0059] For example, the heat storage reservoir 3 is a flat-bottom tank and surrounded by an insulating layer 5.

[0060] In the heat storage reservoir 3, the molten salt forms a so-called hot region 7, in which hot molten salt 9 is arranged, and a cold region 11, in which cold molten salt 13 is arranged. Hot molten salt is understood to be molten salt up to approx. 620° C. Cold molten salt is in the range of 300° C. Both the hot and cold molten salt are always liquid. The cold region 11 is arranged below the hot region 7. The hot region 7 is separated from the cold region 11 by a separating layer 15, wherein the separating layer 15 can be formed as a natural separating layer, i.e. also of molten salt. The separation layer 15 may also have appropriate fittings, such as a floating separating plate.

[0061] In the exemplary embodiment shown in FIG. 1, a thin gas layer 17 is formed above the hot region 7. In principle, however, the aim is to operate the heat storage device 1 according to the invention in such a way that the heat storage reservoir 3 is completely or almost completely filled with molten salt.

[0062] A non-illustrated device for charging and discharging the heat storage reservoir 3 removes hot molten salt 9 from the hot region 7 for discharging, with cooled cold molten salt 13 being introduced into the cold region 11. When charging the heat storage device 1 according to the invention, cold molten salt 13 is removed from the cold region 11 and introduced into the hot region 7 after heating. During charging and discharging, the separating layer 15 thus moves up and down accordingly in the heat storage reservoir 3.

[0063] Since hot molten salt 9 has a low density and thus a larger volume than the cold molten salt 13, it is necessary to compensate for the volume in the heat storage reservoir 3 in order to keep the thin gas layer 17 as constant as possible or to keep the heat storage reservoir 3 completely filled with molten salt.

[0064] Therefore, the heat storage device 1 according to the invention comprises a volume compensation device 19. The volume compensation device 19 has a compensation reservoir 21 which is connected to the cold region 11 in the illustrated state. A compensation fluid is arranged in the compensation reservoir 21, said compensation fluid cooperating with the cold molten salt 13 in the cold region 11 for volume compensation. In the exemplary embodiments illustrated in FIGS. 1-3, the compensation fluid is cold molten salt.

[0065] In FIGS. 2a and 2b, the function of the heat storage device 1 according to the invention as shown in FIG. 1 can be explained in more detail based on the charged state (FIG. 2a) and the discharged state (FIG. 2b).

[0066] In FIG. 2a, the heat storage reservoir 3 is shown in the charged state so that the heat storage reservoir 3 is almost completely filled with hot molten salt 9. Thus, the hot region 7 occupies the largest part of the heat storage reservoir 3. The cold region 11 is only present as a thin lower layer or has been completely removed from the heat storage reservoir 3. Since the hot molten salt 9 in the heat storage device 1 according to the invention has a low density compared to the cold molten salt 13, a larger volume is required for the hot molten salt 9. Thus, the compensation fluid in the form of cold molten salt is forced into the compensation reservoir 21 of the volume compensation device 19. After discharging the heat storage device 1 according to the invention (FIG. 2b), a large part of the heat storage reservoir 3 is filled with cold molten salt 13, so that the cold area 11 accordingly occupies a large proportion in the heat storage reservoir 3. Only a thin layer of hot molten salt 9 is arranged above the cold region 11, so that a correspondingly thin section forms the hot region 7.

[0067] Since the cold molten salt 13 has a greater density than the hot molten salt 9, the cold molten salt 13 occupies a smaller volume in the heat storage reservoir 3, so that the heat storage reservoir 3 would not be completely filled, wherein the supply of cold molten salt by the volume compensation device compensates for the missing volume. Accordingly, the compensation reservoir is largely empty.

[0068] As can be seen from FIGS. 2a and 2b, any thin gas layer 17 present in the heat storage reservoir 3 is always in contact with the hot region 7, so that the gas layer 17 has a constant temperature substantially equal to the temperature of the hot molten salt 9. As a result, there is no temperature-related change in the volume of the gas layer 17 during either charging or discharging of the heat storage device 1. Furthermore, the heat storage device 1 according to the invention is designed as a substantially closed system, so that at least the area in which the hot molten salt 9 is arranged is closed off from the atmosphere in order to reduce or prevent decomposition and outgassing of the hot molten salt 9.

[0069] In FIG. 3, a heat storage device 1 according to the invention is schematically shown in a second embodiment. The heat storage device 1 according to the invention is constructed similarly to the heat storage device 1 shown in FIG. 1. The essential difference to the heat storage device 1 shown in FIG. 1 is that the compensation reservoir 21 of the volume compensation device 19 is arranged above the heat storage reservoir 3. In this case, the compensation reservoir 21 is formed as a basin so that there is a connection to the atmosphere. The compensation reservoir 21 is connected to the cold region 11 via a riser 23. In FIG. 3, the device for charging and discharging the heat storage reservoir 3 is also illustrated. The device for charging and discharging the heat storage reservoir 3 has a discharge pump 25 arranged in the hot region 7. Moreover, the device for charging and discharging the heat storage reservoir 3 has a charging pump 27 arranged in the compensation reservoir 21. The compensation reservoir 21 is thus arranged in the circuit for charging the heat storage device 1. When fully charged, the cold region 11 can also be fully pressed into the compensation reservoir 21 so that the riser 23 is then connected to the separating layer 15 in the charged state.

[0070] The riser 23 is connected to the compensation reservoir 21 via a valve 28. In the discharging process, hot molten salt 9 is supplied to a discharging process 110 by means of the discharge pump 25. The cold molten salt cooled by the discharging process is supplied to the compensation reservoir 21 and, when the valve 28 is open, passes through the riser 23 into the cold region 11 due to the atmospheric pressure acting on the cold molten salt in the compensation reservoir 21.

[0071] When charging the heat storage device 1 according to the invention, the cold molten salt from the compensation reservoir 21 is supplied by means of the charge pump 27 to a charging process 120, which can be carried out by a solar thermal power plant, for example. The heated molten salt is supplied to the hot region 7. The hot molten salt 9 in the hot region 7 presses down the separating layer 15 so that cold molten salt 13 from the cold region 11 is forced through the riser 23 into the compensation reservoir 21 with the valve 28 open.

[0072] The embodiment shown in FIG. 3 has the particular advantage that the discharge pump 25 and the charge pump 27 can be designed cost-effectively, since they require only a very short pump connection.

[0073] As shown in FIG. 3, another reservoir 29 can be arranged next to the heat storage reservoir 3. Said further reservoir can be connected to an overflow 31 of the compensation reservoir 21 so that excess cold molten salt can pass through the overflow 31 into the further reservoir 29. This allows the compensation reservoir 21 to be designed with a relatively small volume. In the discharging process, cold molten salt can be pumped into the compensation reservoir 21 by means of an additional pump 33.

[0074] The further reservoir 29 can have a size adapted to the heat storage reservoir 3 so that the further reservoir 29 can also be used for emptying the heat storage reservoir 3 for inspection or repair purposes. For this purpose, a drain pump 35 is provided in the heat storage reservoir 3, which is connected to the compensation reservoir 21 via a return line.

[0075] In FIGS. 4a and 4b, a third exemplary embodiment of the heat storage device 1 according to the invention is shown schematically in a sectional view, with FIG. 4a illustrating a charged state and FIG. 4b a discharged state. FIGS. 4a and 4b are comparable to FIGS. 2a and 2b.

[0076] The substantial difference between the third exemplary embodiment show in FIGS. 4a and 4b and the first exemplary embodiment shown in FIGS. 2a and 2b of the heat storage device 1 according to the invention is the type of compensation fluid. While cold molten salt is used as compensation fluid in FIGS. 2a and 2b, a gas is used as compensation fluid in the third exemplary embodiment shown in FIGS. 4a and 4b. A gas is thus disposed in the compensation reservoir 21, which gas the volume compensation device 19 can introduce into the heat storage reservoir 3 for volume compensation. Furthermore, a gas retention device 37 is arranged in the heat storage reservoir 3, which may be designed as a plate with a beveled edge. As can be seen from FIG. 4b, the gas 39 introduced into the heat storage reservoir 3 for volume compensation is held in a predetermined section in the separating layer 15 by the gas retention device 37. The use of gas as a compensation fluid has the advantage that the gas is significantly cheaper than the solar salt used for molten salt. Since the compensation fluid in the form of molten salt cannot be used for heat storage, the use of molten salt as a compensation fluid has a cost disadvantage.

[0077] As can be seen from FIGS. 4a and 4b, the cold molten salt 13 in the charged state can also enter the section where the gas 39 is disposed in the discharged state by forcing the cold molten salt 13 under the gas retention device 37. In order to reliably ensure that the gas 39 is introduced into and discharged from the heat storage reservoir 3, a supply line 21a, which connects the compensation reservoir 21 to the cold region 11 or the separating layer 15, respectively, is arranged directly below the gas retention device 37.

[0078] As can be seen from FIG. 4a, the separating layer 15, which in the exemplary embodiment shown in FIGS. 4a and 4b is formed as a natural separating layer by molten salt, is pressed under the gas retention device 37. To avoid mixing of the layers during this process, it may be provided that additional fittings are provided on the gas retention device 37 to stabilize the stratification, such as a diffuser 38. The diffuser 38 ensures that stratification can build up below the gas retention device 37 and that there is no exergetically unfavorable mixing.

[0079] As part of the discharging process of the heat storage device 1 according to the invention, the gas 39 must be introduced from the compensation reservoir 21 into the heat storage reservoir 3. For this purpose, it is necessary that a pressure is generated in the compensation reservoir 21 which forces the gas 39 into the heat storage reservoir 3, since the gas below the gas retention device 37 is subject to hydrostatic pressure due to the liquid salt column above it.

[0080] FIG. 5a-6 show different examples of devices of the volume compensation device 19, by means of which a corresponding pressure for the gas can be adjusted.

[0081] FIGS. 5a and 5b show a so-called semi-open system. The gas transferred from the heat storage reservoir 3 through the conduit 21a into the compensation reservoir 21 can be discharged to the atmosphere by means of an outlet valve 21b. In the exemplary embodiment shown in FIG. 5a, the outlet valve 21b is designed as a pressure relief valve. In the exemplary embodiment shown in FIG. 5b, the outlet valve 21b is designed as a control valve.

[0082] When the gas is introduced into the heat storage reservoir 3 as part of the discharging process of the heat storage device 1 according to the invention, gas is supplied to the compensation reservoir 21 by means of an inlet valve 21c. In the exemplary embodiment shown in FIG. 5a, the inlet valve 21c is designed as a vacuum valve. In the exemplary embodiment shown in FIG. 5b, the inlet valve 21c is illustrated as a control valve. In the exemplary embodiment shown in FIG. 5b, the controllable outlet valve 21b and the controllable inlet valve 21c are controlled by a controller 21d.

[0083] In the exemplary embodiment shown in FIGS. 5c and 5d, the pressure for the gas in the compensation reservoir 21 is thermally generated by causing a change in density and thus a change in volume of the gas by heating or cooling the gas.

[0084] In the exemplary embodiment shown in FIG. 5c, the gas can be transferred from the compensation reservoir 21 by means of a blower 22 into a regeneration storage 41, in which the gas is heated or cooled, thereby causing a change in density and volume of the gas.

[0085] In the exemplary embodiment shown in FIG. 5d, the gas from the compensation reservoir 21 can be supplied by means of a blower 22 to a heating device 43 and a cooling device 44, thereby causing a corresponding change in temperature and thus a change in density and volume of the gas.

[0086] In addition to thermal pressure generation for introducing the gas into the heat storage reservoir 3, mechanical pressure generation is also possible.

[0087] FIG. 6a shows an exemplary embodiment in which the volume compensation device has a second compensation reservoir 21e in addition to the compensation reservoir 21, wherein gas at increased pressure can be transferred into the second compensation reservoir 21e by means of a compressor 24. A control valve 24a allows the compressed gas from the second compensation reservoir 21e to be transferred at an increased pressure into the line 21a and thus into the heat storage reservoir 3.

[0088] In FIG. 6b, a volume change occurs in a mechanical way, while the gas pressure remains constant. The compensation reservoir 21 has a flexible wall 21f that can be moved by a drive device 45, which allows the volume in the compensation reservoir 21 to be changed. When gas is to be introduced into the heat storage reservoir 3, the drive device 45 presses the flexible wall 21f into the compensation reservoir 21 so that the volume of the compensation reservoir 21 is reduced and the gas is forced from the compensation reservoir 21 through the conduit 21a into the heat storage reservoir 3. Conversely, the flexible wall 21f can also be pulled out of the compensation reservoir 21 by the drive device 45 so that the volume of the compensation reservoir 21 is increased. Since the gas is forced out of the heat storage reservoir 3 when the heat storage device 1 according to the invention is charged, little or no effort is required for moving the flexible wall 21f to increase the volume of the compensation reservoir 21. Therefore, instead of the drive device 45, a spring device may also be provided, for example, which is compressed when gas is introduced into the compensation reservoir 21 and the flexible wall 21f is correspondingly deformed, and which compresses the flexible wall 21f accordingly to introduce the gas into the heat storage reservoir 3. The flexible wall 21f can be in the form of a bellows.

[0089] The heat storage device 1 according to the invention has the particular advantage that there is no or only a small volume of gas above the hot molten salt 9, so that the tendency of the salt to decompose is reduced and only slight or no outgassing occurs or increased operating temperatures are made possible, respectively. In this regard, the heat storage reservoir 3 of the heat storage device 1 according to the invention can be operated with an internal pressure that has a difference of less than 500 mbar with respect to the atmosphere, so that the heat storage reservoir 3 is not subject to the Pressure Equipment Directive. If there is a gas phase above the hot region, it has a substantially constant temperature during operation so that no volume compensation is necessary for a volume change of the gas. In this way, the heat storage device 1 according to the invention enables particularly advantageous heat storage in the molten salt.

TABLE-US-00001 List of reference numerals 1 heat storage device 3 heat storage reservoir 5 insulating layer 7 hot region 9 hot molten salt 11 cold region 13 cold molten salt 15 separating layer 17 gas layer 19 volume compensation device 21 compensation reservoir 21a supply line 21b outlet valve 21c inlet valve 21d controller 21e second compensation reservoir 21f flexible wall 22 blower 23 riser 24 compressor 24a control valve 25 discharge pump 27 charge pump 28 valve 29 reservoir 31 overflow 33 additional pump 35 drain pump 37 gas retention device 38 diffuser 39 gas 41 regeneration storage 43 heating device 44 cooling device 45 driving device 120 charging process 110 discharging process