WO2016184961A1 - Container for storing a liquid, and use thereof - Google Patents

Abstract

The invention relates to a container for storing a liquid which has a tendency to break down into gaseous breakdown products under the conditions prevailing in the container (1) and in which a chemical reaction equilibrium between the gaseous breakdown products and the liquid is established. The container (1) accommodates a floating roof (29) and said floating roof (29) comprises floaters (33) with the help of which the floating roof (29) floats on the liquid, the floating roof (29) being guided in the container (1) by means of a sliding seal (45). The invention further relates to a device for storing heat, comprising a first container (57) for storing a cooler liquid and a second container (59) for storing a liquid that is hotter than said liquid, and to a use of the container and the device for storing heat.

Description

 The invention is based on a container for storing a liquid which tends to decompose into gaseous decomposition components at the conditions prevailing in the container and in which a chemical reaction equilibrium is established between gaseous decomposition components and liquid. The invention further relates to a device for storing heat, in which such a container is used and a use of the container or the device for storing heat.

Liquids which tend to decompose into gaseous decomposition components are, for example, molten salts which are used as the heat transfer medium and the heat storage medium. Salt melts are used in particular where conventional heat transfer media and heat storage media can no longer be meaningfully used due to the required high temperatures. An important application of molten salt as a heat transfer medium is solar power plants, in which the heat transfer medium in receivers is heated by solar radiation and stored in a hot storage. With the hot heat transfer medium, water is vaporized and overheated and with the superheated steam, a generator is driven to generate electricity.

In particular, in the used in solar power plants, such as parabolic trough solar power plants, Fresnel solar power plants or tower solar power plants, salt melts based on nitrates or nitrites of alkali metals or alkaline earth metals, often a mixture of nitrates and nitrites is used, there is a risk that the Salt decomposes due to the high temperatures to form gases. For example, nitrate salts of alkali metals and alkaline earth metals form the respective corresponding alkali metal oxides or alkaline earth metal oxides at high temperatures with simultaneous formation of nitrogen monoxide and nitrogen dioxide, hereinafter referred to as nitrogen oxides. The nitrogen oxides dissolve physically in the molten salt and can react with dissolved alkali metal oxides or alkaline earth metal oxides in the sense of a chemical reaction equilibrium. However, the nitrogen oxides in particular can pass into the gas state even with decreasing pressure or increasing concentration and are then no longer available for a reverse reaction. This can lead to a harmful accumulation of alkali metal oxides or alkaline earth metal oxides in the molten salt.

Since the decomposition of the nitrate salts is an equilibrium reaction, the nitrogen oxides dissolved in the molten salt also inhibit the further decomposition of the nitrate salt. By outgassing the nitrogen oxides and the associated reduction in the concentration of nitrogen oxides in the molten salt, this protection is less effective and the salts in the molten salt can further decompose. The formation of the oxides by the decomposition of the nitrate salts is disadvantageous. On the one hand, the decomposition reaction in highly nitrite-containing melts leads to a reduction in the nitrite concentration and thereby to an increase in the melting point. On the other hand, the corrosiveness of the melt increases compared to the commonly used metallic materials, in particular steel. Furthermore, by exceeding the solubility limit of the alkali metal and alkaline earth metal concentration solids can form in the molten salt, which can lead to abrasion on the surfaces of the flowed through system parts and thus also to damage the system components. In addition to abrasion due to entrained solid particles, it is also possible for solids to precipitate out of the molten salt and lead to deposits and deposits on the plant components. This may further result in the blocking of pipelines or heat exchangers.

In order to increase the lifetime of nitrate-containing molten salts, it is currently customary, for example, to regenerate the molten salt as described in WO-A 2014/1 14508.

Alternatively, it is also possible to cover the molten salt with a gas phase, the content of nitrogen oxides is so high that a sufficiently high concentration of dissolved nitrogen oxide is obtained in the molten salt, and thus the decomposition of the nitrate salts can be inhibited. In particular, when used in large containers, which serve as a heat storage in a solar power plant, for example, but this has the disadvantage that due to the cyclic operation, the heat storage cyclic heating and cooling are exposed, leading to significant pressure and volume changes, especially in the gas space. Due to the large volume changes, it is difficult to discharge a sufficiently large amount of nitrogen oxides and to provide for regeneration again. Thus, on-site generation would be necessary to provide a sufficient amount of nitrogen oxides.

It is known to maintain the gas space by consequent conclusion in a vapor recovery system together with the use of gas pressure accumulators or gas volume accumulators, which manages without relevant discharge of gases to the environment. As a result, it is not necessary to deliver large quantities of nitrogen oxides or starting materials for the production of nitrogen oxides. The disadvantage, however, is that the necessary use of the gas pressure accumulator or gas volume storage an additional large investment and maintenance costs is connected. With the floating roof of the container is completed at the known floating roof tanks up to the environment.

For liquids that have a high vapor pressure, for example in petrochemicals, it is known to use floating roof tanks in which a roof is floating on the liquid in the tank. The roof can be sealed by membranes or sliding systems. Such floating roof tanks are known for example from US 2,536,019 or US 4,371,090. Further, JP-A S6484887 describes a floating roof used in a hot water tank. However, none of the tanks described here is used under the conditions prevailing in a solar power plant, in particular at the prevailing temperatures of the heat transfer medium in a solar power plant. Object of the present invention was to provide a container for storing a liquid, in particular a heat transfer medium in a solar power plant, which tends at the conditions prevailing in the container for decomposition into gaseous decomposition components and in which a balance between gaseous decomposition components and liquid adjusts does not have the disadvantages known from the prior art.

The object is achieved by a container for storing a liquid which tends to decompose into gaseous decomposition components at the conditions prevailing in the container and in which sets a chemical reaction equilibrium between gaseous decomposition components and liquid, wherein a floating roof is housed in the container and the floating roof float includes, with which the floating roof floats on the liquid, and wherein the floating roof is guided with a sliding seal in the container.

In contrast to the known systems in which the gas that is formed by decomposition of the liquid is stored in a central gas storage, the size of the gas storage can be greatly reduced by the floating roof or even completely dispensed with a gas storage. The gas collects in a gas space below the floating roof and leakage of the gas into the environment or in a gas phase in the container above the floating roof is obstructed. In this way, damage to the liquid, in particular a molten salt containing nitrates, can be prevented or at least greatly delayed.

A further advantage results when used in a two-storey system in which hotter liquid is stored in a first container and cold liquid is stored in a second container, wherein the first and the second container are connected to each other, so that liquid taken from the first container, cooled and may be introduced into the second container, or alternatively liquid may be withdrawn from the second container, heated and introduced into the first container. Thus, for example, in a solar power plant, the liquid from the second container is heated by solar radiation either in a solar field of a parabolic trough or Fresnel solar power plant or in a central receiver of a tower power plant and introduced into the first tank. The liquid from the first container is used to vaporize and overheat water, releasing heat. The thus cooled liquid is then introduced into the second container. As a result of operation, the liquid level in the first and in the second container changes cyclically, and the gas volume above the liquid in the container also changes. The gas is usually transferred from the container into which the liquid is introduced via a vapor recovery system into the container from which the liquid is withdrawn. As a liquid which is used in a solar power plant as a heat transfer medium, in particular a molten salt is suitable. Typical salts which are used in the form of their melt are nitrates or nitrites of the alkali metals and alkaline earth metals and any mixtures thereof. Particularly preferred is a mixture of potassium nitrate and potassium nitrite. In a solar power plant, however, the hotter and colder liquids have large temperature differences. As a result, the gas in the first container with the higher temperature liquid at the same pressure has a much larger specific volume than the gas in the second container with the colder liquid. In order thus to avoid that the pressure in the first container increases due to the larger specific volume of the gas, it is necessary to remove gas from the system or to store it in a gas reservoir when filling the first and emptying the second container. When the floating roof container of the present invention is used as the first container for storing the hot liquid, the floating roof is preferably designed so that the floating roof has at least one chamber containing thermally insulating material. As a result, a thermal insulation of the liquid is achieved with respect to the formed above the floating roof gas space. The insulation of the floating roof is preferably designed so that the gas in the gas space of the first container has the same temperature as the gas in the second container. As a result, pressure fluctuations of the gas due to the same specific volume at the same temperature and pressure can be compensated. It is therefore no longer necessary, in addition vorzugsehen a gas storage in which the gas can be cached.

In such a system with two containers, it is also possible to provide a floating roof in the second container with the colder liquid. Here, however, the floating roof in particular has the task of preventing foreign substances, for example carbon dioxide, water or aerosol particles, in particular chloride-containing aerosol particles, from being able to enter the liquid from the gas phase.

The penetration of gaseous impurities from the gas phase above the floating roof into the liquid or decomposition gases formed from the liquid into the gas phase above the floating roof is prevented by the use of the gas-tight sliding seal. In particular, when using the container as a heat storage in a solar power plant can not be used seals made of organic materials, in particular of polymers such as polytetrafluoroethylene due to the high temperatures of the liquid received in the container, namely serving as a heat transfer medium molten salt. One possibility is to provide diaphragm seals made of stainless steel. Herbei have the membrane seals at least one diaphragm which bears resiliently against the inner wall of the container. For large containers, as they are used as heat storage in solar power plants, it is also possible to carry out the membrane seal without contact with the inner wall of the container. In this case, no complete sealing is achieved, however, the release of nitrogen oxides from the salt bath salts used as a heat transfer salt melt is thereby reduced so that a sufficiently long life of the molten salt is achieved. However, preference is given to a sliding seal with membranes, which bear flexibly against the wall of the container in order to obtain a gas-tight seal. In order to obtain a complete seal against escaping or incoming gases, it is also advantageous if the sliding seal is thermally insulated from the liquid stored in the container. In this case, the sliding seal can be arranged in a region of the container at a lower temperature, so that more temperature-sensitive materials can be used as a sealing material. A further advantage of the thermal insulation and the arrangement in a region of lower temperature is that the sliding seal is exposed to less corrosion, since in particular with molten salts, the corrosivity increases with increasing temperature. Since the sliding seal to prevent the escape of gases from the liquid or the entry of impurities in the liquid, a contact of the sliding seal with the liquid is not required.

A further improved sealing can be achieved in that sealing chambers are arranged below the sliding seal on the floating cover. The sealing chambers may, for example, as well as the sliding seal comprise a plurality of membranes which bear against the inner wall of the container, wherein between the individual membranes in each case is so large a distance that the membranes do not touch even when moving the floating lid. The thermal insulation of the sliding seal can be realized, for example, by providing insulation between the liquid and the sliding seal over the circumference of the floating cover. Such insulation can be realized, for example, by a plurality of parallel annular ribs along the circumference of the floating lid. Between the annular ribs, gas cushions form, which have an insulating effect. Alternatively, it is also possible to introduce an insulating material, for example inorganic fibers with a high proportion of Al 2 O 3, that is to say with a proportion of Al 2 O 3 of at least 80%, between the ribs. In a design of the insulation by a plurality of parallel annular ribs along the circumference of the floating cover and a gas cushion between the ribs, the insulation can simultaneously take over the function of the seal chambers. If an insulating material is used, this is particularly preferably provided with a steel jacket due to the corrosiveness of the molten salt.

In order to prevent the sliding seal and possibly the membranes of the sealing chambers or the ribs of the insulation exerting too much force on the container wall when the floating roof is moved, it is preferred if the floating roof is made up of at least two segments movably connected to each other. The force acting on the inner wall of the container may result, for example, in that the walls do not ideally run with a constant constant distance but differ from the ideal course due to manufacturing tolerances. Due to the movable segments, the floating roof can be moved up or down without jamming or jamming within the container with increasing or decreasing liquid level.

In order to enable trouble-free movement of the floating lid and to keep the floating roof in position within the container, it is preferred that the Floating roof is guided on at least one guide in the container. The guide can be formed for example in the form of a rail on the container inner wall and a running on the rail groove on the floating roof. Alternatively, it is also possible to provide, for example, guide rods in the container interior as a guide and to form openings in the floating roof, through which the guide rods are guided.

In one embodiment of the invention, passages are formed in the floating roof. Through the ducts internals can be guided through the floating roof in the liquid. Thus, for example, a submersible pump can be provided, with which the liquid can be pumped out of the container. The pump shaft for operating the submersible pump, which is usually guided in a pump shaft guide, and a flow tube for removing the liquid can be guided, for example, in a cladding tube, wherein the cladding tube is guided through the passage in the floating roof. The cladding tube is particularly advantageous when the pump shaft, the pump shaft guide and the flow tube are designed segmented, as is customary in particular for long submersible pumps. This prevents that liquid from the container in the region of the connection points of the individual segments, for example, penetrate into the pump shaft and can damage them. In non-segmented pump shaft guide and flow tube can be dispensed with the cladding tube. In this case, the pump shaft guide and flow tube are each guided through separate bushings in the floating roof.

Furthermore, as an installation, which is guided by a passage in the floating roof, also a dip tube may be provided, is introduced with the liquid with a Unterspiegeleinfüllung into the container. To dampen vibrations during the introduction of liquids, it is possible to fix the dip tube to the bottom of the container. For this purpose, the dip tube can be introduced, for example, in a liquid distributor and jammed in this.

Another way to dampen vibrations is to provide a baffle plate below the mouth of the dip tube in the container. When liquid is introduced, it first flows against the baffle plate and is thereby deflected. A suitable geometry of the baffle plate can influence the flow within the liquid. The baffle plate may for example be provided with openings or conical.

In order to prevent the passage in the floating roof gas from the gas space above the liquid in the gas space above the floating roof can flow out or impurities or gases from the gas space above the floating roof can get into the liquid, the bushings are preferably sealed with a suitable seal , For this purpose, it is possible, for example, to seal the passages with a movable sealing plate. The movable sealing plate ensures that the sealing plates do not exert too much force on the internals when the floating roof rises or falls. For this purpose, the movable sealing plates are designed so that they can move horizontally on the floating roof. At the same time, the sealing plates must be fastened to the floating roof in such a way that they move along when raising and lowering the floating roof and do not get stuck in one position. Preferably, the sealing plates are loose on a flat surface on the top of the floating roof and are guided by the internals. Thus, small manufacturing and assembly deviations of the internals can be compensated by the ideal vertical course. Alternatively, it is also possible to realize the sealing of the bushings with elastic sliding seals.

In particular, when the liquid in the container is a molten salt which tends to creep, it is advantageous if the sliding seal has protection means against creeping up liquid. This avoids that the sliding seal comes into contact with the liquid and is damaged by the liquid, for example by corrosion. For example, a drip edge can be formed on the floating roof as a protective device against creeping upwards liquid. In addition, a minimum distance between the surface of the liquid and the sliding seal should be maintained. The minimum distance is preferably at least 50 cm. When using the container as a heat storage in a solar power plant, high temperature differences between the bottom of the floating roof and the top of the floating roof can occur. These result from the high temperature of the liquid of usually 450 to 550 ° C and the colder gas in the gas space above the floating roof. This is particularly the case when the floating roof is made thermally insulating. In order to compensate for the different thermal expansion and associated stresses occurring due to the temperature differences, the floating roof preferably has means for compensating thermal expansions. Since the temperature differences remain substantially constant in normal operation, compensating paths and / or a suitable bias can be provided as devices for compensating thermal expansions, for example.

In order for the floating roof to float on the liquid, it is equipped with floats. So that the floating roof does not dive into the liquid over a long period of operation, it is necessary for the floats to maintain their volume and not be pressed in. This could be done for example by high pressure or pressure fluctuations. For a pressure-resistant design, it is possible, for example, to fill the floats with a low-density and high-pressure insulation material. Such suitable insulating materials are, for example, ceramics with gas inclusions, for example ceramic foams. The container is particularly preferably used in a solar power plant as a heat storage. However, it is also conceivable to use in any other device in which a liquid is used, which tends under storage conditions to decompose to form gaseous decomposition products, wherein the liquid and the gaseous decomposition products are in the chemical reaction equilibrium.

A device for storing heat comprises a first container for storing a colder liquid and a second container for storing a hotter liquid, wherein the containers are interconnected so that the colder liquid from the first container after receiving heat in the second container flows and out of the th container after heat release in the first container, wherein at least the second container is a container as described above.

Such a device for storing heat is used particularly advantageously in solar thermal power plants, in short solar power plants, for example parabolic trough, Fresnel or tower power plants.

In a particularly preferred embodiment, in each case a gas space is formed in the first container and in the second container above the floating roof and the gas spaces of the first and the second container are connected to each other via a connecting line. Through the connecting line, the gas can flow out of the container that is being filled into the container that is being emptied. As a result, in each case a pressure equalization in the respective containers is realized without additional gas supply. Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description.

1 shows a container with a floating roof according to the invention, FIG. 2 shows a detail of the floating roof,

Figure 3 is a schematic representation of a solar thermal power plant in which a container is used with floating roof.

Figure 1 shows an inventively designed container with floating roof.

A container 1, as used for example in a solar thermal power plant as a storage for hot heat transfer medium, in particular a molten salt, comprises a container bottom 3, a container wall 5 and a lid 7.

Via a dip tube 9 liquid can be introduced into the container. By supplying the liquid through the dip tube 9 can be avoided that arise when introducing the liquid into the container 1 unacceptably large turbulence in the liquid. A further reduction of turbulence when filling the liquid into the container 1 can be achieved by positioning a baffle plate 1 1 below the dip tube 9. The liquid flowing through the dip tube 9 flows onto the baffle plate 1 1, is thereby deflected and distributed, so that set according to the design of the baffle plate 1 1 or the angle in which the baffle plate 1 1 is disposed below the dip tube 9, a targeted flow broadening can be. Another advantage of the baffle plate 1 1 is that the incoming liquid does not bounce directly onto the container bottom 3 and thereby possibly entrained there solids are entrained and stirred up, so that they are distributed in the liquid. The container is designed in the embodiment shown here so that there is always so much liquid in the container 1 that the immersion tube 9 is still immersed in the liquid even when the container 1 is empty.

The removal of the liquid takes place for example via a submersible pump 13. The immersion pump 13 is also immersed in the liquid. About the submersible pump 13 so long liquid can be removed from the container until the intake manifold 15 of the submersible pump 13 is no longer immersed in the liquid. The position of the intake manifold thus results in the minimum level of the liquid in the container 1. The sucked by the submersible pump 13 liquid flows through a flow tube 17 from the container 1. The drive of the submersible pump 13 is carried out with a through the lid 7 of the container 1 Pump shaft 19. For protection against incoming fluid, the pump shaft 19 is guided in a tube 21. Since, in particular in the case of long submersible pumps, that is to say at a high level of the container 1 and a correspondingly long flow tube 17 and pump shaft 19, the flow tube 17 and the pump shaft 19 are segmented, the flow tube 17 and pump shaft 19 are preferably guided in a cladding tube 21. The cladding tube 21 impedes the uncontrolled gas exchange between the bottom and the top of the floating roof. It is preferred that the cladding tube is sealed against the gas phase above the floating roof, while it is open at the lower end. This avoids that gas laden with a high concentration of nitrogen oxides penetrates into the gas space above the floating roof. The cladding tube preferably has such a large diameter that the submerged pump can be pulled through the cladding tube, for example for maintenance purposes.

In the embodiment shown here, a distributor 25 is located below the submersible pump 13. This distributor can be designed, for example, in the form of a perforated bottom. The distributor is located at the position of the lowest liquid level in the container. 1 The distributor 25 is used to dampen turbulence that may result from the in-flow of the liquid, so that the liquid above the distributor 25 remains calm and no waves are created on the surface through which the floating roof 29 can move. If, as shown here, a distributor 25 is provided, it is possible, for example, to guide the dip tube 9 through a passage 27 in the distributor 25 and to fix it on the distributor 25. In addition, the cladding tube 21 of the submersible pump 13 can be fixed to the distributor 25. By fixing the dip tube 9 and submersible pump 13 is avoided that these begin to vibrate and thereby damage to installations or container 1 verur- things can.

According to the invention, a floating roof 29 is received in the container 1. The floating roof 29 floats on the surface 31 of the liquid in the container. For this purpose, float float 33 are formed on the floating roof 29, which float on the liquid and carry the floating roof 29. In the embodiment shown here is not the entire floating roof 29 in contact with the surface 31 of the liquid but only the float 33. Alternatively, it is also possible to make the entire floating roof 29 in the form of floats, so that the entire floating roof 29 on the surface 31 of the liquid floats. In particular, when used as a hot tank of a solar thermal power plant, it is preferred if the floating roof is made thermally insulating. For this it is possible, for example, that Floating roof 29 to be designed as a hollow body and filled with an insulating material. Alternatively, it is also possible to completely manufacture the floating roof 29 from the insulating material. Suitable insulating materials are in particular steel-coated ceramics with gas inclusion, such as, for example, foamed ceramic or foam glass, which are temperature and pressure-stable and make it possible to use very thin covering sheets. Alternatively, it is also possible to use, for example, conventional inorganic fiber mats for thermal insulation, but must then intercept occurring external pressures by a sufficiently stable designed enclosure. In the floating roof bushings for fittings are formed in the embodiment shown here. Through a first passage 35, the dip tube 9 is guided and through a second passage 37, the submersible pump 13. Here, the second passage 37 is designed so large that the pump head of the submersible pump 13 can be inserted through the implementation in the container.

So that no gas can escape from the liquid through the floating roof 29, the passages 35, 37 are preferably provided with a movable sealing plate 39. The movable sealing plate 39 is designed so that it can raise and lower both vertically with the floating roof 29 and also a horizontal movement is possible to not completely vertical tubes of the internals, for example, dip tube 9 and sheath 23, one to to prevent large force on the internals, which can cause damage.

In order to prevent tilting of the floating roof 29, when the floating roof 29 rises or falls, a guide 40 is preferably provided, along which the floating roof 29 is guided. As a guide 40, for example, a guide rod may be attached to the container wall 5 and the floating roof 29 encloses the guide rod so that the floating roof 29 is moved along the guide rod. Alternatively, it is also possible to provide guide rods in the container interior, which are guided by corresponding passages in the floating roof 29. In addition, the internals, such as the dip tube 9 or the cladding tube 23 of the submersible pump 13 can serve as a guide.

Above the floating roof 29 is a gas space 41 between the floating roof 29 and cover 7 of the container. In order to prevent the gas in the gas space from being compressed as the floating roof 29 rises, a gas outlet 43 is provided in the lid.

If the container 1 is part of a two-tank system, as used for example in solar thermal power plants, which is stored in a first container, the colder liquid and in a second container, the warmer liquid, so that in each case empties a container and the other is filled accordingly, it is preferred that the containers are connected to each other via the gas outlet 43 in the lid, so that in each case the gas from the container which is emptied into the container, which is filled, can flow. In a thermal insulation of the floating lid 29, it is possible that the gas phases in the first container and in the second container substantially the same temperature and thus at the same pressure also have the same specific volume.

FIG. 2 shows a detail of the floating roof 29.

The floating roof 29 is guided with a sliding seal 45 on the container wall. With the sliding seal 45, the space below the floating roof 29 is sealed off from the gas space 41, so that no decomposition gas originating from the liquid can escape into the gas space 41. Furthermore, this also prevents, in particular, that gaseous and liquid contaminants can pass from the gas space 41 into the liquid.

To improve the tightness, it is advantageous if a sealing lip 47 is additionally located above the sliding seal. The sealing lip 47 is guided along the container wall 5 and has an additional sealing effect.

Below the sliding seal 45 ribs 49 are formed on the float 33. The ribs 49 are spaced apart, so that in each case between the ribs 49, a gas space 51 is formed. The ribs 49 can be used as an additional seal. Furthermore, in particular the gas spaces 51 act as additional insulation, so that the temperature in the region of the sliding seal 45 is lower than directly above the liquid. As a result, the sliding seal 45 is protected from excessive temperatures and possible damage due to the high temperatures. In particular, this also makes it possible to use sealing materials that would be damaged at the high temperatures of the liquid. In order to further avoid that upward creeping liquid from the container with the sliding seal 45 comes into contact, it is advantageous to attach a drip edge 53 below the sliding seal 45. At the drip edge 53, creeping liquid creeps upwards and falls down again into the liquid. In contrast to the embodiment shown in FIG. 1 with unfilled floats 33, the floats in the embodiment shown in FIG. 2 are filled with a thermally insulating material 55. This avoids that the floats act as thermal bridges and release heat from the liquid to the gas space 41 above the floating roof 29.

FIG. 3 shows a solar thermal power plant in which at least one container 1 with a floating roof 29 is inserted.

In a solar thermal power plant with a first container 57 for storing a cold liquid and a second container 59 for storing a hotter liquid, at least the second container 59 is equipped with a floating roof 29. In the embodiment shown here, the floating roof 29 is constructed of a plurality of segments 61 which are movably connected to each other. The segments 61 are each equipped with floats, so that each segment floats on its own on the surface of the liquid. The Liquid stored in the first tank 57 and the second tank 59 is used as a heat transfer medium and is usually a molten salt. Salts used for the molten salt are, in particular, nitrates and nitrites of the alkali metals and alkaline earth metals, and any mixtures thereof. A commonly used salt is a mixture of potassium nitrate and potassium nitrite in a weight ratio of 60:40.

During operation of the solar thermal power plant, the liquid is removed from the first container 57 at times with solar irradiation and passed through a solar field 63. The solar field 63 has receivers 65, in which the liquid is heated by radiating solar energy. The thus heated liquid is introduced into the second container 59. In this case, the volume of liquid in the first container 57 decreases, which increases the gas space. At the same time, the liquid volume in the second container 59 increases, so that the gas space 41 in the second container 59 decreases. In this case, the gas is introduced from the gas space of the second container 59 via a gas discharge line 67 into the first container 57. Excess gas, which may be generated, for example, by outgassing of gases dissolved in the liquid, which may, for example, when the first container 57 is not equipped with a floating roof, can enter the gas phase, can be removed via a gas outlet 69.

To generate electricity, the hot liquid from the second container 59 is supplied to a first heat exchanger 71 of a steam cycle 73. In the first heat exchanger 71, the water is vaporized and overheated by heat transfer from the hot liquid to the water cycle. The superheated steam thus generated drives a steam turbine 75, which in turn drives a generator 77 for power generation. In the steam turbine 75, the superheated steam is thereby expanded.

The steam flowing out of the steam turbine 75 is condensed in a second heat exchanger 79, the heat being transferred from the water of the steam circuit 73 to a cooling circuit 81. The cooling circuit 81 is usually also operated with water, wherein the water of the cooling circuit 81 is cooled in a cooling tower 83.

After the condensation, the water of the steam cycle 73 is compressed by a pump back to the pressure required to drive the steam turbine 75, before the water again flows into the first heat exchanger 71 for evaporation and overheating. As a receiver 65 in the solar field 63, for example, parabolic troughs or Fresnel receivers can be used. Alternatively, it is also possible to use a central controller of a tower power plant instead of the solar field 63, the liquid then being heated in the tower. LIST OF REFERENCE NUMBERS

 1 container

 3 container bottom

 5 container wall

 7 lids

 9 dip tube

 1 1 baffle plate

 13 submersible pump

 15 intake manifold

 17 flow tube

 19 pump shaft

 21 pipe

 23 cladding tube

 25 distributors

 27 implementation

 29 floating roof

 31 Surface of the liquid

33 swimmers

 35 first implementation

 37 second implementation

 39 movable sealing plate

 40 leadership

 41 gas space

 43 gas outlet

 45 sliding seal

 47 sealing lip

 49 rib

 51 gas space

 53 drip edge

 55 thermally insulating material

57 first container

 59 second container

 61 segment

 63 solar field

 65 receivers

 67 gas shuttle

 69 gas outlet

 71 first heat exchanger

 73 steam cycle

 75 steam turbine

 77 generator

 79 second heat exchanger

81 cooling circuit

 83 cooling tower

Claims

claims 1 . Container for storing a liquid which, in the conditions prevailing in the container (1), tends to decompose into gaseous decomposition components and in which a chemical reaction equilibrium is established between gaseous decomposition components and liquid, characterized in that in the container (1) a floating roof ( 29) is received, wherein the floating roof (29) comprises floats (33), with which the floating roof (29) floats on the liquid, and wherein the floating roof (29) with a sliding seal (45) in the container (1) is guided. 2. Container according to claim 1, characterized in that the sliding seal (45) against the in the container (1) stored liquid is thermally insulated. Container according to claim 1 or 2, characterized in that the floating roof (29) of at least two segments (61) is constructed, wherein the segments (61) are movably connected to each other. Container according to one of claims 1 to 3, characterized in that the floating roof (29) has at least one chamber containing thermally insulating material. Container according to one of claims 1 to 4, characterized in that in the floating roof (29) passages (35, 37) are formed. Container according to claim 5, characterized in that the passages (35, 37) are sealed with a movable sealing plate (39). Container according to one of claims 1 to 6, characterized in that the sliding seal (45) has protection means (53) against creeping up liquid. Container according to one of claims 1 to 7, characterized in that the floating roof (29) is guided on at least one guide in the container. Container according to one of claims 1 to 8, characterized in that the floating roof (29) comprises means for compensating thermal expansions. 10. Container according to one of claims 1 to 9, characterized in that the liquid is a molten salt. 1 1. Container according to claim 10, characterized in that the molten salt is a mixture of nitrite and nitrate salts. 12. A device for storing heat, comprising a first container (57) for storing a colder liquid and a second container (59) for storing a hotter liquid, wherein the containers (57, 59) are interconnected, so that the colder liquid from the first container (57) after receiving heat in the second container (59) flows and from the second container (59) after heat release into the first container (57), wherein at least the second container (59) a container according to one of Claims 1 to 1 1 is. 13. The apparatus according to claim 12, characterized in that in the first container (57) and in the second container (59) above the floating roof (39), a gas space (41) is formed and the gas spaces (41) of the first (57) and second (59) container are connected to each other via a connecting line (67). 14. Use of the container according to one of claims 1 to 1 1 or the device for storing heat according to one of claims 12 or 13 in a solar thermal power plant.