EP2661556A2

EP2661556A2 - Solar thermal power plant and method for operating a solar thermal power plant

Info

Publication number: EP2661556A2
Application number: EP12716384.8A
Authority: EP
Inventors: Matthias ÜBLER; Christian MÜLLER-ELVERS; Peter GRÖPPEL; Pascal Heilmann; Peter MÜRAU
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2011-04-19
Filing date: 2012-04-19
Publication date: 2013-11-13
Also published as: WO2012143425A3; DE102011007650A1; CN103502639A; US20140033708A1; WO2012143425A2; US9765759B2

Abstract

The invention discloses for the first time a possibility for operating solar thermal technology economically. The innovation presented here makes it possible to use a cheap heat transfer fluid (HTF) and to either completely spare or significantly reduce the energy-intensive auxiliary heating at night. For this purpose, a water tank is simply installed in the plant without a threat to the environment. By means of the water tank, the salt is thinned by adding water when the solar heating is not in operation.

Description

description

Solar thermal power plant and method for operating a solar thermal power plant

The invention relates to a solar thermal power plant and method for operating a solar thermal power plant, in particular one with a salt-containing heat metransferfluid (HTF).

Among the regenerative forms of energy generation, solar thermal power plant concepts have the greatest potential of being able to generate a large share of the world's demand for electrical energy without emissions at competitive production costs. Not least, the Desertec or Dil GmbH project focuses He ^¬ direction many square kilometers large solar fields in North Africa and the Middle East, which will operate nelspiegel solar thermal energy for Europe by means of cascaded parabolic trough and / or Fres-. In such systems, a heat transfer fluid circulates in special, kilometer-long absorber tubes, which are heated to process temperatures of up to 600 ° C by the sunbeam focusing / focusing through the aforementioned mirror geometries. Ei ^¬ ne steam-driven turbine is operated via a heat exchange process and release electrical energy. The thus cooled Wärmetransferflu ^¬ id (engl. Heat transfer fluid, "HTF") is in a circular process of re-heating by the thermal energy available to each solar thermal system therefore has two HTF tanks, one with cooled HTF and a hot. HTF.

High demands are placed on the HTF since its characteristic values such as melting point, heat capacity, thermal conductivity, viscosity and spec. Density the final ones

Dictate current development costs and thus determine the competitiveness and cost parity for the conventional way of ^generating energy. Of particular importance is the melting point of the HTF used. The currently used heat transfer media are organic as well as inorganic in nature. The first generation of HTFs used for this purpose are organic thermal oils, the best known representative for solar thermal applications being a eutectic-melting mixture of 26.5% by weight of biphenyl and 73.5% by weight of biphenyl ether (for example from the US Pat. Solutia ™ Therminol ^® VP-1) represents the ER stares at 12 ° C. However, due to the organic molecule nature such mixtures develop at high temperatures quickly steam pressures up to 15 bar, so that the maximum operating temperature of this as "VP-1" known batch is limi ^¬ advantage to below 400 ° C, as from this process temperatures also for thermal Degeneration of organic structures comes.

Since efficiency of power plants is known überproporti ^¬ onal scale with the process temperature, the use of such organic HTFs an economic, solar thermal energy in very high MW _e -Performance faces contrary area. In addition, such a preparation in the event of leakage poses a risk to humans, animals and nature. For this reason, the use of low melting point inorganic salectucts as a heat transfer medium has been focused for decades. He has to be particularly advantageous ^¬ thereby the negligible vapor pressure of liquid salts or mixtures thereof, resulting in a virtually pressureless operating in the absorber pipes possible. Furthermore, molten salts have a factor of two to three higher thermal conductivity and spec. Heat capacity, which can increase the ^ein¬ portable solar energy amount per unit volume in relation to organic thermal oils greatly. The most well-known representative of an inorganic salt mixture used for this purpose is the so-called "Solar Salt", a mixture of sodium nitrate (60 wt .-%) and potassium nitrate (40 wt .-%). This non-toxic and cheaper by a factor of four acce ^¬ reitung compared to thermal oil VP-1 has a Solidustem- temperature of approximately 240 ° C. To reduce the melting point is a Ternärisierung the mixture with calcium nitrate (Eutektikumssolidus: 133 ° C) or an additional Quarternä- ization with lithium nitrate (Eutektikumssolidus: 97 ° C) dedicated ^¬ useful. But especially the latter method is expensive to Ver ^¬ application and worldwide not sufficiently in Multitonnen- available lithium nitrate scale dependent.

Since an economic point of a melting point of less than 150 ° C of the heat transfer medium used in solar thermal power plants is essential, the interest in inorganic Salzeutektika with solidus temperatures below 100 ° C is very large, since just the night operation per se does not generate electricity. Accordingly, energy-intensive ges ^¬ the measures to avoid the "freezing" of a salt mixture in the kilometer-long usually supply talten leitungsrohr- and receiver systems during the night, where the heating of the HTFs fails by the sun.

In general, the solar thermal power plant, so that the pipes do not burst by the Volumenausdeh ^¬ voltage of the solidifying salt and / or so that the system is operated with an external heating at night, a considerable amount of current generated during the day consumed again is not must be restarted in the morning.

The object of the present invention is to make more profitable the use of saline HTFs in solar thermal power plants in which nocturnal heating to avoid freezing of the HTF is reduced or avoided. The present invention is therefore a solar thermal power plant with an anhydrous or what ^¬ serhaltigen salt as a heat exchange fluid (HTF), which comprises at least the following modules: a first cycle with HTF

a second circuit with steam for driving generators wherein the first circuit at least

comprises a solar array with mirror geometries and lines in which the HTF flows,

in which

a first line for the heated HTF from the solar panel leads to the heat exchanger

a second line for the cooled HTF from the heat exchanger leads to the solar field

comprises a conduit for introducing a diluent for the HTF and

the two circuits are connected via the heat exchanger. In addition, the subject of the invention is a method for

Operating a solar thermal power plant, wherein the temperature of the HTF is kept above its melting point in the line system of the solar thermal power plant, that the melting point of the HTFs is shifted to lower temperatures by adding water when the temperature drops.

As a rule, is used as diluent water or a sons ^¬ term highly polar fluid.

By adding water to the HTF in fall of temperature in the pipes of the solar thermal power plant accomplishes two things, firstly is - if the HTF system before ^¬ handen - released hydration, it is more stable so by the exothermic chemical process of forming

Products heated by addition of water molecules in the crystal composite and the second is simply the melting point of the salt or salt mixture by liquefaction lowered.

The present invention, according to an advantageous embodiment, discloses an optionally switchable "pipe" in front of the hot tank into a dilution tank, which is then allowed to flow before the hot tank Solar field is introduced again. This tank is preferably designed to ei ^¬ ner particularly preferred embodiment for printing, since in that - after the separation of the first circuit from the second circuit, the so-called TES cycle - is added to water in defined quantities and the activity is to pressure increases, the be caught for example with over ^¬ pressure valves and capacitors. The addition of water can be continuous or total. After circulating the aqueous salt at night (the salt tank with the anhydrous salt prepare the energy), the heating phase is performed in still separated first circuit ^¬ run, comprising the solar panel. The heating phase causes primarily a water delivery. There are several ways to get rid of water:

1. The water is separated by means of another "expulsion tank" and the salt is conveyed anhydrous into the hot or cold salt tank, since salt tanks are advantageously operated without pressure.

2. The aqueous HTF mixture goes into the "cold" salt tank, which is equipped with pressure relief valve and condenser, also conceivable is the alternative that the aqueous HTF mixture goes into the hot tank, which is then also equipped with pressure relief valves and condenser ,

3. the phase is heated far above the melting point of the anhydrous salt completed in the solar circuit and then suddenly expanded into one of the two salt tanks.

In a solar power plant according to the present invention is an enrichment of the HTFs with water in the first circuit ^¬ run, comprising the solar field, after sunset or during a turn-off time, instead and it is a geson ^¬-made water liberation in the morning, or when booting the plant, before the energy production by solar radiation, possible. An essential benefit is drainage, initial filling, emptying and handling of emergency situations where there is no sun anymore.

The maintenance of the liquid phase within the line and / or pipe system of the installation, in particular of the solar field which generally extends over several kilometers, is essential for the economy and functionality of the entire installation.

Therefore, according to a further advantageous embodiment of the invention, an auxiliary heater is connected to the lines with the HTF in the solar field. Despite the melting point reduction of the salt-containing HTF according to the present invention by the addition of diluents such as water, it may be necessary to provide the absorber tube system with a so-called firing, so external heating. These heating elements, which can enter heat into the pipe system thermally, inductively or in any other way, have hitherto been used in the prior art to maintain the liquid, ie flowing or flowable, state of the salt-containing HTF circulating therein during the switch-off phase or during the night.

In most cases it is recommended to maintain a safety margin of approx. 20 ° C above the actual melting point of the HTF used. If this is not achieved by the Wasserzuga ^¬ be invention, this additional heating is switched on either automatically or manually.

For example, all types of nitrate salts, eutectically melting mixtures such as non-eutectic mixtures, can be used as the "saline HTF".

For example, serves as HTF the readily available Na / K-N03, which does not absorb water of crystallization (Tmax = 600 ° C). But other salts, and especially those with a lower melting point Of course, they are equally suitable. In particular, a crystal water-binding salt such as Ca-Na-K-N03 (Tmax = 500 ° C), ideally suited. In addition, there are a number of novel ternary, quaternary and quinary salt utensils and mixtures which, by appropriate choice of different salt components, can have melting points as low as 65 ° C suitable for this application. However, these blends are very expensive to procure, or even often available in large tonnages of up to 35,000 tonnes or more (when used simultaneously as HTF and as thermal storage).

It can be used so-called sensitive or latent salts. Sensitive means that energy is stored steplessly in the liquid salt, in which the temperature of the salt increases. The opposite to sensitive is "latent": Here, the transition solid -> liquid when melting the salt energy, which is stored because the solidification of these salts, the "latent enthalpy" is free again. In

CSP systems are preferably used sensitive storage, because in the two circuits should be the same material. That's why the required amounts of salt are enormous: for example, 35,000 tonnes for 125 MWe.

As the salt mixtures are, for example, thermally zersetzungslos dehydratable salts and / or salt mixtures / Salzeutektika, of alkali (ie, the cations of Li ^¬ thiums Li ^+, sodium Na ^+, potassium K ^+, rubidium Rb ⁺ and Cs ⁺ Caesi- killed) and or alkaline earth cations (ie the cations of magnesium Mg ²⁺ , calcium Ca ²⁺ , strontium Sr ²⁺ and barium

Ba ²⁺ ) with anions such as nitrates, (hydrogen) carbonates, fluorides, chlorides, (hydrogen) sulfates, bromides, iodides, and / or hydro ^¬ xide, understood alone or in any combination of mixtures.

These can be prepared by the addition of liquid and / or vaporous diluent at temperatures from room temperature to beispielswei ^¬ se, for example, 300 ° C, a melting Point reduction and / or dilution with polar diluent undecomposed and reversible in almost any number. Apart from the abovementioned salts, a nitrate mixture known from DE 10 2010 041460.3 can be used as HTF, which comprises components containing water of crystallization and can be dehydrated thermally without decomposition. From a limited hours ^¬ th temperature this mixture exists as a liquid phase and when heated they are delayed and then steadily the Tied ^¬ ne crystal water. If the release of water of crystallization coincides widely with the eutectic liquidus temperature of the mixture free of water of crystallization, a mixture is obtained which is partly below its actual liquidus temperature (ie with sediment) or completely liquid (ie single-phase).

All mentioned salts may contain water and with any water content in the empirical formula as HTF is ^¬ sets. For example, even diluted salts, so salts with a molecular formula cation (s) / anion (s) with x water molecules per molecule of salt, which do not form "real", ie known, hydrates, but simply store water in the crystal, taken here be. the transition from one salt present simply diluted with water or other polar solvent and a literature Salzhyd ^¬ rat is fluid and to limit the amount of usable materials as HTF here in any way.

In the inventive addition of water to an HTF, which is a thermally decomposable dehydratable mixture, a defined amount of water is useful as an addition. For this, a crystal anhydrous Salzmi ^¬ research, which are used as Wärmeüberträger- and storage medium and can reversibly bind water of crystallization and release continuously supplied with water. Thus, a proportionately lower the content of added water melting point of the mixture. At times, a defined release of energy is recorded (so-called hydration heat in the case of crystalline water-crystallizing compounds), which can be partially used to keep the lines in the solar circuit at a desired temperature.

Advantageously, it is proposed to switch a direction of a water tank to the lines in the solar field, through which is effected, for example, a continuous addition of water, Wasserne ^¬ bel and / or water vapor to the HTF until the desired melting point has been set.

In principle digit melting points ^¬ be realized depending on the water content. As soon as the heating of the HTF in the lines of the solar field starts again, the water-containing salt mixture can be pumped into the hot or cold salt tank and gradually release the water there again.

For example, since the temperature of the cooled HTF is 250 ° C.-290 ° C. in the second "cold" tank, the thermal energy is sufficient to allow the added water of crystallization and / or excess water to evaporate rapidly a pressure relief valve, a steam separator with condenser above the first and / or second tank, which condenses and stores the escaping water vapor at the moment of introduction for the next blending cycle into the water tank.

This is a rapid process because the HTF from the Sun ^¬ larfeld compared to the volume of water added HTFs occupies a much smaller volume (3-5%). In ^¬ play as offset by 700 tons of salt in the solar circuit another 34,700 tons for storage. About 20-30% of the salt comes to the 700 tons of salt, ie the total content of water is less than 1% of the salt mass, which quickly evaporates in the large salt tank at 250 ° C to 290 ° C. , Can help avoid a et ^¬ waigen temporary overpressure as mentioned above, pressure relief valves, are used for example with steam separation, condensation and reflux for pressure reduction. The water may be the solar circuit run over one intermediä ^¬ reindeer, much smaller filled HTF tank by pumping, spraying, dripping, evaporation or any other way are admixed, since the addition of water results for the melting ^¬ point depressants in an increase in volume of the mixture, which can thus be compensated. The dilution of the salt is thus carried out by means of dropping, spraying, Einne ^¬ beln, jettings or other manner, for example in the temperature range of 10-1000 ° C.

The HTF with generated by adding water melting point Ernied ^¬ rigung has a much lower compared to the pure water vapor pressure due to the high ion concentration. This is due to the attractive effect of the charged ions on the dipolar water. For this reason, it is possible to heat a hydrous salt mixture far above 100 ° C, without causing excessive cooking of the bound ^¬ nen / admixed water. Due to the interaction with the salt ions, in contrast to the pure

Water far lower water vapor pressure, so that the ge by the inclusion in the pipe systems developing ge ^¬ pressure may be sufficient to keep this aqueous mixture liquid and especially single-phase. Today's plants that use thermal oil as HTF are for pressures up to

35 bar designed.

To the suggestions in this one achieves a reduced copy ^¬ tion of the melting point of the HTF mixture, so that little or no Zuheizungen in the kilometer-long pipe systems are needed. Freezing can also be prevented. Also, a rapid discharge of the heat transfer medium for maintenance is possible. The first-time start-up of such a mixture as HTF is thus also more easily possible without freezing phenomena occurring (so-called "freeze-ups".) During daytime operation, after heating, the salt / water mixture can be transformed into a "cold""and / or hot tank are pumped to treat the mixture of admixed water. free, whereupon again the anhydrous salt mixture is obtained, which are passed through the lines in the solar field and there again to temperatures up to 600 ° C (eg in Nit ^¬ ratmischungen the first main group of the periodic table, other mixtures also higher) can be heated ,

Since the water-containing medium is only a small fraction of the total volume of the medium used in it can ^¬ elevated temperatures, which always prevail in the storage tank, a continuous tapping volatile water in the form of steam, for example via a Gasphasenkondenser take place. This water can either be used to generate steam for power generation or serve in a reservoir for the re-hydropneumatic HTFs. When using crystal water containing salt components such as calcium nitrate hydrate, is what ^¬ ser part of a salt component and must therefore be at ^¬ fangs not supplied externally. Of course, the technique described can also be used for salt mixtures which do not form a salt hydrate, in particular the nitrate mixtures of the first main group of the periodic system, for example in particular of the binary system Na-K-NC> 3 in any mixture (eutectic and non-eutectic). In this case, the admixture of water according to the invention represents an ordi ^¬ nary aqueous mixture.

In the storage tank, high temperatures prevail even at night, ensuring a liquid phase, because only the decoupled first HTF cycle is diluted with water, whereas the anhydrous salt is stored undiluted in the tanks and generates energy during the night is passed through the heat exchanger in the cold tank.

The present invention with dilution of the HTF, which itself may already be present as hydrous salt, over the night or the dormant state of the solar field, allows the use of cheap salt mixtures in solar thermal power plants in temperature ranges from a few degrees Celsius up to 600 ° C. While known to the expert, calcium nitrate-containing Mischun ^¬ gene, eg the eutectic melting mixture of Ca-Na-K-N03 has a melting point of about 133 ° C, it is limited Ver ^¬ use of this mixture to working temperatures below 500 ° C, since otherwise decomposition into oxides, ie calcium oxide occurs. The decomposition leads to the shift of the melting point in the direction of higher temperatures and the occurrence of insoluble sediment, which has a highly corrosive effect on the entire solar thermal power plant.

The eutectic-melting mixtures of lithium, potassium and sodium nitrate known to those skilled in the art melt at 120 ° C., but are very expensive. By the technique described herein, it is possible to use mixtures of sodium nitrate and potassium nitrate, which melt in the absence of water until tempera ^¬ ren over 223 ° C, but can have any melting points lower due to the invention described technique. At the same time, the maximum working temperature of calcium nitrate-free mixtures is approx. 600 ° C. Such a mixture, eg the eutectic Na-K-N0 ₃ mixture, "Solar Salt" (60% by weight NaNO ₃ , 40% by weight KNO ₃ ) or any other desired mixture, can thus be used as a heat transfer medium ( HTF), as well as thermal storage material (TES), adding water to the solar circuit results in a greatly reduced water vapor pressure in the mixture, which means that the pressure rating of the solar circuit, which is usually certified to 30 bar, can not be exceeded design changes may be used. So can be heated, for example, the ^water-¬ containing decoupled solar circuit in the morning to well over 223 ° C and then abruptly relax in an empty salt tank in the case of Na / K-N03. Since the vapor pressure of the water naturally rises to 300 ° C, the piping system is designed for this load, and at the moment of relaxing to 1 bar in the salt tank, the water evaporates abruptly and can be stored. Since the thermodynamic characteristics and corrosion own sheep ^¬ th of nitrate mixtures are thoroughly investigated, in particular can be made of such mixtures as HTF medium, although these are unusable due to their high melting point of salt operated solar thermal power plants as Wärmeüberträgerme ^¬ dium (HTF) per se.

For example, the presence of water in nitrate ^¬ rule systems lead to corrosion on pipelines. For this reason, steels are to use the lite ^¬ raturbekannt are compatible with aqueous and / or salt hydrates of nitrate type. For this purpose, stainless steels, eg carbon-containing iron steels with carbon contents greater than 0.20%, have proven their worth. Representatives of other steels with German material numbers such as 1.4301, 1.4305, 1.4306, 1.4307, 1.4401, 1.4404, 1.4435, 1.4539, 1.4541, 1.4550, 1.4571, the US counterparts are comple ^¬ tary to the varieties 304, 303, 304L, 316 , 316L, 904L, 321, 316Ti. As useful for further reducing the corrosion behavior of such steels in aqueous salt mixtures, the pretreatment with corrosion inhibitors offers. Particularly advantageous is the one-time or continuous purge of the stainless steel pipe inside walls turns with a phosphate (derivative) solution (for example, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium polyphosphate) of the concent ration ^¬ 1-100 mmol / L.

Especially with the nitrate systems is known that the unweiger ^¬ Lich from the nitrate ions formed by thermal degradation nitrite affects corrosion-inhibiting. In this case, the application of water to a rapid distribution of nitrite within the pipe system.

According to an advantageous embodiment of the power plant, a plant for generating electricity is connected to the heat exchanger. In the following, the invention will be explained in more detail on the basis of exemplary embodiments of the invention, which represent schematic representations of solar thermal power plants. shows a schematic representation of a solar thermal power plant with direct addition of the diluent in the line to the solar ^¬ field,

shows the addition of diluent in the second tank with cooled HTF,

shows an embodiment with intermediate tank in the supply line of the HTFs to the solar field and

shows an embodiment with intermediate tank in the derivative of the HTFs from the solar panel to the first tank with heated HTF.

Figure 1 shows a circuit diagram with the first circuit, a solar panel 1, an optional Zuführung / trace 2, a tank for water addition 3, a steam condenser 4, for example, with upstream steam separator, a first tank 5, which serves as a hot molten salt storage, a pump 6 for hot molten salt, as a connection to the second

Circulation of a heat exchanger unit 7 and / or a steam generator system through which the two circuits are connected, a turbine 8 of the second circuit, with generator 9 and cooling 10. From the heat exchanger 7 back to the solar panel 1, the line via the "cold" tank eleventh , the molten salt storage at temperatures of for example 250 ° C to 290 ° C. in these cold tank results in the example shown here the line 12 to initiate the Verdünnungsmit ^¬ means of. Evident is still the pump for cold molten salt 13 in the solar field 1. During the night, according to this exemplary embodiment, the molten salt leaving the solar field 1 is led via the line 12 into the tank 11, where it is diluted with water. During the daytime phase, line 12 is not open. The solar energy heated above the mirror geometries of the solar panel 1, the anhydrous HTF, for example, thus a Salzme ^¬ dium in the tank (s) 5 and 11 and provides for the generation of steam through the heat exchanger unit 7 generated by turbine 8 via a generator 9 electricity. Water vapor is recondensed via cooling unit 10 to liquid water. At sunset / maintenance / drainage activity, etc., the line 12 is opened and via the water reservoir 3, liquid and / or vaporous water is continuously or discontinuously introduced via the water pump 14 after a salt dilution process. This results in a low ^¬ melting salt mixture, which is decoupled from the steam generating process is circulated. The energy is then generated only via the emptying of the thermal reservoir 5 via

Pump 6 and heat exchanger 7 in the cold salt tank 11. At z. B. Sunrise, the water-containing heat transfer medium in the decoupled solar field cycle 1-> 12-> 13 is pumped into the emptied hot salt tank 5, whereupon rapid evaporation of the contained water occurs. The line 12 is closed. The evaporating water is condensed via the vapor phase condenser (coupled with a vapor separator) 4 and stored in the water tank 3 for the next feed cycle. The increase in volume due to the addition of water must be regulated accordingly.

The heat exchanger unit 7 represents, for example, the combination of economizer, vaporizer, superheater and / or reheater known to the person skilled in the art.

Figure 2 shows again a similar circuit diagram, but with the additional components "15" Intermediär- / Verdünnungstank for water treatment with pump and water inlet unit (sprayer, Vernebier, Eindüser etc.).

12 is not open during the daytime phase. The solar energy heated above the mirror geometries of the solar panel 1 what ^¬ serfreie salt medium in the salt tank 5 and 11 and provides for the steam generation via the heat exchanger unit 7, which generates electricity with steam cycle 7 _^ 8/9 _^ 10. When Sonnenun ^¬ tergang or maintenance / drainage, the line 12 is opened and continuously via the water reservoir 3 liquid, vaporous or sprayed water via the pump 14 in the dilution tank 15 entered. This results in a low-melting salt mixture, which is decoupled, for example, during the night ^¬ operation via 1->12-> 15 is circulated. Since a reduced flow rate may be desirable, a (circulation) pump 16 is used within the decoupled circuit ^¬ run. To avoid (over) pressure peaks during the addition of water in 15, a pressure relief valve 17 can serve for the Ent ^¬ voltage. The energy is generated - decoupled by bypass 12 - on the emptying of the thermal reservoir 5 via heat exchanger unit 7 in the cold salt tank 11. At Son ^¬ sunrise the water-containing heat medium is pumped into the hot tank, whereupon evaporation of the water occurs quickly. To avoid pressure conditions in the storage tank 5, a pressure relief valve 17 may serve. Bypass 12 is closed. The evaporating water is condensed via the vapor phase condenser (coupled with a steam separator) 4 and stored in the water tank 3 for the next feed cycle. Storage tank 15 may be prefilled with molten salt and / or water-diluted molten salt.

FIG. 3 shows a circuit diagram of an embodiment with intermediate tanks. The addition of the water takes place here via a dilution tank 15. A later emptying takes place in the cold salt tank 11.

During the daytime phase the bypass 12 is not open. The solar energy heated above the mirror geometries 1 what ^¬ serfreie salt medium in the salt tank 5 and 11 and provides for the generation of steam through the heat exchanger unit 7, which generates steam circuit 7 _^ _^ 10 8/9 electricity. When Sonnenun ^¬ tergang or maintenance of the bypass 12 is opened and the water reservoir 3 continuously liquid, vaporous or sprayed water via the pump 14 in the Dilution tank 15 registered. This results in a low-melting salt mixture, which is decoupled during the night mode via 1->12-> 15, for example. Since a reduced flow rate may be desirable, a (recirculation) pump 16 operates within the decoupled circuit. to

In order to avoid (over) pressure peaks during the addition of water in 15, a pressure relief valve 17 can serve for the relaxation.

The energy is generated - decoupled by bypass 12 - on the emptying of the thermal reservoir 5 via Wärmetau ^¬ shear unit 7 in the cold salt tank 11. At sunrise, the water-containing heat medium is pumped into the cold tank, whereupon rapid evaporation of the water occurs. This tank is filled at the beginning of the day with molten salt, which has a sufficient residual temperature to dehydrate the water-containing heat transfer medium.

To avoid pressure conditions in tank 11 and 15, a pressure relief valve 17 may serve. Bypass 12 is closed. The evaporating water is condensed via the vapor phase condenser (coupled with a steam separator) 4 and stored in the water tank 3 for the next feed cycle. Storage tank 15 may be prefilled with molten salt and / or water-diluted molten salt.

Finally, FIG. 4 shows an exemplary embodiment in which the solar thermal system is guided without salt storage tanks. The addition of the water is again via a dilution ^¬ tank 15, the drainage then via a Austreibetank 18th

During the daytime phase the bypass 12 is not open. The solar energy heated above the mirror geometries of the solar panel 1, the anhydrous salt medium and provides the Damp ^¬ ferzeugung via heat exchanger unit 7, which generates electricity 10 via Dampfkreis- run 7 _^ _^ 8/9. At sunset or maintenance work, the bypass 12 is opened and continuously via the water reservoir 3 liquid, vapor or sprayed water via the pump 14 in the dilution tank 15 registered. This results in a low-melting salt mixture, which is decoupled during the night mode via 1->12-> 15, for example. Since a reduced Flussge ^¬ speed may be desirable, is a (re- rolling) pump 16 within the decoupled circuit. to

In order to avoid (over) pressure peaks during the addition of water in 15, a pressure relief valve 17 can serve for the relaxation. At sunrise, the water-containing heat medium is pumped into the expulsion tank 18. This is brought to or maintained at temperature by means of feed unit 19 by any means (e.g., gas, coal, oil, electricity) to dewater the feed water-containing medium. For this purpose Austreibetank 18 may already be filled with dehydrated, hot salt medium to ensure a continuous exchange of the medium in 1. This can be useful, the

Temporarily bypass steam production via 7 until 1 is completely replaced.

The invention discloses for the first time a possibility of how solar thermal energy can be operated economically. The innovation presented here makes it possible to use a cheap heat transfer fluid (HTF) as well as to either save the energy-consuming additional heating overnight or to significantly reduce it. For this purpose, a water tank is simply installed in the system without threat to the environment, by the dilution of the salt takes place by adding water when not operating the solar heating.

Claims

claims

1. Solar thermal power plant with a water-containing or anhydrous salt as a heat exchange fluid (HTF) comprising at least the following modules:

a first cycle with HTF

a solar field (1) with mirror geometries and lines in which the HTF flows,

a first line for the heated HTF, which leads from the solar field to the heat exchanger (7)

a second line for the cooled HTF, which leads from the Wärmetau ^¬ shear (7) to the solar field (1) and

a conduit (12) for introducing a diluent for the HTF comprises and

the two circuits are connected via the heat exchanger (7).

2. Power plant according to claim 1, wherein water is used as dilu ^¬ medium.

3. Power plant according to one of claims 1 or 2, wherein lines, pumps, modules and / or tanks of the plant of stainless steel and / or treated with a corrosion-inhibiting coating inside.

4. Power plant according to claim 3, wherein the lines, pumps, modules and / or the tanks of the plant are made of carbon-containing iron steel.

5. Power plant according to one of the preceding claims, wherein the HTF is a hydrous or anhydrous salt with one or more cations selected from the group of alkali and / or alkaline earth cations, and one or more anions selected from the group of nitrates, (Hydrogen) - carbonates, fluorides, chlorides, (hydrogen) sulfates, bromides, iodides, and / or hydroxides.

6. Power plant according to one of the preceding claims, in which a pressure relief valve and / or a steam separator with associated steam condenser are provided on at least one tank.

7. A method for operating a solar thermal power plant, wherein the temperature of the HTF is kept in the line system of the solar thermal power plant above its melting point characterized in that the melting point of the HTF is shifted by the addition of diluent at the drop in temperature to lower temperatures.

8. The process according to claim 7, wherein the addition of the diluent by means of dripping, spraying, misting and / or jetting takes place continuously.

9. The method according to any one of claims 7 or 8, wherein the two circuits of the power plant are decoupled from each other overnight or during maintenance of the system.

10. The method of claim 9, wherein the HTF is heated in the decoupled, the solar field comprehensive cycle before sunrise or start-up of the plant well above the melting point and then suddenly expanded into an empty tank.