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

Abstract

To operate solar thermal technology economically, a cheap heat transfer fluid is used. To either completely spare or significantly reduce the energy-intensive auxiliary heating at night, a water tank is simply installed in the plant without a threat to the environment. With the water tank, the salt HTF is thinned by adding water when the solar heating is not in operation.

Claims

1. A solar thermal power station using a water-free or water-containing salt as a heat transfer fluid (HTF), comprising: a first circuit containing the HTF; a second circuit containing steam to drive generators; and a heat exchanger connecting the first and second circuits, where the first circuit comprises: a solar field comprising mirror geometries and conduits in which the HTF flows; a first conduit for heated HTF which leads from the solar field to the heat exchanger; a heated HTF reservoir arranged along the first conduit; a second conduit for cooled HTF which leads from the heat exchanger to the solar field; a cooled HTF reservoir arranged along the second conduit; a third conduit for introducing a diluent to the HTF; a plurality of pumps including a first pump coupled to the heated HTF reservoir or the cooled HTF reservoir and configured to pump the HTF and diluent into the heated HTF reservoir or cooled HTF reservoir; a plurality of flow valves; and wherein the plurality of flow valves and pumps are controllable to operate the solar thermal power station in the following modes: an energy generation mode in which the flow valves are controlled to pass a flow of HTF through the solar field, the first conduit, the heated HTF reservoir, the heat exchanger, the second conduit, the cooled HTF reservoir, and back into the solar field; and a decoupled mode in which the flow valves are controlled to (a) route the HTF through a decoupled circuit that passes through the solar field but is decoupled from the heat exchanger such that the HTF routed through the decoupled circuit bypasses the heat exchanger, and (b) couple the third conduit to the decoupled circuit to supply diluent to the HTF in the decoupled circuit, the diluent reducing a melting point of the HTF; and wherein during a transition from the decoupled mode to the energy generation mode, the flow valves and the first pump are controlled to pump the HTF and diluent into the heated HTF reservoir or cooled HTF reservoir to rapidly depressurize the HTF and diluent to vaporize and separate the diluent from the HTF.

2. The power station as claimed in claim 1, wherein water is used as the diluent.

3. The power station as claimed in claim 1, wherein the conduits, pumps, and/or cooled and heated HTF reservoirs are made of stainless steel.

4. The power station as claimed in claim 3, wherein the conduits, pumps, and/or cooled and heated HTF reservoirs are made of high carbon stainless steel.

5. The power station as claimed in claim 1, wherein inner surfaces of the conduits, pumps, and/or cooled and heated HTF tanks reservoirs are treated with a corrosion-inhibiting coating.

6. The power station as claimed in claim 1, wherein the HTF is a water-containing or water-free salt having one or more cations selected from the group consisting of alkali metal cations and alkaline earth metal cations, and the HTF has one or more anions selected from the group consisting of nitrates, (hydrogen)carbonates, fluorides, chlorides, (hydrogen)sulfates, bromides, iodides and hydroxides.

7. The power station as claimed in claim 1, wherein an over-pressure valve and/or a vapor separator with an associated vapor condenser are provided on at least one of the cooled HTF reservoir or the heated HTF reservoir.

8. The power station as claimed in claim 1, wherein the heated HTF reservoir comprises a hot salt HTF tank, the first conduit leads from the solar field to the heat exchanger via the hot salt HTF tank, the hot salt HTF tank has an over-pressure valve, a vapor separator and an associated vapor condenser, and the vapor separator removes the diluent from the hot salt HTF tank.

9. The power station as claimed in claim 1, wherein the diluent is water, the HTF is water-free when driving the generators, and the HTF is water-containing overnight.

10. A method of operating a solar thermal power station, comprising: operating the solar thermal power station in an energy generation mode during a day time period, including: heating a salt heat transfer fluid (HTF) using mirrors in a solar field, to thereby produce hot HTF; transferring the hot HTF to a heat exchanger; removing heat from the hot HTF in the heat exchanger to produce a cold HTF and to generate electricity; transferring cold HTF from the heat exchanger to the solar field; operating the solar thermal power station in a decoupled mode during a reduced solar energy period in which the temperature of the HTF decreases, including: adding a diluent to the HTF to thereby reduce a melting point of the HTF and to maintain the HTF at a temperature above the melting point of the HTF; decoupling the solar field from the heat exchanger, such that the HTF does not run from the solar field to the heat exchanger; and transitioning the solar thermal power station from the decoupled mode to the energy generation mode, including delivering the HTF and diluent to a vaporization tank and rapidly depressurizing the HTF and diluent, causing rapid vaporization of the diluent.

11. The method as claimed in claim 10, wherein the diluent is added continuously when the temperature of the HTF decreases by dropwise addition, spraying in, introduction of mist and/or introduction of a jet.

12. The method as claimed in claim 10, wherein the solar field is decoupled from the heat exchanger overnight or during maintenance work.

13. The method as claimed in claim 12, wherein for transitioning the solar thermal power station from the decoupled mode to the energy generation mode, the HTF is heated to significantly above the melting point of the HTF before the solar field is re-coupled to the heat exchanger, and after the HTF is heated to significantly above the melting point of the HTF, the HTF is suddenly depressurized in the vaporization tank.

14. The method as claimed in claim 10, wherein the solar field is decoupled from the heat exchanger when the diluent is added.

15. The method as claimed in claim 10, wherein the diluent is water, the HTF is water-free when driving the generators, and the HTF is water-containing overnight.

16. The method of claim 10, wherein, during operation of the solar thermal power station in the energy generation mode, the vaporization tank operates as a thermal reservoir for the hot HTF.

17. The method of claim 16, wherein, operation of the solar thermal power station in the decoupled mode includes pulping heated HTF remaining in the thermal reservoir through the heat exchanger and into a cold HTF reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 shows a schematic depiction of a solar thermal power station with direct introduction of the diluent into the conduit to the solar field,

(3) FIG. 2 shows the introduction of diluent into the second tank containing cooled HTF,

(4) FIG. 3 shows an embodiment having an intermediate tank in the feed line for the HTF to the solar field and

(5) FIG. 4 shows an embodiment having an intermediate tank in the discharge line for the HTF from the solar field to the first tank containing heated HTF.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(6) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

(7) FIG. 1 shows a flow diagram having the first circuit, a solar field 1, an optional additional firing/accompanying heating facility 2, a tank for addition of water 3, a vapor condenser 4, for example with upstream vapor separator, a first tank 5 which serves as hot salt melt store, a pump 6 for hot salt melt, as connection to the second circuit of a heat exchanger unit 7 and/or a steam generator system via 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 field 1, the conduit goes via the “cold” tank 11, viz. the cold melt store having temperatures of, for example, from 250° C. to 290° C. In the example shown here, the conduit 12 for introduction of the diluent leads into this cold tank. The pump for cold salt melt 13 which sends the salt melt back to the solar field 1 can also be seen. During the night, the salt melt leaving the solar field 1 is, according to this example, conveyed via the conduit 12 into the tank 11 where it is diluted with water.

(8) During the daytime phase, the conduit 12 is not opened. The energy from the sun heats the water-free HTF, for example a salt medium in the tank(s) 5 and 11, by the mirror geometries of the solar field 1 and generates steam via the heat exchanger unit 7 which produces electricity by turbine 8 and a generator 9. Water vapor is recondensed to form liquid water by cooling unit 10. When the sun goes down or during maintenance work/drainage activity, etc., the conduit 12 is opened and liquid and/or gaseous water is introduced continuously or discontinuously via the water reservoir 3 and the water pump 14 to a salt dilution process. This forms a low-melting salt mixture which is circulated in a manner decoupled from the steam generation process. Energy generation is then effected just by emptying the thermal reservoir 5 via pump 6 and heat exchanger 7 into the cold salt tank 11. When, for example, the sun comes up, the water-containing heat transfer medium is pumped in the decoupled solar field circuit 1.fwdarw.12.fwdarw.13 into the emptied hot salt tank 5, whereupon rapid vaporization of the water present occurs. The conduit 12 is closed for this purpose. The vaporizing water is condensed by the vapor phase condenser (coupled to a vapor separator) 4 and stored in the water tank 3 for the next feed cycle. The increase in the volume caused by addition of water has to be appropriately regulated.

(9) The heat exchanger unit 7 is, for example, the combination of economizer, vaporizer, superheater and/or reheater which is known to those skilled in the art.

(10) FIG. 2 again shows a similar flow diagram but with the additional components “15” intermediate/dilution tank for treatment of water, having a pump and water introduction unit (sprayer, mister, injector, etc.).

(11) During the daytime phase, 12 is not opened. The energy from the sun heats the water-free salt medium in the salt tanks 5 and 11 by the mirror geometries of the solar field 1 and generates steam via the heat exchanger unit 7, which generates electricity by the steam circuit 7.fwdarw.8/9.fwdarw.10. When the sun goes down or during maintenance work/drainage, the conduit 12 is opened and liquid, gaseous or sprayed water is continuously introduced via the water reservoir 3 and the pump 14 into the dilution tank 15. This forms a low-melting salt mixture which is, for example during nighttime operation, circulated in a decoupled manner via 1.fwdarw.12.fwdarw.15. Since a reduced flow velocity can be desirable, a (circulation) pump 16 is employed within the decoupled circuit. To avoid (over-)pressure peaks during the introduction of water into 15, an over-pressure valve 17 can serve for depressurization. Energy generation is effected, decoupled by bypass 12, via emptying of the thermal reservoir 5 via heat exchanger unit 7 into the cold salt tank 11. When the sun comes up, the water-containing heat transfer medium is pumped into the hot tank, whereupon rapid vaporization of the water occurs. To avoid pressure conditions in the storage tank 5, an over-pressure valve 17 can be employed. Bypass 12 is closed for this purpose. The vaporized water is condensed by the vapor-phase condenser (coupled with a vapor separator) 4 and stored in the water tank 3 for the next feed cycle. Storage tank 15 can be prefilled with salt melt and/or water-diluted salt melt.

(12) FIG. 3 shows a flow diagram of an embodiment with intermediate tanks. The addition of the water is in this case carried out via a dilution tank 15. Later emptying occurs into the cold salt tank 11.

(13) During the daytime phase, the bypass 12 is not opened. The energy from the sun heats the water-free salt medium in the salt tanks 5 and 11 by the mirror geometries 1 and generates steam via the heat exchanger unit 7, which generates electricity by steam circuit 7.fwdarw.8/9.fwdarw.10. When the sun goes down or in the event of maintenance work, the bypass 12 is opened and liquid, gaseous or sprayed water is introduced via the water reservoir 5 and the pump 14 into the dilution tank 15. This forms a low-melting salt mixture which is, for example during nighttime operation, circulated in a decoupled manner via 1.fwdarw.12.fwdarw.15. Since a reduced flow velocity can be desirable, a (circulation) pump 16 is employed within the decoupled circuit. To avoid (over-)pressure peaks during the introduction of water into 15, an over-pressure valve 17 can be employed for depressurization.

(14) Energy generation is effected, decoupled by bypass 12, via emptying of the thermal reservoir 5 via heat exchanger unit 7 into the cold salt tank 11. When the sun comes up, the water-containing heat transfer medium is pumped into the cold tank, whereupon rapid vaporization of the water occurs. This tank is at the beginning of the day filled with salt melt which has a sufficient residual temperature to dewater the water-containing heat transfer medium.

(15) To avoid pressure conditions in tanks 11 and 15, an over-pressure valve 17 can be employed. Bypass 12 is closed for this purpose. The vaporized water is condensed by the vapor-phase condenser (coupled with a vapor separator) 4 and stored in the water tank 3 for the next feed cycle. Storage tank 15 can be filled with salt melt and/or water-diluted salt melt.

(16) Finally, FIG. 4 shows an example in which the solar thermal plant is operated without salt storage tanks. The introduction of the water is once again effected by a dilution tank 15, and dewatering is then effected via a stripping tank 18.

(17) During the daytime phase, the bypass 12 is not opened. The energy from the sun heats the water-free salt medium via the mirror geometries of the solar field 1 and generates steam via heat exchanger unit 7, which generates electricity via steam circuit 7.fwdarw.8/9.fwdarw.10.

(18) When the sun goes down or during maintenance work, the bypass 12 is opened and liquid, gaseous or sprayed water is continuously introduced via the water reservoir 3 and the pump 14 into the dilution tank 15. This forms a low-melting salt mixture which is, for example during nighttime operation, circulated in a decoupled manner via 1.fwdarw.12.fwdarw.15. Since a reduced flow velocity can be desirable, a (circulation) pump 16 is employed within the decoupled circuit. To avoid (over-)pressure peaks during introduction of water into 15, an over-pressure valve 17 for depressurization can be employed. When the sun comes up, the water-containing heat transfer medium is pumped into the stripping tank 18. This is brought to or maintained at temperature by additional firing unit 19 operated in any way (e.g. gas, coal, oil, electricity) in order to dewater the water-containing medium fed in. For this purpose, stripping tank 18 can be initially filled with dewatered, hot salt medium in order to ensure continuous replacement of the medium in 1. For this purpose, it can be advantageous for the steam generation via 7 to be temporarily bypassed until 1 has been completely replaced.

(19) For the first time there is a possible way of operating a solar thermal plant economically. The novel method presented here makes it possible both to use a cheap heat transfer fluid (HTF) and either to completely save or significantly reduce the energy-consuming supplementary heating overnight. For this purpose, a water tank is simply installed in the plant, without presenting a threat to the environment, and dilution of the salt is effected by addition of water from this tank when solar heating is not operational.

(20) The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).