METHOD FOR OPERATING A SOLAR THERMAL POWER PLANT, AND SOLAR THERMAL POWER PLANT

Abstract

A method for operating a solar thermal power plant comprising multiple solar radiation receivers operated using a molten salt as the heat transfer medium, wherein each solar radiation receiver comprises a reflector device and an absorber tube, includes: preheating of the absorber tubes, in the state in which said tubes are empty of the molten salt, to a temperature T by concentrating solar radiation on the absorber tubes by means of the reflector devices, wherein the temperature T is greater than or equal to the melting temperature of the salt; after reaching the temperature T: introduction of the molten salt into the absorber tubes and recirculated conduction of the molten salt through the absorber tubes while simultaneously repositioning the reflector devices depending on the position of the sun; on ending the operation: release of the molten salt out of the absorber tubes.

Claims

1-19. (canceled)

20. A method for operating a solar thermal power plant comprising a plurality of solar radiation receivers operated using a molten salt as the heat transfer medium, wherein each solar radiation receiver has a reflector device and an absorber pipe, the method comprising the following steps: preheating in a state emptied of molten salt, the absorber pipes to a temperature T by concentrating solar radiation on the absorber pipes by means of the reflector devices, wherein the temperature T is higher than or equal to the melting temperature of the salt; introducing the molten salt into the absorber pipes and conveying the molten salt through the absorber pipes in a recirculating manner, while at the same time adjusting the reflector devices according to the position of the sun; discharging the molten salt from the absorber pipes.

21. Method of claim 20, wherein the reflector devices are defocused when operation is ended.

22. Method of claim 20, wherein when preheating the absorber pipes, a power control of the reflector devices is performed in dependence on the position of the sun and the weather conditions.

23. Method of claim 20, wherein discharging the molten salt from the absorber pipes is effected at least in part due to gravity.

24. Method of claim 20, wherein a secondary heat transfer medium, preferably an inert gas, preferably nitrogen, is fed through the absorber pipes, preferably in a recirculating manner, during the preheating of the absorber pipes.

25. Method of claim 24, wherein for discharging the molten salt from the absorber pipes, the secondary heat transfer medium is introduced into the absorber pipes at a pressure higher than ambient pressure, wherein the secondary heat transfer medium presses the molten salt out of the absorber pipes.

26. Method of claim 20, wherein when discharging the molten salt from the absorber pipes, the molten salt is at least in part pumped out of the absorber pipes.

27. Method of claim 22, wherein during the preheating of the absorber pipes, the reflector devices are focused only partly on the absorber pipes or are periodically focused and defocused.

28. Method of claim 20, wherein when being discharged from the absorber pipes, the molten salt is conducted into at least one thermally insulated storage tank.

29. Method of claim 20, wherein when the molten salt is introduced into the absorber pipes, the secondary heat transfer medium is conducted into at least one secondary storage tank.

30. Method of claim 25, wherein the secondary heat transfer medium remains in the absorber pipes when the power plant is not in operation.

31. Solar thermal power plant for operation using a molten salt as the heat transfer medium and comprising: a plurality of solar radiation receivers, each having a reflector device and an absorber pipe through which the heat transfer medium can be conducted, wherein the absorber pipes are arranged with a gradient in the direction of the at least one storage tank for the molten salt.

32. Solar thermal power plant of claim 31, wherein the absorber pipes of a plurality of reflector devices are connected to form an absorber pipe chain and form a continuous gradient.

33. Solar thermal power plant of claim 31, wherein a supply line for a secondary heat transfer medium opens into an upper end of an absorber pipe or an absorber pipe chain.

34. Solar thermal power plant of claim 32, wherein the solar radiation receivers are arranged in loops, wherein each respective loop is formed by two parallelly arranged absorber pipe chains with the associated reflector devices, and wherein a transverse connection connects the upper ends of the absorber pipe chains.

35. Solar thermal power plant of claim 34, wherein the supply line for a secondary heat transfer medium opens into the transverse connection.

36. Solar thermal power plant of claim 33, wherein by at least one secondary storage tank for the secondary heat transfer medium.

37. Solar thermal power plant of claim 36, wherein the at least one secondary storage tank is formed by at least one storage tank for the molten salt.

38. Solar thermal power plant of claim 33, wherein a pump or a compressor may be arranged in the supply line for the secondary heat transfer medium, by means of which the secondary heat transfer medium can be introduced into an absorber pipe or an absorber pipe chain at a pressure higher than ambient pressure

Description

[0038] The following is a detailed explanation of the invention with reference to the accompanying sole FIGURE.

[0039] The sole FIGURE shows a schematic illustration of a solar thermal power plant 100 according to the present invention. The solar thermal power plant 100 is operated using a molten salt as the heat transfer medium.

[0040] The solar thermal power plant 100 has a plurality of solar radiation receivers 1 that each comprise a reflector device 3. In the embodiment illustrated the solar radiation receivers 1 are designed as parabolic trough collectors so that the reflector devices have a parabolic shape. The solar radiation receivers 1 each comprise an absorber pipe 5. A plurality of solar radiation receivers 1 (four in the embodiment illustrated) are arranged one after the other in a row, the absorber pipes 5 forming an absorber pipe chain. In the embodiment illustrated the absorber pipe chain is designed as a continuous pipe so that the absorber pipes 5 are each partial pipes of the continuous pipe. Two rows of solar radiation receivers with a respective absorber pipe chain are arranged in parallel to each other and are connected to each other at one of their ends by means of a transverse connection 7 so that the solar radiation receivers 1 form a loop 9. The solar thermal power plant 100 may comprise a plurality of these loops 9 of solar radiation receivers 1, although only one loop 9 is illustrated for the sakes of clarity.

[0041] The loop 9 of solar radiation receivers 1 illustrated is arranged to be inclined so that the transverse connection 7 connects two upper ends of the absorber pipe chains. In other words: The absorber pipes 5 of the absorber pipe chains show a gradient. The lower ends of the absorber pipes 5 or the absorber pipe chains are connected with a storage tank 1 for the molten salt. The absorber pipes 5 thus have a gradient in the direction of the storage tank 11. The solar thermal power plant 100 further has a hot salt tank 13. In normal operation the storage tank 11, which preferably is thermally insulated, forms a so-called cold salt tank. The molten salt is conveyed, for example by means of pumps not illustrated herein, from the storage tank 11 through the loop 9 of solar radiation receivers 1 and is heated by the solar radiation reflected from the reflector devices 3 onto the absorber pipes 5. Thereafter, the molten salt is fed into the hot salt tank 13. From the hot salt tank 13 the molten salt is directed to a heat exchanger not illustrated herein, via which the thermal energy may be transferred for further exploitation, for example to a steam turbine process including the generation of electricity. Then, the molten salt is returned into the storage tank 11. During normal operation the molten salt is thus recirculated through the solar radiation receivers, with the molten salt possibly being heated from a temperature of 290 C. to a temperature of about 550 C., for example.

[0042] The storage tank 11 and the hot salt tank 13 each include a nitrogen buffer 15, whereby corrosion by air inclusions and the ageing of the molten salt are avoided.

[0043] When the operation of the solar thermal power plant 100 is ended, the molten salt is discharged from the absorber pipes 5 and is conducted into the storage tank 11. Here, due to the gradient, the molten salt flows towards the storage tank 11 under the effect of gravity. In the embodiment illustrated, when the molten salt is discharged, the molten salt flows through the front solar radiation receivers 1, seen in the normal flow direction (i.e. the flow direction in normal operation), in a direction opposite to the normal flow direction of the molten salt, whereas the rear solar radiation receivers 1, seen in the normal flow direction, are discharged in the normal flow direction. The normal flow direction of the molten salt is indicated by arrows. The solar radiation receivers 1 in a loop 9 are thus very quickly emptied of molten salt by making the molten salt flow simultaneously from the parallelly arranged absorber pipe chains.

[0044] The absorber pipes 5 or the absorber pipe chains are preferably inclined under an angle of 10 with respect to the horizontal plane.

[0045] The solar thermal power plant 100 further comprises a supply line 17 opening into the transverse connection 7 at the upper end of the absorber pipe chains. A secondary heat transfer medium can be introduced into the absorber pipes 5 via the supply line. The secondary heat transfer medium may be nitrogen for example. In this regard, nitrogen from the nitrogen buffer 15 of the storage tank 11 can be used. Preferably the secondary heat transfer medium is introduced into the absorber pipes 5 while the molten salt is discharged. Since nitrogen from the nitrogen buffer 15 is displaced from the storage tank 11 as the molten salt is discharged from the absorber pipes, the same can advantageously be conducted into the absorber pipes 5 via the supply line 17. The supply line 17 may be provided for example with a compressor or a pump arranged therein, via which the secondary heat transfer medium is introduced into the absorber pipes 5 at high pressure. Thereby, the secondary heat transfer medium can be of assistance in discharging the molten salt, the molten salt pressing the secondary heat transfer medium out of the absorber pipes 5.

[0046] To assist in discharging, it is further possible to use a pump not illustrated herein.

[0047] During the operating pause of the solar thermal power plant which for example occurs at night or in periods of bad weather or for maintenance purposes, the secondary heat transfer medium remains in the absorber pipes 5.

[0048] When the solar thermal power plant is started up, first the secondary heat transfer medium is recirculated through the solar radiation receivers 1. From the defocused position assumed during the operating pause, the reflector devices are focused onto the absorber pipes 5 to preheat these for the regular operation. The recirculation of the secondary heat transfer medium distributes the heat relatively uniformly in the absorber pipes 5 so that excessive temperature gradients are avoided that could cause damage to the absorber pipes 5. Depending on the intensity of the solar radiation it may be necessary that the reflector devices are not fully focused on the absorber pipes 5 during the preheating phase, but that a so-called reduced focusing is performed, wherein the focus only affects an edge portion of the absorber pipe, for example. The heat input can thus be reduced. As an alternative it may also be provided that the reflector devices are alternately focused and defocused.

[0049] As soon as the absorber pipes have a temperature T that is higher than or equal to the melting temperature of the salt, the introduction of the molten salt into the absorber pipes 5 can be started. In doing so, the molten salt displaces the secondary heat transfer medium and presses the same into a secondary storage tank. In the embodiment illustrated the secondary storage tank is formed by the storage tank 11, wherein the nitrogen used as the secondary heat transfer medium is stored in the form of the gas buffer contained in the storage tank 11.

[0050] Due to the absorber pipes 5 being preheated to the temperature T it is avoided that the molten salt introduced into the absorber pipes 5 threatens to solidify.

[0051] Thereafter, the regular operation of the solar thermal power plant 100 can be performed, in which the molten salt is recirculated through the solar radiation receivers 1.

[0052] During the preheating process of the absorber pipes the secondary heat transfer medium can be recirculated through the absorber pipes flowing in the normal direction of flow or it can be conducted via the supply line 17 so that the parallel absorber pipe chains of the loop 9 are flown through in parallel.

[0053] The solar thermal power plant 100 of the present invention or the present method for operating a solar thermal power plant 100, respectively, is advantageous in that the molten salt does not remain in the absorber pipes during operating pauses and that the risk of the molten salt solidifying is avoided and a complex heating of the molten salt during the operating pauses becomes obsolete. By discharging the molten salt into a thermally insulated storage tank 11 it becomes possible to temporarily store a great part of the thermal energy contained in the molten salt during the operating pauses so that the energy can be used again when the solar thermal power plant 100 is started again. Only in case of longer operating pauses, for example in bad weather periods or in winter, is heating necessary before starting the power plant, if the molten salt solidifies in the storage tank 11.

[0054] In the solar thermal power plant 100 of the present invention or the present method it may be provided that discharging the molten salt from the absorber pipes is effected before each operating pause. However, it may basically also be provided that the molten salt is discharged from the absorber pipes if the operating pause is planned for a longer predetermined period. For example, the daily emptying process of an entire solar field before a nightly operating pause may be too troublesome if the night hours are rather short in summer. Therefore, the method of the present invention may also be implemented only in longer operating pauses, e.g. during bad weather periods or for maintenance periods.

[0055] The method of the present invention may for example be implemented only for parts of a power plant if repair work is required there.