SOLAR POWER PLANT COMPRISING A FIRST HEAT TRANSFER CIRCUIT AND A SECOND HEAT TRANSFER CIRCUIT

Abstract

The invention relates to a solar power plant with a first heat transfer medium circuit and with a second heat transfer medium circuit, in which the first heat transfer medium circuit comprises a store (3) for hot heat transfer medium and a store (5) for cold heat transfer medium and also a pipeline system (6) connecting the stores (3, 5) for hot heat transfer medium and for cold heat transfer medium and leading through a solar array (7), and the second heat transfer medium circuit comprises a pipeline system (9) connecting the stores (3, 5) for hot heat transfer medium and for cold heat transfer medium and in which at least one heat exchanger (11) for the evaporation and superheating of water is accommodated, the at least one heat exchanger (11) having a region through which the heat transfer medium flows and a region through which water flows, said regions being separated by a heat-conducting wall, so that heat can be transmitted from the heat transfer medium to the water. Each heat exchanger (11) has a break detection system (21), by means of which a possible break of the heat-conducting wall can be detected, and valves (23) for the closing of supply lines (13, 17) and outflow lines (15, 19) for heat transfer medium and water, upon the detection of a break the valves (23) in the supply lines (13, 17) and outflow lines (15, 19) for heat transfer medium and water being closed.

Claims

1.-16. (canceled)

17. A solar power plant with a first heat transfer medium circuit and with a second heat transfer medium circuit, in which the first heat transfer medium circuit comprises a store for hot heat transfer medium and a store for cold heat transfer medium and also a pipeline system connecting the stores for hot heat transfer medium and for cold heat transfer medium and leading through a solar array, and the second heat transfer medium circuit comprises a pipeline system connecting the stores for hot heat transfer medium and for cold heat transfer medium and in which at least one heat exchanger for the evaporation and superheating of water is accommodated, the at least one heat exchanger having a region through which the heat transfer medium flows and a region through which water flows, said regions being separated by a heat-conducting wall, so that heat can be transmitted from the heat transfer medium to the water, wherein each heat exchanger has a break detection system, by means of which a possible break of the heat-conducting wall can be detected, and valves for the closing of supply lines and outflow lines for heat transfer medium and water, upon the detection of a break the valves in the supply lines and outflow lines for heat transfer medium and water being closed.

18. The solar power plant as claimed in claim 17, wherein the pipeline system for the heat transfer medium in the second heat transfer medium circuit has a bypass, to which the supply line and the outflow line for the heat transfer medium are connected, and valves are comprised, which close the bypass during normal operation and, when a break is detected in the heat exchanger, close the supply line and the outflow line to the heat exchanger and open the bypass, so that the heat transfer medium flows through the bypass.

19. The solar power plant as claimed in claim 17, wherein a backflow prevention is positioned in the supply line to the heat exchanger.

20. The solar power plant as claimed in claim 19, wherein the backflow prevention is a diaphragm.

21. The solar power plant as claimed in claim 17, wherein one or more emptying lines are comprised, which are in each case closed by means of securing closures which open when a limit pressure is overshot.

22. The solar power plant as claimed in claim 21, wherein in each case one or more emptying lines issue into a collecting tank.

23. The solar power plant as claimed in claim 21, wherein the emptying lines in each case branch off upwardly from the outflow line.

24. The solar power plant as claimed in claim 21, wherein the emptying line is filled with gas, the gas being held at a pressure which corresponds to the pressure of the heat transfer medium leaving the heat exchanger, so that no heat transfer medium flows into the emptying line.

25. The solar power plant as claimed in claim 21, wherein the securing closure comprises heating, by means of which the securing closure is heated to a temperature above the solidification temperature of the heat transfer medium.

26. The solar power plant as claimed in claim 21, wherein the emptying lines are arranged in one or more outflow lines downstream of at least one heat exchanger in the flow direction of the heat transfer medium or are in each case mounted directly on apparatus flanges of the heat exchanger.

27. The solar power plant as claimed in claim 21, wherein the securing closure is a bursting disk.

28. The solar power plant as claimed in claim 27, wherein the bursting disk is washed around with gas.

29. The solar power plant as claimed in claim 17, wherein a quarantine tank is accommodated in the outflow line.

30. The solar power plant as claimed in claim 29, wherein the quarantine tank is positioned downstream of the emptying line in the flow direction of the heat transfer medium.

31. The solar power plant as claimed in claim 17, wherein the heat transfer medium is a molten salt.

32. The solar power plant as claimed in claim 17, wherein the heat transfer medium is an alkali metal nitrate, an alkali metal nitrite, a mixture of different alkali metal nitrates or of alkali metal nitrites or a mixture of alkali metal nitrate and of alkali metal nitrite.

Description

[0048] In the figures:

[0049] FIG. 1 shows a diagrammatic illustration of the first and the second heat transfer medium circuit of a linearly concentrating solar power plant,

[0050] FIG. 2 shows an outflow line of the heat transfer medium with an emptying line branching off from it,

[0051] FIG. 3 shows a heat exchanger with bursting disks as a securing closure.

[0052] The first heat transfer medium circuit and the second heat transfer medium circuit of a linearly concentrating solar power plant are illustrated in FIG. 1.

[0053] A linearly concentrating solar power plant 1 comprises a hot store 3 and a cold store 5 which are connected to one another by means of a pipeline system 6 of a first heat transfer medium circuit, said pipeline system leading through a solar array 7. In the event of solar radiation, heat transfer medium is conducted out of the cold store 5 through the solar array 7, is heated in the solar array 7 by the radiant solar energy and is led further on to the hot store 3.

[0054] In order to heat the heat transfer medium, for example a molten salt, in the solar array by means of radiant solar energy, receivers are arranged in the solar array. In the receivers, the incident sunlight is reflected in a focused manner with the aid of mirrors onto a pipeline in which the heat transfer medium flows. As a result, the heat transfer medium heats up. In linearly concentrating solar power plants, the receivers are connected in parallel and in series over long distances. In the case of parabolic trough solar power plants, the mirrors are arranged in each case in the form of a parabolic trough around the line, and in Fresnel solar power plants movable mirrors are arranged underneath the pipelines, the mirrors being oriented according to the direction of the solar radiation, in order always to ensure optimal utilization of the radiant solar energy. The receiver lines in the linearly concentrating solar power plant may in this case run linearly parallel to one another, as illustrated here, or else as pipeline loops.

[0055] Alternatively to the solar array 7, illustrated here, of a linearly concentrating solar power plant, it is also possible, for example, to use a tower power plant in which the receiver is arranged as the tip on a tower and the mirrors are oriented onto the tower tip.

[0056] The set-up of a linearly concentrating solar power plant or of a tower power plant and the arrangement of the receivers in the solar array 7 or on the tower of the tower power plant are known to a person skilled in the art.

[0057] When the solar power plant is in operation, the heated heat transfer medium is introduced from the hot store 3 into a second pipeline system 9 of a second heat transfer medium circuit independently of radiant solar energy, that is to say at the times when the sun is not shining. During regular operation, the heat transfer medium is supplied to at least one heat exchanger 11 in which water is preheated, evaporated and superheated. For this purpose, in the heat exchanger 11, heat is transmitted from the heat transfer medium to the water indirectly via a heat-conducting wall, by means of which the region through which the heat transfer medium flows and the region through which the water flows are separated. In this case, it is possible to preheat, evaporate and superheat the water in one heat exchanger or in the plurality of heat exchangers. If a plurality of heat exchangers 11 are used, these may be connected in parallel, so that, in each heat exchanger 11, part of the water is preheated, evaporated and superheated by transmission of heat from part of the heat transfer medium. It is also possible to connect heat exchangers 11 in series. In this case, for example, one heat exchanger is used for evaporating the steam and a further heat exchanger for superheating the steam. It is also possible to connect heat exchangers both in series and in parallel.

[0058] In order to transmit heat from the heat transfer medium to the water in the heat exchanger 11, heat transfer medium is fed into the heat exchanger via a first supply line 13. The heat transfer medium flows through the heat exchanger 11 and leaves this through a first outflow line 15. The water to be evaporated and to be superheated is supplied via a second supply line 17, and the superheated steam generated in the heat exchanger 11 is drawn off through a second outflow line 19 and routed to a turbine. The turbine is driven with the aid of the superheated steam and is connected to a generator in which electrical energy is generated.

[0059] After flowing through the heat exchanger 11, the heat transfer medium flows back into the cold store 5.

[0060] Since high loads act upon the heat-conducting walls in the heat exchanger on account of the high pressure difference between the superheated steam and the heat transfer medium, these walls may break. The result of a break of the heat-conducting wall is that water comes into contact with the heat transfer medium, and if molten salts, in particular nitrites and nitrates of alkali metals, are used, this may lead to a chemical reaction, with nitrogen oxides and alkali metal hydroxides being formed. Moreover, if nitrites are used, the reaction with water also gives rise to nitrates which have a higher solidification temperature than the nitrites. Owing to contact with water, therefore, the heat transfer medium is damaged and can no longer be used during the normal operation of the solar power plant. Moreover, the alkali metal hydroxides which occur have a corrosive action and may damage the material of the plant components of the solar power plant. Due to the formation of nitrogen oxides and also because of the markedly higher pressure in the steam circuit, the pressure in the second heat transfer medium circuit rises.

[0061] In order to recognize a possible break, a break detection system 21 is used. As described above, what are suitable for this are, for example, pressure measurement, a break sensor of a bursting disk or oscillation analysis.

[0062] When a break is detected, the supply line 13 for the heat transfer medium into the heat exchanger 11, the outflow line 15 for the heat transfer medium into the heat exchanger 11 and also the supply line 17 and the outflow line 19 for the water are closed, in order to avoid the situation where heat transfer medium contaminated with water enters the cold store 5 and possibly reaches from there, through the pipeline system 6 and the solar array 7, into the hot store 3. Valves 23 are provided for closing the supply lines 13, 17 and the outflow lines 15, 19 into the heat exchanger 11.

[0063] In order to prevent a pressure shock in the pipeline system 9 of the second heat transfer medium circuit, preferably, as illustrated here, the supply line 13 and the outflow line 15 for the heat transfer medium are connected to one another via a bypass 25. For this purpose, as illustrated here, it is possible to provide three-way valves, a first valve 23.1 being arranged in the supply line 13 of the heat transfer medium to the heat exchanger 11 and a second valve 23.2 being arranged in the outflow line 15 of the heat transfer medium from the heat exchanger 11. In the event of breakage or leakage in the heat exchanger 11, the inflow line 13 and the outflow line 15 are closed and the bypass 25 opened by means of corresponding changeover of the valves 23.1, 23.2. The heat transfer medium can thereby flow further on, unimpeded, and a pressure shock can be avoided. Alternatively, it is also possible, instead of the three-way valves 23.1, 23.2 illustrated here, to provide in each case two two-way valves, in each case one valve being used for closing the inflow line 13 and the outflow line 15 and a second valve being used for opening the bypass. Since the opening and closing of lines can be controlled individually in each case when two two-way valves are used, this embodiment is preferred.

[0064] In order, in the event of a break of a heat-conducting wall in the heat exchanger 11 or in the event of a leak, to prevent a major pressure rise in the pipeline system 9 of the second heat transfer medium, in a preferred embodiment a collecting tank 27 is connected via an emptying line 29 to the outflow line 15 from the heat exchanger 11. For this purpose, the emptying line 29 preferably branches off upwardly from the outflow line 15. By being branched off upwardly, the emptying line, which is preferably flooded with gas, acts as a thermal convection brake.

[0065] In order to avoid the situation where heat transfer medium flows during normal operation into the collecting tank 27, the latter is closed by means of a securing closure 31. The securing closure 31 is in this case configured such that it opens the inflow into the collecting tank 27 in the event of a pressure rise in the outflow line 15 and consequently in the emptying line 29. A suitable securing closure 31 is in this case, for example, a bursting disk.

[0066] In order, furthermore, in the event of a pressure rise due to ingress of the water into the heat transfer medium, to prevent the situation where the heat transfer medium flows with high velocity through the outflow line 15 and, in particular, flows back through the inflow line 13 opposite to the actual flow direction, backflow preventions 33 are preferably installed in the inflow line 13 and the outflow line 15.

[0067] Suitable backflow preventions 33 are, for example, diaphragms in the respective lines, the throughflow cross section being reduced by means of the diaphragms in the region of the respective diaphragm.

[0068] In order, furthermore, to avoid the situation where heat transfer medium contaminated with water enters the cold store before the valves 23 are closed, it is preferable, furthermore, if a quarantine tank 35 is accommodated in the outflow line 15 upstream of the second valve 23.2 in the flow direction of the heat transfer medium. The heat transfer medium flows through the quarantine tank 35, with the result that the transient time between the heat exchanger 11 and the cold store 5 is increased. If heat transfer medium is contaminated with water, this therefore collects in the quarantine tank and can be extracted correspondingly from the quarantine tank, This is advantageous particularly when part of the heat transfer medium contaminated with water has already flowed past the branch-off to the collecting tank 27 before the securing closure 31 opens, or when the pressure in the outflow line 15 is so high that, in spite of the securing closure 31 being opened, part of the heat transfer medium flows further on in the outflow line 15.

[0069] The quarantine tank 35 preferably accommodates fittings, around which the heat transfer medium flows, in order to avoid the situation where full mixing occurs in the quarantine tank 35. The fittings ensure that the heat transfer medium which has flowed first into the quarantine tank 35 is also the first to flow out of the quarantine tank 35 again. Suitable fittings are, for example, floors, around which the heat transfer medium flows in a meandering manner.

[0070] FIG. 2 shows an outflow line of the heat transfer medium with an emptying line branching off from it.

[0071] The emptying line 29 branches off from the outflow line 15 upwardly. In order to protect the securing closure 31 against too high temperatures and against contact with the heat transfer medium during the normal operation of the solar power plant 1, the emptying line 29 is filled with gas. A gas space 41 is consequently formed in the emptying line.

[0072] Filling level measurement 43 with regulation on the emptying line 29 ensures the level of the phase limit 45 between gas and heat transfer medium. If the liquid level is too high, process gas can be conducted into the gas space 41 via a gas line 47. If the level is low, there is no need for any measure.

[0073] Furthermore, a temperature sensor 49 with regulation and heating may be placed in this gas space 41 decoupled thermally from the process conditions in the second heat transfer medium circuit. It is consequently possible to keep the temperature of the gas space 41 reliably always above the solidification temperature of the heat transfer medium.

[0074] Pressure measurement 51, which usually cannot be operated up to the maximum operating temperature, may also be arranged on the thermally insulated gas space 41. Pressure measurement 51 may be used as a detector for a break of a heat-conducting wall in the heat exchanger 11. If a stipulated limit value is overshot, pressure measurement can trigger safety switching, by means of which, for example, the valves 23 are closed.

[0075] Analysis gas may be extracted from the thermally decoupled gas space 41 via an analysis line 53. By the analysis gas being analyzed for water, nitrogen oxides and further reaction products, a break or a small leakage in a heat exchanger 11 can be detected. In addition, it is also possible, when the pressure in the gas space 41 is too high, to discharge gas via the analysis line 53.

[0076] A heat exchanger with bursting disks as a securing closure is illustrated in FIG. 3.

[0077] Alternatively to the embodiment illustrated in FIGS. 1 and 2, in which the emptying line 29 is connected to the outflow line 15, it is also possible to mount the emptying line directly on the heat exchanger 11. For this purpose, at least one flange 61, to which the emptying line 29 can be connected, is formed on the heat exchanger 11. The securing closure 31 is accommodated in the at least one flange 61, the heat exchanger 11 having two flanges 61 in the embodiment illustrated here. If a limit pressure is overshot, the securing closure 31 opens, and the heat transfer medium can flow directly out of the heat exchanger 11 into the emptying line 29.

LIST OF REFERENCE SYMBOLS

[0078] 1 Solar power plant

[0079] 3 Hot store

[0080] 5 Cold store

[0081] 6 Pipeline system of a first heat transfer medium circuit

[0082] 7 Solar array

[0083] 9 Pipeline system of a second heat transfer medium circuit

[0084] 11 Heat exchanger

[0085] 13 Supply line of the heat transfer medium

[0086] 15 Outflow line of the heat transfer medium

[0087] 17 Supply line for water

[0088] 19 Outflow line for steam

[0089] 21 Break detection system

[0090] 23 Valve

[0091] 23.1 First valve

[0092] 23.2 Second valve

[0093] 25 Bypass

[0094] 27 Collecting tank

[0095] 29 Emptying line

[0096] 31 Securing closure

[0097] 33 Backflow prevention

[0098] 35 Quarantine tank

[0099] 41 Gas space

[0100] 43 Filling level measurement

[0101] 45 Phase limit

[0102] 47 Gas line

[0103] 49 Temperature measurement

[0104] 51 Pressure measurement

[0105] 61 Flange