Abstract
A method to operate a steam turbine, a steam turbine, and a concentrated solar power plant with at least a first turbine module with a first stage and at least one second stage, wherein the stages are successively arranged in the flow direction of the steam, a main inlet for channelling steam to the first stage and a bypass arranged parallel to the main inlet for channelling steam to the at least one second stage.
Claims
1. A method to operate a steam turbine, the steam turbine comprising at least a first turbine module with a first stage and at least one second stage, wherein the stages are successively arranged in the flow direction of the steam, a main inlet for channelling steam to the first stage and a bypass arranged parallel to the main inlet for channelling steam to the at least one second stage, the method comprising: a) measuring the temperature of the steam upstream of the turbine module, b) selecting, depending on the measured temperature, whether a first operation mode or a second operation mode is to be used during the operation of the steam turbine, wherein in the first operation mode the first stage and the at least one second stage are used for an expansion of steam and in the second operation mode only the at least one second stage is used for the expansion of steam, and c) channelling steam into the according stage (s) for expansion according to the selected operation mode.
2. The method to operate a steam turbine according to claim 1, wherein, in step a) the temperature of the steam is measured at or near a bifurcation of a feeding pipe of the steam turbine to the main inlet and the bypass of the first turbine module.
3. The method to operate a steam turbine according to claim 1, wherein step c) includes an opening or closing of a bypass valve in the bypass or at the beginning of the bypass.
4. The method to operate a steam turbine according to claim 1, wherein, while the second operation mode is selected, cooling steam is channelled through the first stage to cool the first stage.
5. The method to operate a steam turbine according to claim 4, wherein the cooling steam is preheated.
6. A steam turbine comprising: at least a first turbine module with a first stage and at least one second stage, wherein the stages are successively arranged in the flow direction of the steam, a main inlet for channelling steam to the first stage and a bypass arranged parallel to the main inlet for channelling steam to the at least one second stage, wherein the steam turbine is enabled to perform a method comprising: a) measuring the temperature of the steam upstream of the turbine module, b) selecting, depending on the measured temperature, whether a first operation mode or a second operation mode is to be used during the operation of the steam turbine, wherein in the first operation mode the first stage and the at least one second stage are used for an expansion of steam and in the second operation mode only the at least one second stage is used for the expansion of steam, and c) channelling steam into the according stage (s) for expansion according to the selected operation mode.
7. The steam turbine according to claim 6, wherein the steam turbine comprises a control unit, the control unit enabled to perform the method.
8. The steam turbine according to claim 6, wherein the first turbine module comprises a bypass valve arranged in the bypass or at the beginning of the bypass.
9. The steam turbine according to claim 6, wherein a swallowing capacity of the bypass is larger than the swallowing capacity of the main inlet.
10. The steam turbine according to claim 6, wherein the steam turbine comprises at least two modules, each module with a first stage and at least one second stage, a main inlet for channelling steam to the first stage and a bypass arranged parallel to the main inlet for channelling steam to the at least one second stage, wherein in each respective module the stages are successively arranged in the flow direction of the steam, and wherein each module can be used to perform the method.
11. A concentrated solar power plant comprising: a steam turbine according to claim 6.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention is described with respect to the accompanied figures. The figures show schematically:
[0024] FIG. 1 a first embodiment of a concentrated solar power plant according to the invention and
[0025] FIG. 2 a second embodiment of a concentrated solar power plant according to the invention.
[0026] Elements having the same functions and mode of action are provided in FIGS. 1 and 2 with the same reference signs.
DETAILED DESCRIPTION OF INVENTION
[0027] FIG. 1 shows a possible embodiment of a concentrated solar power plant 30 according to the invention. A steam generator 31, in which the heat input from the sun is used to generate steam, is shown. The steam is led to a steam turbine 1, which comprises in this embodiment a single turbine module 10. In this embodiment, the steam turbine 1 is connected via a gear 34 with a generator 35 to generate electrical power. Of course there are other embodiments of steam turbines 1 according to the invention which do not comprise such gear 34. The turbine module 10 comprises two stages 11, 12 which are successively arranged in the flow direction 2 of the steam. Advantageously, the blading of the different stages 11, 12 are adapted to the expected features of the steam in these stages 11, 12. Advantageously, the blading of the first stage 11 is adapted to high temperature steam and the blading of the second stage 12 is adapted to a steam with a lower temperature and therefore with a high level of moisture. Accordingly the blading of the first stage 11 is not suited well for low temperature steam with a high level of moisture and the blading of the second stage 12 cannot take high steam temperatures. A feeding pipe 3 of the steam turbine 1 is split into a main inlet 13 and a bypass 14. The bypass 14 can be controlled by a bypass valve 15. Using the main inlet 13 steam is channelled into the first stage 11, using the bypass 14 steam can be directly channelled into the second stage 12. Of course also the main inlet 13 can comprise a control valve (not shown) to control the amount of steam channelled through the main inlet 13. In addition, also a shutoff valve (not shown) can be arranged advantageously upstream of the bifurcation to the main inlet 13 and the bypass 14 in the feeding pipe 3 to provide the possibility to completely shut down the flow through the steam turbine 1. In the shown embodiment a control unit 4 is provided to control the bypass valve 15 and advantageously all other valves mentioned above. The control unit 4 is also enabled to receive the measurements of a temperature sensor (not shown), which is located advantageously somewhat before the bifurcation of the feeding pipe 3 to the main inlet 13 and the bypass 14 and provides the temperature value of the steam. The control unit 4 compares this measured temperature value with a control value and takes the decision, whether a first or a second operation mode of the steam turbine 1 should be used in the operation of the steam turbine 1. If a temperature of the steam higher than the control value is measured, the control unit 4 decides to use the first operation mode, in which steam is channelled exclusively via the main inlet 13 into the first stage 11. In the first stage 11 the steam is expanded and therefore cooled. Afterwards it is channelled to the successively arranged second stage 12. If the initial temperature value is smaller than the control value, the control unit 4 switches to the second operation mode and activates the bypass valve 15 to channel steam directly and advantageously exclusively into the second stage 12 of the first turbine module 10 of the steam turbine 1. Therefore, it is possible to use the first stage 11, whose blading is adapted to high temperature, low moisture steam, only if these conditions are present and to use the second stage 12, which is adapted to low temperature, high moisture steam, if these conditions are present. In the second operation mode the first stage 11 is essentially not used for the expansion of steam. Nevertheless, a small amount of cooling steam can still be channelled through the first stage 11, advantageously controlled by the bypass 14 and/or a control valve (not shown) in the main inlet 13, to reduce the temperature and the thermal stress induced by the ventilation losses. These ventilation losses can occur due to the fact that the blading of the first stage 11 is still rotating driven by the second stage 12. If no cooling of the first stage is present, the first stage can even convert the work stored in this rotation into heat. Advantageously a small amount of steam out of the steam in the bypass is taken for the cooling steam. For a further reduction of the thermal stress the small amount of cooling steam can also be reheated. The heating can be done using stored heat, electricity or by burning fuel. Of course this heating can be controlled by additional valves (not shown). This additional heating is especially advantageous in case of a very large and/or fast reduction of the steam temperature. After the second stage 12 of the first turbine module 10 of the steam turbine 1 the steam is channelled through a condenser 33 and after that again in the steam generator 31. The circular flow of the concentrated solar power plant 30 can be continued.
[0028] In FIG. 2 another embodiment of a concentrated solar power plant 30 according to the invention is shown. The steam turbine 1 in this embodiment of the concentrated solar power plant 30 comprises a first turbine module 10 and a second turbine module 20. The first turbine module 10 complies with the turbine module 10 already described according to FIG. 1. The second turbine module 20 also comprises a first stage 21 and a second stage 22, which are successively arranged in the flow direction 2 of the steam. Into the first stage 21 steam can be channelled via a main inlet 23, into the second stage 22 steam can be channelled via a bypass 24. In the bypass 24 a second bypass valve 25 is arranged, which can be operated via a second control unit 4. Of course the second turbine module 20 can also comprise additional valves (not shown) as mentioned according to the turbine module 10 already described according to FIG. 1. Between the two turbine modules 10, 20 a reheater 32 of the concentrated solar power plant 30 is arranged. In this reheater 32 the temperature of the steam coming from the second stage 12 of the first turbine module 10 can be increased and channelled afterwards to the second turbine module 20. Also the second turbine module 20 is enabled to perform a method to operate the steam turbine 1 according to the invention. Therefore, the temperature of the incoming steam after the reheater 32 is measured. According to the temperature value the first 21 and the second stage 22 is used for the expansion of the steam or only the second stage 22 is used for the expansion of the steam. The first operation mode, in which both stages 21, 22 are used, is chosen, if the value of the steam temperature is above a certain control value and the second mode in which only the second stage 22 of the second turbine module 20 is used for the expansion of the steam is chosen, if the value of the steam temperature is below a certain control value. In the second operation mode, of course also a small amount of cooling steam can be channelled through the first stage 21 to reduce the thermal stress induced by ventilation losses. In the shown embodiment of the concentrated solar power plant 30, two control units 4 are shown. Of course, also only a single combined control unit 4 can be provided. In addition, the steam turbine 1 in the shown embodiment comprises two turbine modules 10, 20 with two stages 11, 12, 21, 22 each. Naturally, steam turbines 1 with more than two modules 10, 20 and modules with more than two stages 11, 12, 21, 22 respectively are also possible.
[0029] Summing up a concentrated solar power plant according to the invention and a steam turbine according to the invention respectively, which are both enabled to perform a method according to the invention, allow the usage of steam, which shows a large variability in temperature. Due to the fact, that the stages in the turbine modules used for the expansion of the steam are chosen dependently on the temperature of the steam, the necessity for supplementary firing and/or using buffering with heat storages of heat for the steam in the steam generating system of the concentrated solar power plant can be reduced. The whole machinery can therefore be constructed in a more easily and less complex way, which leads to a reduction in cost both in construction and in maintenance.
