METHOD FOR ADAPTING THE OUTPUT OF A STEAM-TURBINE POWER STATION, AND STEAM-TURBINE POWER STATION

Abstract

Disclosed is a method for rapidly and flexibly adapting the output of a steam-turbine power station (1), preferably for adapting the output to altered network loads, more preferably for providing a positive and/or negative network operating reserve as required, and especially preferably for providing a primary operating reserve and/or a secondary operating reserve. According to the invention, heat released during the discharge of at least one electrically chargeable thermal store (6) is coupled into a feedwater heater section (3) of the power station (1).

Claims

1. A method for quick and flexible adaptation of the power of a steam turbine power plant (1), preferably for power adaptation to changed grid loads, further preferably for the demand-dependent provision of grid control power, particularly preferably for providing primary and/or secondary control power, wherein a heat coupling of at least one electrically chargeable thermal accumulator is provided during the discharge of at least one electrically chargeable thermal accumulator (6) in a feed water preheating section (3) of the power plant (1).

2. A method according to claim 1, wherein in the event of a heat input from the accumulator (6) a steam tapping of a steam turbine (2) of the power plant, which is provided for preheating the feed water, is reduced or stopped.

3. A method according to claim 1 or 2, wherein the feed water for the heat coupling is arranged in a bypass line while bypassing at least one feed water preheater (14,17) of the feed water preheating section (3) to the accumulator (6) heatable with extraction steam (25, 26) of the steam turbine (2).

4. A method according to one of the preceding claims, wherein during the discharge of the accumulator (6) the released thermal energy is coupled primarily into a high-pressure region of the feed-water preheating section (3).

5. A method according to one of the preceding claims, wherein the accumulator (6) is charged as required with electrical energy generated by the power plant.

6. A method according to one of the preceding claims, wherein the accumulator (8) is charged with electrical energy from a power grid, in particular, an interconnected power grid, depending on the requirements.

7. A method according to one of the preceding claims, wherein the power plant (1) is operated at nominal load or in the range between nominal load and minimum load and the accumulator (6) is at least partially discharged in order to provide positive control power and is at least partially charged to provide negative control power.

8. A method according to one of the preceding claims, wherein the accumulator (6) is charged at minimum load operation of the power plant (1) at least partially with electrical energy generated by the power plant (1) in order to provide negative control power.

9. A method according to claim 8, wherein the net power of the power station system at minimum load operation of the power plant (1) is adapted to the demand of grid control power by changing the loading capacity of the accumulator (6).

10. A method according to one of the preceding claims, wherein the loading capacity of the accumulator (8) corresponds to at least the power plant power output at minimum load operation.

11. A method according to one of the preceding claims, wherein the loading capacity of the accumulator (6) is greater than the power level at minimum load operation, and the accumulator (6) is charged with electrical energy from an interconnected power grid, in particular, a interconnected power grid during a minimum load operation of the power plant, in particular, for providing additional negative control power.

12. A method according to one of the preceding claims, wherein the accumulator (8) after shutdown of the power plant (1) is charged with electrical energy from a power grid, in particular an interconnected power grid.

13. A method according to one of the preceding claims, wherein thermal energy is transferred during the discharge of the accumulator (6) to a compressed air flow (8) and the compressed air flow (8) is expanded to provide additional control power before subsequent heat coupling into the feed water preheating section.

14. A steam turbine power plant (1) having at least one steam turbine (2), in particular, designed for carrying out the method according to one of the preceding claims, and having at least one electrically chargeable thermal accumulator (6), wherein heat released during the discharge of the accumulator (6) is introduced into a feed water preheating section (3) of the power plant for heating the feed water.

15. A power plant according to claim 14, wherein the feed water preheating section (3) has at least one feed water preheater (14, 17), which can be heated with extraction steam of the steam turbine (2), and at least a partially feed-water-side bypass line of the feed water (19) is provided past the feed water preheater (14,17) via the accumulator (6).

Description

[0037] The invention is explained in the following by way of example with reference to the drawing. Identical plant components of the embodiments of the invention shown are provided with the same reference numerals. The drawing shows

[0038] FIG. 1 a simplified plant diagram of a steam turbine power plant according to the invention comprising an electrically chargeable thermal accumulator, wherein thermal energy released during the discharge can be coupled into a feed water pre-heating section of the power plant for preheating the feed water,

[0039] FIG. 2 a simplified plant diagram of a modified embodiment of the steam turbine power plant shown in FIG. 1, wherein a hot air flow generated during the discharge of the accumulator is expanded prior to the thermal coupling in an expander,

[0040] FIG. 3 a simplified flow diagram of a method according to the invention for the rapid and flexible adaptation of the power of a steam turbine power plant,

[0041] FIG. 4 a schematic representation of the improvement in the plant dynamics in steam turbine power plants by use of electrically chargeable thermal accumulator for feed water preheating and

[0042] FIG. 5 a schematic representation of the improvement in the plant dynamics by use of electrically chargeable thermal accumulators for preheating feed water during the operation of steam turbine power plants close to nominal load.

[0043] FIG. 1 shows a simplified plant diagram of a steam turbine power plant 1 with a schematically represented steam turbine 2, which can have a high-pressure part, a medium-pressure part and a low-pressure part. Furthermore, a feed water preheating section 3 of a water-steam working circuit 4 is shown schematically, in which feed water for the subsequent evaporation is preheated. The electrical net power or active power 5 generated in the power plant process is fed into an interconnected power grid. Further plant components required for generating power in the steam power process are not shown in FIG. 1.

[0044] For rapid and flexible adaptation of the effective power 5 of the power plant 1, further preferably for providing positive and negative grid control power, if necessary, at least one electrically loadable thermal accumulator is provided. In order to charge the accumulator 6, electrical power 7 can be removed from the interconnected power grid 7 and/or a part of the electrical energy generated by the power plant 1 is used, which leads to a decrease in the effective power 5 fed into the interconnected power grid.

[0045] The electric accumulator 6 can comprise at least one electric heating conductor for converting electrical energy into thermal energy and a heat accumulator material, in particular a bed made of a heat-storing material. The achievable accumulator temperature can be between 1000 C. and 1300 C., preferably between 1100 C. and 1200 C. In order to discharge the accumulator 6 an air flow 8 is guided through the hot heat accumulator material and in this case brought to a temperature of preferably more than 500 C., in particular, more than 700 C. The air flow 8 can be supplied to the accumulator 6 at a pressure greater than 2 bar, in particular, greater than 3 bar, for example, 3.5 bar. A compressor 9 is provided for compressing the air flow. The hot air flow 8 exiting from the accumulator 6 is used for feed water preheating. In the feed water preheating section 3, a preferably indirect heat transfer takes place from the hot air flow 8 to the liquid feed water.

[0046] As will be explained in more detail below with reference to FIG. 3, the coupling of heat energy from the accumulator 6 into the power plant process for preheating the feed water enables rapid and demand-dependent increase in the electrical power of the power plant 1, in particular the provision of positive control power. In addition, the effective power 5 of the power plant, in particular, can be reduced for providing negative control power by loading the accumulator 6 with the current generated by the power plant 1 depending on the demand and thus reduce the feeding of current into the power grid. It is also possible to increase the grid load and thus provide negative control power by charging the accumulator 6 with electrical power 7 from the power grid.

[0047] In the power plant 1 shown in FIG. 2, at least one expander 10 is provided for increasing the efficiency and for increasing the flexibility in the power adaptation of the power plant 1, in order to expand the compressed air flow 8, which is heated in the accumulator 6, after the exit from the accumulator 6 and before the heat transfer to the feed water. The electric power 11 generated in this case can be fed into the power grid.

[0048] FIG. 3 shows a simplified flow diagram of a steam power process for rapid and flexible adaptation of the effective power 5 of a steam turbine power plant 1. It is understood that the power plant 1 can have further plant apparatuses and components (not shown), which are required for implementing the steam power process.

[0049] A conventionally operated steam power process is explained below with reference to FIG. 3. The steam power plant 1 has a steam turbine 2 with at least one high-pressure part 12 and at least one middle- and low-pressure part 13. A feed water preheating section 3 of the power plant 1 has at least one low-pressure preheater 14, a feed water tank 15, a pump 16 and at least one high-pressure preheater 17. An economizer 18 is used for further feed water heating. After the preheating, feed water 19 is evaporated in an evaporator 20 and is heated in a superheater 21 in a conventional manner beyond the evaporation temperature. Superheated steam 22 is then first expanded in the high-pressure part 12 of the steam turbine 2 and subsequently heated again in an intermediate superheater 23. The steam 22 is then completely expanded in the middle- and low-pressure part 13 of the steam turbine 2 and condensed in the condenser 24. The feed water 19 formed during the condensation passes into the feed water tank 15 via the low-pressure preheater 14. The feed water 19 from the feed water tank 15 is supplied to the economizer 18 via the high-pressure preheater 17 by means of the pump 16.

[0050] In the conventionally operated steam power process, the high-pressure preheater 17 and the low-pressure preheater 14 are heated by removing extraction steam 25, 26 from the high-pressure part 12 and the middle- and low-pressure part 13 of the steam turbine 2. The steam extraction results in a reduction in power of the steam turbine 2. In order to increase the effective power 5 generated by the power plant 1, the condensate build-up method is known from the prior art. In this case, the condensate mass flow through the low-pressure preheater 14 is reduced. As a result, the extraction steam flow rate of the low-pressure preheater 14 can be reduced accordingly, so that more steam 22 remains in the steam turbine 2 and, as a result, more electric power is generated by the steam turbine 2. The higher output made available by the condensate build-up is limited by storage volumes for the condensate flow rate and the maximum steam generator output. In addition, the prior art for increasing the effective power 5 is known, to throttle the extraction steam quantities to the high-pressure preheater 17, wherein, however, high thermal loads of the high-pressure preheater 17 occur. Besides, the boiler furnace must be correspondingly over-dimensioned, since the steam generator 20 in this case receives colder feed water 19.

[0051] In order to provide the possibility of achieving a power adaptation of the motor system 1 in a short-term, fast and temporary manner, in particular depending on the requirement, and/or to provide negative grid control power, in the power plant 1 shown in FIG. 3, unlike the conventionally operated steam power process described above, the required heat coupling from an electrically chargeable thermal accumulator 6 is provided. The accumulator 6 can, according to the construction and mode of operation, correspond to the thermal accumulator 6 described with the help of the FIGS. 1 and 2. By means of a bypass, feed water 19 can be guided to the accumulator 6 while bypassing the low-pressure preheater 14 and preheated by heat transfer from the hot air flow 8 heated in the accumulator 6. By means of a further bypass, feed water 19 can be conducted to the accumulator after the pump 16 bypassing the high-pressure preheater 17, and can be further heated there. Subsequently, the heated feed water 19 then passes into the economizer 18. In this case, the system concept shown allows a partial mass flow 27 of the feed water 19 past the low-pressure preheater 14 via the thermal accumulator 8, then to heat and finally to guide it to the feed water tank 15, wherein the remaining part flow rate 28 of the feed water 19 is guided via the low-pressure preheater 14 and is thereby heated. Depending on the storage capacity, the entire feed water flow can also be conducted via the accumulator 6 and can be heated by heat transfer from the hot air stream 8. The same can apply to the high-pressure region of the feed water preheating section 3. A part flow rate 29 of the feed water 19 can be guided via the accumulator 6 to the economizer 18 after the pump 16 past the high-pressure preheater 17, wherein the remaining part flow rate 30 is guided via the high-pressure preheater 17 and is thereby heated. Depending on the storage capacity, the entire feed water flow downstream of the pump 18 can also be guided via the accumulator 6 and thereby heated. Since otherwise large storage capacities are required, it is preferably provided that only the part flow rates 27, 29 of the feed water 19 are guided via the accumulator 6 and are thereby heated.

[0052] At least some of the electric power generated by the steam turbine 2 can be used for charging the accumulator 8, so that the effective power 5 of the power plant 1 is reduced. Charging with electrical power from a power grid is also possible. With the system concept shown in FIG. 3, a rapid and flexible change in the effective power 5 of the power plant 1 can be achieved and a high availability of control reserves can be ensured, so that a very economical operation of the power plant can be achieved.

[0053] The reaction time for increasing or reducing the effective power 5 of the power plant 1 can be in the range of 5 to 20 seconds. The maximum discharge duration of the accumulator 6 is dependent on the heat storage capacity of the accumulator and can be several hours.

[0054] FIG. 4 shows schematically the improvement in the system dynamics of steam turbine power plants using electrically chargeable thermal accumulators for preheating feed water. FIG. 4 shows the power curve 31 of the electrical net power P.sub.netto (effective power) of a conventionally operated power plant and the power curve 32 of the electrical net power P.sub.netto (effective power) of a modified power plant as a function of different measures for improving the system dynamics, wherein the loading and the discharge of at least one electrically chargeable accumulator as described above is provided as a measure for improving the system dynamics in the modified power plant. The conventional power plant system, on the other hand, can have measures known from the prior art for improving the system dynamics, in particular, condensate accumulation.

[0055] The operation of the power plant system in load conditions between the nominal firing power of a power plant furnace or nominal load and the minimum load is illustrated. At nominal load, an effective power P1 is fed into the power grid by the conventionally operated power plant, which corresponds to the nominal power of the power plant. If a power reduction is required, the effective power P1 can be determined, for example, by reducing the condensate mass flow and reducing the firing rate of the steam generator to the effective power P2 over the time period t1, which corresponds to the power of the conventional power plant at minimum load. A further reduction of the effective power of the conventional power plant is only possible by shutting down the power plant, wherein the effective power of the power plant can be reduced to zero from the effective power P2 in the minimum load operation over a period of time t2.

[0056] A power reduction of the modified power plant can be achieved by electrical charging of the thermal accumulator over a time period t3, wherein the effective power P1 falls to a reduced effective power P3 solely by means of the current quantity used for charging the accumulator. As can further be seen from FIG. 4, the reduction of the effective power through charging of the accumulator leads to a distinctly faster power reduction in the modified power plant compared to the conventionally operated power plant. A further reduction of the effective power is then possible by reducing the firing power of the steam generator over a period of time t4, until the effective power P2 is reached at minimum load operation.

[0057] In addition, the thermal accumulator can also be charged at least partially with electrical energy generated by the power plant during a minimum load operation, so that the effective power of the modified power plant can be reduced further to zero by energizing the accumulator from the effective power P2 over a time period t5. If the minimum load operation is continued, the entire electrical energy generated by the modified power plant is then supplied for charging the accumulator and no current is fed into the power grid, which corresponds to an effective power of zero. The charging of the accumulator with the entire electrical energy generated by the power plant can be maintained over a time period t6 or even longer depending on the storage capacity, wherein the time period t6 can preferably be several hours.

[0058] As can be seen from the central region of the power curve 32 of the modified power plant illustrated in FIG. 4, the charging of the thermal accumulator can be stopped as required and thus the effective power of the modified power plant can be increased from zero to the effective power P2, to be precise over a comparatively short time period t7. The power plant can now be operated further at minimum load, for example, over the time period t8 and in this case feed the effective power P2 into the power grid. By changing the loading capacity of the thermal accumulator, the effective power can easily be adapted quickly to the instantaneous demand for grid control power. In this case, preferably zero to 100% of the power plant power can be used for charging the thermal accumulator in the case of minimum load operation, so that a demand-oriented adaptation of the effective power over a large power range is possible.

[0059] As can be seen from FIG. 4, the maximum loading capacity of the thermal accumulator can also be greater than the power plant power at minimum load operation, so that the thermal accumulator can be charged with electrical energy from the interconnected power grid, in particular, to provide additional grid control power. During the minimum load operation of the modified power plant, it is thus possible to provide more negative control power, which is schematically shown in FIG. 4 by negative values for the power curve 32 of the modified power plant.

[0060] In addition, after the modified power plant has been shut down, the electrical charge of the thermal accumulator can be continued with current from the power grid, so that negative control power can continue to be supplied.

[0061] FIG. 5 shows schematically the possibility for power adaptation of the electrical net power P.sub.netto (effective power) in a conventionally operated steam turbine power plant by means of a build-up of condensate (power curve 33) and in a modified steam turbine power plant by coupling to an electrically chargeable thermal accumulator (power curve 34).

[0062] In the case of nominal load operation of the conventionally operated power plant, the condensate build-up method makes it possible to increase the effective power from the nominal power P1 to the power P1 for a comparatively short time period t9, wherein the time period t9 does not exceed the range of a few minutes in the usual power plant design. The power increase can amount to approximately 10% of the nominal power P1. A corresponding power reduction from the nominal power P1 to the reduced power P1 is possible by means of other fast-acting measures for providing power changes, like for example, the throttling of the high-pressure turbine control valves. In order to provide a positive control reserve over a longer period of time, conventional power plants must usually be operated below the nominal furnace capacity, for example at the reduced power output P1.

[0063] The measures provided with the positive and negative control reserves achievable in conventionally operated power plants for improving the system dynamics are indicated schematically in FIG. 5 by the arrows 35, 36.

[0064] Due to the thermal coupling from an electrically chargeable thermal accumulator into the feed water heater section, the modified power plant can be operated over a significantly longer period of time t10, which can be of several hours, at an effective power P1 above the effective power P1 achievable in nominal load operation. The increase in power output by coupling heat from the thermal accumulator can correspond to the increase in power due to condensate accumulation in conventional power plants or can also be above it. In the same order of magnitude, the effective power P1 of the power plant can be reduced by charging the thermal accumulator with electrical energy generated in the power plant process. This is schematically shown in FIG. 5 by the arrows 37, 38. As a result, the operating point of the modified power plant can be increased relative to the operating point of conventionally operated power plants, wherein the same control power range can be offered.

[0065] Alternatively, it is possible to offer a wider control power range, when the operating point of the modified power plant is lowered accordingly to the operating point of the conventionally operated power plant. This possibility is schematically represented in FIG. 5 by the arrows 39, 40.

LIST OF REFERENCE NUMERALS

[0066]

TABLE-US-00001 1 power plant 2 steam turbine 3 feed water preheating section 4 water-steam operating circuit 5 effective power 6 accumulator 7 power 8 air flow 9 compressor 10 expander 11 power 12 high-pressure part 13 medium- and low-pressure part 14 low-pressure preheater 15 feed water tank 16 pump 17 high-pressure preheater 18 economizer 19 feed water 20 evaporator 21 superheater 22 steam 23 intermediate heater 24 condenser 25 extraction steam 26 extraction steam 27 part flow rate 28 part flow rate 29 part flow rate flow 30 part flow rate flow 31 power curve 32 power curve 33 power curve 34 power curve 35 power increase 36 power decrease 37 power increase 38 power decrease 39 power increase 40 power decrease